overboost fuel cut

[bubblehead]

Ok it's just a pretty standard 4.3 without any boost but i've got a very odd fueling/ignition problem which feels exactly like over boost fuel cut on my elan turbo.If you have experienced fuel cut on a boosted engine you will know how bad that feels, well i'm getting the same on my n/a engine! Only happens at 2900 rpm no matter the gear/speed/load or throttle opening and only for a very short time period ie not when the engine is cold or after reaching normal temps but during the warm up phase, so not really a problem to live with but its annoying me.........alot........engine just dies, doesn't stall goes straight to idle..... let off the throttle and i can start accelerating again. From the box of spares i've swapped out the TPS, rotor arm and dizzy cap (genuine lucas)to no avail. I've got spare coils etc and could keep changing bits but the fact it's so specific at 2900 rpm must mean something?? Anyone3 shed some light?

Cheers

[Exige S]

Vacuum advance gone wonkey? MAF dirty?

[blitzracing]

The only thing you can look for is the Rev counter dropping when it happens- least that would show something on the ignition side. The throttle pot can do odd things if the track is worn that you can test with a DVM, but otherwise you really need something like The Steve heath ECUmate to see whats going on sensor wise- no point in guessing, it will cost you more in time and parts than doing the diagnostics properly in the first place.

[bubblehead]

blitzracing said:

The only thing you can look for is the Rev counter dropping when it happens- least that would show something on the ignition side. The throttle pot can do odd things if the track is worn that you can test with a DVM, but otherwise you really need something like The Steve heath ECUmate to see whats going on sensor wise- no point in guessing, it will cost you more in time and parts than doing the diagnostics properly in the first place.

Yep your right gonna order one, I had one of his old ones but let it go with my chim when I sold it. Its a precat so don't think it can be fuelling it's just that it happens exactly at 2900 rpm every time. Update it doesn't do it if I just rev the engine eg no load on the engine and disconnecting the vac advance makes no difference. Blitz what if any input to the ecu does the speedo sender have as that works for the first 10 mins and then stops......long shot I know.

[bubblehead]

Well went to buy one of the new fault code readers only to find the Steve Heath site has ceased trading until July....damn ! In the meantime and as a bit of a shot in the dark i disconnected my speedo sender and would you believe it the problems gone. Still not sure exactly why as info on the speedo input to the ecu is a little sparse/vague and i'm not sure it can cause the problem i was experiencing although the results seem to indicate otherwise. On another note there was a thread recently about an open source fault code reader for windows but i can't find it does anyone have a linky.

Cheers

[virgil]

bubblehead said:

) Still not sure exactly why as info on the speedo input to the ecu is a little sparse/vague Cheers

In the SH bible it says the speedo sends a signal to the ecu so the ecu can tell if the car's moving to assist with the engine idle...not sure if that helps or sheads any light on it....

[blitzracing]

The speed sensor should only affect the idle or it can cut the engine fueling at a certain speed on unstable 4x4 being driven by middle aged women on mobile phones. This facility is removed as far as I know the the TVR fuel maps however, but I dont know what happens if you are on the limp home map.

Update on the freeware:

http://www.pistonheads.co.uk/gassing/topic.asp?h=0...