Baffled by P0304 Cylinder 4 misfire

[AudiGuy-DIY]

This situation has me baffled, so I am looking to the Audizine community for help / confirmation before I have the head rebuilt for this 2.0L CAEB engine.
Here is the situation:
2012 Audi B8 A4, 6-speed manual transmission. My son purchased this car recently, knowing it has a random misfire on cylinder 4. When we initially viewed the car, the dealer let us have it for a few days to check everything thoroughly. It arrived at the dealership with 140K miles and a strong misfire and lean condition due to a cracked intake manifold. They replaced the intake manifold and de-carboned the intake valves, yet it still had a misfire on cylinder 3 (P0303 and P0300). The intake valves were not sealing well, so they sent the head out to have #3 cylinder valves lapped and lifters replaced. They were unable to purchase exhaust lifters locally for cylinder #3, so they exchanged exhaust lifters between cylinders 3 and 4. While the head was off the engine, I examined the cylinders, timing chain tensioner, camshafts, etc. and all appeared to be in good condition. There was no scoring of cylinders and the timing chain tensioner was the new style. After re-installing the head, the engine ran great for a day. No error codes were generated, idle was smooth and fuel trims appeared normal. However, after approximately a day of driving, cylinder #4 began to misfire only when cold (for about the first minute after cold start). Over time (a few weeks of driving) the misfire has continued to become worse, to the point that cylinder 4 misfire (P0304 and P0300) always occurs at idle, even with a warm engine. Occasionally the misfire becomes severe enough to generate a CEL. On a few occasions, a flashing CEL occurred. Scanning engine data shows an increasing cylinder #4 misfire count at the rate of approximately 1 per second at 800 - 1,200 RPM.

Attempting to diagnose the problem, I have exchanged spark plugs, coil packs and fuel injectors between cylinders #1 and #4. Still, the misfire remained with cylinder #4. The PCV valve diaphragm has been replaced. Spark plugs are new. I did notice that the intake manifold was replaced with a salvaged part rather than a new intake manifold. So I have a minos suspicion about the intake manifold. However, I expect an issue with the intake manifold should result in random lean misfires for all cylinders, rather than misfires only on cylinder #4. Yesterday I replaced all four lifters (lash adjusters) in cylinder #4 with new. Yet the misfire continues on cylinder #4. Compression test indicates 185 PSI on all four cylinders - identical readings. I have also exchanged exhaust cam variable lift solenoids between cylinders, with no change in cylinder #4 misfire.

I am running out of anything remaining to suspect other than a problem in the head. However, I am surprised to have such compression test results if the valves are not sealing well. Also, the car dealer sent the head to a machine shop for work before we purchased the car. Supposedly only cylinder #3 valves were lapped because that cylinder was misfiring. The mechanic had sprayed brake cleaner in the closed valves of each cylinder and only #3 leaked through. After lapping the valves, he repeated the test and no fluid leaked through. It seems unlikely that the misfire would move from cylinder #3 to cylinder #4 after re-installing the head. Because of this, the consistent 185 PSI compression test results, and the amount of effort involved in removing and replacing the head, I am searching for any other possible cause of cylinder #4 misfire before assuming the problem is with the head...but I am running out of ideas.

What else might cause a misfire only on cylinder #4? When the flap valve arm in the intake manifold develops a vacuum leak, is it possible that it could be slight enough to affect only cylinder #4?
Any additional ideas are appreciated!

[mtroxel]

You've swapped everything I can think of, and the misfire stays there. All I can think of it either the ECU (unlikely it would just fart on one injector) or the wiring to the cyl #4 injector. Since you have compression and its reasonable to assume you're getting air, fuel is the other ingredient. And I read you've swapped injectors, so a wiring harness issue to that injector is all I have.

[Theiceman]

or put in a bad part ? would suck donkey balls if you had a DOA plug or coil.

[AudiGuy-DIY]

Thanks for the suggestion. I haven't checked the wiring harness closely, other than enough to see that no frayed wires appear near the injector. I will try to trace back from the #4 injector to the ECU. The very confusing point is that, prior to taking the head to the machine shop, the misfire was on cylinder #3...and now it is on #4. I did not yet own the car when the misfire was on cylinder #3 but I had driven it for about a day and recorded ongoing misfires on #3 (P0303). The head work corrected the #3 misfire and later the misfire appeared on cylinder #4. Maybe the cylinder #3 misfire was somehow "covering up" the problem with the #4 cylinder? Otherwise I cannot imagine what would cause the misfire to move from cylinder #3 to #4 (other than the lifters, which I have since replaced).

