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Discussion Starter #1
Hello

My M5 has started acting weird, so I'm asking you guys for help again :)

I'm having a weird issue where my car randomly starts running rough(too rich?).
Symptoms are:
Lots of backfires
Very slow acceleration
Exhaust sounds way deeper than usual
More black soot around exhaust pipes.

The weird part about this, is that all issues goes away by itself after awhile & then re-appers after some time.

There is no SES light, but I got some codes with my Carly scanner.

Any ideas what i should check? :)
 

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My first guess is cam sensor(s) but it could be a number of things. What year is the car, how many miles on it and what engine maintenance has been done in the past?

Unfortunately, those codes don't help us because the app can't identify most of them. You need a scan from a proper BMW specific scanner like a Peake reader, INPA, etc.
 

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@technician117
It's a 1999 production car with 140K miles.

CPS as you mentioned is never changed, would it be time to change them maybe?

Maintenace done in within last 10K:
Vanos solenoid boards
Thermostat
Spark plugs
Fuel Pump + Fuel FIlter
 

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@technician117
It's a 1999 production car with 140K miles.

CPS as you mentioned is never changed, would it be time to change them maybe?
The cam sensors on the pre-facelift cars were an older design prone to failure. BMW actually revised the cam sensors, not sure if it was a rolling change during M5 production or something that came out after, but if you have the original cam sensors from 99 you should certainly change them. I just did the intake cam sensors on my car which were done once around 2008 and noticed a strong improvement in low end acceleration, especially in first and second gear.
 

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Unplug the MAF's so see if there is any change after the DME gets a chance to adapt.

I would do all 4 cam position sensors and be prepared to replace the MAF's.

Regards,
Jerry
 

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Thanks for the replies! :)

I did some live data reading yesterday, I post logs below. (weird MAF values)

After reading data, I disconnected MAF's & will drive around without them for a couple days to let the car adapt & see if something changes.

If nothing changes I'll do CPS sensors first, as they never have been changed.


3rd gear pull data from when car is running good:
10.06.2020 18:22:04 Calculated engine load (%) Short term fuel trim—Bank 1 (%) Short term fuel trim—Bank 2 (%) MAF air flow rate (grams/sec) Long term fuel trim—Bank 1 (%) Long term fuel trim—Bank 2 (%)
10.06.2020 18:22:13 7,843137 -2,343750 0,000000 5,970000 4,687500 3,125000
10.06.2020 18:22:14 17,647058 0,781250 3,906250 25,480000 4,687500 3,125000
10.06.2020 18:22:15 28,235294 -3,125000 -4,687500 54,649998 4,687500 3,125000
10.06.2020 18:22:17 37,647060 -3,125000 0,000000 64,790001 4,687500 3,125000
10.06.2020 18:22:18 40,392159 -4,687500 -1,562500 58,949997 4,687500 3,125000
10.06.2020 18:22:19 35,686275 -1,562500 -3,906250 180,059998 4,687500 3,125000
10.06.2020 18:22:21 0,000000 -100,000000 -100,000000 231,799988 4,687500 3,125000
10.06.2020 18:22:22 100,000000 0,000000 0,000000 270,479980 -100,000000 3,125000
10.06.2020 18:22:24 100,000000 0,000000 -100,000000 302,769989 4,687500 3,125000

3rd gear pull data from when car is running bad:
10.06.2020 18:40:22 9,803922 14,062500 12,500000 12,980000 4,687500 3,125000
10.06.2020 18:40:24 10,196078 8,593750 7,031250 11,520000 4,687500 3,125000
10.06.2020 18:40:25 24,705883 9,375000 10,937500 10,900000 4,687500 3,125000
10.06.2020 18:40:26 27,843138 1,562500 3,125000 26,039999 4,687500 3,125000
10.06.2020 18:40:28 97,647064 0,000000 0,000000 29,439999 4,687500 3,125000
10.06.2020 18:40:29 97,647064 0,000000 0,000000 120,969994 4,687500 3,125000
 

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Thanks for the replies! :)
Personally, I am not sure how to read that data. Perhaps others can help.

I can tell you that fuel trims that show a "+" means it is adding fuel. That means the computer is trying to compensate for a lean condition. A "-" is the opposite; it means the car is running rich.

