'89 Trooper Fuel Pump/Relay/Wiring Question

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'89 Trooper Fuel Pump/Relay/Wiring Question

Postby Hunkofrust » Mon Sep 22, 2008 1:41 am

I have the 2.6L Trooper. It has basically sat for the last few years, driven sporadically. I've driven it last about a month ago then parked it until now. I am stumped with the following while trying to start it;

Truck would crank but not start. Found the fuel pump was not running. I looked in the fuse box and checked all the fuses, then swapped out the engine relay with the fuel pump relay, I then heard the fuel pump start working. I bought a new fuel pump relay, plugged it in, cranked the key....nothing. Fuel pump not working again. I then pulled the engine relay out with the key turned and lo and behold the fuel pump kicked in and I could start the vehicle. I bought a new engine relay, plugged it in, fuel pump does not work. Only by removing the engine relay entirely and turning the key will the fuel pump come on. If I do this and then insert the relay, it cuts out again. I left the key turned to power everything and then played around with the engine relay, when it made contact I could hear a click from what turns out to be another relay in behind the headlight. I pulled that and cleaned everything but it made no difference. I am at a loss with this.

I basically want to get this thing going so I can sell it and not sink a whole lot of money in it to do so.
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Postby SurferJoe » Mon Sep 22, 2008 9:24 am

Let me get back home today after a bit and I'll go over the circuit for you...

Off the cuff...it sounds like you've lost a ground in the fuel pump circuit somewhere...but we'll try a little later..OK?
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Postby Hunkofrust » Mon Sep 22, 2008 9:53 am

Yeah thanks, I'm tired of replacing relays. I'm not much for the electrical side of things and there seems to be so many relays in this truck my head is spinning. I've wiggled every wire I can think of, both up in the engine and at the fuel pump itself, I have a feeling its probably something simple.
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Postby ZuCruTrooper2 » Mon Sep 22, 2008 1:15 pm

Have your alternator tested.

Pulling the engine relay will cause the fuel pump to run with key-on engine-off. This engine does NOT prime itself at all. It only runs the pump with the engine physically cranking (a set of terminals on the starter relay provide the power). Once the engine is spinning fast enough for the alternator to charge, then it will take over and run the fuel pump through the fuel pump relay.

The most common cause of no-fuel on this engine/truck is a bad alternator. Make sure it's tested by checking the white-and-green wire for voltage with the alternator spinning. In fact, before you remove it from the truck, if you have a DMM, check that wire.

Pulling the engine relay is the impending zombie attack alternative.
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Postby Hunkofrust » Tue Sep 23, 2008 1:23 am

[quote="ZuCruTrooper2"]
Pulling the engine relay is the impending zombie attack alternative.

I haven't had time to check the alternator yet. One thing I am curious about is what exactly the engine relay does? When pulled, I can start it up and it seems to run okay. Obviously it does something, how important is it?

Thanks for the reply BTW.
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Postby ZuCruTrooper2 » Tue Sep 23, 2008 1:28 am

Here's what I wrote in the other thread:
The purpose of the engine relay is to keep accessories that are designed to operate with the engine running, only operate with the engine running. It's used to reduce engine-off load on the battery, as well as prevent the pump from running all of the time (at least with me, I leave it in ON so I can listen to the radio and not here the damn beeping; I'm sure others do it too) and from burning up.

You'll notice the blower motor will run as well as the fuel pump. However, the lights on the dash will not fully go out. This is a diagnostic/last resort/emergency measure. If the alternator is not charging, you'll run your battery down.


I forgot to mention it controls the testing of the instrument cluster warning lights (oil, alternator, fuel) when turning the key to ON.

If you have a multimeter, check for continuity between the green and white wire on the alteranator harness and the two furthest forward terminals (if I remember right. they are the farthest apart relatively and point to the front and back of the truck). These are the coil wires for the relay. One goes to ground and the other to the alternator. If you have less than .08 ohms or so, then replace the alternator. If you have high resistance or an open, repair the green and white wire.

HTH, John.
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