I was wondering, what noise should the lift pump make when you turn the key on, because I don't here anything but the glowplug relay when I turn mine on. If the lift pump isn't working, could it be the lift pump, or could it be something else? If so, how do I test it? My truck is a 94 GMC SLE 4x4 K3500 5-speed dually. If anyone can please help it would be most appreciated. I thank everyone very much for their knowledge in helping me with my other problems I had.

The pump won't kick in till after you turn the engine over, if it's still wired as GM intended.

try turning the key all the way to the start with pushing the clutch you maybe able to hear it. Or with the truck running in a quiet spot roll down the drivers window and shut the engine down you should hear the pump of a few seconds until the oil pressure falls off.

I had a 93 Dually with the TD and I replaced 3 of them in 10 years.
Mine would come on for a few second's with the key on to pressurize the system if it sat overnight.
Easiest way to check if it's still working is to start the truck and reach under the truck and grab onto the pump. If it's pumping you will feel it working.
To check if it's the pump that's bad (which it probally is) just disconnect the harness at the pump and start the truck up and check the wire's, one of them should be 12+. If you have power and a good ground then the wiring side is good and it's a bad pump
If it's not working you may not know unless your under heavy acceleration as the pump is a flow thru design. I didn't know one of mine was bad till I went to change the fuel filter. No pump = no fuel to reprime to restart engine. :(

DD

Hello again, I was wondering what that thing is on top of the fuel filter, it looks like a bleed off to me, but I don't know anything about diesel engines. But with the engine running, if you open that should fuel come out? Because that is what I thought someone told me to do to get the air out my fuel system, but I opened mine and nothing came out, with the engine running, does anyone know what this means, or if fuel is supposed to come out of there? Thanks.

it means the OPS to LP isn't working right. Does the lp click when your cycling the glows, you can power the LP at the relay, jump orange to grey wire Check the fuse first.

Something clicks, I always thought is was the glow plug relay that clicked, am I wrong? Could the OPS and LP cause my IP to throw codes? Does the glow plug relay even click, or is it the LP? Thanks qm.

Oh yeah, and what is a OPS? Is it a oil pressure sensor? Cause my pressure gauge works if that has anything to do with it. And also when I opened the bleeder on top of the filter the truck stalled and it took a long time to start if that also contributes to what is wrong with my truck. Thanks.

The OPS has two curcuits, one for the dash gauge and one for the LP. I have mine relayed per HowieE's webpage but it still gives me problems sometimes.

Oh yeah, and what is a OPS? Is it a oil pressure sensor? Cause my pressure gauge works if that has anything to do with it. And also when I opened the bleeder on top of the filter the truck stalled and it took a long time to start if that also contributes to what is wrong with my truck. Thanks.
Like QM said, the Oil Pressure Sender (OPS) is wired for a signal to the gage in the dash and controls power to the Lift Pump (LP).

If you cracked the bleeder open on top of the fuel filter and the engine died, the LP is not working. So either the OPS is dead (very common) or the LP is dead (also common).

On my 95 there's a fuse box under the hood on the driver's side. I used to be able to pull the fuel pump relay from that board and jump pin 87 to one of the other pins to "hotwire" the lift pump. This came in handy for bleeding air from the fuel filter housing and for verifying lift pump operation. Not sure if it's the same on a 94, but if so, this would easily determine whether your LP or your OPS has failed.

Can anyone please tell me where the OPS is located? Thanks for the help everyone. I will replace them parts tomorrow and let everyone know if I am still having any problems.

Well, I am really confused, here is why. I jumped 12v to the lower left terminal in the 12 pin connecter under the dash, and the lift pump started running, ok so the OPS is bad right? Well, I took the 12v power from the 12 pin connecter and I started the ...truck, and the lift pump started working on its own?! So I decided to check the codes and now its flashing 18, 31 (new), 35, 49 (also new)? So now I am in a state of confusion, can anyone help? PLEASE?????? I have no idea where to start. The existing codes are 18,35,54,78. The new codes since I jumped the LP are 31,49,57,62, so now I am getting 8 codes.

18 - Pump Cam Reference Pulse Error
31 - EGR Control Pressure/Baro Sensor Circuit Low (High Vacuum)
35 - Injection Pulse Width Error (Response Time Short)
49 - Service Throttle Soon Lamp Circuit Fault
54 - PCM fuel circuit error
57 - PCM 5 Volt Shorted
62 - Turbo Boost Sensor Circuit Low
78 - Turbo Wastegate Solenoid Fault

Thats ironic, I had a truck come in last week with a simliar list of codes, I'll tell you the same thing I told him. ALL of these codes are caused by one electrical fault, Code 57 is the hint. PCM is missing a reference voltage, that voltage is used by All the other systems that rely on this voltage to operate and give feedback to the ECM. You have what could be a minor electrical problem, maybe fuse box or frayed wire somewhere or the PCM itself. This could be a troublesome one to figure out, but thats what you have to find.

Check ALL your fuses, under the dash and the one for the lift pump on the firewall beside the coolant overflow tank. If you don't find anything there, pull the glove box and take the ECM out and inspect the pins in the connectors.

Thank you Texas Diesel Guy, I will check that out, but I have one question, what is a PCM?, and what does it do? Thanks, I am new to all of this stuff.

