2001 SOHC P0301 - confusing compression numbers

[BobbyBeans]

A friend of mine is buying a new car and she has a 2001 SOHC 5-speed stick with 120,00 miles that she's either going to trade in or possibly sell to me. Other than the following two problems the car is spotless and in very nice shape.

1. The wheels in the front end make noise. It sounds like louder than normal road noise. After reading this forum I think its probably wheel bearings that need to be replaced. Any other opinions?

2. The car idles rough when cold and a little better when warm. When its idling rough there is a noticeable misfire. When it misfires I can hear a faint timing chain chatter - maybe related to the misfile maybe not. The SES light is on and the code is P0301 (misfire on #1 cyl). I have cleared it with my reader but it comes right back. I confirmed the coil packs are producing power by pulling the wires off, turning the lights out (it was night time), having my daughter turn the engine over and I observed the arcing across all 4 coil posts. I replaced the #1 wire with a new one - did not help. I pulled the plugs. All are spotless (recent tuneup I think). They are AC Delco. I should have checked the gap but forgot. I also forgot to do the intake manifold spray test to see if there is an air leak. Now I move on to the compression test. This is were things get strange.

#1 #2 #3 #4
140 175 165 150
120 130 70 145

The first set of number are not good but the 2nd pass totally confuses me. How could there be such a drastic difference in these numbers from one attempt to the next. I'm starting to think my compression tester is broken or I did something very wrong.

Aside from noticeable misfire at idle the car seems to run great. It accelerates quickly and smoothly without any hesitation or stumbling.

Things I need to do/check:
1. Check the spark plug gap.
2. Check for intake manifold leak.
3. Redo the compression test

Does anyone have any other thoughts?

Thanks
-Bob

[OldNuc]

Without further info, front wheel bearings sounds plausible. The noise will change when you turn slightly to one side or the other if its bearings.

The miss at idle can be low compression in one cylinder or a bad plugs or wires. Gap will not fix it unless you fined platinum plugs and a gap of 60 thousandths plus.

You need a screw in compression tester and do not crank it in real tight on the o-ring. Just contact and maybe an eighth of a turn more max. Do the compression test cold and then do it dry and followed by wet. If you are getting a p301 suspect an intake leak if you have a high idle. If the idle is normal then block off the IAC intake port in the throttle body and see if the idle drops to 500 RPM or so. If it does not then you probably have an intake leak.

[BobbyBeans]

Originally Posted by OldNuc

Without further info, front wheel bearings sounds plausible. The noise will change when you turn slightly to one side or the other if its bearings.

The miss at idle can be low compression in one cylinder or a bad plugs or wires. Gap will not fix it unless you fined platinum plugs and a gap of 60 thousandths plus.

You need a screw in compression tester and do not crank it in real tight on the o-ring. Just contact and maybe an eighth of a turn more max. Do the compression test cold and then do it dry and followed by wet. If you are getting a p301 suspect an intake leak if you have a high idle. If the idle is normal then block off the IAC intake port in the throttle body and see if the idle drops to 500 RPM or so. If it does not then you probably have an intake leak.

OldNuc thanks for your quick response.

1. What do you make of my compression numbers? I should not trust them right? I would think that under tightening the compression tester would lead to invalid data sooner than over tightening. What is your reasoning behind a light tighten is better if you don't mind me asking.

2. Would an intake leak cause a noticeable miss?

3. I'm confused by what you are saying about p301, high idle and normal idle. Are you saying either of these cases could exist?

• p301 + high idle = suspect intake leak
• p301 + normal idle + blocked IAC no change = suspect intake leak

Thanks
-Bob

[adventureoflink]

Basically, if the idle surges to around 2,000 RPM or so, you have an intake manifold vaccum leak (although to be fair, IIRC p0507 needs to be present as well). Spraying brake cleaner around the cyl #1 area will confirm the leak.

[OldNuc]

Originally Posted by BobbyBeans

OldNuc thanks for your quick response.

1. What do you make of my compression numbers? I should not trust them right? I would think that under tightening the compression tester would lead to invalid data sooner than over tightening. What is your reasoning behind a light tighten is better if you don't mind me asking.

The sealing o-ring requires minimal pressure to properly seal the connection. Over tightening extrudes the o-ring from the seat area and you get a leak. Also crank the engine with all the other plugs removed, PCM B fuse removed, And throttle held wide open. Crank until the gauge quits increasing.

2. Would an intake leak cause a noticeable miss?

Yes, if its large enough to give you a full closed IAC or an increased idle.

3. I'm confused by what you are saying about p301, high idle and normal idle. Are you saying either of these cases could exist?

