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Technical Misfire, one sooty spark plug, P0300 and P0172 - HELP!

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Technical Misfire, one sooty spark plug, P0300 and P0172 - HELP!

C

Cromatic

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Hello! Sorry in advance for long post :cry:

My check engine light came on a while ago on my 2005 2.2 l petrol Croma.
The fault codes initially said random misfire (code P0300) and intermittently also running too rich (code P0172). On the latest check at the MOT, it only threw code P0300, random misfire. This triggered a MOT failure.

The idle is a bit, but not overly, rough. Only a bit sputtery. The RPM is fluctuating up and down slightly at idle. Sometimes, the car cuts out at idle or when driving very slowly. Then it starts right back up. At higher speeds, everything seems to be working fine, although sometimes when I use too high a gear, the engine seems to run less smoothly. The fuel economy might be a bit worse, although not according to the trip computer.

I replaced all spark plugs and noticed black sooty fouling on plug nr 4 (or whatever plug is closest to the coil pack connector). The other plugs looked fine.

I tried to look for vacuum leaks: The lines I could locate looked ok, I sprayed the intake manifold and all vacuum lines I could find with starting gas, but couldn´t notice any change in idle (but it´s hard to tell when the idle is a bit rough). I also sprayed soapy water over the intake manifold gasket but couldn´t notice any bubbling or rev change. I even blew cigar smoke (!) through the brake booster line into the intake manifold, but couldn´t see any smoke coming out. It probably escaped through the air filter as I didn´t block this passageway, maybe I should have (it was way to easy to blow smoke through the vacuum line, I suspect I need more pressure to work against if the smoke is gonna escape through small cracks). Anyway, vacuum leaks usually causes lean misfires right?

Now, in lieu of better ideas, I ordered a new coil pack. I tried to test the existing one with a multimeter but couldn´t get any ohm-readings anywhere. I tried this with the ignition pack both on and off (i.e., testing both the 9-pin connector of the ICM and the 4-pin connector of the coil pack).

I haven´t tried a compression test of cylinder no 4, maybe I should. I guess it could also be a leaky no 4 injector. I don´t know if either should have thrown a specific P0304 code.

It could also be a defect O2-sensor or MAF I guess, but no such fault codes.

I can´t really tell if the sooty plug number 4 is related to the misfire or not. I thought maybe a defect O2 sensor or vacuum leak should affect all spark plugs equally, and maybe it´s just the no 4 coil that is malfunctioning - hence the new coil pack.

Any other ideas, it would be most appreciated!
 
Cromatic said:
Hello! Sorry in advance for long post :cry:

My check engine light came on a while ago on my 2005 2.2 l petrol Croma.
The fault codes initially said random misfire (code P0300) and intermittently also running too rich (code P0172). On the latest check at the MOT, it only threw code P0300, random misfire. This triggered a MOT failure.

The idle is a bit, but not overly, rough. Only a bit sputtery. The RPM is fluctuating up and down slightly at idle. Sometimes, the car cuts out at idle or when driving very slowly. Then it starts right back up. At higher speeds, everything seems to be working fine, although sometimes when I use too high a gear, the engine seems to run less smoothly. The fuel economy might be a bit worse, although not according to the trip computer.

I replaced all spark plugs and noticed black sooty fouling on plug nr 4 (or whatever plug is closest to the coil pack connector). The other plugs looked fine.

I tried to look for vacuum leaks: The lines I could locate looked ok, I sprayed the intake manifold and all vacuum lines I could find with starting gas, but couldn´t notice any change in idle (but it´s hard to tell when the idle is a bit rough). I also sprayed soapy water over the intake manifold gasket but couldn´t notice any bubbling or rev change. I even blew cigar smoke (!) through the brake booster line into the intake manifold, but couldn´t see any smoke coming out. It probably escaped through the air filter as I didn´t block this passageway, maybe I should have (it was way to easy to blow smoke through the vacuum line, I suspect I need more pressure to work against if the smoke is gonna escape through small cracks). Anyway, vacuum leaks usually causes lean misfires right?

Now, in lieu of better ideas, I ordered a new coil pack. I tried to test the existing one with a multimeter but couldn´t get any ohm-readings anywhere. I tried this with the ignition pack both on and off (i.e., testing both the 9-pin connector of the ICM and the 4-pin connector of the coil pack).

