stuttering on part throttle when driving

[laz11]

My pre cat is suffering from this, usually when the engine has warmed up driving above 50mph. The power gets restricted and the revs are erratic but once i persist and keep my foot down it clears and then drives normally again. The red light flashes on and off usually too when this is happening... oil pressure and level is fine. I had something similar a few years ago and it turned out to be the ecu and eventually had that changed. I will take it to to my indie to get it looked at but any ideas before then would be appreciated. Thanks Lawrence

Edited by laz11 on Sunday 21st September 07:18

[Pagey430]

I'm having the same problem!

Hesitation only occurs at light thottle in any gear, it's fine on tick over and pulls clean and strong on anything more than about half throttle.

I've changed over to Emerald ECU and I can see the mixture goes v.weak on light throttle for some reason.

Interestingly when the revs are held at say 1500rpm on the driveway, the mixture cycles between v.weak then to slightly rich and back again with the revs fluctuating in time with this...very bizzare!

Hve you looked at the throttle potentiometer as the track may be worn and confusing the ECU...this is my next area to look at.

[GreenV8S]

Pagey430 said:

I'm having the same problem!

Hesitation only occurs at light thottle in any gear, it's fine on tick over and pulls clean and strong on anything more than about half throttle.

I've changed over to Emerald ECU and I can see the mixture goes v.weak on light throttle for some reason.

Interestingly when the revs are held at say 1500rpm on the driveway, the mixture cycles between v.weak then to slightly rich and back again with the revs fluctuating in time with this...very bizzare!

Hve you looked at the throttle potentiometer as the track may be worn and confusing the ECU...this is my next area to look at.

Since you have full access to the ECU you should be able to see whether the hesitation is being caused by AFR variations. From the sound of it, you already know you're running too lean under part throttle and this would cause hesitation.

The mixture cycling is probably caused by lambda feedback. Try switching that off to confirm. If that's the problem then you might find it helps to reduce the authority (restrict the amount of correction it can apply) or increase the time constants on the feedback.

[Pagey430]

Many thanks Peter.....this seems to have worked a treat....I turned off the adaptive mapping to get back to open loop and then manually adjusted some of the lean areas of the map and hey presto!..hesitation gone & much more responsive on pick up. There is still some fettling to do as I can see under some light load/speed conditions I still get weak mixture flashing up v.briefly but not enough to notice now....something for when I have some more time.

Thanks again

John

[laz11]

I'm the OP- having been to goodwood and back from brighton today the car didnt miss a beat apart from about 10 seconds when it played up. very strange. Anyway am taking the car for a waxoyl tomorrow so will get the garage to look at it

[Pagey430]

I do apologise I did not mean to hijack your posting, just trying to compare some similiar symptoms with poss solutions...!...us pre-cats got to stick together you know...not that many of us! Good luck with a fix though.

John