Runs Great then stalls

[78tenn]

Please help!! I've had this prob for several years, so I will try to give an explanation and list of the things I've tried to remedy the problem. 78Z that is running great except after 20-30 mins of driving it will just stall for no apparent reason and at any speed or idle. After stalling it usually takes 15-20 mins to restart although it cranks fine. Fuel is clean and pressure is good. New air/flow meter,water temp sensor and connector, new injectors, all new vacuum lines. After it stalls, the spark plugs do fire. Any help is greatly appreciated!

[zbane]

First guess: Rust or crud in the gas tank getting stirred up and pulled into the fuel line, most likely clogging the fuel pump's inline filter.

After setting for a bit, the crud "relaxes" and allows semi normal fuel passage and delivery, but then the cycle repeats...

Look into the tank, and let us know how it looks.

Edited July 26, 2009 by zbane

[kensval]

Here's another possibility (this happened to me): If your carbon canister is gone, and the vent line from your gas tank is hooked directly to manifold vacuum, then the pressure in your gas tank is being lowered not only by the reduction of fuel in your tank, but also by the manifold vacuum. Eventually, you starve your engine of fuel and it won't restart until the pressure equalizes. (I did not hook my vent line to the manifold, a supposed local Z-expert shop did. Not so expert.)

Other possibilities: Loss of signal from the ECU due to a cracked PC board that expands when it gets warm, cutting off the signal to fire the injectors; an intermittently bad fuel pump; bad throttle switch.

Good luck.

Edited July 26, 2009 by kensval

[sblake01]

I had a similar problem when I first bought my 78. It turned out to be a bad main EFI relay that would intermittently work and then not. I could tap on it and the car would stall. Replaced it and the problem never surfaced again.