Occasional Misfire and P0301 Code

[Shrocky5]

Have a problem I've been trying to track down for about a year. Have a 2002 SL2 with the DOHC engine. Randomly the car will start missing, and the SES light will come on with a P0301. Replaced spark plugs with brand new NGK coppers gapped correctly, and replaced wires with OEM AC Delco wires. Number 4 and 1 run together as long as possible. The misfire is most noticable at idle. Seems to go away at speed. Also swapped out ICM and coil packs with two different junk yard units. Nothing seems to solve this problem. Car has about 215k on it. Burns about 1 qt of oil every 3k miles. Dry compression is 170 psi on all cylinders according to my harbor freight gauge. The problem is very intermittent. Could a burnt valve be intermittent? Car does have kind of a rough idle as well when it's not missing. I'm at my wits end with this problem. Haven't found much else by searching the forms. Does anyone have any advice or things I could try?

[gveinot]

If the misfire is always the same cylinder it could be the engine computer. The engine computer signals the ICM which fires the coil packs to produce your spark. Might be worth buying a $100 junk yard engine computer before removing the head and inspecting the valves. Just make sure you get a computer for a DOHC and the transmission type you have ( auto or manual are specific for the computer ) If the misfire varies to different cylinders, I would say the Engine Computer is ok.

[Shrocky5]

Thanks for the advice. I'll check into getting a new computer. I was also thinking about sending injectors off to get them ultrasonicly cleaned. They're original to the car and never really been cleaned or anything. We have reformulated gas here in KY which may not help. Anyone think the injector cleaning could help also?

I don't think I'm mechanically inclined to take the head off. I won't be doing any major mechanical work to the vehicle. It's a secondary car at this point. I plan to just drive it until it dies and junk it. Of course if it's something cheap to fix, I'm all ears. Still want to take care of it. It's served me well since purchased new back in 01.

[Saturn Night]

Originally Posted by Shrocky5

Have a problem I've been trying to track down for about a year. Have a 2002 SL2 with the DOHC engine. Randomly the car will start missing, and the SES light will come on with a P0301. Replaced spark plugs with brand new NGK coppers gapped correctly, and replaced wires with OEM AC Delco wires. Number 4 and 1 run together as long as possible. The misfire is most noticable at idle. Seems to go away at speed. Also swapped out ICM and coil packs with two different junk yard units. Nothing seems to solve this problem. Car has about 215k on it. Burns about 1 qt of oil every 3k miles. Dry compression is 170 psi on all cylinders according to my harbor freight gauge. The problem is very intermittent. Could a burnt valve be intermittent? Car does have kind of a rough idle as well when it's not missing. I'm at my wits end with this problem. Haven't found much else by searching the forms. Does anyone have any advice or things I could try?

If dry compression is 170psi across all four cylinders, this is WAY TOO low. 180psi is the service limit.

Burnt valves are more common in the #3 cylinder, and just before the begin to chip, the compression of that cylinder will be lower than the other three cylinders.

I would redo the compression test. Make sure the throttle is wide open, disconnect the PCM B fuse, pull all four spark plugs, fully charge the battery, and then crank the engine over.

Post the results of each cylinder, which will tell you if your #1 cylinder is about to drop a valve.

[Shrocky5]

Thanks for the advice. I did everything during the first compression test except charge the battery and disconnect the PCM B fuse. I re-tested again doing everything but charging the battery (I don't have a charger), still showing 170 psi on all cylinders dry, with WOT, PCM B fuse disconnect all plugs out. Could it be the cheap harbor freight gauge? Car runs like a scaled dog if I kick it down, and seems to run totally normal other than the slightly rougher idle, and the extremely intermittent misfire. If compression was truly way to low, wouldn't there be other symptoms as well?

Also for what it's worth this problem started last year when it got colder/wetter outside. Problem went away on its own and didn't come back until now. So for a whole year it seemed fine then came back.

[billr]

Compression at 170 is "good enough", don't fret any more about that.

Try swapping the #1 injector with another. If the problem follows the injector, then... it is probably a bad injector. Generally the O-rings on the injectors can be re-used, but check for leakage where they plug into the fuel rail just to be sure.

