Random, intermittent misfire (and I've tried everything)

[elduderino200]

I've been chasing this misfire situation for almost a year and half now...
I'll cut to the chase first, then give you the backstory below:

Codes: P0300, P0301-P306
Random misfire + cylinders 1-6 (all)
(Usually) unnoticeable. No bucking or loss of power. The only reason I can tell is the CEL surprises me and comes on.
I can usually only make it happen when under a load/acceleration but I've noticed thats only because I've put constant power on it long enough for the CEL comes on before the misfire counter resets. Because of this I thought it was a highway-only issue, but I've noticed it's around town too - the counter just resets before the CEL comes on.


What I've replaced:

• Coil pack
• Spark plugs (a half dozen times - NGK, Bosch, cheapo's, etc.)
• Spark plug wires
• Both valve cover gaskets (I wasn't getting any oil on the plugs, but I figured why not)
• Both upstream o2 sensors
• MAF
• Fuel filter
• Air filter
• Coolant temp sensor
• Intake air sensor
• Crankshaft position sensor (twice)
• ECU
• Crankcase/PCV breather hose
• All or nearly all vacuum tubing
• Intake gaskets
• Both throttle body gaskets
• Clutch (obviously unrelated but if it helps diagnose...)

As well as:

• Cleaning the original MAF twice (with MAF cleaner of course, a few months apart - then just replaced the whole thing altogether)
• Putting a can of Techron in and putting a can of Redline in (a ~month apart when the issue returned)
• Swapped injectors from left bank to right and right to left
• Swapped cam position sensors
• Put gas in from countless different stations/brands - all premium. There's also a place nearby that sells ethanol free which I've put in a bunch
• Fuel pressure test (T'd in just before the rail - 50psi)
• Compression test (all 180-190psi)
• Seafoamed (no noticeable change)

Shop tested:

• Smoke test for leaks

The story:
Originally I thought this was an issue caused by putting it under hard continuous acceleration, but I was mistaken. It just seems to happen fairly randomly but its neither constant nor does it last that long when it DOES happen. The misfire counter resets before the CEL comes on - unless I'm on the freeway and can make it happen continuously for 5-10 seconds. It will happen around town but only 2-10 times per cylinder depending on how fast I'm going. If I pull to a stop at a light it will sit at that amount (i.e. not continue to misfire at idle) until the counter resets. The only reason I know it misfires around town is I have vcds hooked up and can watch live or look at the log.


A couple of oddities:
I have changed the spark plugs around and each time I do, something different happens.
One time I put these cheap guys in and it got 20 miles on the freeway just fine, sat for the day, then at night I tried to drive it home and it misfired/bucked like crazy. I got to a gas station a mile or two up the road, put the old ones in and made it home fine (though the bosch's I put back in brought the issue up again later).
More recently I put these guys in and it ran PERFECTLY around town (5 or so miles) - not a single misfire (gf was watching the laptop/vcds live in the passenger seat. We parked, got dinner, then 2 minutes into the drive home it threw out the 2-20 misfires it shows across the cyls. On no particularly tough stretch of road, just accelerating from a stoplight down a hill.

One time it would idle fine but misfire as soon as any gas was given. I took it to the shop and they gave it back a few days later saying that could recreate the issue. I got it back and it no longer misfire immediately after idle, just back to when it was under constant load long enough for the CEL to come on before the misfire counter reset.

It seems like it has something to do with the heat from the engine causing the spark plugs to act erratically but I put NGK +8's in and the same thing happened.

My current Bosch plugs are also pretty carbon fouled, but I can't tell if this is because of them causing it or something else causing it to them. Chicken or the egg situation... I'd be happy to take picture of them if somebody wants it, but it looks like your average dark, sooty, plug.

My last guesses could be a clogged cat, or a coil pack. I don't think it's the coil pack because I get the exact same cylinder misfires with both the original and the new. Could it also be an EGR valve? Fuel pump?


pointless backstory:
Like I said, I've been on this issue for quite some time. I'm a member of the other big audi forum and have asked there and got a ton of great help, but this one seems more active so I figured I'd try here as well.
Here's where I started http://www.audiforums.com/forum/b5-m...-216181/page4/
If somebody suggests something that is already listed there I don't care. Any help at this point is more than welcome.


Sorry for the novel. I was hoping to give enough info to have someone go off.

ANY help whatsoever will be appreciated.


