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lanxer57 11-15-2021 02:08 AM

specifics on compression testing, P0301
I did a compression test, the engine was cold, I tested for 10 "cranking noises" the results:
1;90, 2;110-145, 3;121, 4;130
added some oil:
1;100-145-123, 2;110-145, 3;110, 4;145-120
because I was not sure if this was correct (given the inconsistant results, and how far off they were from 180), I cranked it until it stopped on its own 10 times (usually 4-5 "noises"). this was with oil in the cylinders the results:
1;175, 2;189, 3;170-180, 4;180
How EXACTLY would I get the most accurate readings possible on a compression test? A thread posted in 2003 :cake:(that is 1 month older than I am) by canada-eh said it was best to "crank the engine over 10 times", what EXACTLY does that feel/sound like? The sounds that cranking an engine makes are divided into pulses, how many of these "pulses" counts as cranking the engine over 1 time?
I would like to do it correctly next time.
This is on a 1999 SC1 with the SOCH engine, nearly 170000 miles.
I can not drive it until it passes emissions, and it will not pass with a "service engine" light. I have gotten a code P0301 for a missfire in cylinder 1, as well as the "service" light with the wrench. The light usually comes on after a few seconds (although sometimes it does not come on until the engine is shut off and restarted), but my OBD2 scanner usually takes a very long time to detect the error code. I have tried changing the spark plugs/wires, ignition coil packs with the plate they attach to (could not figure out how to separate them), fuel injectors, ECTS (with coolant), idle air control, EGR valve, (and cleaned as much out of the holes as I could), and MAP sensor. I also sprayed carburator cleaner around the intake manifold, it did not run any different. Dad said it smells like it is running rich (my nose does not work) Any other ideas? (do not be afraid to tell me it needs an engine, I have a 2001 SOCH with the transmission sitting on a pallet in the garage):cool:

billr 11-15-2021 10:11 AM

Re: specifics on compression testing, P0301
Did you hold the throttle wide-open while doing these crankings?

Run it for a bit, then take compression again; and be sure the battery is good enough that voltage doesn't drop below 11V while cranking. This time, don't do any of that "adding oil" routine. That is only confusing things. Yes, adding oil can help determine if the rings/bores are worn, but that is [I]rarely[/I] the case with these engines because of their oil burning issues. And, if you add too much oil, compression will get falsely raised, possibly even to the point of locking the engine rom turning!

PS: Five compression strokes is enough to get full compression on a good cylinder...

alordofchaos 11-15-2021 10:52 AM

Re: specifics on compression testing, P0301
See post 2 in these threads



edit: I read your post again, missed this question

[QUOTE] what EXACTLY does that feel/sound like? The sounds that cranking an engine makes are divided into pulses, how many of these "pulses" counts as cranking the engine over 1 time?[/QUOTE] Hard to describe a sound with words, lol. Needle will jump on the compression gauge on a complete cycle. Another thing you could try, take a video with sound for what you think are 10 cycles. Post a link to it, and we can listen / count and tell you what we are hearing.

2NDSOUT 11-15-2021 01:58 PM

Re: specifics on compression testing, P0301
Your compression numbers, are WAY low...

Regardless if you do a wet or dry compression test... your numbers across all 4 cylinders should read at least 185 or better.

The standard PSI rating across all 3 cylinders for the majority of the S-Series run; was 185 on each cylinder.

As you may know- these engines were known for oil burning... and the only way to really do *Some* kind of fix for oil burning, is to drill small holes in the pistons to allow for some kind of oil draining.

I think you may be chasing your tail on this one; as much as I hate to say that... nothing that you are going to do outside of the engine, is going to bring those compression numbers to a decent working number.

lanxer57 11-15-2021 03:08 PM

Re: specifics on compression testing, P0301
Yes, I had the pedal all the way to the floor.
I do not know if the results for my compression test were accurate, because they are not very consistant, and I may have been doing it wrong.
I will record a video later today, and maybe edit numbers counting the "pulses" of noise that I am discribing.
If the engine is bad, I have another one that was not misfiring after 181,000 miles (at least, before I crashed the car I pulled it out of).

lanxer57 11-15-2021 04:32 PM

Re: specifics on compression testing, P0301
If 10 compression cycles is minimum, how would I count the number of compression cycles?

billr 11-15-2021 05:33 PM

Re: specifics on compression testing, P0301
Normal cranking (battery, starter, and wiring all OK) results in about two strokes per second. Crank for five seconds.

