Engine Performance problem
1992 Chevy Truck 6 cyl Two Wheel Drive Automatic 115000 miles
My 1992 Chevy 1500 with a 4.3 has given me fits. I can not get this truck to start. When I put gas down the TB the truck will start right up and run until the fuel burns off. When the key is turned on the fuel pump does not come on. I pulled the pump and bench tested it and works perfect, good motor speed and pumps plenty. Reinstalled pump after inspecting all connection at tank and up stream wiring.
I then checked the fuses and found nothing there wrong. I replaced the engine bay fuse, fuel pump relay. I hot wired the circuit at the fuse and the pump runs then. Tried to start it and there is no fuel thru the injectors. I assume no power to the injectors as well. I have since replaced the ECM, oil pressure switch as well as the ignition module in the distributor. All this and still no success. I am at my wit's end! Can anyone help me please?
When I put gas down the TB the truck will start right up and run until the fuel burns off
This one here it tells you the ignition system is working otherwise I don't think it will fire up if its no good.
Lets concentrate on the fuel system. Do you hear the fuel pump come On with all these items replaced-if so double check the fuel pressure making sure its within specs. Fuel pressure okay-Now we check for injection pulses.
I need to know what type fuel system? Is it a TBI or CPI Vortec? So that we can continue-
September, 30, 2008 AT 12:24 PM
Thanks for helping!
This truck has the TBI system.
I have never gotten a peep out of the pump even after replacing all the above mentioned parts. As mentioned I can get the pump to come on if I hot wire (jump) the fuel fuse on the firewall next to the fuel pump relay. I can only get the pump to fire in this manner by using a seperate power source I.E. A jumper wire from the positive battery terminal. This is the fuse wired to the relay and ECM with a gray wire. With this I assume the wiring to the pump is sound.
But even with the pump running like that, the injectors are not cycling or spraying any fuel when I have the ignition on.
I am not up on how to properly test whether power is being supplied to the ECM and whether power is coming from the ECM to the relay. I have used a meter on some of the wires and some show hot though I don't remember which.
I am in training at a distance from the house right now so I won't be able to work on the truck until Friday But any help in sending me in the right direction is really appreciated.
October, 3, 2008 AT 8:25 PM
Ok, I have had a chance to check some things. I rechecked the pump and it fires good and pressure is +55 at the TB. It still won't come on with the key/ignition and the wiring checks out when I hot wire from the fuse plug near the relay. I checked power to the relay and the orange input power wire from the ECM is hot with the key on but no other coming out from the relay. Checked for good ground there/ok.
So still no power to pump! Power in to relay but none out and it is a new relay! Arhhh!
Checked power to injectors and the hot wires are hot when key is on and when the other side is grounded they will fire, I hot wired the pump and grounded the injectors one at a time and they sprayed fuel big time and the engine would start. But without manual grounding the injectors will not fire or pulse. Well I am closer but no closer if you know what I mean. I am still at a loss as to what the problem is. Why won't the pump come on and why won't the injectors fire. Please help
October, 5, 2008 AT 5:54 PM
Sounds like a computer problem it grounds the injectors and also the fuel pump relay
October, 6, 2008 AT 6:46 PM
Soonerbills, My truck is fixed. It was the fuel pump but once I changed it, I had to ground a contact on the test connector that specifically tells the ECM to close the fuel relay. Once the pump ran, I removed the ground and started the truck. Without doing that, the ECM did not power the relay. Go look at my post
1993 Chevy Truck No fuel to TBI
, there is a real good information that Merlin2021 provided and the answer may be that simple. The ECM gets it reference pulses from the ignition module to operate the fuel relay to keep it working and will shut down the fuel pump after 2 seconds if you stop trying to start the vehicle or there are no reference pulses. I think this will help you. Send me a post when you have success!
October, 6, 2008 AT 7:15 PM
I forgot to mention this. In your post you mentioned the fuel relay having power on the orange wire but nothing else. Your trucks diagram probably is the same as mine. You mentioned jumping power to the fuel pump wire. If it is a gray wire, then you probably have a green/white wire that the ECM energizes the relay coil with. I use a sewing pin to pierce the wire to read the voltage when you can not get to a contact. You already changed the relay and I bet it's the ECM that is not providing voltage to power the relay because the ECM is shut down and not broke.
Ot know the electrical diagram for your truck but on mine, the coil winding is grounded on one end the the ECM applies power to energize the relay coil. When you turn the key on, 12 vdc is applies to one of the relay contacts and only when the ECM applies voltage to the coil does the contacts close and feed voltage to the fuel pump.
October, 13, 2008 AT 12:37 PM
The truck is now running!
Turned out that a cut wire(green/white) to the relay was the culprit. Previous owner chopped off the o2 wires, ran a straight exhaust and cut through the harness in the process, nailing the relay wire. This fried the ECM and after replacing the harness I was able to get the truck started.
Now I have find out why it's rough running and stalling @ idle.
October, 13, 2008 AT 7:52 PM
Soonerbills, Success feels great now that you fixed your truck. Bummer that one spends so much effort but I can definitely tell you this site saved me some time and I have learned from it. I appreciate the reply that you have it working. Hoped the info I sent helped.