1999 Suburban fuel pump

Be sure to change the fuel pump relay. It can be an annoying intermittent problem.

What was the outcome? I have the same problem.

I have a 1999 K2500 7.4L Suburban. I have been having fue pump issues (pump won't run) for several months. First they replaced the relay. Then they replaced the pump. Then they replaced the pump again (for free) It failed again last week so I took matters into my own hands. After searching through the shop manuals, I fould a picture that shows a ground connection (pightail off the fuel pump wiring harness) attached to the rear frame cross member (just ahead of the fuel tank). I removed the bolt, cleaned the lug and frame and bingo! The pump started working again. Just for added safety, I also ran a seperate wire (12 ga.) From battery ground (on the inside of the right front fender well) back to the ground connection for the fuel pump. Hope this helps?

I have the same Suburban. Replaced the fuel pump a few months ago. Then I replaced the relay switch a few weeks ago. Then it failed again and I pulled on some wires and it seemed like it corrected a short and it started working. Now it seems like there are no hot wires back to the pump at all (using a circuit tester); the relay switch is good, and I hot wired the 87a jack on it anyway.

Oddly I found a an unconnected female connector on a 4 inch wire that comes out of the primary fuse box; it is hot when I jumper the 87a socket of the relay; what is it supposed to connect to?

The lead from the 87a contact on the Fuel Pump Relay goes to a connector called the Fuel Pump Prime Connector. This connector is not used on my Suburban either. The reason it's hot is because the relay makes a connection from the A3 contact to the 87a contact when it is not energized. Since you hot wired the A3 contact (grey wire on the underside of the fuse box) this makes the 87a contact hot also.
The relay gets energized for two seconds each time the ignition is turned on or off and thereafter when the engine starts. This is controlled by the Vehical Control Module (VCM) Pin one of connector C4 (top right corner) on the VCM has a green wire with a white stripe that energizes the 85 contact on the relay, which closes the relay and connects the 87 contact (+12 always hot) to the A3 contact. If you are not getting two seconds of +12V on this lead then I would inpect the connector/wire etc. You can unplug the C4 connector and pop it open to inspect the contacts. You should disconnect the battery first. If you are not getting +12V on the 87 contact of the relay then check the fuse. If everthing checks out, I would replace the relay with an OEM relay from the dealer.

Hi Roger, thanks for your reply.

Yep, I was able to figure out the relay by cutting open the bottom of the fuse box after the photocopy from the dealer of the wiring diagram did me no good.

Turns out the relay is fine and there is power all the way to the pump - sadly. The pump is bad.

So, I replaced the first pump in April after 7 years and 120k miles. At that time I also replaced the fuel filter which was so obstructed that I could barely blow through it.

Then the relay seemed to act up a few months later but it (or whatever the problem was) "fixed itself" and the pump started working again.

Then the relay went totally out a few days later and I replaced it with one from Auto Zone, and all was well. For about three weeks.

Then on Sunday the new pump I installed back in April went out.

After reading some posts about people replacing their Suburban's fuel pumps 2 or 3 or 4 or more times, I am not very excited. Is this a sign of things to come?

Has anyone ever successfully inserted an in-line pump and been done with it?

Regards

Be sure to check the grounding pigtail for the pump wiring harness at the rear crossmember. Mine failed agin this week! I crawled under and wiggled the harness on top of the tank and she fired up. After I got home, I pulled the pigtail off the frame and soldered a new lug onto the wire and bolted it back to the frame. As I mentioned in my first post, I have installed a seperate ground lead staight from the battery to this location and to my trailer connector.
My next step is to buy a weatherproof lockable connector and tie the FP ground lead to the battery ground lead thus illiminating any worry about corrosion/vibration etc. I haven't heard of anyone running and external pump. I have included the wiring diagram from the GM shop manual.

The image came out very tiny, but it looks like it is the same one the dealer gave me.

Where is the fuse for the fuel pump, out of curiosity?

I tried the ground cable trick per your post prior to my removing the pump. I removed the bolt and cleaned under it and on it. (Doesn't that ground run from the fuse box also?).

Anyway, looks like the pump is bad again alright. It's on it's way back to the eBay merchant I got it from. I had to pay $99 to get them to ship me the warranty replacement in advance. They will refund it after they receive my return.

The fuse is located in the under hood fuse box. The diagram on the inside of the lid should indicate which fuse it is.

I don't believe there is any other ground for the fuel pump except the one connected to the chassis. In my case, I suspect the the problem was that the wire connected to the ground lug was making a poor contact. That's why I soldered it. I guess time will tell?

Did you try hot wireing the pump after it was removed from the tank, to confirm that the pump was dead?

By the way, is removing the tank a big deal?

I have reviewed the fuse map on the inside cover of both fuse boxes - no fuel pump fuse (just the fuel pump relay switch).

I am pretty sure I properly hot-wired the pump when I tested it. However, I will be sure to test it before putting the tank back up.

Removing the tank is not that big of a deal (if there is not much fuel in it). There are about a half dozen bolts on the skid plate, and the two bolts on the removable ends of the tank straps. Then you have to disconnect the tank filler and vent hoses from their metal tubes coming from the "gas cap compartment".

But you can't just drop the [45 gallon] tank all the way to the ground because the fuel lines and wires are two short. So, with the truck on jack stands, I lowered the tank onto a wheel rim which kept it elevated about 7 inches above the ground. That gave me plenty of space above the tank to remove the pump.

The biggest pain in the neck is disconnecting the two primary fuel lines (the supply and the return) from the pump because the quick connectors are difficult. I purchased an $8.00 quick connector disconnecter tool at Auto Zone. When I got home with it I remembered why I returned the one from the first time. The pump is designed so that the only exposed part of the nipples is two short to get the tool around. Worthless in this case. So, I ended up jacking the 4 mini spring clips with a mini slot head screwdriver as I pulled the connectors at odd angles.

The Chevy dealer quoted me 4 hours labor and $900 to replace the pump. So instead I purchased one on eBay for $86 and did the entire thing myself as a first timer in about 4 hours.

Putting the tank back up can be a bulky experience - especially if there is too much fuel rolling around in it (my wife helped the first time). But aside from the time I spent diagnosing, I would say that as a second timer I could probably drop the tank, remove and replace the pump, and reinstall the tank in about an hour - if I had a little bit of a helping hand.

The only advantage about hiring the dealership is that this repeating problem would now be their problem and not mine.

I put one in my '98 suburban about 2 years ago. Have not had a problem like you guys are describing. I had a turn signal module burn out and the replacement failed a short time later. The source appears to have been a poblem in my trailer's wiring harness.

Got the new pump in the mail yesterday, and installed it this afternoon. The only difficulties I had were:

1) The pump/tank O-ring gave a lot of resistance, so I had to use a couple of screwdrivers to leverage the pump downward against the C-clip tabs on the lip of the pump opening in the tank. And that can be performed only after lining the pump itself "perfectly" perpendicular to the bottom of the tank. Since there is about 3" of spring-loadedness in the pump, it takes quite a few tries.

2) Getting the tank filler hose over the top of the frame in the tight working quarters.

3) Getting the tank up into position so I could get the first stap around it and its bolt threaded.

Now the pump is in and working and I don't have to ride my motorcycle to work every day any more.

The next work project on the truck is to replace the spewing high pressure power steering hose.

Regards.

Thanks for the info re. The fuel pump R&R. I hope I don't have to go there. So far, so good. Good luck with the PS hose.