Fuel pump problem...I think

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Fuel pump problem...I think

Postby Gary » Sun May 27, 2007 1:37 am

A couple weeks ago my wife couldn't start the Trooper & had it towed home. When I had a chance I looked at the fuse panel & switched the fuel pump relay with another black one that wasn't being used. It started & ran fine. Now today after running a few hours of driving, I tried restarting & it would almost start but not quite. Wive said this was what it did for her. We had it towed home and it started just fine again.

In summary, it seems to not want to start when it is warm, but starts just fine after cooling down.

I am puzzled by this. Anyone have any clues?

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Postby speedyboy6949 » Mon May 28, 2007 2:09 am

It sounds like your fuel pump could be going,in the tank electric fuel pumps suffer from heat faliure quite often. Back in the late 80's gm even put out a tsb saying to keep atleast a 1/4 of a tank of gas .most people don't realize that the fuel pump needs the gas thats in the tank to help keep it cool. All of the domestic brands have gone to the basket type fuel pumps. The pump sits in a basket with a small hole in the bottom and the return line feeds into the basket so the pump is all ways being bathed in fuel. Look at the fuel lines under the hood and see if there is a black cap on one of them. This is for a fuel pressure gauge hook up. The next time it won't start take the cap off and stick a small screw driver in there( it is just like a valve stem) if you don't get a spray of fuel out of it Then it is a fuel related problem. Check to see if there is power at the fuel pump harness. if you have power then the pump is not working. The rednecks in my area use a quart of atf in there gas to help lube the pump.I have never tried it but they all say it will buy you some time before having to replace the pump.I hope this helps you and sorry for any typo's it 1 a.m. and i am more than ready to get some sleep.
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Postby Gary » Mon May 28, 2007 3:35 am

I had half a tank of gas. I don't know if that makes a difference.
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Postby Airtight Troop » Mon May 28, 2007 8:41 am

I had a full tank when mine went out :P It's not about how much you had right then, it's not good practice to run it low. It might just be time for a new one. Mine acted the same way on my '88 when it went out. On my '92, it was the connector on the outside of the tank, it was all corroded and stuff. so I had to rewire it. On my '99, it was the short harness inside the tank, one of the connectors looked as if it had been burned up :shock:
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2.6L fuel pump relay

Postby bendorfold » Mon May 28, 2007 10:46 am

Here are some things to try:

You can jumper the fuel pump relay with the ignition key off - you should hear the pump run. Use a heavy wire like the red one.
Image
If your ignition switch melts, you can start your engine at the starter relay.
Image

The alternator turns on the fuel pump relay, through the engine relay when the engine runs. You can jumper the engine relay to bypass the alternator. You may have a circuit in the alternator that breaks when warm and reconnects when cold.
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Postby Gary » Mon May 28, 2007 12:53 pm

Thanks guys,
You have given me some good ideas. I hope it's not the pump, as it was put in October '05. It is a Bosch that I got from Autozone. I don't know if that is significant.

I'll let you know what the problem was when I figure it out.

Thanks again!

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Postby BLACKDEMON » Wed May 30, 2007 4:06 am

My fuel pump went out recently, today I got my Migo back... My mechanic tried every method this guys just mentined... from the relays to checking the if there was power going to the fuel pump... Those are great ideas to find out if it realy is the pump... He also sprayed some started fliud into the engine intake... It started right up but it died as soon as the fliud was gone.

By the way my pump was the original pump from 1992... So it was just abuot time... You said that your fuel pump was replaced in '05. Do you still have warranty on it? I got mine from the guys at Isuzu recycle in California for $75 + tax and shipping and 6 mounths warranty, the also offer a life time warranty for $30 more... I think thats a great deal.


Good luck!

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Postby cudachris » Thu May 31, 2007 9:48 pm

I had the same problem recently and it was the crankshaft sensor in my distributor.

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Re: 2.6L fuel pump relay

Postby Selahdoor » Tue Oct 04, 2011 11:10 am

bendorfold wrote:The alternator turns on the fuel pump relay, through the engine relay when the engine runs. You can jumper the engine relay to bypass the alternator. You may have a circuit in the alternator that breaks when warm and reconnects when cold.
Image


First, yes I do realize how old this thread is.

Bendor, are you saying that if the alternator fuel pump circuit is not working, putting a jumper in here, bypasses the alternator, and everything else works normally ?

IOW: This doesn't affect anything else.

