Fuel Pump failure causes electrical fire?
12-07-2008, 05:26 PM
#1
Fuel Pump failure causes electrical fire?
Hi everyone, got a frustrating situtation here I hope to get some insight into. I was driving my 1976 Carrera 3.0 and it suddenly dies at a stop light. I start it back up without an issue and it proceeds to die again about 100 feet later, never to start again. Once I get it back into the garage I take a close look and find the fuel pump relay with a burnt hole through it and fused to the relay socket. Also, about 1.5" of the red feed wire of the fuel pump relay fuse is melted, and fuse looks severely hot but NOT blown. Additionally, I see the backup light/brake light/turn signal fuse blown. I track down a short to ground on the wire coming from the backup light sensor to the 11 pin connector in the engine compartment. That doesnt solve the fuel pump issue, but does allow me to replace the lighting fuse with no issues.
At any rate, I still have some short on the fuel pump line. My hypothesis is that the fuel pump has gone bad and shorted to ground inside. I experimented with "hotwiring" the pump and it did make its standard noise but seemed to struggle a little bit before blowing the fuse. Has anyone ever experienced this issue when the fuel pump goes bad? I dont want to go through the process of replacing the pump if it is not bad, as those arent cheap and not returnable. Anyone have any suggestions to test the pump? Maybe resistance values across the terminals?
I am done working on it this weekend, but hope to have some more ideas for next weekend! Thanks everyone!
At any rate, I still have some short on the fuel pump line. My hypothesis is that the fuel pump has gone bad and shorted to ground inside. I experimented with "hotwiring" the pump and it did make its standard noise but seemed to struggle a little bit before blowing the fuse. Has anyone ever experienced this issue when the fuel pump goes bad? I dont want to go through the process of replacing the pump if it is not bad, as those arent cheap and not returnable. Anyone have any suggestions to test the pump? Maybe resistance values across the terminals?
I am done working on it this weekend, but hope to have some more ideas for next weekend! Thanks everyone!
12-07-2008, 06:42 PM
#2
RL Technical Advisor
Hi Matt,
A few ideas:
1) Check continuity of the fuel pump wires and its connector between the pump & fuse panel for shorts or breaks (chafed wires). You'll need to repair or replace any damage to the wiring before the next step.
2) Measure the current draw of the pump.
Generally speaking, these things make noise before they ultimately fail or when the tank get low on gas.
A few ideas:
1) Check continuity of the fuel pump wires and its connector between the pump & fuse panel for shorts or breaks (chafed wires). You'll need to repair or replace any damage to the wiring before the next step.
2) Measure the current draw of the pump.
Generally speaking, these things make noise before they ultimately fail or when the tank get low on gas.
12-07-2008, 08:54 PM
#3
Drifting
SOP...
The inrush surge current of the "vibratory" fuel pump is nothing less than enormous.
The fuel pump fuse in my '78 was so often heated, over-heated, due to these surge current pulses that the fuse "clip" had lost it's "springiness" and would no longer "grip" the fuse to provide a low resistance connection.
I bypassed the OEM fuse with an inline fuse holder.
Don't really know much about the fuel pump relay except it doesn't function as we would normally expect. If the intake airflow throttle plate is closed or if the engine over-revs the relay picks up and only the ignition switching startiing position can then provide power to the fuel pump. Like the diff'l brake pressure detection circuit the over-rev circuit seems to be subject to lock-up, latch-up, if the alternator/regulator over-charges the battery.
If your brake light indicator comes on, latches on, for no obvious reason, seemingly no reason, or the tachometer pulses or surges on occasion, suspect and check for battery overcharge immediately.
But I wouldn't be at all surprised if the fuel pump relay contacts proved to be subject to the same overheating problem of the fuse holder.
"2) Measure the current draw of the fuel pump."
Most meters will read the average current draw and you're actually more interested in just how high the inrush surge cuttents are. O'scope time.
The inrush surge current of the "vibratory" fuel pump is nothing less than enormous.
The fuel pump fuse in my '78 was so often heated, over-heated, due to these surge current pulses that the fuse "clip" had lost it's "springiness" and would no longer "grip" the fuse to provide a low resistance connection.
I bypassed the OEM fuse with an inline fuse holder.
Don't really know much about the fuel pump relay except it doesn't function as we would normally expect. If the intake airflow throttle plate is closed or if the engine over-revs the relay picks up and only the ignition switching startiing position can then provide power to the fuel pump. Like the diff'l brake pressure detection circuit the over-rev circuit seems to be subject to lock-up, latch-up, if the alternator/regulator over-charges the battery.
If your brake light indicator comes on, latches on, for no obvious reason, seemingly no reason, or the tachometer pulses or surges on occasion, suspect and check for battery overcharge immediately.
But I wouldn't be at all surprised if the fuel pump relay contacts proved to be subject to the same overheating problem of the fuse holder.
"2) Measure the current draw of the fuel pump."
Most meters will read the average current draw and you're actually more interested in just how high the inrush surge cuttents are. O'scope time.
12-08-2008, 02:10 PM
#5
Drifting
Yes...
I have been in the computer repair business since '69 and it is not uncommon to have these spring/crimp type fuse holders lose a bit of "spring", overheat, lose more "spring"...etc.
Now you have a backing plate/pad that begins to appear burned or is burned.
I have been in the computer repair business since '69 and it is not uncommon to have these spring/crimp type fuse holders lose a bit of "spring", overheat, lose more "spring"...etc.
Now you have a backing plate/pad that begins to appear burned or is burned.
