Fuel problem
Thread Starter
Intermediate
Joined: Nov 2007
Posts: 30
Likes: 0
From: Metter Georgia
Fuel problem
My '89 'Vette stopped running. I can't hear the fuel pump and can't get voltage to the fuel pump. The fuse is not blown. I have tried to energize the pump through the ALCL terminal "G", but no fuel. I replaced the fuel pump. Where should I look next?
Le Mans Master
Joined: Jan 2006
Posts: 5,620
Likes: 206
From: Orlando FL
I don’t have the drawings for the 89. But I would start checking the FP fuse. Also check any connections or plugs related to the fuel pump.
If you have a FP relay it could be defective if the 89 has one. Also check the oil pressure connect switch. It should feed voltage when oil pressure comes up. It should also have 12 volts on one side of the switch. If no voltage on the switch, work backward to see where it comes from. You can also connect the 2 terminals of the switch and see if the pump starts and if the connector at the tank gets voltage.
If you have a FP relay it could be defective if the 89 has one. Also check the oil pressure connect switch. It should feed voltage when oil pressure comes up. It should also have 12 volts on one side of the switch. If no voltage on the switch, work backward to see where it comes from. You can also connect the 2 terminals of the switch and see if the pump starts and if the connector at the tank gets voltage.
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
The FP fuse is after the relay and also after the oil pressure switch. The OP switch closes at 4 psi, so during cranking if you cannot achieve 4 psi, it won't close and supply 12v to the FP. The ECM closes the FP relay for 2 seconds when the ign sw is in run or crank. The ECM also closes the relay when it gets pulses from the distributor. You need to measure the voltage on the FP relay coil and see if it gets 12v for at least 2 seconds when the ign sw is in run. If not, see if there is 12v on the power side of the OP switch to ensure that the fusible link that powers the ECM and FP is good. If it is, then you need to see if the ECM is getting 12v from the ign sw in run and crank. The ECM could be defective.
Racer
Joined: Jul 2006
Posts: 315
Likes: 0
Oil Pressure Switch Controls Fuel Pump
The FP fuse is after the relay and also after the oil pressure switch. The OP switch closes at 4 psi, so during cranking if you cannot achieve 4 psi, it won't close and supply 12v to the FP. The ECM closes the FP relay for 2 seconds when the ign sw is in run or crank. The ECM also closes the relay when it gets pulses from the distributor. You need to measure the voltage on the FP relay coil and see if it gets 12v for at least 2 seconds when the ign sw is in run. If not, see if there is 12v on the power side of the OP switch to ensure that the fusible link that powers the ECM and FP is good. If it is, then you need to see if the ECM is getting 12v from the ign sw in run and crank. The ECM could be defective.
I read this "The OP switch closes at 4 psi, so during cranking if you cannot achieve 4 psi, it won't close and supply 12v to the FP." and am wondering if this is true for an 85. I have wired +12v to terminal G on the ACLC and the pump ran - that is in the haynes manual as a troubleshooting procedure. Do the newer 85+ vettes have a low oil pressure fuel pump cut off circuit?
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
My car has high mileage and does burn oil and it does get low from time to time. I had a no start condition once and as I cranked I noticed I had something like 5psi oil pressure. It kind of threw me. I checked the book and found the oil pressure and fuel pump ran on the same fuse; checked the fuse and found it was blown. I replaced the fuse and it ran and had normal oil pressure.
I read this "The OP switch closes at 4 psi, so during cranking if you cannot achieve 4 psi, it won't close and supply 12v to the FP." and am wondering if this is true for an 85. I have wired +12v to terminal G on the ACLC and the pump ran - that is in the haynes manual as a troubleshooting procedure. Do the newer 85+ vettes have a low oil pressure fuel pump cut off circuit?
I read this "The OP switch closes at 4 psi, so during cranking if you cannot achieve 4 psi, it won't close and supply 12v to the FP." and am wondering if this is true for an 85. I have wired +12v to terminal G on the ACLC and the pump ran - that is in the haynes manual as a troubleshooting procedure. Do the newer 85+ vettes have a low oil pressure fuel pump cut off circuit?
Racer
Joined: Jul 2006
Posts: 315
Likes: 0
OK. So, that quote was erronious. Yeah, that would actually be a nice feature. I routinely drove 500-800mile trips weekly and the car was running so good that I never popped the hood to check the fluids. Thats when I've seen 0 psi at idle. Thanks.