Have you checked the compression gauge in another engine?

lanxer57 11-15-2021 07:09 PM

Re: specifics on compression testing, P0301
"2 strokes per second" does that mean that the "pulsing" noises are called strokes?
5 seconds of that would add up to 10 strokes, but my starter seems to pull away on its own after 4-7 strokes, so I would need to turn the key more than once. Will that make a difference? I have not seen the pressure gauge visibly go down without manually releasing it, so I do not see why it would.

billr 11-15-2021 08:59 PM

Re: specifics on compression testing, P0301
Yes, the "pulsing" change in sound is from increased resistance to engine rotation when a piston is compressing air; a compression stroke. With all plugs out it is pretty distinct and easy to hear. I assume you do have all plugs out while testing compression.

The starter should be able to crank the engine [I]continuously[/I] until either the battery runs down or the starter burns up; probably well past one minute. If your starting system can't do that, then any compression testing is somewhat suspect, since cranking speed matters. I would try to resolve the cranking issue first.

The point to trying the gauge in another engine is to check its calibration. Even if it doesn't leak down, it may be reading quite wrong. Or you may get a hint that your procedure is not quite right if another engine gives similar poor results.

You first reported a spread from 90-145 psi. If that were really 175-230 it would not be ideal, but adequate for the engine to run OK. I really don't think this is a "gauge calibration" problem, but it would be sad to condemn the engine and then later find it was the [I]gauge[/I] that was bad.

Point is, it is rare to find these engines with poor compression on all cylinders (bad rings), so I am suspicious of your testing. Usually there will be bas compression on only one or two cylinders. A bad valve will kill one, a bad head gasket will kill two.

Are you [I][B]sure[/B][/I] the throttle is going wide open, and that there is no obstruction in the intake ducting/filter while cranking? Low compression on all cylinders is inevitable if the engine can't breathe freely. What altitude are you located at?

lanxer57 11-15-2021 10:00 PM

Re: specifics on compression testing, P0301
Here is the video of how I was counting "pulsing" noises. [url][/url]
Are these actually strokes?
If not, how many noises are in a stroke?

billr 11-15-2021 11:10 PM

Re: specifics on compression testing, P0301
It did not crank log enough for me to identify the sound of the compression strokes, but each of those gauge "ticks" was a stroke.

Not having continuous cranking is a problem, most of us have little experience with testing compression that way. I don't know if the usual compression limit (180) is even valid testing like that.

Also, I'm guessing you are at about 5000' elevation. That will lower compression, even on a good engine, but I don't know how much (guessing about 170 for the lower limit). Maybe somebody living at a similar altitude can advise what they normally get.

Signmaster 11-16-2021 12:00 AM

Re: specifics on compression testing, P0301
Not enough cranking time. Based on the video you're only getting a few full turns of the engine through the compression stroke.

With the car not able to start, it should crank as long as you hold the key to crank. Once you get that figured out, you can watch the gauge "ticks" up and estimate 10 or so full revolutions. I only see three or four bumps on your gauge as you crank, with the pause in between.

Do you have all the plugs out or just the one?

lanxer57 11-16-2021 01:53 AM

Re: specifics on compression testing, P0301
Elevation:5770 feet, or about 0.85 of sea level according to some motorcycle forum. Does that apply to any engine? Even fuel injected ones? If so, than the number for a SOCH at this altitude would be closer to 148-175 PSI.
The compression tester was in one hole, the others plugged with spark plugs.
I will try to get it to crank more next time. The battery DIED as I was finishing up, so that may be a clue...

fetchitfido 11-16-2021 10:50 AM

Re: specifics on compression testing, P0301
Start with a fully charged battery for each test, otherwise the results are invalid due to slow engine speed. Also need the throttle wide open, either a weight on the pedal or locking pliers/clamp at the TB.