The fuel pump only works when the ignition is turned on, etc...
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Re: Fuel pump problem...I think

Postby bendorfold » Mon Dec 19, 2011 10:05 am

Sorry for the tardy reply.

"normally?" - no. If the alt isn't working (or your belt breaks), you get the "start and stall" scenario. This jumper will power the three fuses indicated (one of which is the fuel pump relay). Keep in mind you are running on battery (limited time) power. The terminal labeled "Hot" is powered all the time, so you can't leave the jumpers in - the pump runs as long as the jumper is in. This "fix" might get you home or out of harms way.

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Re: Fuel pump problem...I think

Postby Selahdoor » Mon Dec 19, 2011 2:55 pm

bendorfold wrote:Sorry for the tardy reply.

"normally?" - no. If the alt isn't working (or your belt breaks), you get the "start and stall" scenario. This jumper will power the three fuses indicated (one of which is the fuel pump relay). Keep in mind you are running on battery (limited time) power. The terminal labeled "Hot" is powered all the time, so you can't leave the jumpers in - the pump runs as long as the jumper is in. This "fix" might get you home or out of harms way.


Ah. That's what I thought.

Thanks for the answer.

:D :D :D
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Re: Fuel pump problem...I think

Postby Selahdoor » Tue May 22, 2012 3:42 pm

Since this thread is still being linked to when people have problems with the fuel pump, I thought I'd make an updated info, post.

First off, my fuse box isn't exactly the same as the above. And there are too many different fuseboxes, from year to year alone, let alone from model to model, to be trying to put up examples for every fusebox out there.

I have labeled my relays. You'll need to figure out your own relay's functions, and go from there.

Now here is a way to jumper from the power windows relay slots, to the fuel pump relay slots, to have constant power to the fuel pump, but only with the key turned to the on position. (IOW: The fuel pump isn't getting constant power, even with the vehicle turned off.)
jump1.JPG

You should make a jumper with at least 12ga wire, using two male spade connectors. Then jumper between the two slots indicated.

As far as I know, you could leave it this way, permanently, if you'd like.

But in my opinion, you should get the alternator and the fuel pump relay checked, and fix the problem, not just bypass it.

But this will get you home. And/or get you to your next paycheck.
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Re: Fuel pump problem...I think

Postby MarkB.NV » Thu Jul 05, 2012 3:09 pm

On our camping trip up to redwoods, stopped for gas and after filling up ... Greeted with sputtered and no start condition.

Slapped in the jumper and presto - fired up and on our way. Thanks to all who contributed to this thread, and Jeff, its much nicer with the keyed power rather than having to pull out the jumper every time. :) :) :)
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Re: Fuel pump problem...I think

Postby mattfromtelevision » Sat Jul 07, 2012 2:24 pm

So what if it's not the alternator, fuel pump, or fuel pump relay. I saw mention about distributor crank sensor. What mechanism is used to switch the FP power from the battery to the alternator?
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Re: Fuel pump problem...I think

Postby mattfromtelevision » Sat Jul 07, 2012 3:35 pm

So! In response to myself:

After much testing with the multimeter, I discovered the fuse was blown. The damn fuse!!!! Whoever thinks of the fuse?! Lesson learned.
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Re: Fuel pump problem...I think

Postby sparks5501 » Tue Jul 17, 2012 12:38 pm

i have a 91 trooper 2 . stopped running on the interstate. tested all fuses and relays , also the fuel pump { took it out to test} everything tested good except there was no fire going to the fuel pump relay in the on postion also there is no fire going to the check engine light. the trooper will start with fuel poured into tbi but not run. It also started once with a jumper like illustrated. just didnt run . tried everything on this thread above. Please help thanks.
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Re: Fuel pump problem...I think

Postby powndpuppy » Sat Sep 22, 2012 3:38 am

Ok I'm about to torch my 90 Amigo. I have a similar problem. It just wouldn't start one day, pump wasn't running but the fuse and relay were good. So I replaced the pump and filter and it ran for one day and quit again. the pump I removed still worked though; a bit of a red flag.
Relays in the under the hood fuse panel have all been shuffled or replaced with tested relays, fuses checked and shuffled, resistors on the fuse panel checked and replaced and all it has gotten is worse. Now I don't have any power to the part of the panel that would normally be the "switched" power section to fuses and breakers. No relays click wihen the switch is turned on. I have headlights and starter only. The part of the under-the hood panel that is power on all the time is still working fine though. The car is a 90 Amigo, 4x4, 2.6 multi-port injection with no power accessories. I'm out of ideas but I know this brain pool here isn't. I'm open to suggestions and I'm a quick study. I can't use the bypass shown here because, quite simply, I have no switched power at the fuse panel, no heater relay *click*, no fuel pump relay *click*, no ECM relay *click*, etc. Help??
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Re: Fuel pump problem...I think

Postby Selahdoor » Sat Sep 22, 2012 3:10 pm

sparks5501 wrote:the trooper will start with fuel poured into tbi but not run. It also started once with a jumper like illustrated. just didnt run . tried everything on this thread above. Please help thanks.