Because the machine shop really focused only on the #3 cylinder when lapping valves, if I was absolutely certain that re-working the head would solve the problem, I would take the head back in for machine work. However, removing and replacing the head...only to find it still has a misfire on cylinder #4 would be beyond frustrating!

[AudiGuy-DIY]

or put in a bad part ? would suck donkey balls if you had a DOA plug or coil.

Although that would be VERY frustrating, I don't think that's it. I've swapped the plugs and coil packs between cylinders #4 and #1... and again between #4 and #3, just to be sure the problem did not follow these parts. I'm all about trying the easy stuff first. That said, it is entirely possible that I overlooked something else.

[mtroxel]

Do you have access to VCDS? There is quite a bit of cylinder specific info in there. Timing angle cylinder #1, Timing angle cylinder #2, etc. I wonder if there would be any data from cylinder 4 that would be substantially different than the other 3.

[AudiGuy-DIY]

Do you have access to VCDS? There is quite a bit of cylinder specific info in there. Timing angle cylinder #1, Timing angle cylinder #2, etc. I wonder if there would be any data from cylinder 4 that would be substantially different than the other 3.

I have an OBDeleven, which I've used to view O2 sensor output, fuel trim and to graph timing angle versus engine speed (attempting to coordinate a timing event with a misfire). However, I have not been able to identify any unusual readings. I did read somewhere that a camshaft lobe had slipped on the camshaft and caused timing issues. I suppose I would need a degree wheel and the exact cam lobe life and duration specifications in order to determine whether that could be an issue. I do think that is unlikely but also, at this point, I am beginning to feel like I have ruled out most of the likely causes.

I do wonder if the dealership re-used the previous head gasket when they replaced the head the second time. Perhaps there was a leak very near cylinder #3 previously and, after replacing the head, now the leak is in cylinder #4. This is really reaching for a cause (because I've found no other explanation). But the exhaust smells somewhat "sweet" and the chrome exhaust tips have a green ring around them. Maybe this is only coincidence. There is no indication of coolant in the oil and no over-pressure in the coolant recovery tank.

[mtroxel]

Yea you're thinking some unlikely stuff, but I think that's the way to go. All the usual suspects have been ruled out.

[Jet08]

I assume you did the swap around of the fuel injectors, if so did you replace the blue O rings on the injectors and the inlet manifold gasket?

[AudiGuy-DIY]

I assume you did the swap around of the fuel injectors, if so did you replace the blue O rings on the injectors and the inlet manifold gasket?

I did swap the fuel injectors but, because this was done only as a test, I did not bother to change the fuel injector teflon seals, o-rings or the intake manifold gasket (which was changed recently). Swapping fuel injectors between #4 and #1 cylinders did nothing to change the misfire from cylinder #4 to #1; so I assume the fuel injectors were not the problem. There is no fuel leakage from the fuel injectors; so it appears that the original seals are working well (unless perhaps they could be leaking air / vacuum during the intake stroke). As it currently appears, I will need to remove the intake manifold again soon anyway (to rebuild the head). So I will wait until then to replace these seals...unless another cause of cylinder #4 misfire is identified.

[Buffaloa4m]

i have a very similar issue. i am not a car guy by any means but had a great shop diagnose my issues.. they told me after all the usual checks.. and manifold clean that it was prob and ECU and needed to go to audi. just got a call from audi and the LOBE on cylinder 4 has spun. needs new cam and rockers...

[mtroxel]

just got a call from audi and the LOBE on cylinder 4 has spun. needs new cam and rockers...

That's pretty interesting. Every have any oil consumption issues or oil pressure lights?

