Duntov85

What would cause the engine to die at part throttle while driving, but if you floor the throttle in gear it will restart? The problem is the injectors shut off but as soon as I stab the throttle to full throttle it starts working again immediately.

coupeguy2001

sounds like a problem with either the throttle position sensor, or the MAF, or the maf module in 85 only cars.

CorvetteMike2024

Un plug maf and see if it runs better.

Corvette Mike

Duntov85

I tried 3 different MAFS, my original and 2 remans from seperate companies. ALL acted the same.

I've tried 2 different throttle positions sensors. The throttle position sensor in there now I tested on an oscilloscope. It has a very nice signal free of any gliches or dropouts whatsoever.

The MAF signal monitored on the oscilloscope at the ECM harness looks pretty good is well.

What seems to be happening is I have complete fuel shutoff, but WOT reactivates everything.

What I don't understand is when I accellerating (TPS lets say 1.5+ volts) what would cause the fuel injection to suddenly shut off, but restart only at WOT (giving more gas pedal won't restart the engine - must be full pedal).

If the burnoff module (which powers the MAF sensor in 85) is bad, why would full throttle restart the engine immediately? That doesn't seem logical in this scenario. Burnoff is working. After I shut the engine off I can see the wire turn red hot after a few seconds and then go out. From what I know about the 85 burnoff module it is supposed to do 2 things: 1) Power the MAF, 2) Initiate a burnoff after engine shutdown - and it does both of those things.

It is like the care is going into deceleration mode except for the engine actually dies. In decelleration mode the injectors shut off, but even a little increase in throttle will start the injectors back up. In this case, it requires full throttle.

When this problem occurs though, I can 100% of the time get the engine to restart/injectors pulsing again by stabbing the gas to the floor.

I really don't think it's the MAF or MAF burnoff, or the TPS. I thought about the dist reference signal, but the signal looks good on an oscilloscope. Also, how would full throttle suddenly "fix that"?

ex-x-fire

I would check your grounds, I have seen GMs run very funny that ended up being a poor ground connection. Can you verify that your loosing a pulse to your injectors? Make sure your not loosing spark,use a timing light taped to the windshield, it will only flash w/ spark. Take the cap off the distributor, & check for any slop on the rotor. Any codes?

coupeguy2001

well, if the only thing you do is smash the gas pedal, The only thing that gets a signal is the TPS.
That in turn sends a signal to the ecm that you want max fuel. That turns on injector pulses.
Is this a stick car? If it is, do you put the clutch in when it happens or push it into neutral?
If it's an automatic car, do you put it in neutral first?

another thought, the only other thing tied to the gas pedal is the cruise control module.
maybe there is a short in the digital dash? ....ie ......tach filter short??? ie...... distributor module?..ie........ distributor power?
The computations for the cruise control module is in the digital dash.
Try disconnecting the cruise cable at the throttle body, and when it quits, with it disconnected, does it still come back on?

Duntov85

I got to thinking and really looked at the big picture. With the old computer I had a cylinder select error. With this reman ECm also had a code 33 once. Replaced a bunch of MAFS. Tach went a little nuts on me once.

What is the roots of all RPM. Answer: Distributor reference signal. I'm new to using an oscilloscope on cars. I had a signal though. I got to thinking. If I had no manuals whatsoever what kind of a signal would I expect to have and do I have that signal. Answer: No.

Disconnect the 4 way connector to distributor. Everything looked great. (I'd looked in there before.) Did a pinout of the spade on the distributor side. Cleaned it up very well and carefully splayed the terminal wider for a tighter connection. Reinstalled. Scope shows a very awesome signal free of any kind of glitches. I just didn't know how to use the scope very well, I admit. I know how to use it now.

By the way, the chances of me fixing this without a oscilloscope was probably zero. I was getting to the point I'd have to send it to a shop with one and with someone with experience to use one. (This scope doesn't have waveform samples of what to expect - so I was in the dark there.)

Car runs awesome now. What a bunch of wasted money and time. I'm alot smarter now with C4 electronics now though.

1985 Corvette

Very cool you were able to figure out the electrical problem. Electrical gremlins in these cars usually sends most people packing.

Duntov85

Car kept dying, then died 10 times in 30 miles.

Reman AC Delco ECM had exact same problem as the original ECM. This reman ECM proved to be defective. Replaced with another reman AC Delco ECM...no problems or cutouts in 800+ miles.

FIXED.