P0301 Cylinder 1 misfire after car idles for a few minutes

[rn3037]

I only have the following two codes P0300 and P0301

When I first start the car it idles normal and if I pull each coilpack connector, the idle changes as expected; HOWEVER, after the car idles for about a minute or two, cylinder 1 stops firing and it idles like crap. I can pull the coilpack connector of cylinder of 1 and the idles does NOT change. The only thing I really didn't check is the O2 sensor, not sure if that would cause my symptoms

Any ideas?

2003 A4 1.8T 6spd Quattro, 108k miles

Stock motor just a testpipe and intake:
- New maf
- New coilpacks
- New plugs
- New fuel filter
- Swapped injectors and coilpacks to each cylinder but cyl 1 persists to misfire

Compression:
Cyl1 - 124
Cyl2 - 124
Cyl3 - 150
Cyl4 - 150

[B6 Dude]

Swap plugs with another cylinder to see if that makes a difference. Also check the wiring harness to cylinder 1. Winston was telling me he had misfires because of frayed wires on the harness.

[diagnosticator]

Notice that the compression in cylinders 1 and 2 is low compared to 3 and 4. I think there could be a coolant leak into cylinder 1, from a leaking head gasket between cylinder 1 and 2. Pull the plugs and compare the firing tip appearance between cylinders 1, 2, 3 and 4. I bet cylinder 1 and maybe cylinder 2 plugs will look a lot differernt than the plug tips in cylinders 3 and 4. When you performed the compression test, did you notice the condition of the spark plugs? Are there any symptoms involving the engine cooling and or cabin heat systems?

[rn3037]

I replaced the coilpack connector clips and harness as well..
I will definitely swap the plugs, I can't remember if they looked different, i will certainly take note. The temp stays right in the middle, I don't have any issues with the heat either.
To me the issue looks electrical because the serious misfire doesn't start right when the car turns on, I think if it were mechanical it would misfire right when it starts up.

[diagnosticator]

Maybe, but I'm thinking the leak opens up as the engine warms up from cold. Does the symptom with the delayed misfiring on cylinder 1 happen with the engine hot or cold? The delayed misfires and the low cylinder compression in cylinders 1 and 2 are what I am looking at together, a leaking head gasket is consistant with the symptom behavior. I think if it was electrical, then it would act like you said, without a delayed onset of misfires. Besides the spark plug appearance, another way to see if the head gasket is leaking, is to get a sample of the engine oil, and send it to Blackstone for analysis. The oil analysis will detect any ethylene glycol coolant in the lube oil. Threre is normally no coolant residue in the engine oil. If the lube oil analysis is negative for coolant in the oil, then a bad head gasket will not be the cause, and can be dismissed as a cause for the misfires. You can specify that only a test for ethylene glycol be performed,. instead of the complete test set, to minimize the cost of the test.

[rn3037]

Thanks for the ideas! The misfire will happen all the time when the car is warm.

What are your thoughts on the fact that I can pull the cyl 1 coilpack connector and the car runs the same? After a couple minutes after startup, cylinder 1 is not firing at all.

[diagnosticator]

Since you already replaced the coilpacks and the power supply wiring harness for the CPs, it sounds to me like there is no ignition or combustion in the cylinder. Because cylinder 1 is misfiring all the time, the spark plug for that cyl will definitly have a different appearance than the other plugs, but should also show evidence of what is happening in the cylinder despite the fact the cylinder is misfiring. If the plug is wet with gas, or oil, or coolant, or is dry, is helpful in determining the cause of the misfires. the misfires may be caused by a problem with the injector power supply harness instead of the CP power or a mechanical fault. Thinking about your problems more, with no evidence of symptoms with the cooling system or cabin heat, it is more likely the cause of the misfires is no fuel delivery to cylinder 1 when the misfires occur. Does the engine sound and run different with the injector harness plug disconnected? If not, then the injector is not working/spraying fuel. Check the resistance of injector 1 and compare with the other injectors. Also test for constant 12 volts power supply to the injector when the misfires occur. (Using a DVM with the test leads connected to the power supply wire and engine ground,)

[rn3037]

Great tips! I think you're right, it could be fuel with cyl 1. I will do the multi-meter tests tonight. I never tried disconnecting the injectors with the car on, but I will do that as well to see if i hear a difference.

[rn3037]

Checked resistance on each injector
All 4 were about 3.4 ohms

Checked Voltage from power wire to injector with car on and off (same result)
All 4 had ~14.1-14.4 volts

Pull injector connector of only Cyl 1 upon STARTUP
Car idles crappy, you can tell Cyl1 is working

Pull injector connector of only Cyl1 after ~2 minutes when the car is misfiring like crazy
No change in idle


* Note: I get a very strong fuel smell in the engine bay when the car is running, not like a leak, but an unburnt smell.

