2000 Chevy astro 4.3 fuel pump issue

2000 astro van 4.3 issue.

Alternator seized up so I replaced it and belt. After which fuel pump didn't turn on so replaced it. Still doesn't start. Replaced fuel pump relay, no joy. Replaced ignition switch, no joy.

Here's the weird thing. I can jump the relay and pump runs. Forgot the exact relay number but I am get 2 12v readings on the relay...with relay out and multimeter testing. Getting 4 volts which I assume is sensor. This is all with key off. I thought I should only have 1 12v reading with key off but I'm getting 2.

Haven't checked fuel pressure or spark on distributor.
Should I check that or do I have other issues?

I think you're looking at a bias voltage from the PCM? You've very likely set a fuel pump relay code in the PCM, not that that'll cause your problem.

This video is what you want to watch if you want to understand this better. I also attached the wiring diagram for reference.



You're better off partially plugging the relay into the socket and carefully probing the pins. This will complete the circuit, but still give you access to the terminals.

Key on, with the relay partially installed, retake your readings. One of those 12V readings should be gone. Let us know what you find, and we can go from there.

do you have a scanner that has bi directional controls? or just backprobe or like tyler said leave the relay partially out and check pin 85 for control from the pcm while cranking. should be power side switched

That video is awesome! I've been so confused why I have 12v on 2 pins. I have a meter and test light and will check this tomorrow morning and report back. Thank you very much!

I don't have any fancy tools will just have to partially plug it in and see if it goes away.

No worries, a test light and DMM will work perfectly. I forgot to ask - with the pump relay bypassed (and the pump running), does it start and run? If not, then it's possible that the pump control issue is a symptom of a bigger issue.

I couldn't get it to run the other day but I'll check again. I didn't change the pigtail either but it ran fine with this one on it. I may drop the tank again to check lines and wiring.

It sputtered but didn't start so pcm is alright I'm assuming just not getting fuel. I'm not a mechanic by any means and makes me want to torch this vehicle haha

Ok so did the dam and test light and it did not zero out. Jumped the fuel pump and attempted to start. It fired but did not start. Something is draining the battery and cannot figure out what it is. There is fuel pressure but do not know what psi. Checked the wires to the pump by poking thru them a d got low voltage on gray. Could be I didn't have a good ground...had the dmm of a fuel line.
How could changing the alternator cause all these problems....is there a circuit that the plug for alternator runs on or something?

Throw everything u have at me and I'll try it

I dunno that replacing the alternator would have caused these symptoms, unless the battery is weak (from getting discharged) and causing other issues. Or, is it possible that there's a poor battery connection? How's the cranking speed?

I'm sorry to nag, but it's worth being specific. With the key on, relay partially installed, what are the voltages at all four fuel pump relay pins? And the same readings during cranking. That'll spell out what's happening at the relay.

Ok let's back up. I could not get 12v at the pump when I tested the gray wires. I'm getting 4 to 5v. Can u link a wiring diagram to where these wires go for Me? This may explain my battery drain as well. I'm going to start at the pump and work back instead of chasing ghosts.

Do you have a video explaining what voltage in what wire for the pump.

Sure, we can do that! Here's a link to the engine performance diagram, and a shot of the fuel pump wiring:

www.scannerdanner.com/media/kunena/attac...17/DownloadPdf27.pdf



The diagram shows C310, the main connector that goes from the vehicle to the tank and pump itself. This connector is on the drivers frame rail, just ahead of the tank, if I remember correctly. It contains the fuel pump power and ground, pin A grey and pin G black. I'm not sure where you've been testing before this, but C310 makes an idea testing location if you can put your hands on it.

Grey should have 12V (or close to whatever battery voltage is) whenever the relay is energized. Black should have less than .5V at all times (relay off, relay on, whatever). 4-5V would indicate a voltage drop, or weak source voltage, on the grey wire. Paul has several great videos out there on fuel pump diagnostics, but you could probably start out with these two:

Ok here's what I have.

12v to pump.
Ground good to pump.
60psi pump pressure
0psi prime pressure
No 2 sec prime on computer side of relay.
Jump relay and get 60psi and car sputtered but didn't start.

Looks like from the relay to pump is fine, but relay is not being commanded to close and prime. Guessing it's ecm?

check pcm powers and grounds. also check for the ground at the pcm just to rule a broken wire out

Ok. Where are those at lol.

What are the odds of a crank position sensor?

Possible, but I think Cheryl is right, powers and grounds are a good place to start. I can't pick them all out right now, but they'll be in the PDF diagram I posted earlier.

Did you happen to watch that last video I posted? The symptoms sounds VERY similar to yours.