I DO have VCDS! So anything that needs checking via that, I'm all game.
1999 2.8 A4
All stock
163k

[OverSpun]

How old are your check valves and jet suction pump? My car was misfiring until I realized that all of my check valves and jet suction pump were toast. Fixed. Check those out.

[tymatk]

ICM?

[arbeiter]

What does your MAF read @ idle?

Sent from my SM-N900V using Tapatalk

[elduderino200]

How old are your check valves and jet suction pump? My car was misfiring until I realized that all of my check valves and jet suction pump were toast. Fixed. Check those out.

Both are original. I order them tomorrow! Thanks for the suggestion!

ICM?

I always forget on the 2.8's, either it's built into the single coil, or we don't have one. Thanks though!

What does your MAF read @ idle?

I'll get the vcds on there tomorrow. Off the top of your head do you know the measuring block? I most often only use it for misfires.

[elduderino200]

Both are original. I order them tomorrow!

On their way!

I'll get the vcds on there tomorrow. Off the top of your head do you know the measuring block? I most often only use it for misfires.

3.82 - 3.89 @ idle

6.46 @ 1200

code formatting is a little off but I hope you get the idea:
this was sitting in my driveway @ idle, then revving to 1200 (or so) around :21

Group A:	002			
	Engine speed	Engine load	Injection time	Mass air flow
TIME	RPM	1-2.5/.8-2.5ms	2-5/1.6-5ms	2.8-5.6/10-15g/s
STAMP	/min	ms	ms	g/s
0.01	680	1.35	2.56	3.89
0.5	720	1.35	2.5	3.96
1	680	1.35	2.56	3.82
1.5	720	1.35	2.5	3.96
2	720	1.35	2.5	3.89
2.5	680	1.35	2.56	3.89
3.01	720	1.35	2.5	3.89
3.52	720	1.35	2.5	3.89
4.04	680	1.35	2.5	3.82
4.54	720	1.35	2.5	3.89
5.04	720	1.35	2.43	3.89
5.54	680	1.35	2.5	3.82
6.04	720	1.35	2.5	3.89
6.54	720	1.35	2.5	3.89
7.04	720	1.35	2.5	3.89
7.54	720	1.35	2.5	3.89
8.05	720	1.35	2.5	3.89
8.55	720	1.35	2.43	3.89
9.05	720	1.35	2.5	3.82
9.55	720	1.35	2.5	3.96
10.05	720	1.3	2.43	3.89
10.55	680	1.35	2.56	3.82
11.05	720	1.3	2.5	3.89
11.55	680	1.35	2.56	3.82
12.05	680	1.35	2.5	3.82
12.56	680	1.35	2.5	3.82
13.06	720	1.35	2.62	3.96
13.56	720	1.35	2.56	3.89
14.06	720	1.35	2.56	3.89
14.56	720	1.35	2.56	3.89
15.06	720	1.35	2.56	3.96
15.56	720	1.35	2.56	3.89
16.07	720	1.35	2.69	3.89
16.57	720	1.35	2.56	3.96
17.07	680	1.35	2.56	3.89
17.57	720	1.35	2.69	3.89
18.07	720	1.35	2.56	3.89
18.57	680	1.35	2.69	3.89
19.07	680	1.35	2.69	3.96
19.57	720	1.35	2.69	3.96
20.08	720	1.4	2.75	4.09
20.58	720	1.35	2.62	4.03
21.08	680	1.4	2.75	4.09
21.58	760	1.5	2.94	4.65
22.08	760	1.55	3.2	4.93
22.59	960	1.45	2.82	5.76
23.09	1120	1.25	2.37	5.62
23.59	1080	1.2	2.3	5.28
24.09	1040	1.25	2.37	5.28
24.59	1000	1.3	2.5	5.34
25.09	1040	1.35	2.56	5.62
25.59	1080	1.35	2.43	5.9
26.09	1080	1.3	2.5	5.9
26.59	1120	1.3	2.56	6.11
27.09	1160	1.3	2.43	6.18
27.6	1160	1.25	2.37	6.04
28.1	1160	1.3	2.43	6.11
28.6	1160	1.3	2.43	6.04
29.1	1160	1.3	2.37	6.11
29.61	1160	1.3	2.5	6.18
30.11	1200	1.3	2.5	6.32
30.61	1200	1.3	2.43	6.39
31.11	1200	1.3	2.5	6.32
31.61	1200	1.3	2.5	6.32
32.11	1240	1.3	2.43	6.46
32.61	1240	1.3	2.43	6.46
33.12	1240	1.3	2.3	6.39
33.61	1200	1.3	2.43	6.39
34.12	1240	1.3	2.43	6.46
34.62	1200	1.25	2.43	6.32
35.12	1200	1.3	2.43	6.46
35.62	1200	1.3	2.43	6.46
36.12	1200	1.3	2.43	6.46
36.61	1240	1.3	2.37	6.53
37.12	1200	1.3	2.43	6.46
37.63	1240	1.3	2.5	6.46
38.13	1200	1.3	2.43	6.39
38.63	1200	1.3	2.5	6.32
39.13	1200	1.3	2.43	6.46
39.63	1200	1.3	2.43	6.39
40.12	1240	1.3	2.5	6.39

