1985 Vette fuel problem (I think???)
Thread Starter
5th Gear
Joined: Sep 2005
Posts: 5
Likes: 0
1985 Vette fuel problem (I think???)
My 85 Vette started to run really bad after sitting for a year. When I say bad, it would go down the road but as soon as I gave it any gas it would bog terribly. It got to the point where it would not start at all. I replace the fuel relay switch, the in line fuel filter and the in tank fuel pump. It still won't start. Any suggestions or anyone know someone in Western Massachusetts I can trust to fix it without ripping me off. Any help would be greatly appreciated.
Le Mans Master
Joined: Mar 2004
Posts: 5,107
Likes: 171
From: Dublin CA
Start with basics:
Check for fuel pressure at the rail. If you have a fuel pressure gauge attach it to the fuel rail and test for pressure. It should be some where about 36-39 psi. IF you have fuel then continue on....
Check for spark. Pull spark plug wire and stick screwdriver into the plug wire socket and then lay the screwdriver in a position that will create a spark as it arcs from the screwdriver to the metal on the engine. Turn over the engine and see if you have spark.
Once you have tested for these two things we will continue on.
Check for fuel pressure at the rail. If you have a fuel pressure gauge attach it to the fuel rail and test for pressure. It should be some where about 36-39 psi. IF you have fuel then continue on....
Check for spark. Pull spark plug wire and stick screwdriver into the plug wire socket and then lay the screwdriver in a position that will create a spark as it arcs from the screwdriver to the metal on the engine. Turn over the engine and see if you have spark.
Once you have tested for these two things we will continue on.
Racer
Joined: Apr 2012
Posts: 373
Likes: 31
From: Albion, Indiana
I own an '85 that I purchased in April of this year. Had fuel issues as well. Do you have fuel pressure? I'm no mechanic, but work as a GM parts manager and can slowly figure things out. My problem ended up being a combination of botched fuel pump relay wiring by the PO, and the oil pressure switch failed. Replaced switch, repaired wiring, starts and runs like it was meant to!
Thread Starter
5th Gear
Joined: Sep 2005
Posts: 5
Likes: 0
Start with basics:
Check for fuel pressure at the rail. If you have a fuel pressure gauge attach it to the fuel rail and test for pressure. It should be some where about 36-39 psi. IF you have fuel then continue on....
Check for spark. Pull spark plug wire and stick screwdriver into the plug wire socket and then lay the screwdriver in a position that will create a spark as it arcs from the screwdriver to the metal on the engine. Turn over the engine and see if you have spark.
Once you have tested for these two things we will continue on.
Check for fuel pressure at the rail. If you have a fuel pressure gauge attach it to the fuel rail and test for pressure. It should be some where about 36-39 psi. IF you have fuel then continue on....
Check for spark. Pull spark plug wire and stick screwdriver into the plug wire socket and then lay the screwdriver in a position that will create a spark as it arcs from the screwdriver to the metal on the engine. Turn over the engine and see if you have spark.
Once you have tested for these two things we will continue on.
Team Owner
Joined: Jan 2003
Posts: 20,333
Likes: 263
From: Summerland B.C. Canada
No flash on noid, was there 12v at injector connectors ?
The ignition control module sends a reference signal to ECM to fire injectors. It's the purple/white wire on the 4 pin connector, at base of distributor. My 86 FSM says 1.3v pulse when running/cranking.
The ignition control module sends a reference signal to ECM to fire injectors. It's the purple/white wire on the 4 pin connector, at base of distributor. My 86 FSM says 1.3v pulse when running/cranking.
Team Owner
Joined: Jan 2003
Posts: 20,333
Likes: 263
From: Summerland B.C. Canada
I see your offline line now, so I will add this test, assuming you have 12v at injector connectors.
Connect noid light to injector connector.
Disconnect the 4 way connector at base of dist.
