2004 S60 2.4L Misfire Diagnosis Help

[superiga]

Need help diagnosing something, sorry that this is long but I wanted to be thorough. My 2004 Volvo S60 2.4L with 165k miles is having issues. 2 years ago it had a really bad misfire in cylinder 4, the screen prompted “slow down or shift up.” It was fixed by changing the ignition coil which was cracked. Fast forward and one year ago the misfire comes back, again cylinder 4, no warning message this time but you could definitely feel it just like the first time. I changed the fuel injector, which did nothing, and replaced the spark plug which was very visually bad and that fixed it. After this I replaced every spark plus and ignition coil in the engine to hopefully solve it once and for all. Now, a year after that it’s happening again. I was driving the car and could feel a misfire, there was no warning message, but it went into limp mode suddenly and I couldn’t go over 30mph, and the rpm would not exceed 3k. I parked and checked the codes, misfire cylinder 4 again, and P0420, which it’s had since I bought the car and has never gone away, forgot to mention that. Checked the spark plug, which was black but otherwise definitely fine, and changed the ignition coil again. Limp mode went away and it drove home just fine with no apparent misfire. 2 days after and the misfire is back, but no message. Now today the message came back and it was misfiring, but went away while driving. Something consistent between all of these incidents over the last few years is that 99% of the time the misfire it mostly on a cold start, then it goes away and runs smooth with 5 minutes of driving. Worth mentioning that when I changed the plugs a few months back, they were all black, not just cylinder 4’s. There is also coolant loss, but it appears to be a combo of a cracked or aged overflow tank, and the heater core leaking into the passenger footwell which I’m going to fix soon. No white smoke or smell, no coolant / oil mixing. I have copied below OBD live data from my drive tonight. It was 50 degrees Fahrenheit outside, it was misfiring for the first 5 minutes with the “slow down or shift up,” message, which went away after 5 minutes, and ran smooth the next 10 minutes until I got home. The data was taken at idle right after I parked. Thank you in advance for anybody who might be able to help me diagnose this or lead me in the right direction!

DTC_CNT: 2
FUELSYS1: CL
FUELSYS2: N/A
LOAD_PCT (%): 18.0
ECT (F°): 181
SHRTFT1 (%): 7.0
LONGFT1 (%): 3.9
FRP (psi): 55.3
MAP (inHg): 10.6
RPM (/min): 754
VSS (mph): 0
SPARKADV (°): 12
IAT (F°): 70
MAF (lb/min) 0.360
TP (%): 2.0
O2B1S2 (V): Jumped between 0.105, 0.435, and 0.805 within a couple of seconds.
SHRTFTB1S2 (%): Also jumped between -1.6 and 0.8 in the same couple of seconds.
MIL_DIST (mile): 55
EQ_RAT11: 0.996
O2S11: (ma or f not sure: -0.012

[jonesg]

possible exh gasses in the coolant system, as the engine cools it draw a small amount of coolant into the cyl.
Engine runs rough on startup until the moisture in the cyl burns off .
A bottle of block tester fluid will indicate whether theres exh gas getting in the cyls.
I would do that test first before chasing the other symptoms.


The other symptoms suggest rich condition, plugs, fuel trims show rich mixture, I'd suspect a vac leak.
But I wouldn't bother with that until I could establish whether the head gasket is leaking or not.

[vtl]

Replace the oxygen sensors, especially the front one. https://www.fcpeuro.com/Volvo-parts/S60 ... al&b=Sedan Ask them which one you need. These sensors to be replaced every 100-150k miles.

MAF can be bad, too.