Crank until the gauge stops increasing in value. Run your own start button to the starter if you can't see the gauge from the driver seat. Looks like you stopped cranking 3-5 times in the 8s'll likely take 8-10s per cylinder to get a valid number.

If you add oil, drop 1 teaspoon in the cylinder, crank 1-2 cycles with nothing blocking the cylinders then retest. You just want oil on the cylinder walls to aid in ring sealing, you don't want the added oil on top of the cylinder artificially increasing compression numbers.

According to [URL=""]here[/URL] 6000ft gives 80% of the normal readings...drops 160psi sea level to 128psi. 180psi as the service manual state becomes 144psi. I don't know how accurate the 80% at 6k feet is, but it's inline with other sources at higher and lower altitudes.

I've not seen a S-Series engine (SOHC or DOHC) happy about running at less than 150psi on all 4 and have not seen a running engine at all under 130psi (AllData says 100psi is the min...lmao). Also shouldn't have more than 10psi difference between cylinders, if all 4 are low the engine is just worn out...if 3 are high and 1 is low then that cylinder has a major issue (both usually end up with a replaced/rebuilt engine).

fdryer 11-16-2021 12:00 PM

Re: specifics on compression testing, P0301
[QUOTE=lanxer57;2367471]Elevation:5770 feet, or about 0.85 of sea level according to some motorcycle forum. Does that apply to any engine? Even fuel injected ones? If so, than the number for a SOCH at this altitude would be closer to 148-175 PSI.
The compression tester was in one hole, [B][I]the others plugged with spark plugs.[/I][/B]
I will try to get it to crank more next time. The battery DIED as I was finishing up, so that may be a clue...[/QUOTE]
Save your battery from grief - remove all spark plugs when performing compression tests. This removes useless compression straining the battery while allowing the starter to draw a little less power as the starter runs faster. The engine turns over quicker for better compression results. And remove either the fuel pump fuse or pump relay to stop injectors from adding fuel to each cylinder during compression tests.

The altitude may skew compression values downward since the higher one goes, less dense air occurs.

lanxer57 11-16-2021 09:21 PM

Re: specifics on compression testing, P0301
After having a better idea what I was doing, (at least I thought) I tested again.
Added 1tsp oil to cylinders with syringe:

Cylinder 1 is the one with the misfire, can oil in there DECREASE compression?
These results look minimal at best, is this what is causing it to misfire?

billr 11-16-2021 10:10 PM

Re: specifics on compression testing, P0301
Are you still doing "interrupted" cranking; or have you fixed that and now doing continuous stroke for compression? No, I don't expect oil in the cylinder to ever lower compression.

Back to your actual misfire issue:

What do the plugs and wires look like? What gap are you using?

Have you checked fuel pressure [I]with a gauge[/I]?

Have you tried swapping the ignition coils, tried swapping #1 injector with one from another cylinder?

Are you using live-data to check MAP, TP, and ECT sensors?

Post a picture of how the plug wires are routed.

What is the electrical system voltage when the engine is running at a fast idle (~2000 rpm)?

lanxer57 11-17-2021 02:08 AM

Re: specifics on compression testing, P0301
After removing all other spark plugs, and putting the battery on a trickle charger, it seems to be able to crank continuously most times. I released the pressure whenever it stopped before the needle did.
The plug in cylinder 1 is black like coal, from excessive fuel if my memory is working, the rest are a lighter color, likely from oil that I squirted in there during testing. (there was lots of smoke from burning it off afterwards) The gap should be no different than when it left the NGK factory, I need to find the feeler gauge.
I have not heard of a gauge for fuel pressure, but I will ask for one.
I have not figured yet figured out how to separate the coils from the plate on the back, but have tried swapping them both with the back plate, and the towers all seem to have power going through them, I also swapped the entire fuel injector rail with one from a DOCH in a junkyard, and it acted exactly the same. I could try swapping them individually.
The live data from the sensors mentioned seems to be working with the cheap OBD2 scanner.
It is dark outside now, so pictures would not work until maybe tomorrow.
I have not seen it idle faster than 1200, it usually drops to about 800 in a few minutes, I also need to borrow a multimeter.

