abb890

Hey guys, I have an 85 corvette that's having a bunch of problems and I'm wondering if y'all could help me solve a few of them.

First off is the fuel pump. The car wouldn't start a few weeks ago so we replaced the fuel pump with a new one. The car still wouldn't start and we knew it was a fuel issue because we sprayed some starter fluid into it and it cranked over for a few seconds. This is a list of what we've done and it's still not working.

1. Replaced fuel pump.
2. Replaced fuel filter ( and tested to make sure no gas was coming through the gas lines with the fuel filter off and none was.)
3. took the new fuel pump back out and tested it manually and it the motor wasn't working.
4. Tested the old fuel pump motor and it was working again.
5. put the old fuel pump back in and it ran so we shut if off and after a few minutes it wouldn't start again.
6. Replaced FP fuse yesterday and it fired right up multiple times, until today.

Second is the idle, when the car is running, it's running REALLY rough. The idle jumps and there is a massive pause from hitting the gas to the engine actually revving. Also with this, the battery gauge on the dash stays around 16 or 17v and the bar next to it stays red.

Any ideas on these issues? Any advice or help is greatly appreciated. Thanks! - Addison

playsdixie

first things first...get a gm manual.....issue should be what the pressure is at the fuel rail with key on....85 should be 38# and should stay up for awhile and not drop immediately.....you also may have a vac leak somewhere, spray tb cleaner up/down the vac lines, if rpms increase, there's your leak....when running again, check timing, tps, and do a minimum idle adjustment...also, make sure your IAC is clean ....good luck....

gerardvg

Hi

First thing to do when buying a corvette is buy a shop manual.

http://www.ebay.com/itm/1985-Corvette-Shop-Manual-85-Chevy-Chevrolet-Repair-Service-Book-/361363684335?hash=item5422f43bef
Anyway here is the fuel pump wiring diagram, fuel pumps go like that they will work one day and not the next
Buy a new one from a reputable supplier, test it before installing.

Check the relay (on firewall near the wiper motor) remove the cover and check the contacts are closed, when ignition is turned on.
Will only close for a few seconds until the ecm senses the ignition reference pulses.

Check the orange wire has 12 volts all the time via battery, they have fusable links that will cut power in case of a short.

Note the fuel pump can easily be tested via the under dash aldl connector, connect 12 volts to terminal G the bottom far left one. The fuel pump should run, if it does run then check the relay and orange battery wire has 12 volts.

Only when you have fuel pressure and know the pump works should you do a base idle adjustment. Fuel pressure should be around 30-38 psi (the 85 has 24 lb injectors and has lower fuel pressure compared to 86+.

I recommend disconnecting the ecm plug near battery or disconnect and reconnect battery, removing stored codes when your fuel pump issue is fixed.

The ecm can get itself in knots trying to compensate for problems, most of my rough running is solved by disconnecting and reconnecting the ecm power.

The TPS ( throttle position sensor should be at 0.54 volts dc) ignition on engine off or at idle.

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Tom400CFI

Original pump may have a dead spot in the armature. Why it works some times and not others. Also maybe why fuse blew. What happened today? Pump not run? Fuse blew again?

Solve that before diagnosing idle.

Danlb

Addison--I have an '84 and the other day while accelerating it would sputter and backfire. I noticed the coolant temp gauge would change to the voltage gauge reading 17+ volts with the red light illuminated. Idle would smooth out after voltage dropped below 15 volts. Adding throttle would increase voltage above 15 volts again and the rough running came back. Dash would also get very bright as the red light came back on. Apparently the excessive voltage was causing issues with the ECM. Since the alternator was replace with a rebuilt unit before I bought the car a couple months ago I decided to replace the internal voltage regulator and all is back to normal now.

Good luck in finding the issue with the fuel pump.

Dan

abb890

Thanks for the reply!
I forgot to mention, I already have a GM manual for the corvette. So far I have checked the orange wire going to the relay and confirmed it had 12v at all times. I checked the wire going to the fuse and confirmed it was getting power when the ignition was turned in the on position for a couple of seconds. Finally I checked the light blue wire at the connector where the fuel sender connector is and confirmed it was getting the 2 seconds of power with the ignition on. I'm assuming this means that there is either a wiring issue on the fuel sender itself or it's the fuel pump itself.

Dt86

You need to put a fuel gauge on the fuel rail and see what pressure you have.