Turn ignition to run
Using a test light connected to 12+, quickly touch and remove the probe at the purple/white wire on 4 pin connector.
Each time it is removed, the noid should flash and the fuel pump should run for 2 seconds.
If it doesn't, unplug the throttle position sensor and repeat the test. If the noid flashes now, replace the TPS. If it doesn't, replace ignition module.
If the TPS is sending WOT voltage at closed throttle, this will put the ECM into "clear flood" mode and ECM may not pulse injectors. You can test the TPS before doing the previous probe test, to rule out "clear flood" mode.
You will need to measure the voltage of the top 2 wires on TPS, with ignition in "run" and connector still connected to TPS. (pierce with probes or slide a paper clip or similar, along wire and into connector)
.54 volts =/-.075 at idle
Connect noid light to injector connector.
Disconnect the 4 way connector at base of dist.
Turn ignition to run
Using a test light connected to 12+, quickly touch and remove the probe at the purple/white wire on 4 pin connector.
Each time it is removed, the noid should flash and the fuel pump should run for 2 seconds.
If it doesn't, unplug the throttle position sensor and repeat the test. If the noid flashes now, replace the TPS. If it doesn't, replace ignition module.
If the TPS is sending WOT voltage at closed throttle, this will put the ECM into "clear flood" mode and ECM may not pulse injectors. You can test the TPS before doing the previous probe test, to rule out "clear flood" mode.
You will need to measure the voltage of the top 2 wires on TPS, with ignition in "run" and connector still connected to TPS. (pierce with probes or slide a paper clip or similar, along wire and into connector)
.54 volts =/-.075 at idle
Thread Starter
5th Gear
Joined: Sep 2005
Posts: 5
Likes: 0
Ignition Control Module is working
I took the ingnition control module to NAPA and they tested it and found it to be good. I was hoping they would'nt have. Monday I have my Father-in-Law coming over with his noids to perform the test on the TPS. I will keep everyone up to date. Thanks again for all your help because I just don't know enough about this car, I truly appreciate it.
Mike.
Thread Starter
5th Gear
Joined: Sep 2005
Posts: 5
Likes: 0
I see your offline line now, so I will add this test, assuming you have 12v at injector connectors.
Connect noid light to injector connector.
Disconnect the 4 way connector at base of dist.
Turn ignition to run
Using a test light connected to 12+, quickly touch and remove the probe at the purple/white wire on 4 pin connector.
Each time it is removed, the noid should flash and the fuel pump should run for 2 seconds.
If it doesn't, unplug the throttle position sensor and repeat the test. If the noid flashes now, replace the TPS. If it doesn't, replace ignition module.
If the TPS is sending WOT voltage at closed throttle, this will put the ECM into "clear flood" mode and ECM may not pulse injectors. You can test the TPS before doing the previous probe test, to rule out "clear flood" mode.
You will need to measure the voltage of the top 2 wires on TPS, with ignition in "run" and connector still connected to TPS. (pierce with probes or slide a paper clip or similar, along wire and into connector)
.54 volts =/-.075 at idle
Connect noid light to injector connector.
Disconnect the 4 way connector at base of dist.
Turn ignition to run
Using a test light connected to 12+, quickly touch and remove the probe at the purple/white wire on 4 pin connector.
Each time it is removed, the noid should flash and the fuel pump should run for 2 seconds.
If it doesn't, unplug the throttle position sensor and repeat the test. If the noid flashes now, replace the TPS. If it doesn't, replace ignition module.
If the TPS is sending WOT voltage at closed throttle, this will put the ECM into "clear flood" mode and ECM may not pulse injectors. You can test the TPS before doing the previous probe test, to rule out "clear flood" mode.
You will need to measure the voltage of the top 2 wires on TPS, with ignition in "run" and connector still connected to TPS. (pierce with probes or slide a paper clip or similar, along wire and into connector)
.54 volts =/-.075 at idle
Best regards, Mike.
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