TomM96 11-17-2021 11:09 AM

Re: specifics on compression testing, P0301
Good that you did a compression test (at altitude).
This demonstrated that:
1.) compression is adequate to run (which it does)
2.) There is no deficit in the misfiring cylinder

Moving on:
You observed carbon on spark plug of misfiring cylinder. That plug
is likely defective Now; it may have been bad previously, causing
the misfire. THEREFORE
> Replace black plug with a new clean one of similar design. Do not
use the thin-wire type.
Check if engine runs, and if code set.

Re assess situation.
It is still possible that there is an injector issue, but a fouled plug will
foul/mask any information from testing.

To remove coils from IgCtrlModule, pull out/up OFF the plate/circuit board,
maybe one end before the other (lift one end up, it rocks up, releasing other end).
Check spark across (grounded) plug or coil paks.

TomM96 11-17-2021 11:10 AM

Re: specifics on compression testing, P0301
Best compression test is with WARM engine.

lanxer57 11-17-2021 11:48 AM

Re: specifics on compression testing, P0301
I have replaced the spark plugs recently with NGK plugs, but they may have gone bad afterward, so I will see if the auto parts store has any. (they had to order some last time).
Dad also smelled it running rich, although I can not verify weather it still is because my nose does not work.
It is also almost out of fuel, so I will need to fill up a gas can.

Cheyne 11-17-2021 01:11 PM

Re: specifics on compression testing, P0301
What NGK plugs did you use?

alordofchaos 11-17-2021 03:28 PM

Re: specifics on compression testing, P0301
couple of coil vids (I have not watched)



Pull out your #1 plug and any other plug. Compare gaps, if the same, swap those two plugs. If you still get a P0301, you know the problem was not defective plug - if your misfire moves with the plug, you know it was defective.

Same with fuel injector, if you suspect that. Swap the #1 with one of the others, if the problem moves with the injector, bad part. I saw that you replaced the whole rail - it is unlikely, but possible, that a used rail also had problems with the #1 fuel injector. By switching the #1 with a known good injector, you've ruled that out.

[QUOTE]After removing all other spark plugs, and putting the battery on a trickle charger, it seems to be able to crank continuously most times. I released the pressure whenever it stopped before the needle did.[/QUOTE] Not sure i understand what that last sentences means. Are you getting 10 strokes on you recent test? Recharge the battery if needed between testing cylinders.

[QUOTE]The plug in cylinder 1 is black like coal, from excessive fuel [/QUOTE]could also be insufficient air (very unlikely) or weak spark with incomplete burning.

[QUOTE]The live data from the sensors mentioned seems to be working with the cheap OBD2 scanner.[/QUOTE] What do your IAT, ECTS, and MAP read, on a cold engine, and what is the ambient temp during that read?

billr 11-17-2021 03:59 PM

Re: specifics on compression testing, P0301
What are the compression readings now that you can crank continuous? All plugs out, throttle wide open, 5-10 strokes, no extra oil in cylinders. Warm or cold doesn't matter to me.

alordofchaos 11-17-2021 06:57 PM

Re: specifics on compression testing, P0301
^ ^ ^
Yeah, we;re still kinda guessing here because we don't have numbers we can be confident in
[QUOTE=lanxer57;2367471] Does that apply to any engine? Even fuel injected ones?[/QUOTE] Yes, the fuel supply doesn't matter. As a matter of fact, you should have pulled the PCM-B fuse out, as mentioned in the links I provided upthread. That shuts off the fuel injectors - which both prevents fuel from washing down the oil from the cylinder walls [I]and throwing off your compression reading [/I]- by temporarily sealing any leaks.

You are taking a fixed amount of air at ambient pressure in the cylinder, compressing it, and seeing the pressure after compressed. A low compression number means air is leaking out, either past compression rings or valves (damaged/worn valve or valve seat). At higher altitude, that same amount contains less air to compress.

