• Welcome to The Truck Stop! We see you haven't REGISTERED yet.

    Your truck knowledge is missing!
    • Registration is FREE , all we need is your birthday and email. (We don't share ANY data with ANYONE)
    • We have tons of knowledge here for your diesel truck!
    • Post your own topics and reply to existing threads to help others out!
    • NO ADS! The site is fully functional and ad free!
    CLICK HERE TO REGISTER!

    Problems registering? Click here to contact us!

    Already registered, but need a PASSWORD RESET? CLICK HERE TO RESET YOUR PASSWORD!

lift pump

Riddle_3d

Riddle_3d

New Member
Messages
63
Reaction score
0
Location
Montgomery City, MO
alright, im redoing a bunch on my '93 this weekend (dampner, ANOTHER flexplate (think that was caused by the dampner) newly acquired IP and injectors from a newer engine, slight FTB mod, plumb FP gauge in, new LP, etc etc. i know its alot lol) my question is, when i turn the key on, i hear no lift pump whurr. but, if the truck is running, and you put a pressure gauge in the WIF drain and crack the t-valve, 5 psi idling. could that just be IP draw/ gravity feed? i dont think theres an way my LP was working, so i believe it helped the IP go poo also.
 
I was under the impression that the 93s are supposed to have a pre prime feature. I would check out the fuel pump relay.
 
yeah, i would like it to run at all times. especially because the PO messed something up so he put the starter on a button. i like it like that, but it ,may be a problem. another question, what gives the power to the cold idle advance? it was always on when the truck was running, but theres no back of the head switch or brain to control it :S
 
cold Advnace controlled by a Temp sensor. Not sure where it is on a 93 but On a 6.2 it's on the pass side Head IIRC. If the wiring is butchered and it has power all the time, I'd unplug it until you can figure it out. You can run without it.
 
yeah, thats where it was on my '89. i checked there and its just a pipe plug. i was thinking of wiring up a system off of that temperature switch to aid in things going smoothly
 
I'm not sure what the actual question was, but if its why do you have fuel pressure while idling and none with ignition, its because the OPS sends power to the LP when there is oil pressure.

I have never confirmed the 93 LPs run during WTS, but the electircal schematic suggests it should, and someone else in the past posted that his 1993 manual said it should. The reasons it might not could be a bas LP relay on the passenger side firewall or a bad Glow-plug controller, or butchered wires. Now it would only run during Glow/WTS, not just with ignition.

I suggest doing the OPS relay mod I posted at the end of the LP and OPS troubleshooting thread in the technical reference area. It would make it much more reliable, making sure you get LP priming during glow, and taking the current draw away from the OPS and putting it on a relay.
 
I would not run the power directly off of the ignition power source. Although a relay using battery power, that the coil is excited by the ignition power would be alright, but then you would need to realize that if you leave the ignition in the forward on position the pump will be running, using juice.

The reason the OPS is used is a safety feature, in case you wreck or roll the truck and fuel lines break, engine dies, oil pressure is lost, fuel pump shuts off, fuel stays in tank, not on you or around truck that may be on fire, or could start a fire. Diesel doesnt burn or ignite so easy, so you can play the odds, but the OPS relay mod is not that difficult. Its even easier with an OPS extension like PMDcable.com sells pretty cheap.
 
The WTS prime is from the second relay connected to the Glow plug controller ouptut. The second relay output goes to the normally closed contact of the first relay. I tee off the OPS output to excite the relay coil, and since that wire already goes to the LP its used on the other part of the relay. The battery power source you can use from the power already going to the OPS or any battery power source, fused.

If its hard to read you can PM your email address and I can send the full sized image.
 
Buddy, are you positive the full power runs through the ops to the lp on a 92-93? I am almost positive the 92-93 was actually wired correctly. The idiots got it ass backwards in 94-95 and ran the full lp load through the ops. The reason I say this is that on my 92 the relay went bad and I had no lift pump at all during start and run. 92-93 also uses a different style ops than the 94+ does.
I prefer simplicity. I remove the ops from any thing to do with the lift pump. [I'll take my chances in a wreck] I tee'd into the pink wire for the fuel heater. It is hot with the ignition on. I don't remember the color of the trigger wire for the relay. I cut that and capped it to not have any feedback issues. I ran a wire from the fuel heater pink wire to the trigger for the relay. Lift pump runs as long as the key is on. Takes less than a foot of wire and 2 butte splices.
The cold advance on the 92-93s With the "F" engine only use a temperature switch in the coolant crossover. It turns on the cold advance and the fast idle solenoid. The 6.2s and 6.5s with egr valves also had the temp switch on the rear of the passenger side head. The glow plug controller on the 92-93 is different from the 94+ controller. 92-93 is strictly a timer. PCM doesn't control the glows. 92-93 6.5s with manual trans doesn't have a PCM at all.
 
