Rough running below 4000 - The Unofficial BMW M5 Messageboard (m5board.com)

ECM4 · 12th September 2003, 15:18

The more I drive this car the more its unwillingness below 4000 is begining to annoy me! OK so the S38 3.8's a bit of a screamer with lots of 'overlap' but I don't think it was ment to be like mine! Unless you guys can tell me different........

It really feels 'strangled' and 'coarse' as if the fuel/air ratio was all wrong (too lean!). It's most noticable on a light to medium throttle. Even on full throttle it feels full of 'flat spots' up and maybe beyond this engine speed. You could even say it was an unwillingness to rev.

On a light throttle at 50ish in 5th it feels slightly lumpy but pulls like a train when asked.

Some of this can be blamed on the valve clearances, at least half are too close (@0.20ish) and need to be adjusted soon once I locate the tool!

Is this just a product of early 90's engine management programming (as the previous owner hinted) or could it be something else?

The local dealer's offered to have a look for me!

Mmm-Five · 12th September 2003, 16:38

Whether it's 3rd. 4th, 5th or 6th, mine's smooth (though underpowered) all the way up to 4000rpm and then all hell breaks loose!

I regularly leave it in 6th at 50-55mph when going through the 20 miles of 50mph on the A1.

The only place it is really rough is on tickover!

IvanDias · 12th September 2003, 17:54

Quote:

Originally posted by ECM4
Some of this can be blamed on the valve clearances, at least half are too close (@0.20ish) and need to be adjusted soon once I locate the tool!

Get this done first. It made a great difference on mine. Some dealers never do it on Insp 2, so it *might* never have been done !!

Normal is 0,28 to 0,30.

The BMW tool in expensive, something like £170, (€230-$250), so use a Fiat twin cam engine tool as it`s the same type of thing. Also heard the tool for early Jags will do.

It`s a long job (2-3hrs for an experienced engine mechanic) so budget x2 or x3 if you`ve not done it before.

Personally, I got the BMW Main Dealer to do it for £220 inc VAT.

After that, it`s time to look at spark plugs (and water in the holes), coil packs if appropriate, then more tricky stuff like MAF.

Do valves first.

Ivan.

ECM4 · 12th September 2003, 19:16

It's hardly perceptable. My wife is oblivious to the problem!

Maybe I'm just a perfectionist. I can never just drive a car without finding faults. The more I drive the more faults I need to fix. After a few years its all fixed and I'm bored!!

Ivan, I tend to suspect the clearances have never been done dispite extensive BMW history! I've aquired a Snap-on tool used for Mk1 Golf's. It looks like it might work but need some time to try it out.

Just completed the rest of the inspection 2 which included plugs and so on. There was nothing untoward apart from a suspect (yellow!) oily pool under number 5 coil pack!

Also, the cars into the local specialist on Monday for wheel alignment. He's going to check the fault log.

DrSakke · 12th September 2003, 21:26

Hi!
I would also check the inlet elbow hose after the air flow meter (thoroughly!!!!) I checked and had it checked at every service and still the break in the hose was unnoticed until I asked my local dealer check all the hoses they said the rubber hose was halfway through broken. Could be that it had just broken before the insp. but you´ll never know...
This should be checked as often as possible as the part is inexpensive (original part appr. 20 eur.) and is known to cause disturbances and rougness in engine behaviour. The worst case scenario is burnt pistons!!!!! $$$$$

, because of too lean mixture.
So if the hose is old (or half old), CHECK IT.

Just my two cents

Sakke

DrSakke · 12th September 2003, 21:28

I just have to add...
Mine was broken on the under side so it was hard to discover even with a closer look, you really have to take away the air flow meter/air filter package to be able to check it in the inside...

All the best
Sakke