I haven´t tried a compression test of cylinder no 4, maybe I should. I guess it could also be a leaky no 4 injector. I don´t know if either should have thrown a specific P0304 code.

It could also be a defect O2-sensor or MAF I guess, but no such fault codes.

I can´t really tell if the sooty plug number 4 is related to the misfire or not. I thought maybe a defect O2 sensor or vacuum leak should affect all spark plugs equally, and maybe it´s just the no 4 coil that is malfunctioning - hence the new coil pack.

Any other ideas, it would be most appreciated!
Click to expand...


I'd suspect the injector. It could be damaged injector wiring (shorting to ground) but that's less likely. Do you have Multiecuscan or just a basic code reader? If no MES nesx cheap check is to swap the suspwct injector with one of the others and see if the sooty plug moves with it.


Robert G8RPI.
 
Thanks! I don´t have a code reader yet, but I´ll buy one. The codes I got were from workshops doing diagnostics during service. One of the repair guys thought the O2 sensor should be the next thing to change, because of the rich condition.

Would be interesting to break down the misfires to see where they occur more specifically, to verify that it is mostly cylinder no 4 that is misfiring. How likely is it that a leaky injector would cause a P0300 code as opposed to P0304? It was the randomness of it that made me suspect the coil pack (and the fact that these coil packs are known to fail).

My hope is that the entire coil is weak enough to cause random misfires but that coil no 4 is in such a bad shape that the no 4 cyl runs rich all the time.

FWIW, the mileage isn´t that bad for a 12 yo car, 120 000 km (75000 miles). Sometimes, randomly, other warning lights come and go (ABS, ESP, hill holder malfunction), but only very sporadically.
 
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Hi,
It's hard to tell the probability of a specific misfire detection. Have you tried diconnecting the MAF sensor?
If youdo your own work it is worth looking at Multiecuscan www.multiecuscan.net and a USB ELM 327 adaptor rather than a generic code reader? It does so much more and is Fiat specific.
Not many Cromas here in the UK, less than 800 and few of those are petrol (I have a 16V mJTD).

Robert G8RPI.
 
Thank you for your response.

I will indeed get ELM327-interface + Multiecuscan asap. I find it peculiar that the the only two DTC-codes pertaining to this issue that I have been able to get from the car is P0300 and P0172. I would suspect that failures of the MAF, MAP, TPS, O2 or any other sensors would have trigger corresponding codes?

FWIW, the new ignition coil did not solve anything, the idle is still rough and RPM fluctuating.

I can always try to disconnect and/or clean the MAF-sensor, to see what happens.

Regarding the injector: I listened to the ticking of the solenoids using a stethoscope on each injector, they all sounded the same to me, indicating that they operate the same. But I guess that simple test really does not rule out injector leakage - it sure would explain the one carbon fouled plug.

True enough, the 2.2 petrol Croma is not a common vehicle neither in the UK nor in Sweden. However, the engine itself is a GM Ecotec L61, which is a very common engine. Still difficult to troubleshoot though - for instance, I still haven´t figured out how to locate all the vacuum lines.
 
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I now did a compression test on all cylinders.

I first tried with the engine cold, and got a disheartening result: cylinder no 4 (the one with a sooty spark plug) got around 150-170 PSI, whereas the other three got 195-200 PSI :cry:.

I then took the car for a drive to get the engine up to working temperature.
After that, all four cylinders displayed the same compression of 190-200 PSI.

I know it is mostly recommended that you only do compression tests with a warm engine, even if the Croma eLearn-manual actually does not mention that the engine should be warm when doing the test.

So it´s either one of two things:

1. You can´t rely on compression measurements on a cold engine, and the compression is actually fine.

or

2. The piston rings are worn and when the engine was warm and the rings probably got a bit of extra seal from the engine oil, the compression improved (the same way a squirt of oil directly in the cylinder could improve compression temporarily).

Unfortunately, it would probably be too much of a coincidence that the sooty plug cylinder was the only one that got the poor cold engine compression, or what do you think?
 
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Cromatic said:
<SNIP>

Unfortunately, it would probably be too much of a coincidence that the sooty plug cylinder was the only one that got the poor cold engine compression, or what do you think?
Click to expand...

