Technical Yet another flatspot problem?

[GoBe]

I've got a problem with my mk1 Sei', it's developed a stutter around 2500 rpm when cold, this has been emphasized by a mckrich chip but it's still there under the standard ecu as well. This stutter goes away once the engine gets reasonably warm, but still below normal operating temp, mostly it's a single pause between 2400 and 2500 rpm but some times it'll show signs of the usual flat spot between 2000 and 2500 rpm but not always, and this only happens when the engine is cold.

There is an electrical problem with the car in that the battery light is on all the time and the battery slowly discharges over time, a known good alternator has been fitted and all earthing points have been cleaned up but to no effect on either the battery light or the stutter. I've swapped over a map sensor and a crank sensor without success, though the fact it didn't get better or worse tells me they're okay, this weekend I'll do a service with leads, plugs, fuel filter etc.

The flat spot problem doesn't bother me that much as it's a known issue but this 2400 to 2500 rpm pause is much more worrying, catch the engine wrong and some times it feels like the engine stalls for half a second or so. Does anyone have any bright ideas on what could cause this?

 

[arc]

gexs sei used to stall as the revs dropped, i can't remember if it was ever fixed (the car is now off the road) but signs were pointing toward a vacuum leak.

afaik the chip (mostly) leans out the mixture, the fact that it emphasized the problem could be indication that it is a fuel supply / injector problem.

re the battery light.. that needs to be addressed really too. run the car without the alternator, see if it still stutters then. I upset my alternator once by changing my dashboard lights to LEDs. It ran like crap for a long time, and i was ready to take it to an auto electrician when Custard suggested i swap the light back to a bulb, and tada - it was fine. My point being, it could be something some damn simple you don't reckon its worth checking.. but check everything.

 

[jimbro1000]

Until the electrical system is running at the proper voltage (about 13.4v) rather than off the battery (12v) you are likely to experience all sorts of odd behaviour. For a start the fuel pump will not be running at the same rate which has plenty of knock-on effects, power to the injector(s) will be upset, etc.

It is common to see the ecu under or over fuel if the voltage is outside the normal programmed parameters.