Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
Hi There, I'm Clayso a certified master automobile technician with 30 years of automotive repair and diagnostic experience.
Power to the injectors comes from the #1 & #2 3 amp injector fuses. Verify with a test light there is power at the fuses and on the red and white wires at the injectors. This circuit should have battery voltage during cranking and when the engine is running.
At least 10 volts. I'm putting together a diagram to find where the 3 amp fuses get their power from right now. I'm sure there is no power at the fuses, but check to make sure.
Let me know
The INJ 3 amp fuses power from the ignition switch when the key is in the on position. There should be battery voltage on both sides of the fuses with the key on and at the injectors on the red wire for #1 injector and on the white wire for #2 injector. Let me know if there is power at the fuses ant at the injector connectors.
Put the fuses back in and check for battery voltage at the injector connectors. With the key on there should be battery voltage on the red wire for #1 injector and on the white wire for #2 injector.
Very true. Does your distributor have the coil on top of the cap or is the coil external from the distributor?
I'm pretty sure the rough running problem is the EGR valve is leaking. Once I know what strib is in this Vette I can send you the correct diagnostic procedure for the module and pick up coil.
I was pretty sure you had the integral coil. Verify the thick pink wire going to the cap has battery voltage during cranking. You will have to remove the cap to check the pick up coil and module. Disconnect the pickup coil from the ignition module. Set your voltmeter to the AC scale and disconnect the pick up coil from the module. On the 2 wire connector from the pick up coil check for 500 millivolts AC or higher. Depending on your meter you may see 0.5 volts AC. This is with the engine spinning over. The link below is text book for checking the module and pick up coil.
Distributor Testing and Inspection
If the pick up coil checks good most likely the module is defective. If there is no AC voltage from the pick up coil the pick up coil is defective.
I understand, I just never assume new is good. Injector pulse is also controlled by the ignition module. Do you have a test light? With a test light you can tap ground at the PCM to verify the circuit to the injectors.
Instead of going through the strib checks, try this first. Disconnect the strib 4 wire connector. On ECM side of the connector. Attach a jumper wire to the purple/white wire. Disconnect the TPS connector. Turn the key on and with the loose end of the jumper tap the grey wire on the TPS connector and listen for the fuel pump to energize and the injector to click.
Let me know if the pump comes on and if the injectors click.
The distributor and the ECM control the injector pulse. Power is supplied to the injectors and the ECM pulses ground to the injectors based on the input from the module in the distributor. Either the ECM failed or there is a problem in the wiring or the strib. When you torn the key on does the check engine light come on?
Cool. Try this quick check to see if the distributor and the ECM can comminucate. Disconnect the strib 4 wire connector. On ECM side of the connector. Attach a jumper wire to the purple/white wire. Disconnect the TPS connector. Turn the key on and with the loose end of the jumper tap the grey wire on the TPS connector and listen for the fuel pump to energize and the injector to click.
I'll get you an Assembly Line Data Link (ALDL) connector view to see if the Check Engine Light (CEL) will flash a #12 code.
I'll be here all day tomorrow. Let me know what all you find.
Code 12 is actually a check code for determining the integrity of the ECM's circuit to power and ground.
At the ALDL jump the A terminal to the B terminal and turn the key on. The CEL should flash 12 times 3 times in a row. 12 will flash (*pause**).
You are correct, since the battery has been disconnected there will be no codes stored. To check fuel pressure you would need to adapt a gauge in between the fuel line and the throttle bodies. The specs are 9-13 psi.
At 9-13 psi simply cracking open a line would be enough to verify fuel pressure.
Was the engine running rough at idle? Also how well did it run going down the road?
The easiest place to tie into the fuel system to check pressure is at a filter versus cutting a steel line or trying to adapt to the fittings. Usually on low pressure systems like this, if you have fuel spray any any of the connections when loose and the key on there should be enough pressure for the engine to run.
I use a test light clipped to the battery positive and check the injectors green or light blue wires for a pulse to ground with the engine spinning over. The test light will flash each time the module and the ECM ground the injector.
Once the no start condition is solved you can disconnect the EGR's vacuum and see if the idle improves. If the EGR valve is leaking it basically opens the exhaust straight into the intake, kind of like a vacuum leak. Leaking EGR's are notorious for driveability problems both at idle and under a load. If the EGR valve is flat at the gasket surface you can make a solid gasket out of tin and close the passage from the exhaust to the intake and see if the idle improves.
Let's get it running again and go from there.
That's cool. I'll be here.
Yeah I kinda wondered where you where, I fell asleep on you. I'd never expected a noid light to flash either, very surprising.
The '84 and '85 fuel specifications are very different. 1984 with fuel pressure at 9-13 psi. 1985 with pressure at 24-39 psi. The fuel pressure regulator is what maintains the pressure at the specifications. I've had fuel pumps crap out at the darnedest times, one minute it's peaches and cream and the next nothing.
Let me know how this works out after changing the pump.
Dead heading the pumps is the only way to determine the pressure differences. Dead heading is done by blocking off the return with the pump in operation. This can also be done on the bench with a gauge hooked directly to the pumps discharge port. I don't have any specs for this procedure, but a 20% increase is about normal. It's just one of those try and see things. Worst case scenario is like you say at the regulators diaphragm.
If this vehicle sat for any length of time rebuilding the TBI's and replacing the injectors wouldn't be a bad idea. The links below are for the TBI units.
Fuel Injector Balance Testing
Throttle Body Overhaul
Let me know if you can view and print out the overhaul procedure.
Right on! I've been hoping for some positive results. So basically the pump was simply pumping fuel back into the tank.
I can understand selling it, 1984 was no glory year for the Corvette that's for sure. The last one I owned was a '78 and the only thing it had going for it was the Silver Anniversary and the ride was more comfortable than my '76. I hope you get a good price and a quick sale.
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