sandypants
1/2 ton status
i have an 89 k5 tbi etc. the fuse that controls the fuel pump blows every time i put a new one in there. i looked at the tank looks like all the wires are connected. any ideas?CK5
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fuel pump blowing fuse
- Thread starter sandypants
- Start date
i have an 89 k5 tbi etc. the fuse that controls the fuel pump blows every time i put a new one in there. i looked at the tank looks like all the wires are connected. any ideas?
Blows as soon as you turn the key, or even with the key off it pops as soon as you insert it?
sandypants
1/2 ton status
as soon as i touch the fuse to the box. don't even get a chance to put it in.
Pinched or frayed wire most likely. Done any work on it? Anywhere? If so, go back and check for a wire pinched under a panel or screw.
Otherwise, you are going to have to try to trace it down. Check where the tank is hung in the frame. Odds are the fuel pump wire has come loose and gotten between the tank and frame and gotten pinched.
Otherwise, you are going to have to try to trace it down. Check where the tank is hung in the frame. Odds are the fuel pump wire has come loose and gotten between the tank and frame and gotten pinched.
I don't think that fuse gets power unless the key is in run, does it? Going to have to get someone with TBI or the wiring diagram to tell you.
It wouldn't make sense for there to be power through the fuse with the key off, to blow fuses in the first place. Maybe there is, but I don't know why that wire would need power when the key was in the off position.
It wouldn't make sense for there to be power through the fuse with the key off, to blow fuses in the first place. Maybe there is, but I don't know why that wire would need power when the key was in the off position.
In general, fuses are placed between the power source and the load and any controls.
There are lots of exceptions of course.
An electric fuel pump has several controls. The ignition switch, the computer that lets run for a few seconds when the key is first turned on and then kills it if the engine does not start after a few seconds, and, of course, the kill switch which stops the fuel pump in case of an accident.
If I had to guess, the fuse is probably between the power source and the first control, which ever it it. Most fuse blocks have a power line direct from the battery for systems that need continuous power, a power line from the run position of the ignition switch, and a power line from the acc. side of the switch.
So, the pump fuse would then be powered by the run position. In that case, the short would have to be between the fuse and the ignition switch. Should be easier to find, since there is not as much area to search.
We still need a schematic though.
J.
There are lots of exceptions of course.
An electric fuel pump has several controls. The ignition switch, the computer that lets run for a few seconds when the key is first turned on and then kills it if the engine does not start after a few seconds, and, of course, the kill switch which stops the fuel pump in case of an accident.
If I had to guess, the fuse is probably between the power source and the first control, which ever it it. Most fuse blocks have a power line direct from the battery for systems that need continuous power, a power line from the run position of the ignition switch, and a power line from the acc. side of the switch.
So, the pump fuse would then be powered by the run position. In that case, the short would have to be between the fuse and the ignition switch. Should be easier to find, since there is not as much area to search.
We still need a schematic though.
J.
The TBI fuel pump setup is arranged with the oil pressure switch getting it's power from the same (constant) 12V battery feed the relay does. The ECM is what turns the fuel pump on through the relay, both for the prime function, and cranking/continuous running.
There is obviously a short, which is bad, however is this something that just started happening, or is it a problem that was acquired with the vehicle?
BTW, GM doesn't use a fuel pump kill switch like Ford does. GM's setup uses the oil pressure switch as redundant fuel pump power for a failed fuel pump relay.
There is obviously a short, which is bad, however is this something that just started happening, or is it a problem that was acquired with the vehicle?
BTW, GM doesn't use a fuel pump kill switch like Ford does. GM's setup uses the oil pressure switch as redundant fuel pump power for a failed fuel pump relay.
sandypants
1/2 ton status
no its a new problem. key is off when it does it. at first i did it only every couple months then now every time. i looked at it. see a wire attached to the fram on the driver side before the shock mount. havent done any work yet. in a week or perhaps this weekend if i get the b52 done in the front i will be dropping the tank to do the rear shackle flip i will give all those wire a good look. just wast sure if this was a common fuel pump problem that had a typical problem/solution. thanx guys
Easy test would be to unplug the relay connector, oil pressure switch, fuel pump connector near the tank, and test the fuel pump power wire for continuity to ground.
Still need to know if that fuse is SUPPOSED to have power, that really is crucial, everything I've said so far speculates that it's not supposed to. Pretty unlikely something is getting power when it's not, especially something newly occurring, and on the fuse panel.
If it was intermittent and now constant, I'd expect it's a wire that is chafed or cut through, and just took awhile to get to this point.
Still need to know if that fuse is SUPPOSED to have power, that really is crucial, everything I've said so far speculates that it's not supposed to. Pretty unlikely something is getting power when it's not, especially something newly occurring, and on the fuse panel.
If it was intermittent and now constant, I'd expect it's a wire that is chafed or cut through, and just took awhile to get to this point.
sandypants
1/2 ton status
thanx i really appreciate the help. yea i will let you guys know. perhaps i can call gm and find out. i will take a good look this weekend for sure.
Stomis
Professional Amateur
One thing your forgetting is that most fuel pumps are toggle on by controlling the ground as a safety since technically the ground carries the positive current.
