E36 M3 OBD1 Cold start misfire

[adamcontreras]

I'm not sure how much longer this problem is going to last until it's fixed so I figured I'll start logging here until the problem is resolved. It's been about 6 weeks now that I'm writing this.

Vehicle in question is a 1995 M3 S52 swap, still OBD1. There are a lot of aftermarket parts installed on this car but all by me in the past 8 years so nothing I don't know about. Modifications to the engine; AA stage 2 C38-81 supercharger kit installed 3 years ago, 14psi pulley and tune from 22RPD, 42lb injectors, OBD1 manifold, Riot racing throttle body, AFE throttle body spacer, Snow performance Water meth kit with a solenoid installed so no fluid gets pulled into intake under vacuum, 3.5" 540i Maf, DKM flywheel, E46 M3 factory clutch and 6 speed transmission, I might be forgetting some things but that's the gist of it.

The issue used to be intermittent but has come to the point where every cold start it will misfire for about 10-15 seconds once starting and then clear up. I have an AEM boost gauge and AFR gauge installed that are aiding my diagnosis of the car as well as an Autologic scan tool. If I give it gas the misfire goes away and it revs smoothly. If the car sits there idling at a stand still in closed loop the CEL comes on and off every few minutes or so and stays on for about 10 seconds then goes away. The stomp test is a 1222 which is a vacuum leak per Google. When I check with the scan tool I get a C9 O2 Sensor control (I don't recall the code number)

When the car is cold start misfiring the inhg is at -12 and the AFR is reading about 10.5:1 so pretty damn rich. Once the car warms up I see AFR at 13.8ish up to 15ish at idle and inhg goes to -15 and stays there, seems low but idle is set at 1,000rpms to compensate for the flywheel chatter. Not sure if that would change vacuum since it's in idle.

List of things I have checked (these aren't in a particular order);

1. I've verified wiring to the MAF is done properly by checking continuity of each wire to the ECU, grounds, power all good. Has proper signal of 1.1v once in closed loop. The reason I looked into this is because the KG/hr were at 28 per my works scan tool. I figured it'll be higher than normal with the blower so I took off the belt and it came down to 20kg/hr which seems high to me but nothing crazy enough to cause the issue.

2. Checked for vacuum leaks in the system. We have a smoke machine at work that doesn't build much pressure but can find small leaks. The only thing I found was a leak at the blow off valve provided by AA with the kit, but it was on the side that is made to vent to atmosphere. I attached a vacuum gauge to the end with the vacuum line to the intake and under vacuum the leak is no longer present telling me when the engine is idling the valve is closed not allowing a leak at that area.
Further smoke testing makes the smoke nozzle blow off when it builds so much smoke in the intake telling me there are no other leaks. Also the car makes full boost as it always did so I'm thinking that's fine.

3. Checked o2 response with scan tool. It is switching from ~0.10-0.74 and everywhere in between, it seems to be switching slowly but that might be the scan tool. The o2 sensor is new Bosch as well. I replaced it about a month ago shortly after these issues arose since I have a few on hand. (I fly threw those and AFR sensors since the blower was installed.

4. Removed idle control valve to check function and clean with carb cleaner. Once removed I found it to have a portion inside that knocks back and forth when twisting which is how it was when new. It's only 3 years old, Bosch as well, when cleaning there were no debris inside it.

5. Did a compression check when cold. 150psi across the board which is low but I'd say good. I have a Cometic 0.120MLS head gasket installed to help with the boost going into it. All cylinders within 5psi of each other so no concerns

Things I need to check;

I am starting to think something is getting into a cylinder or multiple causing a misfire at cold start due to having weak spark from a fouled plug. Thinking it's an injector leaking possibly after sitting for a while and that's what causes the rich mixture and possible issue with o2 sensor having codes and engine thinking it has a vacuum leak because of the increased fuel consumption? Hoping it's that and not something else leaking into there if anything. I will be pulling the plugs an looking into the cylinders with a camera we have here that goes into spaces like that. Also thinking I only get the CEL at idle because there's not enough air compensating for a leaking injector?

I might check into O2 sensor wiring if needed being that I'm getting that code.

Something I've been dealing with since as long as I can remember (not sure if related?) is if I am moving over 10mph and up if I go into neutral or clutch in the rpm's surge from 200rpm to 1200rpm and on bad occasions the car will die. I've never been able to figure this one out so I just blip the throttle on decel in neutral. Same issue I've had on my other 2 OBD1 E36's so I figured it's part of the car. As soon as I idle it's dead set at 950rpm or so per the needle.

I'm no expert but I'm determined to fix this issue with my own hands and maybe someone else's knowledge if anyone here has suggestions please throw them out.

Thank you,
Adam

[adamcontreras]

Went in there on my lunch break, removed all of the plugs to find cylinder 5 looking awfully white. Checked all cylinders with a camera and they all had slight moisture which I believe is from the water meth kit? It's also raining here so I'm not sure if that could cause condensation? Anyways I saw in cylinder 5 a pool of blue fluid (obviously coolant) sitting on top of the piston. Cranked it over with plugs out and a rag over the hole to blow out coolant. I'm going to do an oil change on it tonight so the oil is clean while it sits and waits for the new Cometic gasket to arrive and I'll be pulling the head off Friday after work and sending to machine shop.

I have not overheated the car since these symptoms arose so I'm not too sure what's going on here. I was in a car accident in January that cracked the radiator and caused a leak. Not sure if the auto-body shop drove it around while it was there for 5 months? That would be a bummer.

I'll let y'all know if the issue is resolved. I just don't see why this would have anything to do with my CEL though. Definitely the misfire at cold start would be related but an O2 sensor?

[adamcontreras]

Talking to myself here but the head gasket managed my cold start misfire. Smooth easy repair. Note to everyone when removing cylinder head leave the exhaust manifold bolted on the head. Saves so much time removing and installing it on a bench.