Odd Fuel Pump Issue

[BattelWagun]

The other day my fuel pump went out on me. I'm not surprised it had 120k on it and I run the tank to E all the time... Anyways, I got the pump replaced at a shop since I needed the truck back ASAP because the beater car isnt running to well these days. With the old pump (and I know for a fact almost all of these trucks) I would hear it cycle a few seconds before I turned the engine over and after I shut it off. The new pump doesn't do that! It's annoying as the shop said it's supposed to be like that (I'm pretty sure it's not...) and it makes starting harder now too. The engine used to start after maybe 1 second(id hear it turn over once) when it was warm. Now it takes a few seconds (turns over 3-5 times). I know nobody can diagnose this issue but I'm wondering if anyone has encountered the same problem because I know come next winter, it'll get to be a complete ***** to start like that.

 

[SunlitComet]

The initial 2 second run is triggered by the PCM to the fuel pump relay so if it does not do that but run with plenty of pressure after finally starting then I would suspect something screwy with your computer. Bear in mine I say this becuase My tech data says in '99's the pcm has total control of fuel pump relay unlike a couple of years earlier where the pcm did the initial pressure charge but oil pressure kept it running long term. not sure which year it changed over but both get the same results.

 

[BattelWagun]

well that screws me over haha. Not gonna be getting the pcm reprogrammed any time soon... It's been getting real hard to start too, almost 20 revolutions and then it barely stutters to life. No SES light either, this is pissing me off.

 

[SunlitComet]

I don't think reprogramming will help. it sounds like yours uses a oil pressure switch for running mode. My diagrams maybe overlapping between newer model years. In that case your computer might have lost it trigger output and cranking the engine builds the minimum oil pressure to activate the relay on its own. and the pump creeps up the pressure. the oil pressure switch for pump would have orange and grey wire.

 

[BattelWagun]

Allright well it looks like im going wire hunting this weekend! thanks a lot man, i hope thats the problem.

 

[SunlitComet]

this is for the one with a oil presuure switch controlled fuel pump.

 

[BattelWagun]

Much thanks for the diagram, you got some good shit sunlitcomet!

 

[SunlitComet]

forgot to mention on the above picture the relay is only use by the PCM for priming only so check that first. it may have faulted out.

 

[BattelWagun]

Alright so here's what I just did:
I unplugged the relay and tried to start it, no beans.
I started it and pulled the relay, and it died out. (hold in mind it wasn't warmed up yet, but oil gauge read 40 psi) I did however unplug what I think may be the fuel pump switch, there is a black block near the front drivers side that has a fuel line from the frame going in, and a line going out to the injectors. on this block is an electrical box with a plugh that has what appears to be a weather ridden grey and orange wires. I unplugged that, it had no effect on the engines behavior whatsoever. Let me know if you want a picture, i took one because it's hard to explain.

 

[SunlitComet]

yes please so I can match up with data and clarify the data.

---------- Post added at 06:26 PM ---------- Previous post was at 06:21 PM ----------

also those color are the power feed in and out on the fuel pump relay. that was not the one you pulled out and died is it? Pictures are good right now. will look for the fuel rail switch you decribed.