Slight stutter / hesitation at low revs - Page 2 - BMW M5 Forum and M6 Forums
E34 M5 Discussion 1988-1995 Sedan and Touring

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Old 7th March 2019, 03:03 PM Thread Starter
lukai
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I finally got round to replacing the dizzy cap and rotor, and judging by the markings they were from 2006 & 2007. The car has only done about 8,000 miles since then so they looked in fairly decent shape, with no sign of moisture.

I replaced them regardless but the problem is still persistent, and still intermittent.

I checked all the leads were seated properly and also sprayed some carb cleaner around the intake plenum but didn't notice any change in revs. So I'm hoping there are no vac leaks, unless there is a very specific area I should have targeted?

So I guess my options now are new coolant temp sensor / new ignition leads?

I've read somewhere that the ignition coils could be another source of the issue? Also fuel filter maybe?

Any advice on what to tackle next would be much appreciated.

Thanks,
Luke
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Old 7th March 2019, 05:14 PM
SCBMW
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Replace the Coolant Temp Sensor (that really controls fuel mix). Because your issue goes away after warm up, it could be that the cold start ohm reading on the CTS is faulty. It operates in a given range and signals the computer (based on coolant temp) to change fuel mix.once engine reaches operating temp it remains constant if operating normally. You could test this but if never replaced or unknown save time and replace the part anyway for $20 to $25. Report back.

2003 M5 Titanium / Imola, bone stock
1986 535 B35, stahl headers, LTWFW, Supersprint
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Old 10th March 2019, 11:52 AM
MattH
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another thought here...

if the problem can show at startup then you can look at the temp of each exhaust manifold pipe using an infra red thermometer. If one is lower than all the others then you know the problem is cylinder specific. That may help narrow it down.
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Old 17th March 2019, 08:19 AM
911racer
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Change the fuel filter. It’s cheap and easy to do. As mentioned above. Bring it back to stage Zero first. Also clean the air idle control valve and replace all the vacuum lines.
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Old 10th April 2019, 10:14 PM
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My issue turned out to be obvious. I replaced the cap, plugs, and the coolant temp sensor at the same time.

BK05864
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Old 11th April 2019, 02:16 AM
SCBMW
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Well shoooo... that will cause issues. Hey, glad it was something simple and confirmed...no gremlins. Glad you found it!

2003 M5 Titanium / Imola, bone stock
1986 535 B35, stahl headers, LTWFW, Supersprint
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Old 13th April 2019, 10:43 PM
davidoli
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Lukai , try to find someone with a known good 3.6 MAF , as this could well be the source of your issue .

D

Better a day as a tiger than a lifetime as a sheep !

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Old 23rd April 2019, 06:45 AM
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What does the hesitation feel like?

I had a failing fuel pump cut power on both my '91 M5 and a '95 540i. It was usually at lower RPMs and partial-full throttle, maybe 40%-100% throttle. Power would cut off momentarily as if somebody had turned a switch on and off for a millisecond. Downshifting and getting higher into the rev band and it would never happen. It first happened in the 540i that I owned, and when I felt it in the M5 I immediately ordered a fuel pump and it went away.

I have been daily driving E34s for about 15 years now. Fuel pump failures are pretty common. Even if the symptoms I described do not match up with yours, I would replace the pump and filter, and inspect the fuel lines while you are at it.

Trevor
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Old 30th May 2019, 02:32 PM Thread Starter
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Quote:
Originally Posted by 91Champagne View Post
What does the hesitation feel like?

I had a failing fuel pump cut power on both my '91 M5 and a '95 540i. It was usually at lower RPMs and partial-full throttle, maybe 40%-100% throttle. Power would cut off momentarily as if somebody had turned a switch on and off for a millisecond. Downshifting and getting higher into the rev band and it would never happen. It first happened in the 540i that I owned, and when I felt it in the M5 I immediately ordered a fuel pump and it went away.

I have been daily driving E34s for about 15 years now. Fuel pump failures are pretty common. Even if the symptoms I described do not match up with yours, I would replace the pump and filter, and inspect the fuel lines while you are at it.

Trevor
Hi Trevor,

Thanks for the info. Those symptoms do sound a lot like what I have been experiencing.

Since my last update I had replaced the fuel filter and rubber boot to the intake plenum (mine had a crack in it) but this still didn't solve the issue.

After reading your post I finally got round to getting a new fuel pump in last week and it drives so much better now.

The issue can still be felt if you are in too high a gear and put your foot down a bit, but I'm wondering if that just normal? If you change down properly it pretty much never happens.

I still might get the ignition leads changed over as a precaution, and I also have a coolant temp sensor that i might try swapping out... but it is a bosch rather than oem and I have since heard it is best not to put anything other than oem sensors in? Would the bosch sensor be okay?

Thanks,
Luke
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