No power to fuel pump

Mike8Guthrie · 12-24-2023, 12:45 AM

Needing some help with my daily driver 2004 3.4 Alero 176,000 miles. Went to drive it after it was sitting for 2 days and crank no start. Didn’t hear fuel pump prime so I knew it was a fuel issue. Checked all fuses, and decided to jump relay and starts and runs perfect. Tried a different relay and still no fuel. Ignition switch and cylinder was replaced a year ago. No security light or check engine light. Have not done bypass yet. Clean all factory car I’ve had for about 4 years. Could it be in the ignition switch or key cylinder? Anyone had this issue?
Thanks Mike

[ion] C2 · 12-24-2023, 12:05 PM

The PCM sends the power to the relay's coil telling it to activate. Trying to find in the factory service manual a diagnosis procedure but it doesn't seem to have one for fuel pump operation.

If everything runs when you force the relay to provide power, then it's unlikely that the PCM is trying to prevent the car from starting, so the problem is possibly physical (wiring/connection shorted out/corroded somehow). Could install a switch that goes to the relay's wire and manually turn it on, acts as a security measure too lol.

Mike8Guthrie · 12-24-2023, 11:40 PM

Ok, thanks. I got to check a few things today and I have power 11.84v to pin 30 and 86 with key on. 87 pin is to fuel pump and 85 is to ground. I could not get continuity to ground when key was turned on. I?ve read where it only grounds for the first few seconds if car does not start and I checked as soon as key was turned on.

leroBob · 12-25-2023, 02:18 AM

Following

dbral · 12-26-2023, 12:46 AM

The 2001 svc. manual shows g103 as the ground for the fuel pump relay control side. G103 is a splice pack (small grey/black plastic box) that is attached to a bell housing bolt/stud at about the 3 o'clock position viewed from rear of engine almost in line with the trans. range switch. You can open up the splice pack and check for corrosion/poor connections.

The 2001 is set-up like Ion said with the pcm sending a 12v signal to relay for pump turn on. Cannot speak for your 2004 but sounds like you are on the right track with the ground circuit. The '01 schematic shows no connectors in between the under hood elec. center and g103 to check in that circuit.

Mike8Guthrie · 12-26-2023, 07:49 AM

Thanks, I found a ground cluster on the left fender and took it apart and cleaned but still no luck.

Mike8Guthrie · 12-26-2023, 09:45 PM

Checked for corrosion in the fuse box and pcm. Both looked fine. Seen another post where it was in there ABS harness so I disconnected that and still no ground to fuel pump relay. Anyone else run into this issue?

dbral · 12-26-2023, 11:50 PM

Sorry but do not have any info on the '04 to help. Here is a link to a supposed '04 schematic from the web but cannot confirm this.

https://www.justanswer.com/car/3j473...ont-start.html

Might have to click on the "see more" button to view.

The splice pack for g103 on our '01 is under the exhaust crossover tube attached to a bell housing bolt. Our '01 has a splice pack on the fender like yours. That is g101.

Mike8Guthrie · 12-27-2023, 09:47 AM

Sounds great! Thanks for the info

Mike8Guthrie · 12-27-2023, 08:11 PM

Thanks dbral! That was it!! It was the ground splice pack on the block under the exhaust crossover. Mice got up there and chewed 2 wires in 1/2 and was working on 2 more. It was tough to disconnect everything to be able to pull them up to get to where I could work on them but they are fixed! Now to do some mouse hunting and leave the Alero in my shop for a couple days. Thanks again!!

[ion] C2 · 12-27-2023, 11:17 PM

awesome

rodents chewed through my christmas lights in 6 spots last week

dbral · 12-28-2023, 07:23 PM

Awesome bud, good find!

Oh yeah, rodents are friggin destructive

leroBob · 12-30-2023, 07:23 AM

6 spots!? Where do you live where you have that type of rodent problem? I hate cats but I'd have to get an outside cat.

[ion] C2 · 12-30-2023, 04:33 PM

it was just one pack rat that lives in a particular rock pile

killed him the next day

Mike8Guthrie · 01-07-2024, 09:21 AM

lerobob, only 1 spot. A mouse chewed threw the bundle of wires leading to the ground splice pack. It got ahold of 4 wires which 2 were chewed in 1/2. Those ground wires are extremely small like 20 gauge or smaller. Crazy thing is I’ve only caught 2 mice since all of this! I leave bait out year around in protective container. We live out in the country in Oklahoma. As far as cats go we can’t keep them around. We have tried 4 and they just run off.