Hunting Down A Strange Misfire ('09 S60 2.5T AWD)

[RecedingTwo]

(Crossposted from Swedespeed to help narrow down the problem)
https://www.swedespeed.com/threads/hunt ... st-8171160

I’ve been experiencing random misfires on my S60 (68k miles) across all cylinders, although never at the same time. The misfires don’t trigger a CEL and aren’t noticeable while driving—only visible via VIDA or an OBD scanner. They (seem?) to mostly occur after the engine is warm, often after about 15 minutes of driving.

Here’s what I’ve tested and replaced so far:

• Replaced spark plugs, air filter, oil, crankshaft position sensor (non-OEM), fuel filter, fuel pressure sensor, coils, injectors, and MAF.

• Tested PCV, checked for combustion leaks, and replaced the oil filler cap gasket.

• Checked fuel pressure (400kpa VIDA, rail gauge matches), fuel pump duty cycle (40-45%—seems high?), and tested for a blown head gasket (all clear).

I've also had a shop do leak down, compression (156 psi across all cylinders), and vacuum tests, all good. They had trouble connecting their tool to the CEM, but I’ve had no issues with VIDA 2014d & DICE, and no codes. I have a feeling that they weren't using VIDA though. They cleaned the CEM contacts anyway.

Oddly, I don’t feel the misfires at all, but they’re logged in VIDA. I also notice occasional "jerks" in stop/go traffic, possibly transmission-related. Fuel trims are also strange: after a cold start, long-term trim rises to 1.11 but drops to 1.06-1.08 after a restart (logged when it was roughly when 50-65F outside).

Lastly I did replace the crankshaft position sensor with a non-OEM part last year (Carquest) due to a ECM-5000 code (wanted to use OEM but didn't have time for shipping), but no codes have since reappeared & things like fuel trim are the same as before.

I'm just super stumped at this point. I feel like I've tried most of the go-to suggestions as far as misfires go without any improvement. Hoping some Volvo-tech gurus can point me in the right direction for diagnosing further.

[br0dy519]

Make sure the integrity of the wiring to all of the ignition coils is in good condition. Remove the cover if you haven't already. It traps heat in there and cooks the conduit, which needs to be replaced.

Make sure your starter and alternator are in good condition. I had a starter that was causing electromagnetic interference and made it hard to actually start the car. There are threads on moving some wiring away from the starter that cause a crankshaft position sensor issue.

Just throwing a couple ideas out there.

[dikidera]

Cold starts always need a richer mixture but I am not sure it is logged as an LTFT. It is possible that either the unburnt fuel is being exhausted due to the misfire(s) confusing the ECM, or your mixture is overly rich causing the fuel trims to try and lean it out.

Start checking the electrical wiring as mentioned above, these cars are now old and only getting older, the electrical installation becomes rock hard and brittle,cracking, exposing many wires and allowing them to short to ground or other unexpected things, including oxidation and corrosion.

[RecedingTwo]

Last I checked the coil pack wiring was good (didn’t see any cracks or splits with clean grounding points) but I can check again.

Ill try to see if I can move the starter wiring away from the crank sensor, I wouldn’t be surprised if the starter was near death given its age haha. Is there a write up on which wire to move?

And as for the trims, wouldn’t a LTFT of 1.08 (ish) mean that the ECU was detecting a lean mixture and is adding fuel to compensate? The weird thing is that the idle trim is fairly close to 0, like -0.19% to 0.23%. I almost feel like the trim stays lower (like 1.03) if I drive slowly & never above 50mph, whereas if I drive on the highway it tends to always creep up to that 1.08 number.

If it helps I seem to have good vacuum, around 18/19in/Hg at idle with the car in drive & AC/fan off. 24ish when coasting at 60mph on the highway. The only thing I noticed was when idling, I sometimes can feel an “odd shake” and when this happens the vacuum will drop to 16 for a brief second.

[dikidera]

Yes it can mean that as well. It depends on how the ECM is displaying it. I have definitely seen inverse lambda being used when adding more fuel, it is calculated as 1/Lambda.

[RecedingTwo]

Ah good to know, leave it to Volvo to make it confusing haha. Is there a way to tell if it’s the inverse? The values I posted are the ones from VIDA.

So Ive done a basic check of some easily accessible wires - like front O2, coils, etc. and nothing seemed broken or wrong. Ill do a deeper dive later this week though.

Quick question, is there a oil-temperature sensor on this car, and where would it be? I wanted to check it because I remembered that when I monitored the oil temperature in VIDA the value wouldn’t increase with driving - it would only change when I restarted the car completely (last I remembered). Could that sensor be used to induce higher fuel trims as a part of the warming up process?

[dikidera]

A read from a generic OBD device(those bluetooth dongles) will display it in negative or positive percentage.

Another way to confirm is, when you go to the Vehicle Communication and select ECM, on the Parameters tab there should be a clickable link at the bottom called 'Description'. When you click that look for the parameter and it will usually explain what the parameter is and what it represents.

[RecedingTwo]

Found a leak! I was trying to smoke test the system for a second time, and this time with a much better light I was able to find a leak around the base of the PTC where it meets the intake pipe. This video shows the leak (ignore the clear hoses -they go to my catch can):



Does anyone know if the PTC is known to leak air? It doesn't seem like a huge leak; video makes it look bigger than it actually is - could explain the slightly higher fuel trims I was experiencing.

Would replacing the PTC work or should I replace the entire pipe? Could be a good excuse to get the do88 intake, good thing it's almost black friday I guess lol.

[dikidera]

Good you found the source! Anything plastic can and will crack given time and heat. Either way, replace what is broken and test.

[RecedingTwo]

Might just replace the PTC grommet for now since it's so cheap ($10 at FCP Euro). Is it a pain to get the PTC off & on the intake? I've already taken the intake pipe off & on before so not too worried about that part.

Also how would I go about checking if my PTC is clogged? I don't think it is, my car passes the glove test for the PCV and all, but figured I should check it to be sure.