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I went for a spirited drive this AM in my 2006 997.1 c4, and this afternoon, during some leisurely driving the car suddenly experienced, then continued to experience cylinder misfires after a gentle stop into a red light. I limped the car home at around 2krpm, about 20 miles. Above about 2,500 rpm with throttle > ~30%, the misbalance is significant and felt like "pushing it". At idle the misfires can be felt. At 2k, car was relatively smooth and felt within "mechanical sympathy" range. This is noticeable, continuous misfiring at all RPMs - not "a few here and there". Oil pressure, Oil Temp, Water Temp all fine.
The car is in good shape. I've recently removed the airbox / replaced the filter / and replaced the water pump. Car ran fine for about 1-200 miles thereafter until the misfires today. The car has lower mileage - approx 45k miles. It is a fair-weather car that sees about 1500 miles a year. The last time I drove it was last Thursday prior to today. Last thursday day, I drove the car in the low gas (gas light) state for about 15 miles, then fully refilled - i rarely do this. Bore scope of all cylinders fine during PPE about 2,500 miles ago.
OBD showed the following codes in order, though these are simply a fraction of the hundreds / thousands I experienced over ~20 miles.
is the fuel trim + on Bank 1 - on Bank 2 "within range"?
it's not a particularly hot day today - around 75-80 degrees. is IAT of 100F normal on a warm car? Doesn't seem too high.
the 32 degree spark advance at 2krpm and low load seems way high - does the fuel map call for this much advance at some very extreme AFR?
is the MAF output within range?
So basically, all but C4/5 misfired - both banks.
This seems to rule out:
- single cylinder compression failure
- single cylinder spark plug / coil pack failure
- any single bank scoring related failure (zero indication of piston slap)
I'm thinking it may be any number of below:
- Air supply issue - air intake post MAF - need to check nothing is open / loose, maybe re-seat filter
- MAF issue? if anyone can tell me if that flow rate seems "ok" - I'll clean it, but a "sudden" fouling seems improbable
- Bad gas (composition) can rule out with filling with better gas / octane booster perhaps?
- Bad gas (sedimentation) - can all the injectors get fouled instantly there should be plenty of filtration well before the injectors...
- Fuel pressure issue? Pump going out? - how to test system pressure? Can purchase a Foxwell - this is a Carrera 4, so I believe it has redundant / two pumps due to the odd shape of the tank.
Clear codes.
Soon after cold engine startup, try to reproduce the problem. (Is engine bay heat affecting anything?)
Clear codes.
Reseat MAF connector. Try to reproduce the problem.
Clear codes.
Clean MAF. Try to reproduce the problem.
Clear codes.
Change out (most of) the gasoline. Try to reproduce the problem.
I had a few moments with the car earlier today before seeing these posts. Thanks guys.
- cold start - same misfires
- cleaned MAF with CRC very liberally, start- same misfires
- cleared codes, start - same misfires
- didn't see any loose lines, and the Throttle Body tube was property cinched.
Any way to test resistance on the MAF to ensure within range? The MAF itself looked very clean / no visible dust.
I'll drain the tank via the test port method. There's a bit more than half a tank in there.
You may not be able to effectively measure the resistance of the MAF directly but I believe that on some of the diagnostic tools (like Durametric) you can view the voltage (and under the conditions that provide the best information). Perhaps an experienced Durametric user will jump in to offer that guidance.
I got my foxwell yesterday and did some diagnostics today:
Cleaned MAF again, then:
MAF Accessories on, engine off: ~1.02V
MAF engine on (during warmup enrichment): 1.6V
MAF at 800 after warmup enrichment: 1.43-44V These values seem within range please confirm
Cam deviation within 1 degree
Fuel trim both banks around .97/1
After clearing codes on the DME, Cyl 1/2 triggered misfires. On checking cylinder roughness, presented as follows:
C1: -3
C6: -4 C2: 16 (very high)
C4: -7
C3: -1.6
C5: 3 (deviates from 1/6/4/3 but not that high)
Seems C2 and 5 are consistently "rougher" than the others with the MAF in. While I didn't see the C2 misfire counter go up, C1/2 misfire codes came up on the OBD. Now I'm wondering if it might be a spark or fueling issue in that one cylinder. Does one bad coil potentially cause other coils to misfire? Seems unlikely but is it possible over a ~20 minute duration such as when I limped home?