[QUOTE=OldNuc]Nominal compression for a high mileage good condition DOHC is 190-220psi and[B] SOHC is 175-205[/B]psi.[/QUOTE]Using the 80% adjustment fetchhitfido provided, the SOHC range should be 140-164 psi. Or 149-174 if you use your 85%

[QUOTE]Do not screw it into the head past the point the sealing o-ring just contacts the head. Do not overtighten as it will leak.[/QUOTE]

lanxer57 11-18-2021 01:19 AM

Re: specifics on compression testing, P0301
The new spark plugs that I installed a few weeks ago are NGK, BKR4ESA-11 according to what is printed on the box.
The ones installed by a previous owner were autolite double platinum APP 3926, something I believe is specifically advised against for S series.
For my last test on reply #16, I removed all spark plugs, fully charged the battery, removed the PCM B fuse, and propped up the gauge on a large pair of channel locks in order to see the needle moving. The top row shows the results of that before adding oil, the bottom row shows results after squirting 1 TSP of oil in all of them with a syringe. For the tests with the oil added, the trickle charger stopped working (likely the faulty garage outlet), so I can not be sure if it was still fully charged.
I will need to conduct more tests on another day, I had other things today.

billr 11-18-2021 01:47 AM

Re: specifics on compression testing, P0301
I can't rely on your results of reply #16 until you answer my question of #17: was that cranking (for 16) continuous, not interrupted like before?

If the cranking [I]was[/I] continuous for each compression test, then it doesn't seem likely compression is the issue; although there may still be a problem with exhaust valves. Compression can be fine, even if exhaust valves are not opening. That is pretty rare, though, so let's get back to the easier (and more likely) stuff first.

Swap around the injectors and coils, and check plug gap. You can not assume plug gap (or anything else) is OK just because the plugs are new. Our modern retail policy of "anything is returnable" ensures nothing is sure to be [I]really[/I] new.

How about those plug wires? I would like to see the routing, but how about the condition? If they look at all old, I would replace them. It is pretty hard to tell if a plug wire is breaking down intermittently or only under certain operating conditions.

lanxer57 11-18-2021 02:48 PM

Re: specifics on compression testing, P0301
yes, I got it to crank continuously with all spark plugs removed, I released the pressure from he guage whenever it did stop before the needle did. The spark plug wires were replaced with the plugs, and should be brand new. I may be able to check plug gaps, and swap fuel injectors when I return home.

billr 11-18-2021 03:15 PM

Re: specifics on compression testing, P0301
Try swapping coils, too.

It seems, then, that your (dry) compression is in the 145-160 range on all cylinders Do we all agree that is OK for a SOHC at 5770' altitude?

alordofchaos 11-18-2021 10:35 PM

Re: specifics on compression testing, P0301
[QUOTE=billr;2367555] Do we all agree that is OK for a SOHC at 5770' altitude?[/QUOTE]
Yes, I agree with moving on - switching out [I]known good[/I] (not [I]new/different[/I]) parts.

[QUOTE]You can not assume . . . (or anything else) is OK just because the . . . are new.[/QUOTE] exactly. Installed a few new, out of the box, defective parts then pulled my hair out trying to troubleshoot because I assumed the new part was good. In this case, you are better off using known good parts for troubleshooting.

Autolite double platinum is actually OK for these cars (I did not check the specific number you listed for fitment in the SOHC). The double platinum are not fine-wire plugs - most platinum plugs are single plat / fine wire.

I ran double plats in my DOHC with no issues (no gain,either, so went back to coppers)

1996SL11.9L 11-20-2021 07:22 AM

Re: specifics on compression testing, P0301
I would start by replacing the spark plug in cylinder 1. If the missfire goes away and or the plug turns black again Iíd look at the fuel injector for that cylinder. It appears itís stuck open and running that cylinder rich or youíre burning major oil in that cylinder.

lanxer57 11-20-2021 08:13 PM

Re: specifics on compression testing, P0301
I have not yet had time to switch anything out, but I did do a test the fuel pressure.
With key on, engine off, it started a 42 PSI, dropping to 38 PSI after about 5 minutes. At idle, it bounced around for a few seconds before settling at 47 PSI.
I also tested vacuum at the valve cover to intake hose. it quickly reached 5 inches of mercury, before settling just below 10.

billr 11-20-2021 09:41 PM

Re: specifics on compression testing, P0301
I would prefer not to get into fuel-pressure, just yet; except to say I don't think it would affect only one cylinder. Let's pursue the coil/injector swapping first.

for you, is #1 cylinder the one on the passenger-side; where the serp belt is?