[elduderino200]

No dice with the new parts :(
I did notice there was a lag with me putting a load on the car and the misfires. I pushed it getting onto the highway and it was only a few seconds after I reached cruising speed that they started to count up. I then got off and was able to do it again but this time by pushing the clutch in and revving it up to 5k or so for a few seconds. The misfires didn't count up as I was doing it but a few seconds after going back and driving normally they did.
That has to be a clue right? Heat? Fuel pressure?

Again I'm open to any and all suggestions!

[bhusted]

Have you replaced any of the other vacuum lines? The 30v has a spiderweb of braided vacuum hoses above the throttle body. I replaced all of the hoses when I still had a 30v and noticed a difference in mileage. Never had misfires though. I also see that you replaced the PCV hoses. Did you also get the one that goes under the throttle body on the driver's side down low? Some kits neglect that one.

[vrmm]

If I was in your shoes I'd try lowering the gap on your plugs. I doubt that'll work. I don't even run 8 as a heat range(1.8t) and my egts go to 1700 -.- Stock is 6 is it not? I don't know squat about 2.8's, but triple checking vacuum lines isn't the worst idea. I've had lines blow off from boost and not cause misfires, but it's worth looking over.

Your idle rpms seem low from what I get. Mine has 800-900.

[elduderino200]

Yes I've replaced all the lines above the TB with new vacuum hosing.
The pcv hose I got didn't have that extra piece. I got this one https://www.amazon.com/gp/aw/d/B00BQ...?ie=UTF8&psc=1

[bhusted]

There is another one of those corrugated hoses under the intake on the driver's side near the back. When I replaced mine it was worse than the ones that connected to the valve covers.

https://www.europaparts.com/crankcas...xQXRoCq6zw_wcB

[elduderino200]

If I was in your shoes I'd try lowering the gap on your plugs. I doubt that'll work.

I've tried more than a few different sets of plugs all with relatively different gaps, and unfortunately nothing has worked. I believe stock gap is supposed to be .3, so would lowering it help misfires at (or just after) a heavy load? I'm all game to try it, I just don't see the logic behind it.

I don't even run 8 as a heat range(1.8t) and my egts go to 1700 -.- Stock is 6 is it not? I don't know squat about 2.8's, but triple checking vacuum lines isn't the worst idea.

My theory that the plugs were heating up and causing the misfires as the car heated up may not hold much weight, but would getting lower temp plugs help? Keep in mind mine are pretty sooty which I thought was a sign of too-cold to begin with.

Your idle rpms seem low from what I get. Mine has 800-900.

I can't find what stock should be nor can I find how to change it. It has never misfired at idle though.


Also, would running a can of seafoam through help? I can't see why it would at this point, but could there be some carbon buildup in there that blocks just enough airflow that it matters at heavy load but not under casual driving conditions?
As you can see I'm really reaching for ideas here.

- - - Updated - - -

There is another one of those corrugated hoses under the intake on the driver's side near the back. When I replaced mine it was worse than the ones that connected to the valve covers.

https://www.europaparts.com/crankcas...xQXRoCq6zw_wcB

On its way! Thanks

[Quattro420]

Is there water under your battery and around the booster?

[elduderino200]

Yes. The plastic weather piece that runs along the bottom of the windshield has some cracks that leak water into that area. I wouldn't say there's standing water but it's certainly wet along with leaves/debris.

[vrmm]

If you're wanting to find something that would be causing detonation I wouldn't pick the plugs first. Loads of carbon deposits would be more likely than plugs, but still doesn't seem like a likely cause.
Lowering the gap to say.... .028 is what I would try, but even if that did help, which it won't, you'd still have a different problem elsewhere. Being naturally aspirated it shouldn't need to be lowered.
After a wot a lower gap wouldn't help. You could shine a light through your spark plug hole and see what the pistons look like to determine if there's a ton of carbon or not. Still don't think that'd be it though.
I guess I don't have any useful advice :) Good luck!