The Cylinder 1 plug did look a little different, it had more unburnt fuel on the plug, the other 3 plugs looked leaner (correct combustion)


Cylinder 1


Cylinder 3

[diagnosticator]

Thanks for the updated information. Based on the latest results, I think the #1 injector is faulty. Besides the electrical properties, the mechanical parts of the spray nozzle can malfunction independently from the electrical function. I recommend swapping #1 injector with any one of the other three, then run the engine and determine if the misfiring cylinder follows the #1 injector to the new cylinder location. You will need to replace the #1 injector after confirming the misfires move with the injector swap, to the new cylinder.

The reason #1 cylinder is firing at cold start up, then develops misfires after a few minutes of warm up, is most likely due to the ECU increasing the injector drive pulse width when rich cold start and warm up air/fuel mixtures are are required, then after a few miniutes warm up, the ECU reduces the injector pulse width to lean the air/fuel mixture for warm engine operation.
Since the injector mechanical nozzle parts are not spraying enough fuel, or the fuel spray is very distorted, due to a nozzle defect, there is not enough fuel for the mass air flow into the cylinder, after a couple of minutes of warm up, the resulting air/fuel mixture is to lean to support combustion, thus the misfires with the engine warmed up. The injector is spraying fuel, but not enough for a correct air/fuel mixture, so the air/fuel charge in the cylinder does not ignite, and raw fuel is pumped through cylinder #1 causing the unburned fuel smell.

The ECU OBD II engine monitors do not evaluate the injector mechanical function, so there is no DTC for faulty spray nozzles.

If this was my problem, I am confident enough about the cause of the misfires to skip the injector swap test, and replace the faulty #1 injector with a known good used injector. But you can decide what to do first.

[rn3037]

Thanks again for the informative feedback, that assumption sounds very probable. I will swap the injectors and send an update.

Here is a vid I made last night, I noticed that the misfire ONLY occurs at idle, if I hold the rpms to ~2000 the misfire stops. This would make sense if the injector was faulty as I'm giving it more fuel.

You may have to zoom in but watch the misfire count on cyl1 vs the rpms, you will see that when the rpms are low (idle) the misfire is constant, but when they increase, the misfire stops

http://youtu.be/7ieXVe_BiWI

[diagnosticator]

Yeah, that video provides clear evidence in support of the idle misfires from a faulty #1 injector nozzle. Nothing else really fits the symptoms and other evidence that exists (and does not exist,) as well as a bad injector in this case.

[rn3037]

Ok more troubleshooting needed, again it is only misfiring when the rpms are ~770 at idle, if I rev to ~2200 the misfire goes away. Valve problem in Cyl1 ?
These are the only codes I am getting, why would I get P0300 when I don't see any other cylinder misfire, only cyl1?

16684 - Random/Multiple Cylinder Misfire Detected
P0300 - 008 - Implausible Signal - Intermittent
16685 - Cylinder 1 Misfire Detected
P0301 - 008 - Implausible Signal - Intermittent


Swapped #1 and #4 injector, coilpack, and sparkplug
Misfire still in cyl 1

Used #2 injector plug on cyl#1 injector
Misfire still in cyl 1

[diagnosticator]

That is suprising! That leaves only the valves and low compression as the cause then. One of the hydraulic cam followers must be pumping up and holding a valve open at idle speed. This allows the cylinder compression to drop a lot, below the minimum compression pressure required to burn the fuel in the cylinder, so the torque output from cylinder #1 is very weak and intermittent as a result. The ECU can only detect a misfire, by monitoring the crankshaft angular velocity, when a misfire occurs, the crank angular velocity deviates from the normal instantaneous velocity, with a momentary dip in the crank angular velocity when the power stroke should be accelerating the crankshaft. Unfortunately, relacing the cam followers in cylinder 1 requires pulling the camshafts out first. This is also consistant with the low compression test results for #1 cylinder.

[rn3037]

Yep, sounds like it, so do you think I should just replace the cam followers and see how it behaves after?

[rn3037]

Ok, put some fresh 93 octane in, fuel injector cleaner, soldered the #1 and #2 injector wires and did some highway pulls/logs. I did get a bunch of misfires again at idle, but then I drove around and never get them while driving and when I came back to let the car cool down, no misfires.

BUT I did uncover that it is running VERY lean at WOT, why is my requested A/F in the 13-14's? Is this a bad O2 sensor?






MAF readings look fine for a stock car with a test pipe

[B6 Dude]

13's are richer than stoic (14.7)

[rn3037]

I"m not sure about howt he stock tune is but at WOT and full boost, shouldn't the A/F be mid low 11's ?