I'd say the chance was about 1 in 4
icon12.gif



If the warm compression is OK there is no gross failure. The next logical step is to rule out the injector(s). This means a leakage and spray pattern test, swap two around or replace the suspect one. I don't know if you have to "tell" the ECU an injector code when changing them on this engine or not.


Robert G8RPI.
 
g8rpi said:
I don't know if you have to "tell" the ECU an injector code when changing them on this engine or not.
Robert G8RPI.
Click to expand...

Looking on MultiECUScan at the Croma 2005 2.2 then injector coding is not supported. I also checked a few other petrol engine models and they also have no injector coding support.

Have never really thought about this but it seems that injector coding is for diesel injectors only.

This is an interesting read: http://www.carwood.co.uk/latest-news/test-article-one-copy-copy-copy
 
g8rpi said:
I'd say the chance was about 1 in 4
icon12.gif
Click to expand...

Haha, well given one (and only one) sooty sparkplug and the possibility of getting a low compression reading in any combination of cylinders, the likelihood of getting low compression only in the sooty cylinder by way of chance is probably more like 1 in 14 I think ;).

And maybe that´s what happened, because when I repeated the cold exercise the next morning, all cylinders were at around 200 PSI on multiple tests. Except that it probably wasn´t chance but more likely some mistake on my part :bang:.

On to the injector, if I´m lucky my friend will come over with discarded lab supplies he has revived in the form of an oscilloscope and an ultrasound bath.
 
Or I think actually, 1 in 15 is more correct...:)

Anyway - I removed the suspected fuel injector and it seems to be stuck open. You are not supposed to be able to flush gas through it with a syringe in either direction when it is removed, right? The solenoid is only supposed to open when voltage is applied, otherwise closed? No wonder it´s rich...

On the other hand, if it is stuck open like it seems to be now I would expect the problems to be much worse, like reeking gas from the exhaust, really rough idle, black exhaust smoke etc.
 
After spraying through the injector several times with throttle body cleaner and compressed air (using a 9v battery to activate the solenoid) I seem to have unstuck it. It now opens, closes and holds pressure without leakage, as far as I can tell. The spray pattern seem ok, and the internal resistance is 12 ohms. Now I´ll just change the o-rings and put the injector back in the engine.

We´re yet to see if this 25 $ solution solves my rough idle and CEL issue though...:confused:
 
This little thread and problem / diagnosis / resolution has so many quality positives regarding knowledge, experience, not being ripped off by not so ..... garages.

What I'm saying is that any computer diagnostic program can read thrown error codes and then offer possible causes. The PLAUSABILITY of any situation/diagnosis requires the experience and knowledge of a suitably trains and experience technician.

Sadly in recent years old school technicians are fewer and far between meanwhile the manufacturers put 100% faith in their diagnostics information delivered from their systems and many end customer facing garages take the bait. New turbo, new this, new that required when all that was required was a simple "clean up".

Even if my vehicle is under manufacturer's warranty and all reported faults etc. are fixed free of charge I still get concerned about my car being subjected to multiple procedures and unknown (personally trusted) technicians working against a stipulated "authorised time" when I know in many cases the "time" is wishful thinking OR they can undercut the authorised time benefitting the dealer.

For company cars owners, lease contract, fixed whatever owners they do not possibly care. For those of us that personally buy our vehicles we have different quality, agenda, service, etc criteria. This criteria is we care, we love (read protect our investment), we are not as stupid etc etc that the industry would like to think we are.
 
OT: I completely agree with not being able to trust mechanics, that´s actually the main reason I am doing this myself - I expect to be ripped off.

When I first got the CEL, I took the car to an Fiat-authorized garage. Even though the idle was rough and it threw a P0300, they didn´t even bother to check the spark plugs! If they had, they would have noticed the sooty one and could have worked from there (and would probably have gotten paid more in the end).

Instead, they just removed the coil pack and checked for oil in the spark plug wells (?) and when they couldn´t find any, they just cleared the CEL and told me to keep driving. If the light came back on, they would replace the O2-sensor. For this nonsense they charged me the equivalent of 120 GBP. Wrong on so many levels, just the fact that they told me to keep driving with a rich mixture tells me they probably wanted to ruin my cat.... ;).