• p301 + high idle = suspect intake leak
• p301 + normal idle + blocked IAC no change = suspect intake leak

The IAC will close to maintain the commanded RPM. Any intake leak will increase RPM and the PCM will command the IAC closed to compensate for the increase. A small leak will result in a closed IAC and very slightly increased idle RPM. Once the IAC is full closed the idle RPM will increase as the leak rate is increased. When the deviation from commanded idle RPM and actual RPM exceeds 100 RPM the PCM will set a SES light for the deviation. So you could have an idle RPM that is 75 RPM high and have a large intake leak. Usually you see the misfire condition when the idle is noticeably above normal.

Thanks
-Bob

Compression numbers are suspect. Leaking tester or fuel washing of cylinder walls. Pulling the PCM B fuse disables the fuel pump, injectors and ignition.

[BobbyBeans]

Originally Posted by OldNuc

Compression numbers are suspect. Leaking tester or fuel washing of cylinder walls. Pulling the PCM B fuse disables the fuel pump, injectors and ignition.

I did tighten down on the compression test hose pretty good so maybe that does explain why my numbers were all over the map. I'll definitely need to redo that test.

I pulled the fuel pump fuse not the PCM B fuse. Does that matter much? I did smell a faint fuel small when I was doing the test. Where is the PCM B fuse?

Thanks for the other details about the IAC and PCM logic.

[rc1488]

You have an intake manifold gasket leak which is causing the miss. Spray the gasket with carb cleaner for confirmation.

re-do your compression test as said above. Richpin has a video for this if needed.

[OldNuc]

Originally Posted by BobbyBeans

I did tighten down on the compression test hose pretty good so maybe that does explain why my numbers were all over the map. I'll definitely need to redo that test.

I pulled the fuel pump fuse not the PCM B fuse. Does that matter much? I did smell a faint fuel small when I was doing the test. Where is the PCM B fuse?

Thanks for the other details about the IAC and PCM logic.

PCM B fuse is in the fuse box under the hood. the locater is in the lid. The PCM B fuse basically kills the entire PCM so it never knows you are cranking the engine. The cranking of the starter is old tech switch action, no computer involved.

As has been mentioned, you probably have a vacuum leak but the compression test will eliminate any internal mechanical issues as being the cause.

[BobbyBeans]

Yes it is an intake manifold leak around or near cylinder #1. I spayed carb cleaner around that area and the idle dropped immediately. A 3 second stream of carb cleaner just about stalled the engine. Spraying around the other cylinders produced no noticeable change in rpm.

QUESTION: Is it possible a leak like this could cause the P0301 code?

I still need to repeat that compression test to make sure the engine is ok.

This forum continues to impress and amaze me. Thank you all for being here because after all a great forum, like think one, is only as good as its members.

-Bob

[madpogue]

Originally Posted by BobbyBeans

QUESTION: Is it possible a leak like this could cause the P0301 code?

Not just "could"; a #1 runner IM gasket leak is most likely _the_ cause of your 301.

I still need to repeat that compression test to make sure the engine is ok.

+1; given the wild variation, prime suspect is the procedure itself, but another test with a known good tester is in order.

[OldNuc]

The p301 is probably from an intake leak. And, you should also have either an elevated idle or a closed IAC valve. Once you get decent compression readings that will confirm it is a bad intake gasket.

[BobbyBeans]

Originally Posted by OldNuc

The p301 is probably from an intake leak. And, you should also have either an elevated idle or a closed IAC valve. Once you get decent compression readings that will confirm it is a bad intake gasket.

Compression test redo will be tomorrow.

I called the dealer today to get an estimate for an intake manifold gasket job and they quoted $480. I realize that its all labor because the gasket is $7 but that seems high. That would be like 5 hrs of labor. Hmm, maybe that is about right. I'm pretty sure I can do that job although it will take me all weekend and maybe more If the compression test is ok I am pretty certain I will buy this car and fix the IM gasket and replace the wheel bearings myself (dealer wants $550 for the bearing job on both side).

[rc1488]

I can do it for half the price for both the IM and wheel bearings. I'd give you entire new spindles. It wouldn't be until middle of May though unless you came here to Albany.

[BobbyBeans]

Originally Posted by rc1488

I can do it for half the price for both the IM and wheel bearings. I'd give you entire new spindles. It wouldn't be until middle of May though unless you came here to Albany.

Do I get a price break if I bring it to Albany? I may take you up on that some day but as for this car ...

I have decided to buy it. The seller (a friend) and I brought it back to the shop where she did her repairs. They did the compression test and the numbers were not great but expected for a car with 120,000 and burning some oil. The good news was the compression was very consistent across the cylinders. They confirmed the #1 miss was caused by the intake manifold leak. Their labor estimate to replace the IM gasket was $340. I declined and told them I'd do it myself. They were nice enough to offer to print out FSM pages for that job. I did take them up on that. The front wheel bearing had been done by them so the part was still under warranty but they wanted $150 for the labor which seemed reasonable to I had them do that. So, once I fix the IM leak the car should be in pretty good shape. Buying the car for $800 + $150 for the bearing labor + about $50 for IM parts ... all totaled about $1000. If the engine lasts 3 years I'm happy any more and its just icing on the cake

The bottom line (reason for original post) is that I was right to suspect my compression numbers and they where wrong because I either overtightened the tester hose or the tester gage is broken (or both).

