BMW M5 Forum and M6 Forums banner

21 - 38 of 38 Posts

·
Registered
Joined
·
13 Posts
I know the car has a leaky valve cover gasket as well as weeping around the oil scavenge pumps. So what you’ve said about running a vacuum in the crankcase is very relevant. Unmetered air is officially the hypothesis - Really great feedback.

You’re right regarding the lens of prior experience. I started on be mk2 then the e36 w Bosch 403. This is a completely different animal and I’m already in way over my head but i love the sting of battle!
 

·
Registered
Joined
·
4 Posts
Sailor24 providing a lot of great input here - many thanks. In the spirit of trying to help you triangulate into what the cause may be and since I'm struggling with the same issue, i offer that I had the valve cover gasket and spark plugs replaced on mine 14k miles ago... Also, when my car was limping, i unplugged the MAFs to try and get home (thinking maybe one was bad even though new OEM) but the problem persisted the next 5 miles. However, except for that one very hot day when the issue arose, the oil temp has not gotten that high again nor has the limp mode/misfires reoccurred.
 

·
Registered
Joined
·
10,108 Posts
I know the car has a leaky valve cover gasket
Can you actually see oil leaking out? If you can it is a pretty big air leak and might be the lone cause of the fuel trim codes and could be big enough to cause the poor performance.
If the oil is coming out it usually means the leak is big enough to cancel the vacuum completely. Maybe you should start there.
 

·
Registered
01 Carbon/Silverstone Exhaust: Jedders-HJS high flow cats-resonator delete-Xpipe-Eisenman cans
Joined
·
2,569 Posts
Pulsapharer, another possibility might be an old fuel pump. When the brushes get old the pump draws more amps. On a hot day the fuel is hotter and as the tank gets lower the cooling of the fuel pump is diminished. You might try filling the tank and driving when it's cooler out and see if the symptoms are there or not.
Regarding medik, sure sounds like MAFS to me. Rich codes on both banks. I know this has been debated before but I don't see how a vacuum leak causes rich codes.
 

·
Registered
Joined
·
420 Posts
Pulsapharer, another possibility might be an old fuel pump. When the brushes get old the pump draws more amps. On a hot day the fuel is hotter and as the tank gets lower the cooling of the fuel pump is diminished. You might try filling the tank and driving when it's cooler out and see if the symptoms are there or not.
Regarding medik, sure sounds like MAFS to me. Rich codes on both banks. I know this has been debated before but I don't see how a vacuum leak causes rich codes.
Because if there is an air leak post MAF, it is not being recognized (metered) by the device that tells the ECU how much air is incoming (MAFs.) The MAFs say one thing but what entering the engine is a different amount.
 

·
Registered
Joined
·
10,108 Posts
I don't see how a vacuum leak causes rich codes.
That is so simple. More air is getting in than is being recorded by the MAF. The O2 see that and the DME turns the fuel rate up. Eventually it hits the max it can turn the rate up to and delivers the rich code. Yes opposite of the way people think and even how it deals with another code report, but.... This can make it confusing but that is the way it works.
 

·
Registered
01 Carbon/Silverstone Exhaust: Jedders-HJS high flow cats-resonator delete-Xpipe-Eisenman cans
Joined
·
2,569 Posts
I understand your reasoning but I beg to disagree. The DME is smart enough to know that it is adding fuel because there is a lean condition and it will report lean codes.
 

·
Registered
Joined
·
10,108 Posts
I understand your reasoning but I beg to disagree. The DME is smart enough to know that it is adding fuel because there is a lean condition and it will report lean codes.
I know what you are thinking and maybe the BMW engineers said this is dumb. But the dude that is responsible for OBDII complience said well I have to report this code this way for that because it is the law, so we are going to keep it simple so the mechanics don't have two different ways. You have to understand OBDII is a legal way of doing things it is not a choice and often it does not make sense. This issue is consistant with all OBD cars. Yes for hex codes they could have changed it but likely consistency was why they left it the same.
 

·
Registered
Joined
·
320 Posts
Anything past 12 o'clock for coolant temp on public roads is too hot, so I would first troubleshoot the cooling system. What is your KTEMP reading?
I'm curious as to the source of this statement. I've had two of these cars over the years, and both of them would creep over 6 o'clock during the peak of the summer in phx.
 

