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Discussion Starter #1
I checked voltage at the rear fuel pump connector (behind the bumper) and discovered I only have 7.8 volts with the engine running. I have read about a fuel pump hotwire kit from Racetronix (which I just ordered) but now I'm wondering how well this will work since there is only 7.8 volts available to energize the coil of the hotwire relay. I have read that a Bosch style relay requires about 8 volts to energize the coil and the drop out voltage is anywhere from 1-5 volts. Has anyone who has installed the hotwire kit had any issues thus far? What voltage did you have at the connector before installing the hotwire kit?
 

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my battery had power problem . engine would crank but the volts to the FP was 8volts. this was at the rear connector. so I put charger on it and with key on prime time it was 11.5 volts .. with engine running volts were 13volts.

put a fused 10AMP jumper wire on the under hood prime wire key off .. now you can measure volts and fuel pressures and also check for how much fuel flow ..

with key on and low volts sure can be the relay contacts pitted and volt drop.
 

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Discussion Starter #3
my battery had power problem . engine would crank but the volts to the FP was 8volts. this was at the rear connector. so I put charger on it and with key on prime time it was 11.5 volts .. with engine running volts were 13volts.

put a fused 10AMP jumper wire on the under hood prime wire key off .. now you can measure volts and fuel pressures and also check for how much fuel flow ..

with key on and low volts sure can be the relay contacts pitted and volt drop.
I verified voltage in the "prime" mode and only got 7.8 volts with the connector disconnected and also connected and back probing the wire, I then started the vehicle and still only get 7.8 volts while the engine is running. I've been having an issue at idle where the engine surges (RPM's up and down and my fuel pressure drops slightly (about 34psi idling, and around 36psi driving) which I suspected was too low and causing my issue which made me check for fuel pump voltage at the rear connector.
 

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I verified voltage in the "prime" mode and only got 7.8 volts with the connector disconnected and also connected and back probing the wire, I then started the vehicle and still only get 7.8 volts while the engine is running. I've been having an issue at idle where the engine surges (RPM's up and down and my fuel pressure drops slightly (about 34psi idling, and around 36psi driving) which I suspected was too low and causing my issue which made me check for fuel pump voltage at the rear connector.
so with the FP connector disconnected that means IMO your meter is bad. check the batteries in it .

now if the FP connector was connected and you measured the voltage then 8volts would IMO not create enough for the pump to operate correctly.. I also should have stated the FP on my 96 Impala draws 4.2amps with the prime wire powered up and the battery charger on the battery. should be 13volts with charger on the battery ... I do have a 1.5volt drop from battery to the rear FP connector FP operating ..

at Idle I got 36-37psi ... I then pulled off the vac line on the FP Reg and plugged that vac hose .. got 43psi .. rev'd engine it did fluctuate slightly .

you have to check the in trunk wiring on the driver side.. that is how the FP wires pass and go thru the connector in the trunk.. my 96IMP the wires are gray + and black - ..connector C400 .. the exterior connector C402..........do not use body ground when checking volts .if the voltage is low you can measure the black wire to the body steel should be ZERO volts ..if not zero then a bad ground .. ground is in the trunk by the trunk hinge DS..
 

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Find the drop...
I recently found a low voltage issue that was affecting everything off ignition.
PO aftermarket alarm install was the culprit. That's a huge voltage loss and should be fixed even if you install an aftermarket harness.
 

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Discussion Starter #6
so with the FP connector disconnected that means IMO your meter is bad. check the batteries in it .

now if the FP connector was connected and you measured the voltage then 8volts would IMO not create enough for the pump to operate correctly.. I also should have stated the FP on my 96 Impala draws 4.2amps with the prime wire powered up and the battery charger on the battery. should be 13volts with charger on the battery ... I do have a 1.5volt drop from battery to the rear FP connector FP operating ..

at Idle I got 36-37psi ... I then pulled off the vac line on the FP Reg and plugged that vac hose .. got 43psi .. rev'd engine it did fluctuate slightly .

you have to check the in trunk wiring on the driver side.. that is how the FP wires pass and go thru the connector in the trunk.. my 96IMP the wires are gray + and black - ..connector C400 .. the exterior connector C402..........do not use body ground when checking volts .if the voltage is low you can measure the black wire to the body steel should be ZERO volts ..if not zero then a bad ground .. ground is in the trunk by the trunk hinge DS..
First off , I was using a test light that has a digital volt gauge in it so the ground clamp was attached to the fuel tank strap bolt and test light probe to the HOT wire at connector. The connector being disconnected or not has no bearing on the reading I get. I also got the same reading when attaching the test light ground clamp to the negative wire in the connector and the probe of the test light to the HOT wire. Tomorrow if it's not raining I'm going to inspect all connector points and also the relay and terminals for any corrosion and may just replace the relay as a PM part.
 

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First off , I was using a test light that has a digital volt gauge in it so the ground clamp was attached to the fuel tank strap bolt and test light probe to the HOT wire at connector. The connector being disconnected or not has no bearing on the reading I get. I also got the same reading when attaching the test light ground clamp to the negative wire in the connector and the probe of the test light to the HOT wire. Tomorrow if it's not raining I'm going to inspect all connector points and also the relay and terminals for any corrosion and may just replace the relay as a PM part.
IMO do not use any body ground sheet metal .. fuel tank straps that no..
measure the voltage using the power and ground wires not the body metal.. that is most likely why its wacky..

test light no, I do not have , those IMO useless , not accurate but very cheapo .. good if you checking for lamp problems or fuse ..
I have 10 meters ... some are 50 yrs old .. some times I use the old one so the needle on the meter indicates a fluctuation / bad connection..
 