bk95td said:
Buddy, are you positive the full power runs through the ops to the lp on a 92-93? I am almost positive the 92-93 was actually wired correctly. The idiots got it ass backwards in 94-95 and ran the full lp load through the ops. The reason I say this is that on my 92 the relay went bad and I had no lift pump at all during start and run. 92-93 also uses a different style ops than the 94+ does.
I prefer simplicity. I remove the ops from any thing to do with the lift pump. [I'll take my chances in a wreck] I tee'd into the pink wire for the fuel heater. It is hot with the ignition on. I don't remember the color of the trigger wire for the relay. I cut that and capped it to not have any feedback issues. I ran a wire from the fuel heater pink wire to the trigger for the relay. Lift pump runs as long as the key is on. Takes less than a foot of wire and 2 butte splices.
The cold advance on the 92-93s With the "F" engine only use a temperature switch in the coolant crossover. It turns on the cold advance and the fast idle solenoid. The 6.2s and 6.5s with egr valves also had the temp switch on the rear of the passenger side head. The glow plug controller on the 92-93 is different from the 94+ controller. 92-93 is strictly a timer. PCM doesn't control the glows. 92-93 6.5s with manual trans doesn't have a PCM at all.
Click to expand...

I didnt know 93's had a cold advance or high idle! Mine idles 600 at all times which is low anyways considering it is a 5 speed but high idle would help warming up when cold. BTW is there a way to check actuall RPM to given tach on 93's my Speedo is nearly dead on but rpm seems 100-200 low.
 
Yeah, the older glow units work off radiant heat or something, so if the controller was hot it wouldnt glow as long. Otherwise just timed. Your 1992 may have been hacked up previous to you getting it.

I have a schematic for the 1993 lift pump relay and OPS and its the same relationship as the 1994, except the 1993 schematic shows the purple/white wire to the relay from the ignition in the start position, T's and goes to the glow controller. The 93 Glow controller harness has ignition power, ground, glow power going back into it, and then the wire that goes back the LP relay. The 94 doesnt have that tie in bwtween the glow controller and LP relay, and the 94 doesnt have glow power going back into itself. I am presuming that the glow power that goes back into is tied to the wire that goes to the LP relay, so the LP would run during glow time. Contacts B and C of the glow controller would have to be shorted/tied together. And if they forgot to tie them together in the contoller or new versions of the controller eliminated that then it wouldnt prime.

The schematics look like crap when you reduce file size, and its already hard to numbers or letters on them. So posting it wouldn't help, but I could email it to you.
 
Last edited:
As far as I can tell the wiring in my 92 hasn't been hacked at all.[yet] The glow control may have been replaced. It never has had the lift pump run while the glows are on. It may run in start. It definatly ran through the relay in run. Yes , please send me the schematics. I've never tried the key in start with it in gear to see if it runs like the 95 does.
 
Sounds like GM or someone messed up the wiring in a lot of trucks. 92 and 93 has the LP relay and LP fuse on passenger side. If it doesnt run while cranking then the CRK fuse could be blown under the dash. I think most people never look at that CRK fuse or know what its for.

And I realized that the OPS output and the LP relay output are before the LP fuse on the firewall in all years.
 
another thing, if it is run off oil pressure, mine isnt working. it never runs after the truck is shut off for the few seconds that it should still have oil pressure. i know the wiring on my truck is completely fubarred as well. anyone have a complete engine bay schematic of the truck they could email me?
 
just did some research on the back of my block now that i can see it.... 506 block. not the original one. explains all the unplugged sensors:mad2::mad2::mad2: the dampner i ordered was for a '95 (saw 141 on the back of the block while changing flexplate before) but the casting number s 12555506, 97+. this thing is a total cluster****
 
My 95 has a 506 block not sure of the year, my 93 also has a newer block which i assume is a 506 too, I will find out when I swap the ops and get a new balancer for it. Is there any difference in balancers and ops on a 506 block vs others? I thought all parts are innerchangeable?
 
You must log in or register to reply here.
Back
Top