Flat spot from 3000 to 4000

[Christian]

Hi @ll!

I've a nice little question for the techheads in here...

I've upped the boost to 15psi something like 1 and a half years ago. No problems with it most of the time.
BUT:
My car has got a flat spot between 3000 and 4000 RPM.
Fitting new spark plugs helped quite a bit, but didn't completely cure the problem.

Now a mate and I fitted a borrowed lamda-tester (around 2000 BP worth) and fitted it.
Guess what... car leans from 0.9 to 1,0 lamda in this area!! DOH!
BUT - and that does stop me from thinking it's the fuel pump - above 4000 everything is fine and the mixture goes down to 0,88 @ redline.
So????
Any ideas what my problem could be???

I was thinking about fuel cut (as I have the standard chip in there ATM) and will figure this out.

But I can't quite imagine that fuel cut is so smooth or little like in my case.
I mean it's there to prevent engine damage, but this (leaning out the mixture) does HELP damaging the engine.

Waddaya think? http://300zx.co.uk/200sx/ubb/smile.gif


Christian

[Richy_Boy]

This is no way the fuel cut. IThis does exactly what it says on the tin.. You'll be banging your head on the steering wheel when this happens!

Sounds like you need to either beef up your fuel pump, or get a stage 1 chip or something.


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Rich

180 to 210 BHP @???? rpm
S13 J reg Graphite Grey - ND200, Koni Adj., 17" wheelz, dropped. Broken.

[Clong]

Don't know wether this is plausilble or not but between 3000 and 4000 rpm represents about 70-90 mph on the speedo. From various friends who own motorbikes, their performance bikes do the same thing, as their electronic mapping leans the mixture to allow the bike to pass emissions at the 70 mph mark. Its not tested at any other speed, so the mapping corrects again for maximum power at other rpm. The result power curves shows a signifcant dip in the power produced. This may be what is happening in your car and a new ignition map would solve this. On the other hand this could be a load of pants!!

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1990 Blue S13
Mongoose 'zorst
K&N, ND Boost upgrade, Saab FMIC.`