750iL Mystery Problem

[perishalive92]

Hello all,
I apologize if I am posting this in the wrong spot. I am very new to these forums. I am experiencing a very odd issue with my 1996 750iL. If I put pedal to the metal a couple of times all will be great. All 12 cylinders fire and the car accelerates forward as it should. However, my engine seems to want to go into limp mode afterwards yet throws ZERO codes. If I accelerate hard a few times 6 cylinders will stop firing. The odd thing is, the car will accelerate on 12 cylinders fine until it hits 2000rpm at which point is cuts out half of the engine.

Now, if I turn my car off for XXXX amount of minutes (usually around five) all 12 cylinders will fire again past 2000rpm like normal. But again, no codes are ever thrown. Ive cleaned the throttle body, replaced all spark plugs(no misfiring in case you are wondering), replaced air filters, fresh oil change, etc. I'm lost as to what could cause such an issue. Anyone have any ideas?

[psjr]

Often just a bad coil.

[perishalive92]

I know these engines have 2 coils, but im hard pressed to locate them. I know they are not a traditional coil. Could you possibly give me a link to purchase said coil?

Often just a bad coil.

[XAlt]

http://www.bimmerforums.com/forum/sh...0#post29313200

http://www.pelicanparts.com/catalog/...ELIGNT_pg2.htm

[perishalive92]

Thank you guys. I will purchase a few of these and let you all know the results!

[psjr]

Cheapest thing to do would be to get some used from someone parting a 740, as they are the same coil.

[perishalive92]

Alright guys so I replaced both ignition coils. The one located on the passenger side was horribly corroded. I though the issue was solved but today half the engine cut off after 2000rpm after a few hard accelerations. Not sure what the issue is now. One of the Ecu has a problem maybe? Maybe the distributor or rotor or something? Im lost with this issue. Only codes being thrown is misfiring in all cylinders and O2 sensors.

[perishalive92]

Very odd thing I discovered today in the shop. When i plugged in the very odd looking circle conector to read the ecu codes (i tried obd2 port first but it kept directing me to use the circle port, I cannot recall the name of said port) it kept telling me it could not read. This is making me believe that one of the ecu is malfunctioning which could also explain my issue. How would I go about finding out which is bad or would it be best to replace both?

[740iSport303]

If the cover on the under hood port is not fully attached, the ODB port doesn't work and likewise, if the cover on the ODB port is not in place, the under hood port doesn't work either.

[perishalive92]

Ok so my V12 is still doing the crappy 6 cylinder deal after a hard acceleration. Im beyond confused as to why. Ive replaced the passenger side ignition coil, all 12 plugs, both air intake filters, and both distributor caps with new rotors. I notice a slight misfire when my car is at idle but once I give it gas it is fine until about past 2000rpm when the engine will cut off one cylinder bank and run off of the other. My car runs on all 12 until it hits about 2000rpm. Why is this??

Note: I also smell gas from the very front of the engine on the passenger side. Any ideas?? This is beyond annoying!!

[xboss]

Maybe try another battery. Low volts can cause tons of module bugs and high RPM demand tons of power. It may be that or a bad connection. Either way, you will give it a battery nap when you swap batteries which could help as well.

[perishalive92]

I will get my current battery load tested and also try another to see if it helps at all and I will respond with the results.

[psjr]

Perhaps a clogged cat?

[perishalive92]

I was thinking the same until i found out that 3 of my 4 o2 sensors arent working. Ill still open the cats tho.

[xboss]

The post cat sensors dont matter much an even can be deleted.

[perishalive92]

I know that both post o2 sensors are out for sure and only one of the pre cat o2 sensors currently work. Its the passenger side cylinder bank that keeps shutting off. I have multiple misfires in all cylinders except for 2 of them and not sure if thats related to my issue. Like i said, all 12 plugs are new as is both ignition coils and dist caps and rotors. The ignition wiring also is in good condition. Im getting the battery load tested now to see if the battery is the issue.

[perishalive92]

Ok its definitely NOT the battery. Just had it tested at 2 places and both say the battery is perfect under full load. Now, let's assume that my cats are the problem. What I would like to know is A) can clogged cats result in misfires and B) would removing my cats or cat delete, correct my issue or mess up the car more? I am new to the exhaust side of cars and am unaware of any symptoms or corrections for such issues.

[XAlt]

Clogged cats will cause massive misfires off the charts.

Cat delete will be fine, just keep the resonator.

[perishalive92]

Alright, i'll take apart my cats tomorrow and see if it is indeed clogged and post here with an update. It only misfires when at idle. Under load this is not an issue, which I've read can be related to cats being clogged.

In the mean time, I am ordering valve cover gaskets and am considering getting a rebuild kit for my fuel injectors as I smell gas heavily from the front of the engine. I'll be in that area changing valve covers as it is so I might as well get intake manifold gaskets and check out the injectors. I'm just hoping the cats are my problem and once I remove them the misfires will cease.

[Frankie]

Just curious: If you remove your cats, how will your engine operate without throwing codes...resulting in failure to pass a state inspection?

[perishalive92]

Good question. My state doesnt regulate nor have inspections. Im not concerned with the downstream o2 sensors causing codes to be thrown as those do not affect how the engine operates. It only checks to see if the cats are doing their job. I can live with that. Im only concerned with my upstream o2 sensors, both of which I am replacing later today and will post with an update.

[perishalive92]

Update: I replaced my upstream o2 sensor today with a Bosch. Before i bought the new sensor my engine went into 6 cylinders only and hasnt came out of 6 cylinders since. I drove it straight home and changed out the sensor. Changing the o2 sensor did nothing. My car is now permenantly in 6 cylinder and its driving me crazy. What is going on?

[MKIVJZA80]

look for vac leaks, do smoke test. my car did the EXACT thing when throttle body boots were bad. changed them and it stopped doing so until i tampered with the old evap hoses and brake booster hoses that connect to intake manifold. old, hard, and leaking. have new ones coming in and i think that should be the end of the vacuum leaks... for now!

coils, wires, plugs, distributors, intake manifold gaskets- all done.

- - - Updated - - -

what codes are you getting?

[perishalive92]

Im goin to get codes pulled today. Will reply in a few.

[perishalive92]

Ok so after getting codes pulled, I am almost certain my issue is a failed ignition coil. Cylinders 7-12 were not firing whatsoever, which is the bank that is currently not running (drivers side). I also have a few other codes that I'm not sure what they mean. THey are as follows:

P0135 O2 Heater Circuit (Bank 1, Sensor 1)
P0130 O2 Circuit (Bank 1, Sensor 1)
P1270 Control Module Self-Test, Torque Monitoring

The last one im concerned about the most. It doesn't sound good and im unsure exactly what it is implying. I changed the upstream O2 sensor on Bank 2, but I did not see any sensors on Bank 1 except the downstream O2 sensor. Now, the wiring harness on both sides has wires cut out of them. The wires and connectors to both O2 sensors are intact that lead up to whatever monitors them. I'm not sure what the other wires are though. I will post a picture if needed.