[Quattro420]

[QUOTE=AudiGuy-DIY;13740568]This situation has me baffled, so I am looking to the Audizine community for help / confirmation before I have the head rebuilt for this 2.0L CAEB engine.
Here is the situation:
2012 Audi B8 A4, 6-speed manual transmission. My son purchased this car recently, knowing it has a random misfire on cylinder 4. When we initially viewed the car, the dealer let us have it for a few days to check everything thoroughly. It arrived at the dealership with 140K miles and a strong misfire and lean condition due to a cracked intake manifold. They replaced the intake manifold and de-carboned the intake valves, yet it still had a misfire on cylinder 3 (P0303 and P0300). The intake valves were not sealing well, so they sent the head out to have #3 cylinder valves lapped and lifters replaced. They were unable to purchase exhaust lifters locally for cylinder #3, so they exchanged exhaust lifters between cylinders 3 and 4. While the head was off the engine, I examined the cylinders, timing chain tensioner, camshafts, etc. and all appeared to be in good condition. There was no scoring of cylinders and the timing chain tensioner was the new style. After re-installing the head, the engine ran great for a day. No error codes were generated, idle was smooth and fuel trims appeared normal. However, after approximately a day of driving, cylinder #4 began to misfire only when cold (for about the first minute after cold start). Over time (a few weeks of driving) the misfire has continued to become worse, to the point that cylinder 4 misfire (P0304 and P0300) always occurs at idle, even with a warm engine. Occasionally the misfire becomes severe enough to generate a CEL. On a few occasions, a flashing CEL occurred. Scanning engine data shows an increasing cylinder #4 misfire count at the rate of approximately 1 per second at 800 - 1,200 RPM.

Attempting to diagnose the problem, I have exchanged spark plugs, coil packs and fuel injectors between cylinders #1 and #4. Still, the misfire remained with cylinder #4. The PCV valve diaphragm has been replaced. Spark plugs are new. I did notice that the intake manifold was replaced with a salvaged part rather than a new intake manifold. So I have a minos suspicion about the intake manifold. However, I expect an issue with the intake manifold should result in random lean misfires for all cylinders, rather than misfires only on cylinder #4. Yesterday I replaced all four lifters (lash adjusters) in cylinder #4 with new. Yet the misfire continues on cylinder #4. Compression test indicates 185 PSI on all four cylinders - identical readings. I have also exchanged exhaust cam variable lift solenoids between cylinders, with no change in cylinder #4 misfire.

I am running out of anything remaining to suspect other than a problem in the head. However, I am surprised to have such compression test results if the valves are not sealing well. Also, the car dealer sent the head to a machine shop for work before we purchased the car. Supposedly only cylinder #3 valves were lapped because that cylinder was misfiring. The mechanic had sprayed brake cleaner in the closed valves of each cylinder and only #3 leaked through. After lapping the valves, he repeated the test and no fluid leaked through. It seems unlikely that the misfire would move from cylinder #3 to cylinder #4 after re-installing the head. Because of this, the consistent 185 PSI compression test results, and the amount of effort involved in removing and replacing the head, I am searching for any other possible cause of cylinder #4 misfire before assuming the problem is with the head...but I am running out of ideas.

What else might cause a misfire only on cylinder #4? When the flap valve arm in the intake manifold develops a vacuum leak, is it possible that it could be slight enough to affect only cylinder #4?


maybe number 3/4 lifter is faulty?

You stated that you had a miss fire on cylinder 3 found the valves in need of lapping so you had that done and during the process they switch the lifters from cylinder 3 to cylinder 4 and now you have a miss on 4?

[S4_SH1640]

I have the same issue, misfires on all cylinders, and sometimes only on cyl 1. independent shops and audi is scratching their heads because we changed all parts mentioned above... plus more.

you're in ct, and it would be nice if we can swap ECUs. however, we may have different part #s since yours is manual?

[AudiGuy-DIY]

[QUOTE=Quattro420;13751795]

maybe number 3/4 lifter is faulty?

You stated that you had a miss fire on cylinder 3 found the valves in need of lapping so you had that done and during the process they switch the lifters from cylinder 3 to cylinder 4 and now you have a miss on 4?

I had suspected this also, so two weeks ago I replaced the lifters in cylinder 4. After all of this...same result: random misfire on cylinder 4 (particularly when cold).

[AudiGuy-DIY]

I have the same issue, misfires on all cylinders, and sometimes only on cyl 1. independent shops and audi is scratching their heads because we changed all parts mentioned above... plus more.

you're in ct, and it would be nice if we can swap ECUs. however, we may have different part #s since yours is manual?

