Fuel pump again??ARRRRGGGGG

[exalteduser]

(94 s10 blazer "W")
so apparantly it doesnt matter if you pony up the extra cash for the Delphi fuel pump, new sender, strainer and all that jazz, the f###in things still only last a year. (not a new tank but i got that thing spotless inside when i changed it.)

do fuel pumps go out with no warning though? ive had 4 go out in my life and they always acted up a little first. this thing has less than 8k miles on it and i come out from work to nothing. Almost like a wiring issue its been really rainy.

i have 11.98 volts
(thats after i ran the battery down cranking, checking for spark etc.)on the grey wire at the back of the blazer where it hooks into the harness(when turn key), which leads me to think the pump is dead(it wont buzz or turn on). i tried running a hot 12v line to it also to no avail, couldnt find the "test wire" everyone talks about.

fuse is fine, relay is fine, and yes ive changed the filter lately since i know someone is going to suggest that.

Any thoughts????????

[exalteduser]

Everyone keeps talking about a red test wire for the fuel pump, my 94 s10 blazer has no such thing. i have on the passenger side firewall near center a grey wire with a plug that goes to nothing. could this be it? there is absolutely nothing on drivers side. A pic would be awesome!!!!!!!!!!!!!!!!

[old_master]

Should be red but, the wire that runs from the fuel pump relay to the pump is grey, so it could be either color.

At the fuel pump relay you can jumper the orange wire, (hot at all times) to the grey wire, (feeds the pump) and accomplish the same thing, (hot wire the pump).

[exalteduser]

I also read that pin G hooks to this circuit
http://blazerforum.com/forum/1st-gen...-blazer-58972/

still would like to see a picture though

[old_master]

I'm not certain that pin G of the ALDL does go to the pump. The schematic I have shows the grey wire going directly to the pump, not to the ALDL at all. Does the orange wire at the relay show battery voltage at all times? Did you try jumpering it, (orange to grey) at the relay?

[exalteduser]

not yet, im home and the blazer is parked at my work 14 miles away. you can read my problem in my other thread below this one. I think this method is null anyway since i have 12v at the rear connector when i turn key to run...

[old_master]

If you have battery voltage and ground at the fuel pump when you initially turn the ignition to the run position, and the pump doesn't run, the pump is the problem.

[jdl]

Charge the battery. Engine cranking, check for voltage and ground at the fuel pump connector. Gray wire is voltage, black wire is ground. for the pump motor.

Use a gage and check fuel pressure. Check fuel pump amp draw. If you drive mostly with the tank close to empty, that doesn't help. Send an email to delphi, see what they think?

[exalteduser]

plan is to take the ground bolt out and wire brush all that and put back on, i didnt do that when i changed this before. im hoping like hell thats the issue. im just outside of the warranty, i swear delphi had more than 1 year warranty

[old_master]

Whenever there is high resistance, especially in the ground circuit, it will shorten the life of the pump. Resistance from the black wire at the fuel pump connector to chassis ground should be less than 5 ohms.

[exalteduser]

tried all above nothing worked. resistance was 0.1

So i decided to siphon out some gas to the wifes van, i turned on the key after 4 cans (2gal each) to read the gauge, and what do you know the pump kicks on so i fired the blazer right up.....

i can think of 3 things why, tell me if im wrong
1. the hose i put in tank jostled the pump/unit and it decided to start again
2. the tank was too full ( i had just filled up) and maybe there is some way it shorted out like a loose wire near the top
3. its doing like alot of dying fuel pumps do and just picking and choosing when it wants to work or not.

Any thoughts?? i didnt drive it home yet cause i had just borrowed a car. if it starts after work tomorrow ill drive home

[old_master]

Sounds like you've had this problem before so check the terminals in the vehicle harness connector that connects to the fuel pump module. There might be a poor crimp right from the factory when the vehicle was built. Sticking your test probe in there when you tested it originally, may have been enough to make a good connection. Stranger things have happened.

If that checks out OK..... you've got battery voltage and ground at the module connector consistently when it should, it might have a poor/loose connection in the module connector, or right at the pump itself.

[exalteduser]

What ended up happening is the ground wire inside the tank on the sending unit melted. it burnt up the plastic plug in and the pin was black.

[old_master]

Originally Posted by old_master

....it might have a poor/loose connection in the module connector, or right at the pump itself.

Bingo! Good job following through and finding it. Glad I could help. Thanks for posting back.

[Rick Norwood]

I am guessing that if the black wire melted inside the tank, it was probably because of a bad ground OUTSIDE of the tank, or a bad connection at the connector.

As Old Master has stated many times, bad grounds cause High resistance. When the resistance is high in a circuit, the wire starts heating up and acually becomes a fuse of sorts at the weakest point in the circuit. The high resistance will continue to heat the wire and eventually melt the insulation off of the wire, melt the connector, and ultimately burn the copper wire.

I know you stated that the connector burnt and the pin was blackened, but it's possible that it was the weakest point in the circuit, and not necessarily the initial culprit. I sure hope you cleaned up the entire ground circuit when you had the tank apart.

Good Job for getting it fixed.