ATTN: winfred, or whoever knows about the E38 740iL

[bimmerd00d]

1997 740iL, i've been driving this the past few days, great car. It has recently thrown a check engine light, I took it to auto zone and it says random cylinder misfire. I changed the plugs (Bosch) and it was fixed for about a day. Today it returned, and it seems to run kinda sluggish once teh light goes on. When i was entering the highway today, i ran full throttle through the first 3 gears or so, and the CEL started blinking, and it lost about 50% of it's power. When i exited and came to a stop light, i noticed that it was running very very rough, kind of like an old muscle car with an aggressive cam. I then took it back to auto zone and it threw the same code. Started it up to leave auto zone, CEL still lit, but it's not running rough anymore. Seems to start running rough only if you run it to high rpm's, and continues to do so until you shut it off. Any suggestions?

[winfred]

vacuum plate on the back of the intake, and possibly a plugged cat (sometimes blows the plate) id replace the plate just because they go out every few years and it's probably due, and check the backpressure at the pre cat o2 sensor ports to check if one is clogged, anything under about a 1/2 psi at about 3k rpm is ok, one bad cat will drive it nuts. the intake port and throttle body gaskets can leak and piss it off as well

[bimmerd00d]

how will it respond to having the cats removed? I dont know the exact o2 sensor locations on this car, and not sure how it will run. We don't really have the funds to throw 2 new cats on the car at the moment either. Also, there has to be something causing the cats to fail, and theoretically, it will happen again unless we fix the source of the problem. Any ideas?

[DueyT]

BD, cats usually fail after one or both O2 sensors fail, the car runs rich and eventually the excess unburned gas overheats the cats and they start to fuse internally and loose their ability to a) properly catalyze unburnt fuel, and b) plug up and really increase back pressure. The O2 sensors for the 740iL are directly ahead (like about 2") of the two catalytic convertors. Just for your into, they have a 22mm hex head/collar on them. Soaking the O2 sensors in WD-40 or break-free for a few days helps when you're trying to remove them.

Hope that helps, cheers.
Duey

[winfred]

the obdII computer will not like not having cats on it, it will definatly throw a check engine light, not sure how it will run. the cats on the v8 cars suck they all break up and clog it's almost unusual to see orignal factory cats on a v8 car


how will it respond to having the cats removed? I dont know the exact o2 sensor locations on this car, and not sure how it will run. We don't really have the funds to throw 2 new cats on the car at the moment either. Also, there has to be something causing the cats to fail, and theoretically, it will happen again unless we fix the source of the problem. Any ideas?

[DueyT]

the obdII computer will not like not having cats on it, it will definatly throw a check engine light, not sure how it will run. the cats on the v8 cars suck they all break up and clog it's almost unusual to see orignal factory cats on a v8 car
...except Jeff and me running Nikasil! :p

Cheers,
Duey

[rapidel]

Please check your ignition coils.
I have a cardboard box full of 'em.