OBC Code help on my 740iL pleaseeeeee !!!!!

[Jazzman]

Fellow bimmernuts, my '94 740iL suddently lit up the "Check Engine" light, followed by a drop in the idle to about 400-550 RPM. The car will run fine but soon as it stops at idle it will drop in idle again and run rough, and this time followed by a weird screeching sound ...... either a wiped bearing sound or a sticky belt screech that disappears soon as you rev the engine. Also after a shut down and then a restart, the engine puffs up some white smoke that clears up after a short stab at the throttle. I did a stomp test and it gave me a code 1212. It's not even six months ago that I replaced the two oxygen sensors, the in-tank fuel pump and the two fuel filters so I know it is not any of those items. Please help on where to start, the Bentley is not the specific.

[winfred]

most likely the pcv plate
http://members.cox.net/wdixon27/v8%20pcv
http://members.cox.net/wdixon27/v8%20pcv%202


Fellow bimmernuts, my '94 740iL suddently lit up the "Check Engine" light, followed by a drop in the idle to about 400-550 RPM. The car will run fine but soon as it stops at idle it will drop in idle again and run rough, and this time followed by a weird screeching sound ...... either a wiped bearing sound or a sticky belt screech that disappears soon as you rev the engine. Also after a shut down and then a restart, the engine puffs up some white smoke that clears up after a short stab at the throttle. I did a stomp test and it gave me a code 1212. It's not even six months ago that I replaced the two oxygen sensors, the in-tank fuel pump and the two fuel filters so I know it is not any of those items. Please help on where to start, the Bentley is not the specific.

[Jazzman]

Winfred, can you explain a little further? What effect does the PCV plate has on the engine that will drive the 1212 code? Is the PCV plate a normally replaced item on a high mileage engine? Thanks for yor wisdom, Winfred. I am a regular forum browser in the 5 and sometimes in the 7 forums so I know how much knowledge you pass on to fellow nuts.

[winfred]

the plate has a diaphram that ruptures and makes a vacuum leak that can change in severity, and it can also cause the engine to draw in oil from the crank case, they can go out every few years, if it was me id pull the intake and do all of the gaskets and get them out of the way (they can get hard and leak) and make replacing the plate easyer to change. the 02 code probably comes from the unmetered air throwing the mixture off


Winfred, can you explain a little further? What effect does the PCV plate has on the engine that will drive the 1212 code? Is the PCV plate a normally replaced item on a high mileage engine? Thanks for yor wisdom, Winfred. I am a regular forum browser in the 5 and sometimes in the 7 forums so I know how much knowledge you pass on to fellow nuts.

[Jazzman]

So, is this PCV plate replaced as a whole or can I just replace the diaphram? Also, from the looks of the pictures you attached it will be a bear to replace the whole thing with the engine in place. Are those torx bolt the holds the plate in place? Thanks again Winfred for the great info.

the plate has a diaphram that ruptures and makes a vacuum leak that can change in severity, and it can also cause the engine to draw in oil from the crank case, they can go out every few years, if it was me id pull the intake and do all of the gaskets and get them out of the way (they can get hard and leak) and make replacing the plate easyer to change. the 02 code probably comes from the unmetered air throwing the mixture off

[winfred]

it runs $40-50 and you replace the whole thing, it can be done inplace but it's a bitch and the torx are usually overtightened

[632 Regal]

those are torx and i believe you replace the whole plate. it is a bitch to do but a few people have replaced them on this forum with good results.

[Jazzman]

Winfred, this afternoon i started it and ran it for a few minutes and then try to remove the oil filler cap. The idea was presented to me that I should have a HUGE vacuum from the filler neck, and if I have pressure instead of vacuum then the culprit is most probably the PCV plate behind the intake manifold that you suggested. I took the cap off and just to twist it open is tough because of the big vacuum, and what a vacuum when I finally got the cap off, so that shot down the PCV theory. But then as the engine again is idling rough with the screeching sound with it, I pulled the plug off the MAF sensor and the idle smoothed out to almost normal, WITH NO SCREECHING sound. As soon as I plug the sensor back the symptoms again showed up. Now does that confirm a possible bad MAF sensor?

[winfred]

disconnecting the maf puts the computer into a limp mode and it ignores most sensor inputs and runs a preset rich mixture, i suggested the pcv plate because, it's a common failure on the v8s, you mentened a puff/cloud of smoke, sometimes when the plate fails it makes a honking noise and crappy idle, all classic pcv plate simptoms, you may try spraying some carb cleaner under and around the intake to check for vacuum leaks while it's running bad, it will smooth out when you hit the leak, another thing that screws with the m60 is one partially clogged cat (which can blow the plate) that messes with the computer bad sometimes, give unplugging the computer a shot to see if it runs better for a short while after being reset, if nothing else it will clear the current ce codes till whatever is pissing it off teaches it bad habbits again


Winfred, this afternoon i started it and ran it for a few minutes and then try to remove the oil filler cap. The idea was presented to me that I should have a HUGE vacuum from the filler neck, and if I have pressure instead of vacuum then the culprit is most probably the PCV plate behind the intake manifold that you suggested. I took the cap off and just to twist it open is tough because of the big vacuum, and what a vacuum when I finally got the cap off, so that shot down the PCV theory. But then as the engine again is idling rough with the screeching sound with it, I pulled the plug off the MAF sensor and the idle smoothed out to almost normal, WITH NO SCREECHING sound. As soon as I plug the sensor back the symptoms again showed up. Now does that confirm a possible bad MAF sensor?