Lean can often be a vacuum leak somewhere along the line. STFT is the current reading, while LTFT are the cumulative readings. If your LTFT is maxed out, that means the computer is reading a lean condition the computer can no longer compensate for. I can't remember the max amount (25%?).

You can run a dynamic "MAF" test (really a fuel system test). There is load of info here. But basically, access the onboard computer readouts. Go to test 4, option 2. You should be reading L/H. Do a few runs up to redline. WOT. 1st gear is usually too quick, so look for some room to do a 2nd gear run. Get the L/H just before you hit redline (try not to hit the rev limiter cutout, but don't be too worried if you do). You can run to 6900 or 7000 (rev limiter should be 7100). Post those readings and you can get feedback. It will give a good idea on the health of the overall fuel system and typically the health of the MAF's.

You should also check you O2 sensors. They have a useful life. There are 4, 2 precat and 2 postcat. When/if you install replacements, I suggest you do 1 at a time. It is very easy to plug them into the wrong receptacles. It has happened to many a good mechanic on this forum!!!

I am assuming fuel pump is good and fuel filter has seen regular changes. If you don't know your last fuel filter change, time to do. Under the drivers door sill if I recall correctly. Not hard, just a little messy. Check the FAQ's here on how to do.

Regards,
Jerry
 

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One of your codes is 0001 which is fuel pump relay. It is not really the relay though but the path to ground from relay thru the pump to ground. Since it is still running likely one of the 4 brushes is losing contact at times so you get the code and less pressure. It would also explain why the car is adding fuel.
Follow this thread for testing the relay but you likely need a fuel pump.
 

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It is not really the relay though but the path to ground from relay thru the pump to ground. Since it is still running likely one of the 4 brushes is losing contact at times so you get the code and less pressure.
@Sailor24 Interesting idea, I had not thought about that at all. :D
However i tested bypassing the relay as described in the thread, unfortunately still have the same problems :/
Do you think it still can be the pump which is the problem?
 

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It is a pretty common problem to have the pumps wear out. If you have that code every time you read the codes it is a safe bet. This is what I would do, clear the codes. wait until you feel the problem then stop and read the codes again. Clear them and read again if you drive some miles without the problem check the codes and see what codes are there.
It still does not rule out another wire problem some where between the relay and the pump but at some point you have to gamble.
If you had some pigtails set up and a volt meter you could pull over while having the issue and take some voltage tests, but that is far to complicated to save the price of a fuel pump. There have been some reported ground issues with the system so it could also be that. Likely if you leave it long enough you will get a no start while hot or stall that you can test properly. You could run with a fuel pressure gauge hooked up and routed under your wiper blade and watch the pressure.
Replacing a known old pump for a new one is not a bad thing anyway, they wear out so it gets rid of a problem that might happen anyway. It is hard to say without having the car, in front of me but it is something for you to look at and explore. All those other things that have been mentioned I would do anyway especially the CPS replacement.
 

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Hello, I'm finally back to working on the car again.

fuel pump + filter was changed 8K ago, but to eliminate the pump i tried reinstalling the old pump but still have the same issues.
I measured the wiring, but everything seems ok there.

I have not monitored fuel pressure yet, however I have another symptom i have overlooked.
At the fuel filter there is a "sucking/vacuum" noice when the car is running from the regulator.
@Sailor24 I could not find anything on this online, but have you heard/seen this before and know if its normal or something wrong with the regulator?

Note: CPS is not changed yet so it could still be the cause, but I'm doing those last as it seems to be a PITA (no local dealer, otherwise i would let them do the job)
 

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Looking at your logging data I highly suspect a vacuum leak. Data when car is running bad at low load (first line) STFTs are high on both banks (adding fuel). At high load (last two lines) STFTs are 0 when vacuum is low.
You need to sort out that sucking sound at the FPR. Could be the vacuum line, any of the fuel lines, or even the regulator connection to the filter.
 

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I have not monitored fuel pressure yet, however I have another symptom i have overlooked.
At the fuel filter there is a "sucking/vacuum" noice when the car is running from the regulator.
I don't know but it is reasonable that the regulator might make noise because it is mechanical. I still want to know about the 01 code does it always come back? That is what you need to be looking for first because it is a clear indication of an electrical fault in the fuel supply system. It would have to be fixed first before you do anything else.
 
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