[OldNuc]

Wheel bearing job is one of those things that does take as a minimum a press to do. The good news is the replacement will also be under warranty.

Sounds like you will end up with a decent car out of all of this.

[snoops454]

That's a creampuff there. You got yourself a good deal, infact you shouldn't take advantage of friends like that... J/K

That car should pay for itself in less than a year.

[BobbyBeans]

Originally Posted by snoops454

That's a creampuff there. You got yourself a good deal, infact you shouldn't take advantage of friends like that... J/K

That car should pay for itself in less than a year.

Hey, it was all my friend's idea ... I know you're just kidding (me too)

Its for my daughter. She said she's willing to learn how to drive a stick and I think its a much better car than the "97 project car" in the garage. Btw, that project car was to be hers. I'll still work on the project car and if she decides the stick is too hard then she'll have to wait for the project car and I'll take the stick for me (almost hoping that's what happens). But if she's good with the stick then I'll unload the project car after I fix it up ... 'cause its just too much fun ripping that project car apart and I'll still leaning a lot from it.

I started the 2001 intake manifold gasket job today and I have a few questions ... but I think I'll start a new thread for that.

Thanks
-Bob

[BobbyBeans]

... decided to just continue this thread instead

I'm replacing the intake manifold gasket on this 2001 SL1 SOHC because I've got a misfire on cylinder #1 and when I spray around the outside of #1 the rpm drops. So I'm into the tear down and I have a few questions:

1. How do you remove the fuel injector electrical connection on the 2001. I know how to do it on the 97 now but these are different. For some reason these type connectors befuddle me. Its very frustrating because normally I'm a petty smart guy (you'll just have to trust me on that one ) but these connectors make me feel like an idiot. See the attached picture.

2. I disconnected a hose at the master brake booster (I think) and it made a "whooshing" sound like something was under vacuum pressure but not any more. Was that bad? Did I hurt anything? See the attached picture.

3. One last hose to remove but its clip is facing the firewall. Why do they do that? See the attached picture. I just can't seem to get at it. The other end of this heater hose goes into the firewall and I was able to work its clip back (car jacked me working beneath) but when I twist the hose its male connected moves a little so I was afraid of snapping it.

Thanks
-Bob

[OldNuc]

Originally Posted by BobbyBeans

... decided to just continue this thread instead

I'm replacing the intake manifold gasket on this 2001 SL1 SOHC because I've got a misfire on cylinder #1 and when I spray around the outside of #1 the rpm drops. So I'm into the tear down and I have a few questions:

1. How do you remove the fuel injector electrical connection on the 2001. I know how to do it on the 97 now but these are different. For some reason these type connectors befuddle me. Its very frustrating because normally I'm a petty smart guy (you'll just have to trust me on that one ) but these connectors make me feel like an idiot. See the attached picture.

The blue connector lock is the release. you get underneath it from below and spring it out away from the body of the injector to release the tab. There is a tab sticking out from the side of the injector that the blue lock slips over to lock the connector in place.


2. I disconnected a hose at the master brake booster (I think) and it made a "whooshing" sound like something was under vacuum pressure but not any more. Was that bad? Did I hurt anything? See the attached picture.

No, you just let the vacuum out of the booster. Put a smear of the dreaded dielectric grease on that fitting when you go to put it all back together and it will go in easier.

3. One last hose to remove but its clip is facing the firewall. Why do they do that? See the attached picture. I just can't seem to get at it. The other end of this heater hose goes into the firewall and I was able to work its clip back (car jacked me working beneath) but when I twist the hose its male connected moves a little so I was afraid of snapping it.

Don't twist it, you will make the heater core leak. Just hook the ear you can not see in the picture and pull. That will release enough of the tension that the clamp will turn on the hose. Or, it is not an expensive hose, got a knife.

Thanks
-Bob

Just remember, you are having fun now.

[BobbyBeans]

Originally Posted by OldNuc

...The blue connector lock is the release. you get underneath it from below and spring it out away from the body of the injector to release the tab. There is a tab sticking out from the side of the injector that the blue lock slips over to lock the connector in place.

Please take a look at the attached picture. Does this show what you mean? If so, how do I get underneath? Do you use a finger nail? A very small screw driver? What actually lifts off? Is it the entire plastic piece including the blue lock as I have circled in red in the picture or is it just the smaller plastic piece where the wires attach?

Thanks
-Bob