I was myself uninformed at the time, but doing research online, and getting some good tips from you guys, I have learnt a lot and gotten to know my engine in the process. So some good have come out of all this, but my trust in shops are at an all time low.

OnT: unfortunately, my injector cleaning didn´t solve the problem. However, I followed Roberts advice and switched the injectors around, and sure enough, the sootiness followed the suspected injector. So I guess (hope) it´s the (only) culprit.

I have now ordered a set of 4 (properly) refurbished injectors from a shop in California. I´ll change them all out and pray to some Italian gods...I´ll let you know.
 
After the US Postal Service managed to lose my first set of injectors somewhere in the States, a second set recently arrived in the mail (hence the delay).

I swapped out all four injectors, which was straightforward enough, and as far as I can tell after a fairly short test drive, there is a noticeable improvement; the idle feels and sounds smoother and the tachometer is now rock steady at just over 900 RPM:s, i.e. no more hunting.

Now, if this fix actually solved my problem or if the improvement was just a figment of my imagination is yet to be verified. The next step is obviously to reset the CEL and wait for it to never come back on :). Tomorrow, I´ll get the interface cable.

Two more questions:
1. Is it possible to reset the CEL and clear the error codes using only the freeware version of MultiECUscan and an ordinary ELM327-cable (i.e. not the green adapter cable)?

2. I´ve heard that some codes get cleared automatically by the ECU, which then also turns off the CEL, if a fault is fixed (after a few cycles of engine warmup-cooldown). Is this true for the Croma, and do you know if that only pertains to specific error codes?

Thank you!
 
Hi,
Three on/off cycles might clear the light, but the codes will still be stored. You don't need an adaptor lead to reset with Multiecuscan,but you do need the registered version for the Croma. Still cheper than a dealer doing it though, only €50. If we don't support the writer (who is a Forum member) they will have little incentive to provide continued support. Treat the car to a tankful of premium fuel to help clean out any deposits from the faulty injector.

Robert G8RPI
 
Bought the cable, bought the multiecuscan license, cleared the codes, and passed the MOT (including the emission control)- phew. Of course, I´ll need to drive it some more to see if it stays this way.

I heeded Robert G8RPI´s advice and filled up the tank with premium gas. Ironically, after doing so, the car cut out three times in a row just after leaving the pumps, and was hard to start. This is the first time this happens after changing the injectors.

This is also the first time after depressurizing the fuel rail (when changing the injectors) that I even opened the gas cap, which I had left screwed on during the depressurization (accidentally, most guides mention this should be unscrewed). I don´t know if that has anything to do with it. Obviously, the new fuel wouldn´t even have reached the injectors by the time the engine stalled. Maybe it was just a coincidence, but it was strange nevertheless.

Anyway, this isolated mishap did not trigger any error codes and the car ran fine afterwards. Hopefully a one-time occurrence :confused:
 
After a few weeks of driving, I have noticed some things:

-When coasting slowly, like stepping of the throttle when approaching a red light, the RPMs will fluctuate slightly, usually between 500-1000 RPMs, until it reaches a stable idle of about 900 RPMs. It doesn´t cut out/stall when this happens. This seems to be a common problem as you can find hundreds of posts about this issue online, but the suggestions and verified fixes varies wildly so no specific clue there.

-It does not cut out like it used to (except for that one occasion mentioned in my previous post), however it has cut out at two different occasions when going slowly in reverse right after starting (with warm engine, on level ground) - the last time it happened three times in a row until I gave enough throttle to keep it from doing so.

I don´t know if these symptoms are related, and otherwise the car is running fine without and without throwing any error codes. But of course I want to make sure this is not a sign of impending trouble. Could it be a vacuum leak? I did try to locate one earlier using plenty of starting gas around the engine bay but could not locate anything dodgy, but I guess if the leak is small or hidden enough, it could escape detection.

To sum up, I have already:
-Changed out injectors
-Cleaned MAF
-Changed spark plugs
-Changed air filter

Any suggestions?

EDIT: Just noticed that according to the eLearn manual, the idle speed for the 2.2 petrol i supposed to be 750 +/- 50 RPM - I´m at slightly above 900 RPMs. This could indeed indicate a vacuum leak.
 
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