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Hello all, My E36 has been misfiring recently, and am at my wits end with trying to find the culprit. I have no clue as to what it is. So, story time.

My car is a 1998 BMW M3. S52. I purchased the car 3 years ago for cheap, as it was automatic and had a slight blown head gasket. The head gAsket leak was from 1 oil jacket to the block and 1 cooling jacket to the block, consuming about 1 quart of oil every month and 1 cup of coolant every 3 days, of driving to work and school. I've done some mods and maintenance on the car, including a cooling system rebuild, 5 speed swap, and M50 manifold conversion. About 2 months ago, I was driving home from work when my car began to misfire. I shut it down, and started it back up, and the mis was gone. The mis came back intermittently, it would misfire once every few days then it threw the car into limp mode. A set of eBay coil packs fixed it, and it didn't misfire for a few weeks. The misfire returned to mis once every few days, turned to once a day, turned into once a drive, turned into once every ten minutes. The car got to the point where it will misfire after 30 seconds every time the engine is ran. As I was preparing to redo the headgasket, I pulled the trigger on it as the car was undrivable due to the misfire. OBD codes were random misfire, and then misfire codes for specific cylinders but in random intervals, I would get a misfire on cyl 2, clear the codes, mis on cyl 5 and 6, clear, mis on cyl 3, like that. Compression numbers before the headgasket from cyl 1 to cyl 6: 170, 165, 171, 173, 168, 170. I did the headgasket job, cleaned the block as best I could, had the head sent in to a machine shop where they resurfaced it and checked the valve seals, head came back in perfect shape. Re-installed and torqued everything to spec, ran compression numbers from cyl 1-6: 187, 195, 200, 191, 192, 196. Yet on start up, the misfire was still present. Chasing the misfire so far, I have replaced: fuel pump, fuel filter, fuel pressure regulator, 3 injectors, (other 3 are less than a year old) and fuel rail holds 50psi at idle, o2 sensor at bank 2 was replaced due to a CEL for that sensor, MAF is less than a year old, replaced Cam position sensor, replaced all 6 coil packs with OEM as well as new spark plugs. Smoke tested the intake manifold shows zero vacuum leaks, including no vacuum leaks in the valve cover. I took the car to a local auto shop, Oceanside motor sports for Diagnosis, they found the auto parts guy had sold me spark plugs for a Volvo with the wrong spark plug gap and heat, so they gave me a set of NGK Lazer platinum plugs. On first start up, the car ran better than it has in the whole time I had owned it. From the 10 mile drive from the shop back to my house, the misfire had come back with a vengeance and showed no signs of improvement, I am sceptical of returning the car to the shop as I basically paid $250 for a set of spark plugs that didn't fix anything.

Any advice on what I should do or any ideas as to what it could be? I'm done with throwing money at this car and I want it fixed. I've done hours of research and have not seen any problems like this, it seems a new set of coil packs and a new fuel filter does it for everyone. Thanks.
 

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Ambitious But Rubbish
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1,231 Posts
Did you replace the boots for the coil packs as well as the coil packs themselves?

eBay coils are your first mistake but you put OEM on - good correction. NGK plugs are good, do you know the model number of the ones you put in?

You may have a wiring issue which will suck to track down. My M52 'vert had one, turns out it was wiring to one of the injectors that I had to re-do.
 

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hookersandblow
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The only way for water to get in there is through the drain plugs for the windshield cowling. It happened on my old car and it isn't going to cause a misfire, it'll completely shut down the car. It fries the whole thing and you're left with a 3000lb paperweight. I ended up getting a new DME because the old one was shot
 

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Check your knock sensor assembly. There are two sensors bolted to the engine under intake manifold that mesh into a single connector. If either of the sensors is bad or loose they send false knock indications to the DME which in turn tries to adjust engine timing to fix the false knock. It will totally hose up your ignition timing.

Also make certain that all the ground straps from the frame in the valve cover are connected. The one by the fire wall is the one that's typically missed. If those ground straps aren't in place you'll get inadequate firing of the coil packs which will give you intermittent/random mis-fires.
 
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