·
Registered
Joined
·
82 Posts
I'm curious as to the source of this statement. I've had two of these cars over the years, and both of them would creep over 6 o'clock during the peak of the summer in phx.
Are you referring to oil or coolant temp? 6 o'clock infers oil temp, given the direction the needle sweeps.
 

·
Registered
Joined
·
10,108 Posts
The DME is smart enough to know that it is adding fuel because there is a lean condition and it will report lean codes.
It turns out it might be simpler than all that and things are getting lost in translation. The OBDII code you will get if you read them will be "exceeded maximum rich adjustment", that is pretty clear, means the fuel has been turned up to the max it can go. If you look on different sheets it will be slightly different but the meaning is clear.
Take a bunch of those wordings and throw them in google translate and you will get a bunch of different german definitions. Now take those results and translate them back. You will get different results than were inputted in most cases.
You should also remember that the codes are almost always referencing the state of the computer not the state of the car.
 

·
Registered
Joined
·
13 Posts
It turns out it might be simpler than all that and things are getting lost in translation. The OBDII code you will get if you read them will be "exceeded maximum rich adjustment", that is pretty clear, means the fuel has been turned up to the max it can go. If you look on different sheets it will be slightly different but the meaning is clear.
Take a bunch of those wordings and throw them in google translate and you will get a bunch of different german definitions. Now take those results and translate them back. You will get different results than were inputted in most cases.
You should also remember that the codes are almost always referencing the state of the computer not the state of the car.
Sailor - This makes complete sense re: lean vs rich codes. The DME is basically running a feedback loop and when it maxes out one the parameters it’s going to throw a single code (root causes could be wildly different but the end result being the same). Fuel pump being tired is consistent with the ancillary evidence gathered in particular that the fuel pump was protesting loudly when I got back to the driveway it sounded like a muffled cordless drill running at full speed.

I am not sure the extent of the valve cover leak but would say it’s class 1 at the moment. The garage is looking it over today. However the symptoms have not been reproducible (hypothesis - it hasn’t been terribly hot again since then and I’ve put nearly 50 more miles on the car since, albeit gentle due to clutch issues I mentioned).

Will post an update once I’ve got some more worthwhile intel to share. Thanks guys
 

·
Registered
Joined
·
10,108 Posts
Now that makes sense.
It would be nice if that was the only thing that code meant, but it is not. I think that is why it gets so confusing. In OBD there is another code that represents this but it is an optional code some cars report both under the single code as BMW does with this code.
The other definition is that there was a change to the rich setting that exceeded some value. We see this when someone has bad MAFs and put new ones in. The DME makes a major, fast change and throws the code. Opposite code when it is a MAF change, but that does not mean the car has exceeded it's max adjustment to lean, it just means a big adjustment was made and in this example returned to normal trims from full rich.
 

·
Registered
01 Carbon/Silverstone Exhaust: Jedders-HJS high flow cats-resonator delete-Xpipe-Eisenman cans
Joined
·
2,569 Posts
Based on all of that, looking at fuel trims is even more important. I wish I had an easy way to pull up fuel trims on my head unit while driving.
 

·
Registered
Joined
·
452 Posts
It would be nice if that was the only thing that code meant, but it is not. I think that is why it gets so confusing. In OBD there is another code that represents this but it is an optional code some cars report both under the single code as BMW does with this code.
The other definition is that there was a change to the rich setting that exceeded some value. We see this when someone has bad MAFs and put new ones in. The DME makes a major, fast change and throws the code. Opposite code when it is a MAF change, but that does not mean the car has exceeded it's max adjustment to lean, it just means a big adjustment was made and in this example returned to normal trims from full rich.
Mine has always had a bit of a hot day slow traffic or high load low rpm stumble-
Then I recently removed plenum to do leaky cam covers and change plugs-
Found that usual vacuum line to the throttle body problem, it was crumbling at the end onto the little elbow, fixed that with a bit of new tube..
And 2 of the earth low tension wires on the spark plug / coil harness were not secured to the head, the little bolts had fallen out,
And the earth strap that goes from the head to the block under the spark plug cover was all green and corroded.
Fixed the bolts back but didn’t get time to remove and clean that earth strap.
Put it all back together and it all seemed fixed. No more stumbling when hot.
After a week it started the bad behaviour just a little bit on low rpm high gear acceleration, but nowhere near as bad as before.
I’ll get back to that earth strap soon.
This all could be related to the OP issue too...
 
21 - 38 of 38 Posts
Top