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92 GMC 6.2 Diesel lift pump won't work after injector pump replacement

10K views 13 replies 8 participants last post by  jrsavoie 
#1 ·
Hey Everyone,

I'm new to the site, my dad suggested it to me after I had issues with my injector pump replacement.

I have a 92 GMC 1/2 ton with a 6.2 diesel. I've been driving it for the last 15 years. Honestly best truck I've ever owned.

The truck became harder to start, then after about a month or so whenever the truck would heat up to operating temperature and then you would shut it off. When you would try start it again the truck would not start until the engine cooled off.

The signs to me was that the injector pump was failing. I put about 250k on the truck and never changed the pump. Dad figured u can get about 200k on the pumps before replacing them so that made sense that I needed to change the injector pump.

I pulled the injector pump out of a 90 diesel I'm restoring, I needed to pull this pump anyways because I'm installing a turbo from a 93 6.5 on it. I'm putting the pump from the 93 parts truck into my restoration project.

I completely installed the pump from my running 1990 into my 1992. I hooked everything up correctly or at least I think I did. I turned the key on and turned it over hoping the lift pump would kick in so I can bleed the injectors and fill the new fuel filter I installed.

I figured I could use the lift pump to bleed up to the replacement fuel filter using that valve on the top of the filter housing. No matter what I did the lift pump would just not kick on.

Next I thought well maybe the oil pressure sending unit failed. I've replaced 3 of these over the years. So I jumped the plug on the oil pressure sending unit. I wasn't sure which prongs to jumper so I did all three individually with each other and no luck the lift would not start.

Has anyone else ever had an issue like this? My next thought is to check the fuses for the lift pump or maybe a relay...

Any help would be much appreciated.

Tommy
 
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#2 ·
:welcome:


Hard starting when hot, is a couple causes. The head rotor is worn on the IP, poor cool water on it when it wont start and see if it fires up. If it does, your pump is wearing out. Or, the engine is worn and has lower compression, add a manual glow plug switch and see if it will fire.


With your pump, have you checked if there is power @ the pump? If it has power and does nothing, the pump is dead. If it has no power, then you know to trouble shoot the other end of the wiring.
 
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#3 ·
That makes sense forsure. Would you say plug the oil pressure sending unit back in turn the key on and then check the wires or harness heading to the lift pump?

Or should I jumper the oil pressure sending unit and leave it jumpered to check for power to the lift pump?
 
#6 ·
Yup, as well as what BigBoy said.
A test light can be your best friend
 
#4 ·
I would defiantly look for power at the OPS and the lift pump, and if you have power and ground to the pump, then you'll need a lift pump.
 
#5 ·
Oh ya BTW....

Welcome to Diesel Place... The Big Show!!! :coolnana:
 
#8 ·
Welcome to Diesel Place, good advise above, test for power at OPS and lift pump. We usually run ours direct, with a switch, so as to have total control, and not relayed thru OPS....J&J.
 
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#9 ·
You can jumper the fuel pump relay to make the pump run. At least I think you can... I don't do much with the GMT400 trucks. But that's something I would check.
 
#10 ·
I would jumper the lift pump - even if I had to make a fused harness to do it.

I'm thinking you should be able to do the dual lift pump relay upgrade to save OPS's and then have a on/off switch to run the lift pump whenever you so desire - I would start there. Get in touch with leroydiesel.com and see if his left pump relay upgrade is plug and play on your truck. It comes with an on/off switch now
 
#11 ·
Ah hell... if I can teach JC electrical, I can walk you through a relay upgrade.


View attachment Relay.bmp


That's the jist of the relay, just swap the words on pin 87 to fuel pump and your golden.
 
#12 ·
Ah hell... if I can teach JC electrical, I can walk you through a relay upgrade.


View attachment 492602


That's the jist of the relay, just swap the words on pin 87 to fuel pump and your golden.

That's missing the safety feature of running off the OPS and the prime feature of running of the glow plug controller.

There are other links on here that show those features. Do not cut and splice wires. Get the proper connectors - that I have previously posted links to - Though IIRC the plugs for the 92 may be different - Make it so you unplug the lift pump and plug the wiring harness in between the 2 plugs you just disconnected.
 
#14 · (Edited)
When you change the lift pump, oil the lines up real good. While the lines are disconnected - slide the fittings back and coat the lines with good anti-seize.

I also put some on the threads.

I also oil the lines and threads on everything, every chance I get.

Be careful with what products you use and how you use them. I've had brake clean, PB and others melt / ruin stuff before my eyes. I've seen corrugated plastic tubing shrivel on contact
 
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