[elduderino200]

Like I've said before, any suggestion is help to me, so I'll take it.
Next time it's not pouring out, I'll take them down to .28. Due to all this diagnosing, I've got a few spare sets of plugs so I can do the gapping inside then just make the switch and have the current plugs spare.

[Quattro420]

Make sure there's no water in your brake booster, the vacuum line can suck water into it

[elduderino200]

Make sure there's no water in your brake booster, the vacuum line can suck water into it

Interesting. I went out today and took the battery out and cleaning out all the gunk, leaves, dirt from under it and tried to get as much from underneath the brake booster as I could but there wasn't an easy way to get under it.

Is there a way to get water out of the booster? I don't know if there's any in there yet as I didn't have time to really look and check after removing the debris.

[elduderino200]

Nope :( nothing but air in the booster. Thanks for the suggestion.

Got me thinking? Could the vacuum pump be going out? Or strong enough to drive my car around town but not strong enough when I push it hard?

[elduderino200]

Another thought:

At one point in my diagnosing I was told to unplug the MAF to see if that helped. It was quickly refuted as diagnosis technique because evidently this causes the computer to just put it in a loop where it knows the correct fuel/air ratio to put in. The thing is, I THINK my car runs better with it unplugged. I can't be certain but it feels a bit smoother.
Of course VCDS can't log misfires with it unplugged (god knows why) so I can't tell for sure.
If I knew it ran better could this be of help though? Could this rule out electrical and spark issues? It would HAVE to be something with the fuel or air right?

[elduderino200]

I should also mention, I've found it definitely does misfire at idle. Just once or twice before the counter resets though.

[elduderino200]

Fuel Pressure Regulator


the goddamn fuckin fpr. a $30 part.


thanks for everybody's help!

[bhusted]

Glad you found it.

[elduderino200]

just kidding!

back to it's old tricks...

Interesting that I replaced the fpr, put it through every scenario I could to mimic the issues before and it didn't give a SINGLE misfire, and now just going around the block and theyre back.

last thing I could possibly change is the fuel pump. so why not!

[bhusted]

Just realized that you're local. I'd be happy to meet up and try to help trouble shoot.

[SN95Audi87]

Fuel, Spark, and Air. If the other two are operating accordlingly. Time to start looking a fuel system as a whole. Let us know if the pump went bad.

[elduderino200]

I'm really starting to look at fuel as an issue.

I was under the impression fuel pumps didn't "intermittently" go bad like in my scenario, but it seems that may be the case.
Why did it work flawlessly for an hour or so two days ago? Lord knows. But hopefully it's something as 'simple' as a fuel pump. Despite the fact the shops says they tested the pressure and all was well.

I've pm'd bhusted and hopefully he'll have time soon to help me look at it. I'm sure a set of experienced eyes will at least provide me with a few more possibilities to look down.

[TOOGECKO]

Any progress with this as ffar as resolution? I think I may have a similar gremlin

[elduderino200]

No major breakthroughs so far.

I did meet up with bhusted this morning and he was very helpful in eliminating ignition as an issue. So we're left with air or fuel.

At the moment I'm researching knock sensors as he and I both feel no lag in the engine so it may just be something like that.

Please do post anything you find regarding your issue. All feedback/tips are welcome!

[elduderino200]

Well I unplugged one of the knock sensors and went for a drive, then unplugged the other as well and went for a drive and both times I was getting the same misfires.
I'm not sure whether that means anything but my theory was that if I unplugged them I would get either no 'recorded' misfires or something else. Seeing as it gave me the exact same symptoms, I'm guessing it's not an issue with the knock sensors.

[bhusted]

Very surprising. Like you, I wonder how the ECU can report misfires without the knock sensors plugged in. Are you sure that you had actually unplugged the knock sensors and not something else?

[bhusted]

Thinking about this some more...While we were working you mentioned dropping something into the bell-housing and causing some damage. According to some other sources, one way for the ECU to detect misfires is an analysis of the crank position sensor signal. http://ilot.edu.pl/KONES/2001/JOK200...%201-2/R39.pdf

Is it possible that either the sensor or flywheel tone ring was damaged and not repaired? From my experience, the engine won't run at all if the ECU is not getting a valid CPS signal, but if some of the "windows" in the flywheel ring were damaged, I wonder if the ECU would interpret them as misfires occasionally. This would also support the result that some cylinders seem to get more misfire counts than others.

