Fuel pump keeps blowing fuses - 99 Jeep TJ
09-22-2010, 04:19 PM
#1
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Fuel pump keeps blowing fuses - 99 Jeep TJ Should there be two fuses for a pump, one for the ignition and one for the relay itself or do you just need the one for the relay?
If two are required, I've got one under the dash that is a 10 amp, this is the one that blows. It only pops when I'm accelerating with the turn signal on (while passing). Not sure what the turn signal has to do with it since it isn't on the same fuse. It's plugged in via the cluster fuse with one of those double fuse add-on wires then runs to a cut off switch under the dash, from there it goes to the great beyond where I haven't tracked it yet.
Is there a ground on the fuel pump itself and if it weren't making good contact would it cause a fuse to blow under high load? I know a fuse will blow when a wire goes to ground but wasn't sure if it would also do it if there was a bad ground.
EDIT: if it matters, it's a LQ9/4L60E swap, I have no details on the fuel pump as the whole swap was done before I bought the jeep.
If two are required, I've got one under the dash that is a 10 amp, this is the one that blows. It only pops when I'm accelerating with the turn signal on (while passing). Not sure what the turn signal has to do with it since it isn't on the same fuse. It's plugged in via the cluster fuse with one of those double fuse add-on wires then runs to a cut off switch under the dash, from there it goes to the great beyond where I haven't tracked it yet.
Is there a ground on the fuel pump itself and if it weren't making good contact would it cause a fuse to blow under high load? I know a fuse will blow when a wire goes to ground but wasn't sure if it would also do it if there was a bad ground.
EDIT: if it matters, it's a LQ9/4L60E swap, I have no details on the fuel pump as the whole swap was done before I bought the jeep.
Last edited by TierAngst; 09-22-2010 at 04:26 PM.
09-22-2010, 07:17 PM
#2
Putting too little voltage to an electric motor causes it to draw more current. So yeah, bad grounds or a dirty connection can cause a voltage drop and cause you to blow a fuse. A 10 amp fuse is a pretty big fuse for a pump so something is wrong.
Turn signals can cause voltage to go up and down, so if the pump voltage is low the turn signal could help push it over the edge.
If the "add on wire" is one of those things that cut through the insulation to contact the wire, then that would be the first thing I replace. Get rid of crimp on connector and solder the two wires together.
Make sure there is a ground wire going from the pump back to a common ground in the dash. Some people ground the pump to the frame and that can cause problems as the frame rusts and ages.
Oh, and clean your battery posts, even if they look clean. I once had a car that the engine would momentarily die everytime I hit the turn signal. Turned out to be dirty battery posts.
Turn signals can cause voltage to go up and down, so if the pump voltage is low the turn signal could help push it over the edge.
If the "add on wire" is one of those things that cut through the insulation to contact the wire, then that would be the first thing I replace. Get rid of crimp on connector and solder the two wires together.
Make sure there is a ground wire going from the pump back to a common ground in the dash. Some people ground the pump to the frame and that can cause problems as the frame rusts and ages.
Oh, and clean your battery posts, even if they look clean. I once had a car that the engine would momentarily die everytime I hit the turn signal. Turned out to be dirty battery posts.
09-22-2010, 07:50 PM
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It's one of those.
Yeah, could be the battery terminals. Those damn things keep corroding on me and I have to clean them often, I have half a mind to replace them with the side posts and get a new battery. I'll check everything you mentioned and see how it goes.
10-04-2010, 03:27 PM
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Re-ran the ground wire for the fuel pump up to the engine, didn't help the problem. Swapped in a new battery since I don't drive my other car right now and had it sitting out. Haven't got it tested yet since I ran out of fuses. I did try to swap the fuse into another switched spot in the block but even if the fuel pump kicks on it still won't start in most other spots, it's back where it was for now but just wondering why it would matter??
10-05-2010, 03:49 PM
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Battery isn't the culprit. Going to check my transmission wiring since it seems to blow exactly at 5k when the transmission goes to up-shift. Still not sure how that relates to the turn signal though or why it would only do it on an upshift. Any thoughts?
10-05-2010, 07:28 PM
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I am fairly certain that current and voltage are proportional. Think of the pump motor as a resistor, since V=I*R if the voltage rises the current will too. So a bad ground would actually use less current as there is a greater resistive path.
One thing in the initial post stands out to me and that is you said the fuse blows under acceleration, if your alternator has bad regulation it could be pushing up your voltage as you accelerate maybe. Do you have a voltage gauge on your dash to see what the 12V line looks like?
One thing in the initial post stands out to me and that is you said the fuse blows under acceleration, if your alternator has bad regulation it could be pushing up your voltage as you accelerate maybe. Do you have a voltage gauge on your dash to see what the 12V line looks like?
