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Old 09-03-2014, 03:01 PM
JONMRC JONMRC is offline
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Default O2 numbers drop to zero on acceleration??

Hey All-
I'm new to the Buick forum and the proud new owner of an '85 GN. This car is basically stock, it just has the simple upgrades you do to start tuning- fuel pump, hot wires, injectors, turbo tweek 94, scanmaster, 87 computer, MAF translator, cold air. Currently the EGR is disconnected but not removed (bought it that way). So I have gotten my o2 numbers around 800 at idle, but any real acceleration and my numbers actually drop to ZERO for a few seconds! and remain low until the heavy acceleration is gone. I have richened the MAF settings, but it doesn't seem to help.
The first punch of the throttle seems strong, but then weak from there.
I've been looking for vacuum leaks, and actually found one to the MAP, thought that would fix it, but it didn't.

Any suggestions? I know I have to get this right before I start final tuning and adding boost.

Thanks in advance
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Old 09-03-2014, 03:20 PM
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kenmosher kenmosher is offline
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Location: CO
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Default Re: O2 numbers drop to zero on acceleration??

Sounds like you have a weak/failing fuel pump. Those are pretty strong indicators that you aren't getting enough fuel.

BTW, 800mv at idle is eye watering RICH. You want idle to be around 450-550 mv or else you'll be fouling plugs (and killing the catalytic converter if it still has one).

Monitor fuel pressure and see if it drops (my guess is it does) under acceleration.
Ken Mosher
1987 GN original owner 650+ HP Black
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1985, low, oxygen, scanmaster, troubleshooting

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