Ah Ha! Thermostat stuck open - Page 4 - The Unofficial BMW M5 Messageboard (m5board.com)

rassi · 29th February 2008, 22:25

Seems you have covered the most likely culprits. Could also be an airleak or a fuel supply problem, but rather than guessing, why not get it on a rolling road and get the hp and torque printed out? That would give an indication to your problem?

xr4tic · 29th February 2008, 22:35

I think you need to try to find an M5 owner local to you, and drive their car, see if they feel the same

gmakishima · 29th February 2008, 23:18

Could it be a problem with the drive by wire sensor for the accelerator? I am the second owner of my beast and the original owner had to have his replaced under warranty because it wasn't responding correctly. I think a faulty sensor could cause hesitation.

M5CCIE · 29th February 2008, 23:30

Replace the fuel filter if not already done and throw some techron in the tank. See if that makes a difference.

everycredit · 1st March 2008, 00:38

Bad fuel is common. If it's hesitating, it's most likely due to misfire. Check the active or pending code and see which set is misfiring. If they are all odd or all even, check the spark plug well on that bank. If you notice lots of oil and fuel, you're getting a short circuit. Clean out the mess, check spark plugs for fouling, and replace valve seal. That was my issue.

MarkQC · 1st March 2008, 01:04

...could be gas (run a tank of 93) or could be a cam sensor or something related to the VANOS which is trying to prevent knock as you lag the motor at low rpm, and try to dump more fuel in than it can handle as it's in a high gear...or not

BUT - I don't lean on the car at 2000 rpm

as I try to keep it above that even in normal driving - lagging a high performance motor is a recipe for carbon build up, and all kinds of problems...

...take her out and run the rpm's,

burn the crap out for a few hours above 4000 rpm, drive her like you stole her...

nerio02 · 1st March 2008, 01:28

i'm in the same boat as you for the engine problem. the car stumbels up to about 2000-2500 rpm. i'm also on a search what this can be.maybe a bad spark plug or just to mutch/to little fuel in low gears,the feeling i get is like it holds back a 10'th off a sec like it overfuels/or gets less fuel(dont know how to explain it correctly,sorry)

i was wondering also iff it could be a exhaust cps thats going south. i have no codes,no problems stationary,.. problem began when i drove my car on a big speedbump that i never saw in the middle off the night.since then i have this problem. in a addition sometimes the rpm will rise and go down for a brief sec ONLY when my car is on a ramp, a car bridge, or when i put it in reverse.

really strange. mafs are new and fully functional so thats not the cullprit
i recently did a dyno and the car runs only 370 engine horspower and 480 torque but with a nice lineair curve. there is certainly something wrong, but what???thats why i suspect a exhaust cps, but no codes and im not that fortunate to trow 1000's on suspicions only.did that to mutch already....

tommorow the car goes in for inspection 1, maybe after the new sparkplugs,filters, etc... it will be better. iff so i will let you know.

jcdavis · 1st March 2008, 13:57

I have already done all that has been suggested on the board. What really frusturates me is that the M Technician said he didn't feel anything out of the normal when driving my car. He drove it home for 3 days so he had plenty of time to troubleshoot. New: MAFS, Plugs(black as coal when changed), 02 sensors, fuel filter, thermostat, and 1 two week trip to BMW. When I start the car up first thing in the morning, for about 60 seconds the car is nice and crisp. After that I start to feel the sputtering/hesitation. It is kinda of getting old putting money into my car and it not fixing the problem.

nerio02 · 1st March 2008, 19:45

i'm just back from my friend that did a service on the car,new plugs,new air filters,new oilfilter,ect... but i told him to change the oil separators in front off the plenium to + the two hoses that come with it.(2 black cone shaped objects) the hesitations are gone,is it because off the new plugs??who knows but the hoses from the oil separators where tottally inpregnated with oil and the were at least half closed by old oil residue, same for the two cones.my old sparkplugs lookt like almost new after 7000 miles,full dry ,not black, and very clean so the engine run's fine. i think.

JCdavis have you changed those oil separators allready ?? they arent that expensive,maybe try those as a last attempt.i thought it costed me about 120-150 $ for the two with work max. i cant say specific how mutch because i forgot my bill ..

. its a fairly easy job to do yourself also by the way,and takes about a hour (goofing around)30min max, iff you work like a pro

.

i was giving up also after trowing my money in it again, but for now it seems to be working.i will post back in some days, iff it stays ok.because it could be the new plugs etc.. that camouflages my problem for now.

any way good luck in your search mate.

MarkQC · 1st March 2008, 20:54

nerio02 - how many kilometers on your car? (wondering about my hoses/oil seperators..)