10-05-2010, 07:36 PM
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First thing I did was have the alternator and battery tested. Yes, there is a gauge and it stays rock solid at around 14v. Also thought of the previous point but the ground was an easy fix and probably needed to be done anyways . . . and of course I was really hoping for something that didn't involve ripping the jeep apart to get the wiring sorted out.
Fairly convinced at this point that it has something to do with the PCM or transmission since it always happens at exactly the shift point. I checked over the wiring for both and they don't seem to be shorted anywhere.
Fairly convinced at this point that it has something to do with the PCM or transmission since it always happens at exactly the shift point. I checked over the wiring for both and they don't seem to be shorted anywhere.
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10-05-2010, 10:46 PM
#8
Just trying to help.
Wired thru the cut off switch. Put in as an anti theft switch. Would it make sense to jump the cut off switch? It is the 12 volt to the computer and I think it's always hot. I didn't put one on my 98 LS6. Trying to think what is different from my 98. The only thing I can think of is that due to the plow on my 98 I added a Painless relay that has two keyed hot and one always hot instead of using the fuse box. Same Howell harness. Same 4l60E trans.
The harness has two wires for 12 volt. One for constant 12 volt and the other for 12 volt on start AND run when the key is relaxed after the engine fires and runs.
So in a nut shell the jeep runs and starts perfectly. When you are going in a straight line, no turn signal at 5000 rpm it blows the main fuel pump fuse? First gear, Second gear? Just asking again and trying to help.\
If you at lower rpm and hit the turn signal does the fuse blow and if it does is it the same one as the shift at 5000 rpm?
Wired thru the cut off switch. Put in as an anti theft switch. Would it make sense to jump the cut off switch? It is the 12 volt to the computer and I think it's always hot. I didn't put one on my 98 LS6. Trying to think what is different from my 98. The only thing I can think of is that due to the plow on my 98 I added a Painless relay that has two keyed hot and one always hot instead of using the fuse box. Same Howell harness. Same 4l60E trans.
The harness has two wires for 12 volt. One for constant 12 volt and the other for 12 volt on start AND run when the key is relaxed after the engine fires and runs.
So in a nut shell the jeep runs and starts perfectly. When you are going in a straight line, no turn signal at 5000 rpm it blows the main fuel pump fuse? First gear, Second gear? Just asking again and trying to help.\
If you at lower rpm and hit the turn signal does the fuse blow and if it does is it the same one as the shift at 5000 rpm?
10-05-2010, 10:53 PM
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Always the same fuse, always at 5k when shifting. You said that wire is for the pcm constant voltage? Right now it's a switched wire and the fuel pump kicks on if the fuse is moved to the always on empty spot on the panel. If I knew exactly what the wire was for and where it went I could remove all of it and run a new one to bypass everything. It almost looks like it is fused in two different spots which doesn't make sense to me.
10-05-2010, 11:39 PM
#10
OK let's start over. Which fuse blows? The one on the Jeep fuse block that has 12 volts on start and run and supplies the 12 volt to the computer under start and run? Or the piggy back fuse shown in your photo? Or is it the Howell harness fuse on the Howell fuse block?
The intent of the cut off switch was if it is switched off no 12 volt current to the LS1 computer so the engine will crank but without the computer no fuel pump, no spark and no start.
Per the Howell wiring instruction, orange wire is constant hot to the computer. Pink wire is switched on during crank and run.
I'm baffled by the blown fuse at 5000 rpm shift. Does it blow the fuse when you just rev it up to 5000 in park ot neutral?
The intent of the cut off switch was if it is switched off no 12 volt current to the LS1 computer so the engine will crank but without the computer no fuel pump, no spark and no start.
Per the Howell wiring instruction, orange wire is constant hot to the computer. Pink wire is switched on during crank and run.
I'm baffled by the blown fuse at 5000 rpm shift. Does it blow the fuse when you just rev it up to 5000 in park ot neutral?
10-06-2010, 07:35 AM
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You had a 10amp fuse piggy backed into the 10amp gauge spot. The one added is blowing.
Just did an idle revv with and without the blinker going, freely revvs all the way up. I also noticed the shift point is set to 5500 on the tach, which if I remember right that is where it shifts under heavy throttle. So that throws out the shifting part causing a problem.
From what you're saying it's a PCM issue and not a fuel pump issue?
Just did an idle revv with and without the blinker going, freely revvs all the way up. I also noticed the shift point is set to 5500 on the tach, which if I remember right that is where it shifts under heavy throttle. So that throws out the shifting part causing a problem.
From what you're saying it's a PCM issue and not a fuel pump issue?
