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Discussion Starter #1
i have been having trouble with my m5 ever since a rainy day about two months ago. While driving up the on ramp to the freeway my car choked and shut off. Upon trying to restart the car choked again and turned off. I had the car towed to the dealer. When the car got to the dealer i replaced the old nasty dinan air filters and hoped i didnt get any water in my engine. The next day car started up fine and ran good as new but when i went to crank it again after being warm it did the same as the day it cut off. finally the check engine light came on so we ran it on the machine and it came up with a misfire in all cylinders and a lean mixture code. didnt tell me much. i replaced the fuel pump and filter and checked the MAFS. still same problem . Then replaced the idle control valve, still same problem. the car only starts right sometimes. if the car is cold the car will start right up and run strong. once it warms up i will try to start is and the rpms will stay very low, under 1000 and just jump eventually cutting off. if i try to give it any gas it will usually bog down and cut off also. after a few trys the engine will start up like nothing was ever wrong. any suggestions?
 

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Discussion Starter #3 (Edited)
i have `close to 70,000on the clock i haev pretty much replced evry hose on the car. a have been reading about some part of he vanos going bad with similiar simpoms but it seems like mine is much worse
 

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i have `close to 70,000on the clock i haev pretty much replced evry hose on the car. a have been reading about some part of he vanos going bad with similiar simpoms but it seems like mine is much worse
Fuel pump relay going bad when hot?
Regards,
Jerry
 

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besides the fuel pump relay i would change the main realy while your at it it wont hurt to change both it will cost you under a 100 bucks for both
 

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I suggest the fuel pressure regulator ... happened on my 320i. Very experienced dealer parts manager (20+ years) ordered the part for me and said, "I don't think that's it, John. I've never sold one before."

My 320i had the very same problem ... started fine when cold, wouldn't start after many attempts when hot. Finally, started and "stuttered" and "coughed" until it ran fine.

FIXED my problem. Very obscure, but it can get a pin hole in the diaphragm.

(A guess, but the symptoms are exactly the same as I had.)
 

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What do you mean you "checked" the MAFS? Did you replace them? Honestly that's probably the only way you could check to see if they are contributing given your situation (unable to drive when hot).
 

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Discussion Starter #9
i guess i didnt check them but the dealer took a look at them blowing them out . said that they were fine. im not sure how they checked them.
 

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Discussion Starter #10
where is the fuel pressure regulator located in our cars? how much roughly you think that would be for the part
 

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Right in front of the fuel filter. Basically you access it exactly as if you were changing the filter itself. You could verify since your car will act up almost at will by hooking up a pressure gauge on the fuel rail and leave it connected until the car acts up again and then check it.
 

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i guess i didnt check them but the dealer took a look at them blowing them out . said that they were fine. im not sure how they checked them.
Try disconnecting both MAFs and see how the car runs.

(The dealer IS an idiot. That is most definitely NOT the way to test mafs)

Report back

A
 

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Try disconnecting both MAFs and see how the car runs.

(The dealer IS an idiot. That is most definitely NOT the way to test mafs)

Report back

A
Beat me to the punch on this... oh well I'd say pull them but probably just replace them if they are old, or especially original. 70k is right around the average for the MAFS going kaput.
 

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A,

+1...lol:biggrin:: and btw he might want to back track on what the dealer said they checked:hihi:
Try disconnecting both MAFs and see how the car runs.

(The dealer IS an idiot. That is most definitely NOT the way to test mafs)

Report back

A
 

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Try disconnecting both MAFs and see how the car runs.

Let me expand. Simply disconnect the plugs from the MAFs and see how the car runs. If the mafs are truly hosed, sometimes the car will run better with NO maf signal at all, it uses a default value. If it runs OK, then starts stumbling when you reconnect, easy call.

A
 

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Discussion Starter #16
i will test the MAFS today. the pressure gauge will have to wait till monday. will the MAFS throw a code
 

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i will test the MAFS today. the pressure gauge will have to wait till monday. will the MAFS throw a code
Ard and Nabio are right. When you disconnect the MAFs..the CPU makes "assumptions" based on average values. On most "normally" functioning M5s, this leads to a slightly rich mixture...hence a slight smell of gasoline from the exhaust...and a noticeable decrease in power.

With REALLY bad MAFs, the engine might actually run better on assumed values.

Unforunately, the MAFS don't tend to "throw a code" until they are really bad (if at all). This is the reason that the Dealerships got out of replacing these for such a long time....no code. However, after disconnecting your MAFs entirely...you WILL most likely generate a code.

This is literally a 30 second test. Given your situation, and given the miles on your beast, I would go ahead and replace your MAFs either way. At a coupl of hundred bucks, this is a pretty cheap maintenance item on your Beast.

Good luck,
Brian
 

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Discussion Starter #18
ok it was the MAFS i replaced both with the same bosch. car is running fine at first but threw another check engine after installation. the codes didnt say much. I have dinan software on my m5. is it ok to reset the parameters for the new sensors?
 

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Absolutely reset whatever needs to be reset. A healthy M5 should be able to be reset without anything going on. How you reset the Dinan software I don't know, but if it's anything like the DME then turn the key to on then off 10 times (cycle them). Otherwise just follow whatever directions Dinan gave you.

The MAFS are extremely important to the operation of your beast, because essentially half the information that the DME uses to determine what needs to be done to have your engine run comes from them. Good luck and remember, how the dealer "checks" things is they just pull codes and see if anything says its bad. Like a child, the S62 very often has no idea when it is sick so it's up to you to be proactive. Enjoy the beast now that it is better.
 

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There is a lot more to diagnosing these engines than the way you are doing it. Has anyone looked at the datastream. What is your longterm fuel trim or your short term fuel trim? What is the MAF and O2's reading at?Believe it or not with a lean condition it could be a number of things, but more than likely not a fuel problem but an air problem. Check the mafs, but it could be a vacuum leak. What was the code when the check engine light set, the exact code/s? I have BMW's set an O2 sensor code when it was a CTS ( Coolant Temp Sensor ) These vehicles have become more and more senitive over the years and the DME on these vehicles need good information from each of the sensors to have the car run at peak performance. When that Check Engine light comes on, the DME is saying that there is a fault somewhere and that it is simulating what a sensor should be or it is compensating for a failure from the values it has programed into it. You need to give more information to have someone actually diagnose the problem than just take a guess. Guessing is just going to cost you money and not fix your car. If you need an honest mechanic, check out IATN.net for mechanics in your area. Members of this site are normally well educated in diagnostics of all vehicles, but they will tell you on that site if they are european specialist.
 
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