Anyone had this happen ?

[razzle99]

From time to time (usually when driving on part throttle at lowish speeds) the engine revs drop very briefly - feels as if fuel is momentarily blocked from getting through and then pick up right away. Never seems to happen when throttle is firmly planted.

Not sure if this is a co-incidence, but never noticed it until I ran a couple of consecutive tanks of Optimax (BP is our local station so had been using Ultimate). Switched back to Ultimate and it seems better but still occurs. Any ideas ?

BTW - Just heard the wife pull up in it just now, sounded like she was having no such problems

[DustyC]

I find that Optimax makes it run slightly lumpier at low speeds.
BP ultimate seems to make it very smooth though.

Been experimanting with this just lately and thats definitly the way it appears to be. It can be a pain in traffic when on Optimax but is no problem on Ultimate.
Strange but true.

[razzle99]

Thanks for that Dusty. Best I dedicate a tank or two of Ultimate this weekend to research purposes.

[starmist]

If you have a slight exhaust leak and additional air is being sensed by the Lambda sensor, it will try to alter the fuel map when it shouldn't be, and this can cause slight lurching on light throttle. Also make sure your vacuum advance is tight. If it's loose, the advance that operates on light throttle can mess up.

[DustyC]

I have a slight exhaust manifold leak (hopefully just gasket, yet to find out).

[donatien]

starmist said:

If you have a slight exhaust leak and additional air is being sensed by the Lambda sensor, it will try to alter the fuel map when it shouldn't be, and this can cause slight lurching on light throttle. Also make sure your vacuum advance is tight. If it's loose, the advance that operates on light throttle can mess up.

Good call - make sure all vacuum advance pipes are intact. There's a thin pipe from the plenum to a disk on the dizzy. Make sure the disk is firmly attached too.

Also, offbeat idling can be linked to a dirty stepper motor.

Dave

[DustyC]

Mines only very slight, but im a fussy bugger thats wants a balanced engine!

[tegriffic]

DustyC said:

I have a slight exhaust manifold leak (hopefully just gasket, yet to find out).

That probably will be the bolts working loose. It'll get worse and then eventually the gasket will tear. On my Griff, the top bolt at cylinder one seems to be a favourite. You just need to check them now and again.

>> Edited by tegriffic on Friday 21st May 13:05

[Guillotine]

sounds like the fan/s cutting in to me.

extra load on the electrical system causes revs to drop slightly till the ecu adapts. TADTS!

[j9nhy]

Had same problem for a short while but could not tell if i has an electrcal fault at the time too!! Seemed to sort itself after a few heavy blasts --- but the fuel type did cross my mind at the time

[razzle99]

Cheers everyone, a few things to check out then. Will start with checking vacuum thingies as the car is running & idling smoothly even at tickover & low speed - It's more of a brief stutter in the revs on part throttle

[Guillotine]

or a dirty/iffy throttle pot.

[BogBeast]

Guillotine said:

or a dirty/iffy throttle pot.

seconded..

[demo2]

BTW - Just heard the wife pull up in it

did i read that right?

[razzle99]

You did indeed demo. Ours is an equal opportunities Griff - more than happy to terrify drivers of either sex.