Weirdly, after removing the MAF, the roughness on all cylinders is near 0 on the Foxwell, but the car needs some pedal on start to get into idle and in no way feels "normal" - still feels rough.
Will pull heat plate and check coil condition, don't know last time they were changed. It doesn't really seem like an MAF issue anymore.
We do not know the milage (or the operating hours which is better) but .1 cars go through coil paks at an alarming rate ( aprox 40,000 miles, like water pumps). Coil pak problems throw misfire codes (if you are lucky) and other stuff that makes no sense. Coil pak failures occur all of a sudden and usually when the engine gets warm, however this is an electrical /thermal issue and can do crazy stuff. Ignore all the other codes until you check for coil pak problems. .2 cars have the same potential problem but they last about 90,000 miles.
Report back.
To continue to diagnose without waiting on new parts, swap the suspect coil to another position that's not throwing codes, and see if the misfire follows it.
Thanks jchapura and ffloyd, I'll pull the coils tomorrow to physically examine and flip flop. The car is around 45k so right at the interval.
Do you guys know how to do this electronically via Durametric / other diagnostic tool? In searches others have mentioned using Durametric to "shut off injectors" which would be similar to cycling off a faulty cylinder, I'd also like to trigger the high/low cam solenoids to test if it's I might be experiencing overly advanced timing in bank 1 that maybe doesn't jive with the idle AFR.
I don't like the idea of "throwing parts at things" but it seems the coil work is due at this time and will at the very least rule out one failure possibility.
According to another Rennlister - "If you have durametric or foxwell and could run it...to...hear the solenoids actuating (key on not running- DME/Active tests/Driving Links Active/ Run Variocam lift 1+2) ".
AHA there it is - thank you sir. I was unable to find that menu path.
I shut off C2 injection and the idle was worse - dropped from ~800 to 650. It's possible C2 roughness isn't representative of a full misfire. I'll cycle the coils to see if the roughness follows.
Engaging variocam while off, the solenoids fired. Engaging with the engine running, the engine quickly sputtered to death which seems to suggest Variocam is fine.
Examine each coil when you remove it. If you see any cracking in plastic housing, you found your problem. It is obvious on the failed packs I have seen.
Pulled all the coils and plugs today, new plugs and coils arrive tomorrow, the advertised-to-be stronger "rennline" coils were the same price as the Berus on Pelican so I got those:
Sp1 dry, brown Grey, slight oil at base, none on thread. Coil split all sides top bottom.
Sp2 dry, dark brown, slight oil at base, sticky thread, coil split all sides, extra at bottom.
Sp3 same as 1, split 3 sides plus base.
Sp4 similar to 2 but more carbon fouling, cool split two sides, top and bottom
Sp5 browner than 1,3, less fouling that 2,4. No oil on thread, slight at base. Coil split the sides, top and slight bottom.
Sp6 between 5 and 1 on fouling. Little to no oil at base.
Summary: From spark plugs, 2 & 5 seemed to have some fouling which may be indicative of a cold / weak coil. 4 seemed to have a bit of carbon fouling (not just browner like 2/5.
All coils were cracked, but 2 cracked extra. 5 no more cracked than the others. The coils were Beru with the Porsche oem symbol on them as well - assume these were original.
Tomorrow I will bore scope the cylinders, particularly 4 - as i worry the fouling may be caused by oil while 2/5 seem to be a bad burn / richness.
08-04-2023, 11:09 PM
Sudden misfire - multiple cylinders
