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Discussion Starter #1
hey all hopefully someone else had this issue or can help.
2000 M5 140k miles muffler and resonators removed
i started to notice a hesitation when accelerating hard then a massive loss of power feels like a moped motor under the hood exhaust went blatty then just completely stalled out ses light came on with MAF code and exhaust cam positioning sensor "b"
i replaced the sensor (driver side exhaust)
2 new oem MAF's
new plugs
new valve cover gaskets
new fuel filter
new fuel pressure regulator
tested vacumm pressure no leaks detected
pulled out the fuel pump and bench tested it works excellent
(no more codes stored or pending)
start the car still runs like crap now it just starts and gives a terrible idle for a few seconds and stalls
to even keep it at idle for a short time i have to keep tapping the gas easily and it will hardly rev will not even get to 3k rpm's
if i hold the gas down it will just stall out
 

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Sounds like one or both MAFs are not working properly. Double-check the connections, and if you still have the old ones, put them back in and see what happens. Even new parts can sometimes be faulty.

Best of luck.
 

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Discussion Starter #3
yea i had thought that as a possible well but ive tried mixing them up swapping around etc same result i was leaning toward maybe intake cam sensors but really prefer not to waste the money if thats not the issue. When one of the bad maf's were hooked up it was giving bad mass air circuit flow and was corrected with the new ones so pretty sure thats not the issue
 

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What, if any codes are coming up now?
 

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Discussion Starter #5
nope no codes stored or pending
original codes were for maf and camshaft position sensor "b" exhaust
 

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nope no codes stored or pending
original codes were for maf and camshaft position sensor "b" exhaust
Could be the CPS. It would probably not hurt to change out all the CPS (intake and exhaust). A new one may trigger an old one to go bad. I have seen stranger things happen.
 
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Discussion Starter #7
yea thats kinda what i am leaning toward as well at least i have 1 new one done so far i prefer to use oem parts i know pelicanparts has them for $100 each you know of anywhere they are cheaper and still oem?
 

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yea thats kinda what i am leaning toward as well at least i have 1 new one done so far i prefer to use oem parts i know pelicanparts has them for $100 each you know of anywhere they are cheaper and still oem?
Go here. Type in the part number and be pleasantly surprised.
 

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Welcome to the board.

If your MAFS are new, you can rule that out, or remove them entirely to prove that the idle problem persists. A better test would be reading fuel trims. Despite your vacuum tester result, I would still look for a leak, if your car can't even idle properly. E.g., the leak could be near the O2 sensors by the cats, or in the notorious plastic elbow in the engine valley. Those O2 sensors (pre-cat especially) and CPS (intake+exhaust, both sides) are consumables, too.
 

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Discussion Starter #10
thanks for the help everyone its truly appreciated ill hop under the car today today and check for leaks again and worst case ill order the sensors and report back what i come up with
 

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The term "blatty exhaust note" and a CPS code has NEVER been associated with anything other than a bad CPS...IMO

Did you say you replaced the one bad sensor, but not the other three? I used to think they were 'good' or 'bad', with the bad ones throwing a code. This is incorrect- they can begin to fail and cause issues prior to tripping codes.

Have you UNPLUGGED the MAFs? try this. If it starts and idles, you'll know.

Also, keep in mind that the DME adapts to aging sensors and inputs- fix one, abruptly, and the whole thing can be 'upset'. Not saying that is this issue...
 

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Discussion Starter #13
yea i replaced both MAF sensors. When i unplug one or both it really makes no difference at all. starts struggles to idle for a few seconds and dies.
got under the car last night no leaks around the cats i ordered the other 3 remaining sensors yesterday should be here middle of next week
 

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Does the car run so badly you can't get scanner readings or get it to a shop? Do you have a scanner, INPA, DIS, Autotap (not just a code reader)? It's very hard to diagnose this type of problem without data.

The fact you have no codes is relevant. It points to stuff that is notoriously reluctant to set codes (MAFS, CPSs, and VANOS solenoids), although yours is running so badly, I would have expected codes. Or to a mechanical problem that the DME has no way of detecting, like a bad vacuum leak.

And I think ard may have a point - the DME adaptations on the bad MAF's and bad CPS may have maxed out and now you can't get the engine running long enough for it to relearn. A scanner that resets adaptations like INPA would be useful.
 

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Discussion Starter #15
it will not run at all i can get it start and gently feather the gas to keep it running but thats about it no way of getting it to the shop. no and DIS is a pain to get running ill look into autotap never tried it but i can get my hands on most software without a problem. Vanos (both) were replaced at bmw 10k miles ago and mafs are new after i replaced the 1 exhaust cam sensor it actually runs worse so i am thinking the other 3 need to be replaced with it i have them ordered
 

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Back to the fuel pump...how did you test this? The pump needs to be able to deliver fuel under pressure- not just pump gas with no backpressure. Have you measured fuel pressure during starting and (attempted) idle?

Make sure that "OEM" maf isnt a cheap counterfeit...but it doesnt sound like that is the primary issue
 

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Discussion Starter #17
all i did was pop it out and bench test sounded strong i could go there today and test pressure at the regulator i am assuming? na i bought the oem bosch mafs
 

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Yes, you should do the in-car fuel pressure test just to rule it out. A bench test doesn't test the pump under load. And it's under a lot of load since it has to generate more than >72 psi.
 

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I would think you should look at the MAF sensors again. This is a classic MAF problem. Maybe the units themselves are in great shape, but when you installed them you got them dirty? They really need to be clean. In fact, you should always wear clean/new latex gloves. Try to clean these guys and re-install. Finger prints can do bad things. I hope it is something simple such as this. GL
 

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Discussion Starter #20
ok i have replaced the rest of the cam sensors so now has 4 new cam sensors and the new mafs all testing correctly still runs like crap but i did as requested and tested fuel pressure at the regulator and its pretty much not getting any real fuel to it. so apparently bench testing the pump was useless new pump on the way ill report back once its in. on the upside it should love all her new parts when shes up and going again :)
 
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