lanxer57 11-21-2021 09:07 PM

Re: specifics on compression testing, P0301
I checked the spark plug gap, they were all 0.040 inches. I cleaned them with a rag, and put them back in. I switched the misfiring cylinder 1 plug with the cylinder 2 plug. The "service" light did not come back on for at least half an hour of idling in park, and turning the engine off several times. it only came back on when I turned it off for 30 seconds to retrieve my license to drive it down the street and back. It did not explode, but it was not driving faster than 20 MPH or longer than 1 minute either.:stoplight When I selected a setting for OEM DTCs for saturn, I found 47 codes, many of them contradictory, with the label "did not complete SC" or something similar. Global OBD2 did not find any codes after 40 minutes:clock: of idling with "service" light on, so I do not know weather or not switching the spark plugs changed anything.

lanxer57 11-22-2021 01:41 AM

Re: specifics on compression testing, P0301
after driving up and down the street, half of the saturn specific codes vanished, but still no global OBD2 codes.

billr 11-22-2021 10:13 AM

Re: specifics on compression testing, P0301
Post what codes are set now.

Was the original problem [I]only[/I] that a P0301 was set, was the engine running OK?

PS: I do understand that the P0301 prevented you from passing smog test; an important problem in itself.

1996SL11.9L 11-22-2021 10:30 AM

Re: specifics on compression testing, P0301
Everytime my wrench light came on on my 96 it was to tell me the check engine light bulb was blown.

Your check engine light comes on at key on and goes off at engine run and no missfire codes?

lanxer57 11-22-2021 03:53 PM

Re: specifics on compression testing, P0301
The engine was running rough, with low pitch noises coming from exhaust. I always assumed that this was caused by the misfire that was detected by the OBD2 reader. These noises show up intermittently, and when present, get louder when moving the vehicle up and down the driveway. They were last heard the day before I changed the fuel injectors. I will try using another OBD2 reader to see if that is the problem, and watch for any light bulbs that may be out.

lanxer57 11-22-2021 09:21 PM

Re: specifics on compression testing, P0301
The lights that show up with with key on, engine off are "service engine soon", "service" wrench, battery, oil, low fuel, and parking brake. When started, all turn off except parking brake (I am on a sloped driveway), "service" wrench usually comes back after a minute or so. The low coolant lights flashes sometimes, but it is filed to the maximum cold level, and the resevoir was recently cleaned, so I think it is because of the sloped driveway. I tried a different OBD2 reader, this one does not have live data. It did not find any codes in "global" mode either. The status light is orange, flashing red icons for O2 sensor, catalytic converter, EVAP, and EGR. There are 27 error codes in OEM enhanced mode for saturn, some repeat multiple times, some appear to be contradictory. This is the order they appeared in: P1640, P1641, P1620, P1640, P1641, P1620, P1640, P1641, P1620, P0133, P0401, P0420, P0440, P0130, P1134, P1133, P1602, P1380, P0733, P0734, P0741, P0748, P1582, P1584, P0442, P1441, P0446

billr 11-22-2021 10:33 PM

Re: specifics on compression testing, P0301
But the original P0301 has not returned? Ugh! Does the car drive OK?

Whenever I see a long and eclectic list of codes like this I suspect the PCM, power/ground connections to the PCM, or the code reader.

Try a different code reader, take it to your FLAPS, if necessary, for a free read. Check the PCM 5V supply, easiest done at the MAP sensor or TP sensor or EGR valve. Check voltages at the PCM power and ground pins, back-probing and with the PCM fully powered up (KOEO).

lanxer57 11-23-2021 02:40 AM

Re: specifics on compression testing, P0301
Passing an emissions test is the most important thing to fix, but I did notice that the brakes desperately need to be bled (the pedal almost sunk to the floor, and the brakes gave little response), and the wheels were rubbing something when turned. I am also reluctant to drive it outside of small residential streets until I can get the automatic transmission to stop leaking. (maybe I should replace the side cover gasket again?)
At speeds not exceeding 20 MPH, and driving VERY conservatively, the engine seemed to work fine. It did shift a little hard, but I thought it had to "relearn" how after getting the valve body replaced.
I suspected that "did not complete SC" might refer to some kind of test that needs to be done after removing the PCM-B fuse, but these tests are said to involve going 55 MPH, and than coasting to 20 MPH, something that I believe is illegal (at least where I live) because it would be considered "impeding traffic". Even if that kind of behavior is legal, driving at all in a vehicle that has not passed an emissions test is not legal either.

