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GMC Jimmy No Start - Revisited

Q. Hello Mr Ciulla, Thank you for e-mailing us and letting us know that you replied to our question. The problem has only gotten worse since I posted that question and if you don't mind I would like to ask you about it. To remind you, 1991, GMC Jimmy, S-15 4 WD 4.3 liter 6 cylinder, approximately 185,000 miles on her.

GMC Jimmy No Start - Revisited

One day about two weeks ago my husband went to leave the store and it sounded like it had a little trouble starting. The next day leaving work, the same. It made it home but has not cranked up since. The first thing(s) we did was to replace the fuel pump, filter and spark plugs. It still would not crank.

We were advised it was the oil sending unit, so of course we replaced it, still no crank. We had tested the relay and thought it was fine but still two days ago we bought another one and replaced it.

HERE is where the latest problem arises, Upon installing the new relay, my husband went to check the wiring and the orange wire feeding into the relay has correct voltage BUT the tan/gray wire coming out does not. The check engine light is coming on BUT the computer will not feed us any codes?

So to respond to your reply is that, there is spark, fuel cannot shoot from injectors because there is no power to the pump, and the check engine light is on but not helping. We have checked all the fuses and they are fine.

Another internet mechanic told us that it is the ECM. My husbands face just cringed, it has already nickled and dimed us to death. And yet another mechanic told us it was the squid in the intake manifold. We feel it is most likely electrical, the injection system is electrical in our truck and this is the one area we really are at a loss in.

We did trace all the wires and they are all intact, no rips or breaks. Any further assistance you can give us would be greatly appreciated. We understand you are extremely busy.

Thank You and God Bless You, Carmen

A. If you know which wire at the pump relay is going to the pump, get a fused jumper wire and put one terminal to the constant power terminal and the other to the wire that goes to the pump. Then listen to the pump to see if it's running. If so, try to start it up.

If not, you still have a problem with the wires to the pump or something else in the tank. If it does start, the truck should start without the jumper due to the oil pressure switch. It acts as a backup circuit if the relay fails. Once there is 6 lbs of oil pressure the switch should close and turn on the pump.

The ECM grounds the coil circuit of the pump relay so with a test light hooked to the battery positive terminal one of the relay terminals should light the test light for 2-3 seconds after the key is turned on.

Additional Information provided courtesy of ALLDATA

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