10-06-2010, 10:14 PM
#12
Ok so it blows the piggy back fuse. I believe that wire comes from one side of the anti theft switch. Just follow the wire back to switch. Let's take the anti theft switch out of the equation. Take the two wires from either side of the switch and wire them together. Could be the switch is creating enough resistance to blow the ten amp fuse. I looked at my jeep and the piggy back fuse is plugged into position#12, the "cluster" fuse. Did you try a 15 amp fuse instead of the 10 amp?
It has been known the pin connector that supplies connections to the instrument cluster corrodes and the cluster acts strange. Almost like it has a bad ground.
Pull the relays that are supplied with the howell harness and make sure there is no corrosion on the pins.
I'm not an expert on the PCM but I think they are pretty bullet proof.
Let me know what you find.
It has been known the pin connector that supplies connections to the instrument cluster corrodes and the cluster acts strange. Almost like it has a bad ground.
Pull the relays that are supplied with the howell harness and make sure there is no corrosion on the pins.
I'm not an expert on the PCM but I think they are pretty bullet proof.
Let me know what you find.
10-07-2010, 06:38 AM
#13
That is true for everything but an electric motor. If you measure the resistance of of the motor windings it will be a fraction of an ohm. The windings are nothing more than a coil of wire. But spin that coil of wire in a magnetic field and it induces a reverse voltage, just like an alternator. Believe me, a bad ground or too low of voltage and it will slow the pump down causing it to draw excess current.
I'll bet you a donut if you could measure the voltage across the pump when all this happens the voltage is low. At max RPM you might have belt slippage causing lowered output voltage. Depending on how you have things wired you might have a voltage drop in the harness somewhere that is just enough to cause a low voltage. If the two things above combine than anything adding extra load might cause enough of a voltage drop somewhere to cause your problem. Does your trans have a lock up converter? Do those things require 12V in any way? Always have sticks myself.
Whatever you do a larger fuse is not the answer.
Try running a jumper wire straight from the battery through a fuse and to the pump. See if that help.
You might have a single dirty or loose connector somewhere.
10-07-2010, 09:35 AM
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So, it can or can't be a bad ground somewhere?
Did manage to find one other spot that works with the jumper, but when I tried it out it still blows the fuse. Assuming the factory jeep fuse block is good (since no other fuses are blowing on it) I'm not going to try tracing any of them out. When I checked to see if the new spot would fix the problem I kept a much closer eye on the tach this time to see when it blows. It IS during upshift at 5.5k. With that being said, what is special about that shift vs all others? I'm thinking it would be something internal to the PCM or something to do with the transmission and not the fuel pump.
The transmission does have a lock up converter (which operates normally) since it's a 4L60E.
I'm going to triple check the wiring on the transmission since I did move them around when installing the new shifter, but the first couple times everything looked good. Will pay special attention to the connectors and if I have to, will get some electrical contact cleaner and spray them down.
Did manage to find one other spot that works with the jumper, but when I tried it out it still blows the fuse. Assuming the factory jeep fuse block is good (since no other fuses are blowing on it) I'm not going to try tracing any of them out. When I checked to see if the new spot would fix the problem I kept a much closer eye on the tach this time to see when it blows. It IS during upshift at 5.5k. With that being said, what is special about that shift vs all others? I'm thinking it would be something internal to the PCM or something to do with the transmission and not the fuel pump.
The transmission does have a lock up converter (which operates normally) since it's a 4L60E.
I'm going to triple check the wiring on the transmission since I did move them around when installing the new shifter, but the first couple times everything looked good. Will pay special attention to the connectors and if I have to, will get some electrical contact cleaner and spray them down.
10-07-2010, 01:55 PM
#17
Not with an electric motor.
Jam the rotor on the pump and watch what happens to the current. Running too low of a voltage slows the pump down (less torque) causing the same thing to happen.
so yes, absolutely, a bad ground could make the pump blow fuses. So could a lot of other things, but this is where I would start looking.
Jam the rotor on the pump and watch what happens to the current. Running too low of a voltage slows the pump down (less torque) causing the same thing to happen.
so yes, absolutely, a bad ground could make the pump blow fuses. So could a lot of other things, but this is where I would start looking.
10-08-2010, 08:32 AM
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Found this going to the transmission. It's the only thing I found that even remotely resembled problematic. Most of the wires for the conversion are very well shielded from grounding. The only thing I see are some not so great butt connectors and crimping done. Learned my lesson with those a while ago.
It's the purple wire with a black stripe that had a bad connection but re-crimped and re-taped the other as well just to be sure. Not sure what that wire is but since it's going to the transmission and my problem happens during a shift I hope this is the cure!
10-08-2010, 05:25 PM
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That wasn't it either. There is a relay that goes into that same bundle though, can a relay short out internally? I thought when relays went bad they stuck open, not closed??