fdryer 11-23-2021 02:11 PM

Re: specifics on compression testing, P0301
Are you aware of removing the pcm fuse, battery disconnect or push button reset on an obd reader or scantool resets the check engine light and erases error codes? Any errors that aren't corrected reappear on the next startup. Whether you know it or not, once the pcm is reset with the cel off, the car won't pass state emissions inspection because the pcm was reset to factory defaults with readers/scantools displaying the vehicle in Not Ready status. Instant failure at emissions inspection. Resetting the pcm requires the vehicle driven the minimum 'drive cycle' of 50 miles to have the pcm learn all new emissions parameters involving measuring coolant temps from cold start to fully warmed up, egr operation, both O2 sensors, map, throttle position and evap system. You can search for GMs drive cycle but it basically means driving in local and highway conditions with stops along the way as emission monitors are learned and compared with programmed values. Inspection stations are well aware by reading obd status the same way diyers can with commercial or personal readers and scantools.

If each measured parameter falls within range then the obd system sets a ready status. If all parameters are within range the system will have a ready status, meaning the car already passed its self tests relative to emissions testing and will pass state/federal emissions inspection. A reader or scantool with this function should display all the monitors and whether or not each one went from not ready to ready status. Your state DMV will have info on how many monitors can fail yet pass inspection. Some states allow one or two monitors to fail but still pass inspection. Other states won't allow a vehicle on the road if one monitor fails. Readers or scantools will display which monitors haven't reached ready status. A good reader will tell whether or not a vehicle is ready for emissions inspection long before visiting state inspection stations.

lanxer57 11-23-2021 07:25 PM

Re: specifics on compression testing, P0301
Would a reset trigger a service wrench light? Any ideas on how to complete a drive cycle in an unregistered, uninsured vehicle without drawing attention from the police?:arr:

fdryer 11-23-2021 08:30 PM

Re: specifics on compression testing, P0301
My limited knowledge of OBDII doesn't have any info stating resetting the engine computer triggers a wrench error/light. You can wander thru everyone posting threads about resetting their PCMs with battery disconnect, pcm fuse pulling or using a reader to reset the cel. None have ever seen their wrench light turn on for manual resets. Even my L300 doesn't turn on its wrench light when I manually reset errors. Your wrench light indicates something unrelated to emissions triggered the light. Something as minor as a burned out instrument panel or turn signal lamp. Generic readers won't decode wrench errors. Manufacturer specific readers or scantools can. Emissions errors take priority over minor issues lie a burned out tail light so the majority of readers decode only emissions related error codes, P type. C codes are for chassis, U for network and B for body control module error codes.

Unfortunately, once anyone manually resets their cel just before state emissions inspection will be seen by inspectors as a Not Ready status as soon as they plug in their state computer to a vehicle. They don't see anymore info than we do with personal readers. Most members here with this issue are given a friendly warning that their system was reset and will need to be driven a few days or so and return for another scan when daily driving meets all the parameters for the GM drive cycle. Many perform their drive by simply using their vehicle in normal everyday driving and return to find out their car passes. Others find out one or several monitors haven't completed and cannot pass inspection until repairs and follow-up drive is recognised by the on board diagnostic system as a correct repair to change the remaining monitors to ready. Some complete a drive cycle the same day, others take a few days while some take longer. All due to variable daily driving routines. The ones that can't complete a drive cycle are shown which monitors are still pending (not ready status). Many aren't aware of just leaving the error code alone and making honest attempts at repairs then let the obd system automatically detect corrected errors to reset error light automatically. Some errors are reset automatically on the next ignition on/drive while others reset the light but require up to three drive cycles (ignition on, startup, drive, ignition off) before a pending error code is erased and a ready status is seen on a reader/scantool. It's simply easier to use a good reader or scantool to determine when repairs are made, let the system reset any errors, and check for ready status before inspection takes place.

