'96 Tahoe-Fuel pump power supply mystery

[itsagaas]

This is about my '96 Tahoe LT 2 Dr. 4WD 5.7L (350 c.i.) with 134k miles. I drove the truck about 75 miles during which it was running great w/ all gauges reading normal. I had 1/4 tank of gas. After parking the truck for about 2 hours I then went to start it for the drive toward home. It cranked and cranked but no start. No codes either. This happened once before last summer when a new fuel pump relay fixed the problem. So after bumming a ride to the auto parts house, I did a field install of a new relay while in the parking lot where I was stranded. Still NO START. Cranking sounded normal and strong. Then had it hauled via flatbed tow to the Chevy dealer near home. They said the truck needed a new fuel pump and fuel tank sending unit (sending unit was needed due to rusted fuel supply and return tubes that would likely break off when removed...which they did. The I.D. of the lines was like new with only exterior rust).
The Chevy dealer's estimate was really heavy @ $1,450 so I hauled the truck home. Bought all genuine GM & AC-Delco parts and did the replacement. Also went for a new fuel tank while I was at it. Before putting the tank back in the truck, and with the truck up on heavy duty jackstands, I put my multimeter on the gray wire connector pin which powers the fuel pump. This connector is on the rear frame crossmember directly above the front of the fuel tank. My wife got in the truck (yup, I trust her) and cranked it over a few times so I could check the power supply to the fuel pump. NO POWER to the fuel pump. The battery connections are good. Note that I did have the battery ground disconnected during the pump & sending unit removal/replacement....this was reconnected for the power supply to the pump test described above. I did put my multimeter ground lead in a few different places on the frame to eliminate bad ground to the meter as an issue. All fuses in the fuse/relay box under the hood are good and I tried the fuel pump power supply check procedure with two different fuel pump relays plugged in.
I have the GM vehicle specific service manual (both volumes) and checked the schematic for the fuel pump circuit. Nothing jumped out at me as the next thing to check. Suppose I could check the gray wire continuity from the fuse/relay block back to the connector pin.
Would greatly appreciate any other recommendations on what to check next or solutions found by other members with similar truck issues in the past.
Thanks!

 

[41racing]

Your gray wire might check good for continuity, but still be bad. If all the strands are broken except for one you'll have continuity, but it won't carry enough voltage to run the pump. It should show up on your meter though. Try jumping power to the wire at the relay and then see if you have it down at the tank. Are you sure it's the gray wire? I was thinking it was the purple wire, but I can't remember for sure. You might want to double check that. Hope this helps.

 

[itsagaas]

Thanks for the suggestion. Will report back once I have it all sorted out.

 

[WH0DAMAN]

Did you replace the fuel pump pig tail (car side)as well?

 

[itsagaas]

Good idea. Yes, replaced the pigtail where the harness connects to the new fuel pump and sender 3 pin (+ ground) connector.
Thanks, Ken

 

[itsagaas]

Closure

Finished the job today and the truck runs great!

As for the electrical anomaly, after checking the gray power supply wire to the fuel pump all the way along its routing, I added a jumper wire from the terminal block stud (battery voltage) to the socket where PIN #30 of the fuel pump relay plugs in. With the jumper in place I went back under the truck and checked power to the gray wire terminal pin supplying the fuel pump. Now there was power. Figured that I must have had a bad replacement fuel pump relay.
I installed the new tank with fuel pump and sending unit then plugged in a new AC-Delco fuel pump relay (GM Part # 12193602/ACD#D954A).
Turned the key to position 2 a few times to build up fuel line pressure and check for leaks. All was good with the line fittings so engaged the starter and it fired right up.

The fuel lines running from the rear to the front of the truck are pretty well rusted on the OD. I will replace them when some warmer weather comes along. Any recommendations for where to buy either pre-bent or braided stainless fuel supply and return lines appreciated.
Thanks,
Ken

 

[inthechateau]

I've had several fuel pump problems with my 96 pump. First pump I cut an access panel hole in the floor under the rear seat. just had to replace momp last night 5 years since last replacement and all I had to do was drill out rivets and scrape off body panel sealer. Right to pump and was done in an hour. Good job on the trouble shooting though. Why did you go for a new tank? Plastic tank and other than some dirt inside never seen the need for a new one.

 

[itsagaas]

Needed to get a new tank for two reasons. Old tank had some significant rust. However, the major reason was that I could not get the locking ring loosened up and mistakenly removed the locking ring retaining fixture which was spot welded to the tank. The two issues combined led me do go for a new tank.
Thanks for the info on your approach.