|
01-10-2019, 01:12 PM | #1 |
Registered User
Join Date: Apr 2010
Location: Gooding, I.D.
Posts: 225
|
GMT400 Wiring Woes
1992 Chevy silverado k1500. 350, 5 speed, 4x4. Truck started idling rough the night before as I was pulling in to park it. Next morning I had to feather the throttle to keep it running. Got it warmed up and started backing up and it died. I knew the fuel pump was older so I replaced the pump and filter. Replaced fuel pump relay, ignition module in the distributor, oil pressure sensor. I found the injector A and B fuse was burnt. Replaced and hasn't blown since. With a test light the grey wire on the fuel pump relay goes hot for about 2 seconds when the key is turned. At the plug under the master cylinder where the grey and black/white wires go back to the fuel pump I get a 2 second shot with the key. With the key on at the pump the purple wire for the gauge is hot but nothing from the grey. The fuel pump just won't kick on. This has been tried with the old pump and the new. The best I can figure is a short somewhere but I can't find an exact wiring diagram to trace all the fuel system wiring. At this point I'm ready to find another truck to transplant my powertrain into. Anybody have any helpful advise?
|
01-10-2019, 02:41 PM | #2 |
Msgt USAF Ret
Join Date: Jan 2005
Location: Kalamazoo, Michigan
Posts: 8,715
|
Re: GMT400 Wiring Woes
Here is all I have on the 88 to 98 wiring diagrams.
It doesn't look like the wire colors match with yours too well but it may help.
__________________
VetteVet metallic green 67 stepside 74 corvette convertible 1965 Harley sportster 1995 Harley wide glide Growing old is hell, but it beats the alternative. |
01-10-2019, 04:43 PM | #3 |
Registered User
Join Date: Apr 2010
Location: Gooding, I.D.
Posts: 225
|
Re: GMT400 Wiring Woes
thanks Vettevet. I have the top one. I'll look over the bottom one better this evening. Once I get caught up with everyone elses cars here I'll get back to mine. I've got feelers out so I can upgrade to an extended cab but until then I still need something to drive.
|
01-13-2019, 03:37 PM | #4 |
Old member
Join Date: Jan 2002
Location: Liberty, & Garden City S.C. , U.S.
Posts: 19,943
|
Re: GMT400 Wiring Woes
Most late models run a oil pressure switch to the fuel pump so if loss of oil pressure the fuel will shut off before engine damage. Have you worked on the oil system of late. Maybe bumped are knocked a connector loss.
__________________
1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs. |
01-13-2019, 11:12 PM | #5 |
Registered User
Join Date: Apr 2010
Location: Gooding, I.D.
Posts: 225
|
Re: GMT400 Wiring Woes
I haven't had to do anything since I put the motor in a couple years ago. I pulled the oil pressure sending unit. Noticed there was some oil clean back on the plug so I went ahead and replaced it. As well as the fuel pump, fuel pump relay, fuses, ignition module, and distributor. As far as I can tell it's a short somewhere. I didn't have time to play with it this weekend. Had to finish up a toyota head job and a transfer case in a tahoe.
|
01-14-2019, 12:11 AM | #6 |
Moderator
Join Date: Aug 2017
Location: Cabarrus
Posts: 417
|
Re: GMT400 Wiring Woes
Have you verified that both injectors are getting power and spraying fuel? I had a similar issue in my 89 suburban that I just sold. After wasting $200 on injectors and an ignition control module, it was the injector driver in the ecm burned up. Open up the ECM case and look for anything burned. Should be behind the glove box.