The obd system automatically runs on every engine run, monitors everything and if nothing fails, leaves the cel off. If at any time a fault occurs, monitoring halts at the error and resumes only if a correct repair occurs and is detected on the next ignition on/drive. The system is left alone with a correct repair as all monitors aren't reset and the corrected error is detected on the next startup to erase the error code and turn off the light. This is the best way to an inspection coming up if an error code pops up, not manually resetting errors. If the error remains, the halted obd system simply waits with all other monitors in ready status for the correct repair to occur and detected to switch the one not ready status to ready. Leaving the obd system alone and fixing the error correctly lets the system detect the corrected error to resume monitoring, clearing the error to return a vehicle to legislated emissions requirements immediately. Manually resetting errors erases all parameters and requires a drive cycle to relearn them.

You'll have to call DMV for directions on how to get your obd system to run to get all monitors to ready status. Your alternative might be driving around, carefully avoiding police at night to let the obd system run its course. Having a reader or scantool plugged in can help determine which monitors are ready or not to tell you whether the car is ready for inspection or not. You'll need a reader that will display emissions monitors in ready or not ready status.

lanxer57 11-23-2021 11:27 PM

Re: specifics on compression testing, P0301
The instrament panel? The left turn signal indicator is burned out, would that cause it? The horn is also not working. Does the PCM care about the horn? I never use it.

1996SL11.9L 11-24-2021 10:08 AM

Re: specifics on compression testing, P0301
Itís possible that the wrench is for your turn signal lamp.

My Innova hand held scanner and MacMentor I think are the only devices able to read the non OBD GM specific trouble codes.

fetchitfido 11-24-2021 10:20 AM

Re: specifics on compression testing, P0301
The "[COLOR="Orange"]Service(Wrench)[/COLOR]" light is for non Emissions related things, like burned out indicator bulbs.

Reading what it has for a code requires at least a Tech II level tool, if not a Tech II specifically.

Has no impact on emissions, but it's up to the inspector as to it passing inspection or not.

fdryer 11-24-2021 01:59 PM

Re: specifics on compression testing, P0301
If you don't have a better ($$$) reader or scantool to decode wrench light error codes, the cheapest alternative is repairing what's broke. If you can replace a burned out turn signal light bulb, try it. You have nothing to lose but time and a few dollars. The horn failure may be either the steering wheel touch switch or horn itself. The horn and switch can be tested by disconnecting the horn and connecting a 12v bulb or measure for 12v when the horn switch is pressed.

Electronics uses circuits to measure for open or grounded (short) connections as feedback for programmed error codes. These circuits were designed when computerized systems grew from demand for better monitoring of vehicle electronics and electrical systems. The easiest one to understand is the battery light - on with ignition before starting, off after starting and on when the engine's running to indicate something wrong with the electrical system. The battery light replaced older ammeter and voltage meter to eliminate gauges not necessary for the average driver unfamiliar with amperage or voltage gauges. The 'idiot' light is all that's needed when alternators replaced generators with external voltage regulators using relays. Solid state electronic voltage regulators built into alternators allowed a simple battery light to inform the driver of one of three states of electrical system operation.

lanxer57 11-30-2021 12:22 AM

Re: specifics on compression testing, P0301
All the bulbs on the instrument panel are now working.
I also tried to fix a transmission leak by sealing the valve body cover gasket with rtv silicone. I drove it for a few minutes and it did not blow up at speeds up to 40mph while almost flooring it. It did shift a little bit hard, but was not slipping. The service wrench light did not return until I drove uphill at about 25mph for at least 10 seconds, and the wrench light came back... P0733, incorrect 3rd gear ratio. I also looked underneath it, and trans fluid is still dripping, but it is no longer pooled up around the edges of the valve body cover (where the bolts are). I recently swapped the valve body with one from my 2001 SOCH, could that be causing this new code? The turn signal switch also seems to only work intermittently.

fetchitfido 11-30-2021 01:14 PM

Re: specifics on compression testing, P0301
The Service (wrench) light does not come on for engine/transmission codes. Only the Service Engine Soon light does engine/transmission codes. They're in a similar spot, but different lights. Wrench light is #5, SES is #4 in the below picture.


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