s52 swap intermittent miss fire

[dmjensen]

i recently swapped an s52 into my 92 e30 vert. i did all the wiring mys self, took the time to find all my own pin outs. left it obd2 and had the dme flashed of all the unnecessary components. i even have the stock exhaust.

the problem is that i'll be driving it just fine and it could run awesome for three days in a row with no problems, but it will randomly start to miss fire and then it will continue to do so until i shut the car off and let it sit for about 10 minutes. then its fine.

i had bosch +4 plugs, i read somewhere that could cause it. so i switched to ngk iridium plugs. i pulled the codes from it a few days ago and go a bank too lean, 4 5 and 6 miss fire and 2 3 and 4 o2 sensors.

i dont have # 3 or 4 plugged in so that takes care of that.

now my question is, the primary o2 sensors are basically my AFR sensor so if they are bad will that cause the vehicle to miss once in a while like mine is doing?

[7pilot]

I would recommend, ensuring that the DME has a reliable power supply and enure that it and the engine are well grounded.
Make sure that the coils are to spec and are well grounded.
Make sure that the DME is not getting too hot...problem overheating the drivers for the ignition.
I would also pull the instrument cluster, use some de-oxidizer then some di-electric grease on the connectors behind the instrument panel.

m

[dmjensen]

it does, the engine has two ground straps ( frame to block ) and the engine has 40k miles so the coils are more then likely fine. im not sure if the dme is getting too hot but i cant see why it would be the problem because this happens when the engine is just started or even after 30 minutes of driving

[DesertBMW]

I told you in another post, technica flash tunes have this problem. Member The Volta had the very similar problem and he sent his DME back to Technica and so far he did not get his ecu back nor the money.
When you check the codes what codes do you get?

[dmjensen]

I checked the codes a few days ago and i dont remeber the numbers off the top of my head. im going to re scan it tomorrow and put in a new o2 sensor to see what happens. If it corrects it, awesome.

I was asking if anyone else had this problem though, not your opinion on dme flashes. Volta probally had an odd case because thats the first ive ever heard of it and ive read up on everything since you told me.

[328ijunkie]

I told you in another post, technica flash tunes have this problem. Member The Volta had the very similar problem and he sent his DME back to Technica and so far he did not get his ecu back nor the money.
When you check the codes what codes do you get?

Dont let up do you?...

[dmjensen]

Dont let up do you?...

Give advise, dont be sassy.

[328ijunkie]

^lol. Just frustrating is all. On to your issue:

Youre running OBD2. The ECU is smart enough to where it will completely shut down individual cylinders if it feels the need to. If your Bank 2 O2 sensor is dead and giving the ECU crap readings it may freak out and shut those cyls down temporarily till it feels they can fire again safely. Listen to what the ECU is yelling at you about. One of the perks of having an advanced ECU is diagnostics. If its saying Bank 2 is running lean then youve got some issues there. Its narrowed it down for you to cylinders 4-6. Bad coils? Bad injectors? Intake leak on that part of the motor?.

[dmjensen]

i have a vac leak in my brake booster that i plan on solving soon. but is 456 in the back of the engine or the front. if it's the back then its probably a mixture of bad o2 sensor and vac leak

[328ijunkie]

cyl 1 is at the front so 4-6 is at the rear. Your booster connection on your Intake Manifold its biased at the rear cylinders so im pretty sure thats your problem. The O2 sensor may be fine. What codes exactly is it reading? If its only reading status codes (to lean or rich or out of adaptation limits) then the O2 sensor is prob fine.

[dmjensen]

no it gives me an o2 code for #2. we cleared the codes and plugged off the vac line to the booster then drove it and it had the same miss fire / o2 codes but i didnt have the system too lean code.

[328ijunkie]

You have the o2 sensors plugged in right? Just to check. Back to front and front to back.

[dmjensen]

correct. i put in a new sensor today and it seems to run smoother and dosn't have rough starts as bad. i havent scanned it for codes yet but i'll update as soon as i find out