Could be bad connections at the pump. (Or problems in the lines going back to the pump.)
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Re: Fuel pump problem...I think

Postby Selahdoor » Sat Sep 22, 2012 3:11 pm

powndpuppy wrote:I can't use the bypass shown here because, quite simply, I have no switched power at the fuse panel, no heater relay *click*, no fuel pump relay *click*, no ECM relay *click*, etc. Help??

Check your fusible links.
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Re: Fuel pump problem...I think

Postby powndpuppy » Sat Sep 22, 2012 5:20 pm

[quote="Selador"]
Check your fusible links.[/quote]

Well (looks chagrined) ô¿ô I know what fusible links have looked like my whole life, a short loop of "wire" with a plug on each end. I don't find anything like that. That having been said, I'd also freely admit that if the appearance of fusible links has changed in recent years I'd not know what to look for. A little pink plastic box with a clear plastic top, perhaps? I was thinking that was a breaker. If it looks like the above=noted wire, I haven't found anything like that under the dash nor under the hood. Any more tips from the combined brain pool here?
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Re: Fuel pump problem...I think

Postby bendorfold » Sat Sep 22, 2012 6:00 pm

If memory serves me well, fusible links are in a box, about 1"x4" - covered, between the battery and the radiator support.
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Re: Fuel pump problem...I think

Postby Selahdoor » Sun Sep 23, 2012 4:45 pm

bendorfold wrote:If memory serves me well, fusible links are in a box, about 1"x4" - covered, between the battery and the radiator support.

True. On the 2.6 troopers, 87 to 91.

That's as much as I know for certain. They could be the same on every isuzu out there.

Or they could be different on his amigo.

~~~~~~~

powndpuppy, look for the box bendorfold described. It'll be a little black rectangular box between the battery and the headlight. The top snaps off. Inside you'll find 4 fusible links exactly as you think they should appear.

If you do not have that box, then I do not know where your FLs are.

Also, look for one more fusible link, in the positive connection at the battery post. Some have a small plastic box there, that can be unplugged. I think that might have a fusible link in it as well.
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Re: Fuel pump problem...I think

Postby powndpuppy » Sun Feb 24, 2013 7:17 pm

They're apparently different on my not-so-"amigo". I hot-wired the pump from under the dash. Now I have switched fuel pump and nothing else is powered up (ignition is in-op, resistor for fuel injectors in the little metal box is not getting warm. haven't checked for power yet. i had spark before, now it is gone...) I'm about to call the junkyard on this one or swap to the V6 C***y drivetrain.

Selador wrote:
bendorfold wrote:If memory serves me well, fusible links are in a box, about 1"x4" - covered, between the battery and the radiator support.

True. On the 2.6 troopers, 87 to 91.

That's as much as I know for certain. They could be the same on every isuzu out there.

Or they could be different on his amigo.

~~~~~~~

powndpuppy, look for the box bendorfold described. It'll be a little black rectangular box between the battery and the headlight. The top snaps off. Inside you'll find 4 fusible links exactly as you think they should appear.

If you do not have that box, then I do not know where your FLs are.

Also, look for one more fusible link, in the positive connection at the battery post. Some have a small plastic box there, that can be unplugged. I think that might have a fusible link in it as well.
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Re: Fuel pump problem...I think

Postby DieselDoc1217 » Wed Apr 10, 2013 12:06 am

Hey All,

I followed the diagnostics and repairs outlined in this article and the troop is alive again! I employed Jeffs modification on the fuel pump so its hot only when on. Thanks! (Just as an aside for anyone who does this fix, if you bypass the relay, you may get a fuel caution light. And if the alternator has croaked causing this problem in the first place, the discharge light may be on as well.)
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Re: Fuel pump problem...I think

Postby zudorf » Wed Apr 24, 2013 8:43 pm

Having similar issues mentioned in this thread. Going to try the jumper in the morning. Had to leave it at the golf course today. Bummer. :cry:
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