[Shrocky5]

Pulled the fuel rail last night to inspect the injectors. They all looked fine. Decided while I had everything apart it would be a good investment to just go ahead and send them off for ultrasonic cleaning and proper testing. With over 200k miles it couldn't hurt anything. I marked the injector that was in cylinder 1 and will be sure to install it in a different cylinder (assuming my mark is still there). I'll post the results of the cleaning in a week or so when I get them back. Fingers crossed. Hopefully this will be $80 well spent.

[2NDSOUT]

As odd as it may sound- Your ICM could be the suspect here. I know you mentioned that you have put Junkyard ICM units in your car. For what it is worth; if you are planning to keep the car for an extended amount of time; and rather then throwing used parts at your car... in my opinion, an used ICM from a JY; is the equivalent of putting a used battery in your car.

You can find new ICM units that retail for ~$120 +/-....Honestly- since the ICM is, in essence- an electrical part; electrical parts don't always last forever; and the basis of cleaning a 17 year old part, and having it work as good as it was when it was new, is probably not going to happen. The same goes for coil packs as well.

I had a condition in my 99 Sedan back in October- and rather then trying to go through the rigamaroll of cleaning and swapping out almost 20 year old parts- it was a no question for me, just buying new parts and being done with it.

Just my thoughts.

[Shrocky5]

Ya I may look into getting a new icm and coil packs if I don't see any improvement from injector cleaning. Got results back from cleaning company. They stated that the injectors had moderate flow loss, and pattern irregularities. I guess maybe I haven't been as diligent with the fuel system cleaners as I should have been over the years. Said they cleaned up nicely and I can rule them out as being the problem if car still acts up after they're reinstalled. He said they're not leaking nor are there any electrical issues with them. I'll post more detailed results, once I get them back and installed in the car. Crossing my fingers.

[fdryer]

Did the place that did injector cleaning send a full report for posting?

[Shrocky5]

It is included in the package with the injectors he said. I was just going off the email he sent me today. Injectors should be back Saturday, but due to the snowstorm this weekend may not be able to get them back in the car until the first part of next week. I will post the report when I get it.

[2NDSOUT]

Originally Posted by Shrocky5

It is included in the package with the injectors he said. I was just going off the email he sent me today. Injectors should be back Saturday, but due to the snowstorm this weekend may not be able to get them back in the car until the first part of next week. I will post the report when I get it.

Snowstorm... Ha... I'll believe it when I see it. I've lived in Cincinnati for 30 years, and if you know if you've lived in Erlanger for a long time- we are not far from each other. The "Snowstorms" that we have had over the years, sometimes are built up hype. The last time the weather was predicted here to get 4-5 inches of snow, we got a light dusting. Another time, we were told it was going to be a heavy snow, and it was rain and freezing rain... and then other times, the weather goes completely around Cincinnati.

I'll believe it when I see snow falling... until then... Hot Air being blown around over the TV airwaves.

[Shrocky5]

Ha you're right. I think Steve Raleigh on WCPO teams up with Kroger and gets a kick back on all the bread and milk they sell. I'm sure Chopper 9 will be covering the extent of the snow and reporting any and all casualties caused by this massive snowstorm. God rest our souls.

[alordofchaos]

Just curious - who do you use for injector cleaning? I've heard good things about Witch Hunter but have never tried them. I've been lucky so far, I guess.

[Shrocky5]

I used Mr. Injector. There was someone on YouTube that sent their injectors there and had the owner of the shop film the whole process to see what all goes on. The place had great reviews online so I decided to give it a try.

It's $17.50/per injector. Witch hunter was $22/per injector I belive. Mr. Injectors shop is in the Spokane, WA area (its actually in Idaho).

Can't post a link yet but it's mrinjector dot us. Or just Google search Mr. Injector.

[Shrocky5]

Luckily was able to get everything reinstalled during the break in the weather. So far... the results are extremely positive. The engine idles MUCH smoother than it has in years. I also had a slight hesitation sometimes when you went to accelerate, but not enough to cause the transmission to downshift. That is gone as of now. Overall the results are positive and I think the cleaning was worth the money. The flow was really off before on all the injectors. None of them were even. Only one scored fair in the pattern test, while the others scored good. They all scored good after the cleaning.