__________________
Alex 1967 C50 292ci Lumber truck 1967 C50 292ci Dump truck 1967 C60 366ci Fire truck |
01-15-2019, 11:04 PM | #7 | |
Registered User
Join Date: Jul 2014
Location: North-central Virginia
Posts: 1,103
|
Re: GMT400 Wiring Woes
Quote:
The fuel pump would be energized through the fuel pump relay, but if that quit, it could also be energized through the oil switch. Thus, a customer might complain that he had to crank his truck for quite a while before it would start. This would indicate the relay had burned out, and simply needed replacing. Since the oil switch was in parallel with the relay, and not in series, it could open from lack of oil and the engine would continue to run on the relay. Evidently GM didn't trust their relays... Edit to add: The "diagram 3" posted above agrees with me on this. Look closely at the oil pressure/fuel pump sensor and the fuel pump relay. You'll notice they are in series. Also, you likely don't have that hot fuel module mentioned. That was a work-around for heavy duty trucks or big blocks. These were more susceptible to vapor lock due to underhood temperatures, and needed to keep the fuel pump running longer than usual in a hot-start situation to expel the vapor lock. Last edited by kipps; 01-15-2019 at 11:16 PM. |
|
01-15-2019, 11:14 PM | #8 |
Registered User
Join Date: Jul 2014
Location: North-central Virginia
Posts: 1,103
|
Re: GMT400 Wiring Woes
Note the "fuel pump prime connector" just below the fuel pump relay. It should be an empty terminal on a red wire protruding out of the harness mere inches away from the relay on the firewall. Connect a wire from the positive post of the battery(probably should fuse that wire, but I never did) to that terminal, and it will energize the pump. If you don't hear the pump run, the problem has to be downstream. Either the wiring, the switching valve, or the pump itself.
Edit to add: looking at the diagram I posted, that test terminal might not be where I said it was. On my '87 v20, it was at the fuel pump relay, but it may have moved to the ALDL by the time your truck was built. (ALDL -- Assembly Line Data Link -- also known as the obd1 port) Last edited by kipps; 01-15-2019 at 11:27 PM. |
01-16-2019, 11:03 PM | #9 |
Moderator
Join Date: Oct 2008
Location: Wentworth, NH
Posts: 4,961
|
Re: GMT400 Wiring Woes
If you're getting a 2 sec pulse at key on then the ECM and fuel pump relay are working the way they should.
Here's the 1992 GM CK Wiring manual. mediafire.com/1992_ST-375-92-EDD_Chevrolet_CK_Wiring_Manual.pdf The rest of the 1992 service manuals from my library are in my signature. Sounds like you have it pretty well nailed down to an open in the fuel pump power wire between the relay and the fuel pump. Start looking for damage along those wires. Look at the pump ground too. It'd be obnoxious to get the pump power fixed and have a dodgy ground hang you up.
__________________
1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...
And please let us know if and how your repairs were successful. Last edited by hatzie; 01-16-2019 at 11:09 PM. |
01-17-2019, 09:36 AM | #10 |
Registered User
Join Date: Apr 2011
Location: Klein Texas
Posts: 3,852
|
Re: GMT400 Wiring Woes
If you didn't notice there is an inline fuse (on the firewall) for the fuel pump between the relay and the pump.
Yes, the oil pressure switch is just a redundant path to power if the relay fails. Pretty simple circuit. It should be easy to fix
__________________
My Classics: '72 K20 Suburban + '65 Dodge Town Wagon '72 Corvette Roadster +'67 Corvette Roadster '73 Z-28 Camaro '63 Ford SWB Uni Pickup '50 Ford Coupe |
01-20-2019, 11:39 AM | #11 |
Registered User
Join Date: Apr 2010
Location: Gooding, I.D.
Posts: 225
|
Re: GMT400 Wiring Woes
Thanks you guys. I have checked the fuse. swapped the relay out, swapped distributor with ignition module out from my spare parts. Interior fuses. injector fuse was blown but hasn't tripped again. I just haven't had time to mess with it as of yet. Boss still has me swamped. I have to track down a speed sensor issue on a tahoe and put an oil pump in a 07 pontiac today. Maybe by next month I'll have time to do something on my own truck.
|
Bookmarks |
|
|