Actually what is so confusing is that my misfire is only on cylinder 4. This limits the possible causes. If you are having misfires on all cylinders, this opens many other possibilities (vacuum leaks, timing issue, O2 sensor issues, exhaust issues, PCV leak, ECU, general lean / rich conditions, low fuel pressure, etc, etc). There are a long list of common causes between cylinders. If all of these common issues have been eliminated, it could be worth swapping ECUs as a test. However, I am unsure if all adaptations, serial numbers and equipment would need to be re-coded to match our vehicles in order for this to work.

[AudiGuy-DIY]

i have a very similar issue. i am not a car guy by any means but had a great shop diagnose my issues.. they told me after all the usual checks.. and manifold clean that it was prob and ECU and needed to go to audi. just got a call from audi and the LOBE on cylinder 4 has spun. needs new cam and rockers...

This is interesting indeed! I suppose if a cylinder 4 lobe spun only slightly it could cause a misfire without affecting compression. My misfire is only a low speed and mainly when cold. Perhaps the engine is more susceptible to the slight difference in lift timing when it is cold. Sometimes when the engine starts cold, it has a steady cylinder 4 misfire for about a minute. Then a slight (but rhythmic) ticking noise begins at exactly the same time the misfire stops. The ticking sounds almost like an old lifter or a fuel injector. I've not been able to locate the source. Maybe this has something to do with the variable lift timing solenoid. I've swapped these solenoids between cylinders 4 and 1 but if the issue is with the cam lobe instead of the solenoid, this would explain why the misfire remains with cylinder 4. It still seems a little strange that I have perfectly balanced 185 psi compression on all four cylinders and no issue with seating of the valves in cylinder 4.

[Novarider]

We've seen a few cases of a bad HPFP causing misfires like this that nobody could diagnose. They changed the HPFP and it went away completely.

[AudiGuy-DIY]

We've seen a few cases of a bad HPFP causing misfires like this that nobody could diagnose. They changed the HPFP and it went away completely.

This is certainly something to investigate. For those cases, were no fuel pressure errors being generated? It does seem that this misfire is reduced when the girl tank is more than 1/2 full, which could support the HPFP issue. However, would a weak HPFP cause a misfire only on a single cylinder? My misfire is consistently on cylinder 4.

There are 4 lobes on the HPFP cam, so I suppose it is *possible* that there could be some sort of timing effect to the pulses from the fuel pump if one of those lobes is worn more than the others. Of course that would be a problem with the cam rather than the HPFP in that case. If I knew the HPFP was the problem, I'd happily pick up a new one today! However, that's a rather expensive test if it does not solve the problem. Any idea how to test the theory of a "weak" or erratic HPFP?

[Novarider]

This is certainly something to investigate. For those cases, were no fuel pressure errors being generated? It does seem that this misfire is reduced when the girl tank is more than 1/2 full, which could support the HPFP issue. However, would a weak HPFP cause a misfire only on a single cylinder? My misfire is consistently on cylinder 4.

There are 4 lobes on the HPFP cam, so I suppose it is *possible* that there could be some sort of timing effect to the pulses from the fuel pump if one of those lobes is worn more than the others. Of course that would be a problem with the cam rather than the HPFP in that case. If I knew the HPFP was the problem, I'd happily pick up a new one today! However, that's a rather expensive test if it does not solve the problem. Any idea how to test the theory of a "weak" or erratic HPFP?

No pressure issues, they had misfires on a single cylinder they couldn't figure out like you. I don't know of a way to test the HPFP.

[Buffaloa4m]

Actually what is so confusing is that my misfire is only on cylinder 4. This limits the possible causes. If you are having misfires on all cylinders, this opens many other possibilities (vacuum leaks, timing issue, O2 sensor issues, exhaust issues, PCV leak, ECU, general lean / rich conditions, low fuel pressure, etc, etc). There are a long list of common causes between cylinders. If all of these common issues have been eliminated, it could be worth swapping ECUs as a test. However, I am unsure if all adaptations, serial numbers and equipment would need to be re-coded to match our vehicles in order for this to work.

I have been having this issue been fighting with the car for two months.. Audi has now determined that the CAM LOBE has spun on the 4th cylindar. All i need is a new camshaft... lifters and when they were in there the chain was majorly stretched. prob do to cam LOBE.. a4 6 speed.. 2013 but late 2012 build 70k miles...

[Buffaloa4m]

please see my comment below.. I would like to know what your resolution of the p0304 issue was.. Mine i would say was catastrophic. I have been having this issue been fighting with the car for two months.. Audi has now determined that the CAM LOBE has spun on the 4th cylindar. All i need is a new camshaft... lifters and when they were in there the chain was majorly stretched. prob do to cam LOBE.. a4 6 speed.. 2013 but late 2012 build 70k miles...