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First off , I was using a test light that has a digital volt gauge in it so the ground clamp was attached to the fuel tank strap bolt and test light probe to the HOT wire at connector. The connector being disconnected or not has no bearing on the reading I get. I also got the same reading when attaching the test light ground clamp to the negative wire in the connector and the probe of the test light to the HOT wire. Tomorrow if it's not raining I'm going to inspect all connector points and also the relay and terminals for any corrosion and may just replace the relay as a PM part.
I would recommend you get yourself a DVM (Digital Volt Meter) and use that instead. When you check for Voltage, dont use the Chassis or other metal fro the Ground Probe. There are to many issues with the Intrunk Ground or the circuit itself that you could be getting a good Ground for your Test, but not a true ground actually going to the Pump. Instead, I prefer to measure with the 2 Probes of the DVM actually connected to the Pins of the connector itself. In this case I believe that is the Black and Gray Wires. I would also unplug the connector from the intank plug just in case something in the trunk (bad Pump, Loose/burnt connection, etc) is pulling down the circuit.

If all looks good and you got near 12V there, then u know for certain the issue is in the tank. If not, then use the Schematic I posted in this recent thread to trace out the Circuit from the Fuse block back. Could be as simple as a bad relay although the Prime overide wire should bypass that circuit.

https://www.impalassforum.com/vBulletin/34-engine-problems-maintenance/1315422-no-start-no-fuel-pressure-pump-keeps-running-key.html
 

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Discussion Starter #9
I would recommend you get yourself a DVM (Digital Volt Meter) and use that instead. When you check for Voltage, dont use the Chassis or other metal fro the Ground Probe. There are to many issues with the Intrunk Ground or the circuit itself that you could be getting a good Ground for your Test, but not a true ground actually going to the Pump. Instead, I prefer to measure with the 2 Probes of the DVM actually connected to the Pins of the connector itself. In this case I believe that is the Black and Gray Wires. I would also unplug the connector from the intank plug just in case something in the trunk (bad Pump, Loose/burnt connection, etc) is pulling down the circuit.

If all looks good and you got near 12V there, then u know for certain the issue is in the tank. If not, then use the Schematic I posted in this recent thread to trace out the Circuit from the Fuse block back. Could be as simple as a bad relay although the Prime overide wire should bypass that circuit.

https://www.impalassforum.com/vBulletin/34-engine-problems-maintenance/1315422-no-start-no-fuel-pressure-pump-keeps-running-key.html
The digital test light I'm using is a Snap-on EECT424 and by all means not a junk HF type test light. I'm certainly not opposed to using my Fluke 375 meter to recheck my work but as I've already stated I have checked this wiring both from a chassis ground and also directly from the pins at the connector and get the same voltage either way and I KNOW there is an issue regardless of the reading I'm getting. I just ordered a new relay as PM measure and will ohm out the old relay versus the new one before I install it and then recheck my voltage before and after the new relay is installed. While the relay is removed I will also check voltage at the relay connector and then ohm out the wire from the relay to the rear connector.


This is certainly not my first rodeo either as I have to make electrical checks on equipment all day at work so I do know something about what I'm doing.
 

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Spray a little electrical contact cleaner in relay connectors remove & reinstall relay a few times.
This will clean the connectors internally.
Swap in a relay from a different circuit in there & re-test.

If it was a poor relay connection wire/terminal burnage would likely occur and damage the terminals and/or wires.
Poor connections almost always produce excessive heat & damage.
 

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Discussion Starter #11
Ok, I'm a dumbass. I got my new relay and pulled the old one out to inspect the wiring terminals and everything was good there. I did check the resistance of the new relay against the old one and the old one was 88 ohms and the new one is 100 ohms. I then went ahead and installed the new relay and rechecked voltage at the wiring connect at the bumper and found I had 11.5 volts at prime and 14.5 with engine running. I then realized that I had previously checked voltage on the PURPLE wire accidentally rather then the gray wire. I need to slow down, now I'm back to my original thoughts that the fuel pump may be the issue.
 

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Ok, I'm a dumbass. I got my new relay and pulled the old one out to inspect the wiring terminals and everything was good there. I did check the resistance of the new relay against the old one and the old one was 88 ohms and the new one is 100 ohms. I then went ahead and installed the new relay and rechecked voltage at the wiring connect at the bumper and found I had 11.5 volts at prime and 14.5 with engine running. I then realized that I had previously checked voltage on the PURPLE wire accidentally rather then the gray wire. I need to slow down, now I'm back to my original thoughts that the fuel pump may be the issue.
on the 96 Imp there are 3 relays under the dash in the left side of the brake switch .. relay block those 3 relays are the same GM part number of the FP relay.. the relay on the driver side is for interior lamps.. pull that int lamp relay and install for the FP .. the last digits 3 on the FP relay is 866.. same as those 3 relays on that relay block..

your volts are good .. prime 11.5volts is what I have had since new .. if battery is at 12.75volts engine off key on ..
 
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