[elduderino200]

While it's very very possible that the bit I dropped down in there caused some damage and is recognized now as misfires, I think it's not why we're seeing them, for a few reasons.

First, the misfires had been happening well before I dropped the bit down there. I dropped the bit down there (and had to have it fished out) in September of '15 and this misfire issue has been plaguing me since the summer of '14.

Second, the shop never mentioned an issue with the flywheel when they dropped it to fish the part. What sheared was the rear main seal (which was obviously replaced) and the flywheel was put back with a new clutch kit because mine was getting old. No mention of any damage to the flywheel 'windows'.

Lastly, and I may be wrong on this one, but if I think I understand from that paper that the CPS reads the 'windows' independently. So each time I started the car up it would register some specific 'windows' with cylinders and the damaged cylinders would be those that we see the false misfires on. However in my case we ALWAYS see cyl 4 as the main culprit and others following. Were the flywheel damaged I would the most offending cylinder would jump around.

[nemick]

Does your car still have stock injectors?

[Quattro420]

If this were my car I would install a fuel pressure gauge, hook up vag watch my misfire data car running, I'd spay my Ignition module with water and see if it shows any misfires then tape the fuel pressure gauge to the windshield and go for a drive. If your getting p0300-p0306 then it's got to be something related to all cylinders ( fuel vacuum ignition mod ECM ect) if your pcv is gone to shit (valve cover gaskets half moon gaskets leaking oil) then that can cause internment misfires. If all that turns up ok and the car still misfires it's a long shot but you can try to source another ECM go to the dealer and get it programmed and try to see, make sure there's no exhaust leaks by the O2 sensors. If you always have one cylinder that seems to stand out more then others for misfires then swap injectors, plugs, not saying you did this but make sure the wires aren't crossed and installed onto correct spark plugs, check compression and do a leak down test, and then make sure you don't have a broken valve spring.

[elduderino200]

Very surprising. Like you, I wonder how the ECU can report misfires without the knock sensors plugged in. Are you sure that you had actually unplugged the knock sensors and not something else?

99% sure they were the right sensors. They were the 3 pin blue ones found at the back with the o2's, crank sensors, etc.

Also here:

http://www.autozone.com/repairguides...00c152800c2d35

[elduderino200]

Does your car still have stock injectors?

Still on stock injectors.
I did switch them for one bank to the other but the problems stayed put so I was fairly certain the injectors weren't the issue.

If you or anybody else is confident the injectors are the issue, I don't mind switching them back to see if that changes anything, it's a pretty easy job, and free.

[elduderino200]

If this were my car I would install a fuel pressure gauge, hook up vag watch my misfire data car running, I'd spay my Ignition module with water and see if it shows any misfires then tape the fuel pressure gauge to the windshield and go for a drive. If your getting p0300-p0306 then it's got to be something related to all cylinders ( fuel vacuum ignition mod ECM ect) if your pcv is gone to shit (valve cover gaskets half moon gaskets leaking oil) then that can cause internment misfires. If all that turns up ok and the car still misfires it's a long shot but you can try to source another ECM go to the dealer and get it programmed and try to see, make sure there's no exhaust leaks by the O2 sensors. If you always have one cylinder that seems to stand out more then others for misfires then swap injectors, plugs, not saying you did this but make sure the wires aren't crossed and installed onto correct spark plugs, check compression and do a leak down test, and then make sure you don't have a broken valve spring.

Fuel pressure gauge is on the way. So I'll have to wait until tomorrow or tuesday to check.

I changed out most of my pcv tubes and it didn't fix anything. I also changed my valve cover gaskets but I did NOT change the half-moon gaskets when I did it. If that's a possible issue I can go back.

I forgot to ask, does anybody know stock fuel pressure for the 2.8? I can find it for the 1.8 and I'm not sure that's the same.

[nemick]

I don't know the precise fuel pressure that's called for by Audi, but I would want to see around 40-45 psi. There may be a port on the fuel rail for checking with a hand held gauge, which could be installed temporarily for driving tests.

[elduderino200]

Sadly I didn't see one but the kit I brought as a 'T' fitting so I'll pop that in the line before the rail and take it for a spin around the block