[AudiGuy-DIY]

please see my comment below.. I would like to know what your resolution of the p0304 issue was.. Mine i would say was catastrophic. I have been having this issue been fighting with the car for two months.. Audi has now determined that the CAM LOBE has spun on the 4th cylindar. All i need is a new camshaft... lifters and when they were in there the chain was majorly stretched. prob do to cam LOBE.. a4 6 speed.. 2013 but late 2012 build 70k miles...

I have not identified the cause of my P0304 yet. The misfire happens only at idle. Increasing the RPM only slightly results in no misfire (determined by monitoring misfires per 1,000 revolutions, using OBDeleven). Sometimes the misfire becomes substantially worse. This seems to happen when the fuel tank is below 1/2 full. However, I am not 100% certain of this correlation.

Did the Audi dealership remove your camshaft and measure the cam lobe separation in order to determine that the cam lobe had slipped? If they already had the camshaft removed, that would have been the perfect time to replace it. You said your issue was catastrophic. Did the slipped lobe cause the piston to strike the valve?

If a #4 cam lobe had slipped only enough to cause minor issue with valve timing, I can imagine that could cause the problem I'm experiencing also. However, the lobe would need to have slipped only enough to affect idle combustion. Measured parameters indicate my timing chain had not stretched and cam timing is correct but I am unable to isolate cylinder 4 cam timing. So I cannot eliminate this as a cause. I would welcome any suggestion about how to measure correct cam lobe angle without removing the camshaft.

[tomsgtr]

You have a misfire at idle but no misfire at higher RPM? what is fuel trims at? Short term and long term? Don't say it was good. Actual numbers. Have you ever tried to do a dynamic / running compression test? You may have good static pressure but you could have a VE issue on that cylinder. Possible tight valve guide clearance could cause the valve to hang up and stick.

[AudiGuy-DIY]

You have a misfire at idle but no misfire at higher RPM? what is fuel trims at? Short term and long term? Don't say it was good. Actual numbers. Have you ever tried to do a dynamic / running compression test? You may have good static pressure but you could have a VE issue on that cylinder. Possible tight valve guide clearance could cause the valve to hang up and stick.

I'll need to check fuel trims and get back to you. I've seen short term trim range from slightly negative to "more" positive but I do not recall exact numbers now...will check.
I've not done a running compression test. Would this be done at operating temperature? If so, I'd be concerned that the o-ring that seals the compression gage could melt. Also, my compression gage measures peak pressure, typically obtained after a few seconds of engine cranking. Is an instantaneous pressure gage needed (instead of a peak gage) needed to perform a dynamic compression test?

[tomsgtr]

if you have a typical compression tester, you have to remove the schrader valve. There's plenty of videos on doing a dynamic compression test on youtube. as far as fuel trims.. look at total fuel trims.. short+long term added together. I need fuel trims at idle and at 2500 rpm.

[thebrad]

I am very curious to know if and when this gets resolved. My 2010 B8 2.0t has been plagued with cylinder 2 (P0302) misfires at idle, and ONLY at idle. Flashing CEL at idle, sometimes triggering the EPC light and then stops flashing once I start moving again. With a misfire counter running, it completely stops when driving, but continues to misfire pretty bad when back to idle. Very frustrating and I've been trying to track down the cause. Any insight would be greatly appreciated. Thank you!

[AudiGuy-DIY]

After battling intermittent misfires on cylinder 4 for the greater part of a year, I am finally updating this thread with the solution (for this specific case). Ultimately this was a problem with the head, possibly a very minor valve sealing issue, something worn on the camshaft, etc. Replacing all lifters did not solve the problem. However, one day a few louder click sounds were heard from the engine and the variable exhaust lift solenoid seemed to have stopped working. Shortly after replacing that solenoid, a much louder sound was heard. Apparently something was binding the exhaust camshaft position slider because that slider cracked, sending its spring and steel ball flying inside the cam cover and destroying the cam slider. Fortunately only the upper valvetrain components appeared damaged. The small metal pieces either lodged under the cam area or found their way to the oil pan. Replacing the head (and cleaning the debris from the oil pan) solved the misfire. The engine has been running well for several months since the new head was installed.