1.
> Pattern: Before: Good | After: Good
> Flow: Before: 41 | After: 45 | 7.1% Increase

2.
> Pattern: Before: Good | After: Good
> Flow: Before: 44 | After: 45 | 2.3% Increase

3.
> Pattern: Before: Fair | After: Good
> Flow: Before: 41 | After: 45 | 9.8% Increase

4. There was no change in the 4th injector. Results were the same before and after.

Overall I think it was worth the $80, and might be worth trying if you have a higher mileage engine with the original set of injectors. New injectors are $140/piece now for decent quality ones. Only place I could even find new ones is NAPA. My Saturn has 220k and still everything is original. I'm happy with the results thus far. The misfire was intermittent enough that I won't be able to tell for a while if that cured it or not. Only time will tell. Fingers crossed though.

[Cheyne]

New OE injectors for yours can be found for ~65 each, so it was more economical to send them off. New OE for 96-mid 00 DOHC are available for 24.00 ea. I got them recently for 10% off that so 86.40 delivered for a set of 4.

[Shrocky5]

Ya. I could only find them at NAPA for OEM Delphi ones. It looks like Rock Auto must have got 4 in. They are listing 4 Delphis now for $72/each. I'm always afraid of eBay and Amazon for that stuff because you never know if you're getting a knock off or not.

Also it may be worth mentioning... I had a hard time finding a video demonstration online for removing the fuel rail from the later model 3rd Gen DOHC engine with the different throttle body design. If anyone wants to remove the fuel rail and wants a video reference look for the Car Saturn Intake Manifold removal video. It goes over removing the rail for that particular application.

I'm a visual learner. Can always learn alot more from a video then a diagram in a book.

[Saturn Night]

Originally Posted by Shrocky5

Ya I may look into getting a new icm and coil packs if I don't see any improvement from injector cleaning. Got results back from cleaning company. They stated that the injectors had moderate flow loss, and pattern irregularities. I guess maybe I haven't been as diligent with the fuel system cleaners as I should have been over the years. Said they cleaned up nicely and I can rule them out as being the problem if car still acts up after they're reinstalled. He said they're not leaking nor are there any electrical issues with them. I'll post more detailed results, once I get them back and installed in the car. Crossing my fingers.

Switch to ethanol-free fuel, BEFORE dumping periodic fuel system cleaners into the tank.

Ethanol-blended fuels allow the system to absorb moisture, which will wear the injectors out and cause corrosion in the system.

Fuel additives are typically very harsh solvents and increase the octane rating of your fuel. This is BAD for older cars, as the PCM will NOT add the required spark advance to properly burn off the fuel before the exhaust valves begin to open.

This WILL lead to a burnt valve, in the #3 cylinder. I have burnt valves, from using fuel system additives, on two DOHC engines over the years. First was a 2.3L Quad 4 "low output"(150hp) DOHC, and the other was my Saturn 1.9L DOHC in the SC2. I am too broke to keep blowing engines, and 1995 is a standalone year, so engine availability is drying up too.

IF you feel you must use fuel system cleaners, ONLY use Lucas Fuel System treatment. It is petroleum based which helps with keeping a slight layer of lubrication over the injector pintles and lubricates the fuel pump(this stuff can actually quiet a noisy, failing fuel pump and temporarily extend its lifespan).

To my knowledge, it doesn't increase octane nearly as much, and will not harm the O2 sensors or converter elements in your catalytic converter.

[Saturn Night]

Originally Posted by 2NDSOUT

Snowstorm... Ha... I'll believe it when I see it. I've lived in Cincinnati for 30 years, and if you know if you've lived in Erlanger for a long time- we are not far from each other. The "Snowstorms" that we have had over the years, sometimes are built up hype. The last time the weather was predicted here to get 4-5 inches of snow, we got a light dusting. Another time, we were told it was going to be a heavy snow, and it was rain and freezing rain... and then other times, the weather goes completely around Cincinnati.

I'll believe it when I see snow falling... until then... Hot Air being blown around over the TV airwaves.

You know you are from Ohio, when any or all of the following apply:

You give directions to a destination in "minutes", instead of miles.

You think deer season is a national holiday.

You know which letters in "Cincinnati" are doubled.

You can drive 65mph on ice, without flinching.

You know all four seasons of the year: Winter, Still Winter, Almost Winter, and Road Construction

You have to run both your air conditioner and your heater in the same day.

And.....

You know you are from Ohio, when it is better to drive in the winter time because all the potholes are filled in with snow......