Well, I am really confused, here is why. I jumped 12v to the lower left terminal in the 12 pin connecter under the dash, and the lift pump started running, ok so the OPS is bad right? Well, I took the 12v power from the 12 pin connecter and I started the ...truck, and the lift pump started working on its own?! So I decided to check the codes and now its flashing 18, 31 (new), 35, 49 (also new)? So now I am in a state of confusion, can anyone help? PLEASE?????? I have no idea where to start. The existing codes are 18,35,54,78. The new codes since I jumped the LP are 31,49,57,62, so now I am getting 8 codes.
OK someone help me here, WHere did he jump this at ?????????????

I have one question, what is a PCM?, and what does it do?
Sorry, I just had to quote that, its the Powertrain Control Module. Takes inputs from all your sensors, engine, tranny, throttle position, etc. and uses those to control everything from engine speed to boost pressure to tranny shifting. Its a small computer, and without the proper voltage it can't do its job.

Could you tell me where the PCM is located? This is my first diesel, and GMC for that matter, lol. Thanks Texas Diesel Guy.

In your truck, you will have to remove the glove box. There are four screws that you'll need a 7mm socket to take out. Take out the black "bucket" and the computer will be to the right under your passenger side speaker in the dash. There will be two spring steel clips holding it to a tray. Just slide it out and you'll probably have to unplug the wire harnesses before you get it all the way out of the dash. It's tight, but can be done with some patience.

Be careful what you short (or jumper), any mistake is a sure way to anger a computer. The cronology of this post shows new codes after jumping the lift pump, is this correct.

I might not be remembering correctly but when I jumped my lift pump to test it, I thought I did it in the relay panel under the hood not the PCM reader under the dash?

That OBDI ALDL terminal is the wire to the lift pump - TechX tests for applied voltage as demanded, and can control lift pump on-off.

Applying +12v power to that pin would not damage any component - accidentally brushing the +12v across some of the other ALDL pins would cerainly cause some possibly irretrievable damage.

Cleanly insert the wire first, then apply the other end of the secured wire to +12v power source.

Well I looked for any frayed wires and checked all connectors, and I haven't found anything out of the ordinary, should I start by replacing the PCM? Or start somewhere else? The truck runs pretty good, not as powerful as some, and hard to start for the first time of the day, or sitting for awhile, but it seems to run good. The SES light does come on over 2000 rpm's, does that have anything to do with the PCM maybe? Someone told me that it sounded out of time when I start it? Just replaced the crankshaft position sensor. It helped with the cutting out a little bit, but it still cuts out, the other day it cut out so bad, I was going about 55mph and the truck just started slowing down like if I let off of the acclerator, it never died, but when I pushed the accelerator, it didn't give it any fuel it seemed like, so I shut it off and restarted it and drove home, it didn't do it again, but it cut out alot till I got home. Have no idea what could cause that, any suggestions would help tremendously. Thanks.

Hey 94, have you determined if the lift pump and/or OPS is working correctly?
Your problem sounds like a fuel issue to me. I'd make sure that is working right first.

Definitely verify pump operation first, then check to see if all those codes are 'hard' codes or not. Try wiggling the wires at the PCM with the truck running and while watching a scanner for anomolies indicating wiring problems.

Everything ...works, just don't know if it ...works properly, lol. Ever since I jumped the 12v to the ALDL for the lift pump it has been ...working, it wasn't ...working prior to that. Wich is weird, but I have been reading in other threads about peoples ...trucks blowing black smoke when a sign of the turbo or turbo wg isn't working properly. I know for a fact that my wg isn't working properly, the vac pump is shot and I am not getting vaccuum to the solenoid, and it doesn't blow any black smoke that I can tell at all, it just smokes white smoke when you first start it? If the fuel system was working properly should it blow black smoke since the turbo isn't catching up with the fuel? I am starting to wonder if the ...truck is worth all this time and money? (no offense to GMC's, its just the truck seems to be getting worse everytime I fix something). Its hard for me to afford to keep putting money in this truck, and I definitly can't afford to trade if in for another truck. Trucks around here are outrageous!!!!

P.S. If you remember, in the previous posts in this thread all the codes for the IP going bad are showing, should I start saving up to replace it? The local part store has one for 854 dollars, is that reasonably priced? And how do I tell if the codes are "hard" codes?

The local 'parts store' has rebuild injection pumps? What sort of place is this?
Hard codes will return immediately when cleared, indicating a problem that is constant. If you clear them and they go away, then it could be caused by a loose wire or somethign similair.

The parts store is an O'Reilly's, don't know if you have one up there. But is that a bad price or should I just try it out? How do you clear codes?

The "rebuilt" 6.5 pumps are all built at the same place. They have used pmd's on them and are built very cheaply. One rebuilder supplies pumps for all the major auto supply houses. NAPA ,O'Reilly, AutoZone, AdvanceAuto to name a few.

Ok, should I just go to the local dealership and buy one there? Now, when I get a new IP, what do I have to do to change it out? Is it something I can do myself, like any adjusting or anything? And how do I clear codes?

Clear codes by disconnecting the battery for a couple of minutes.

Ok, I tried contacting ssdieselsupply.com for a injection pump, and they are telling me to replace my PMD first, because it is the factory one, and hasn't been relocated, and that could be causing my IP to throw codes? So should I try to replace the PMD first, then go from there? Cause I can buy a new IP minus the PMD if my IP is bad.

You do not have to disconnect the batteries to clear codes.

Right from the FAQ at the top of the forum or click here:

http://dieselplace.com/forum/showthread.php?t=16399

3. It is helpful to the diagnostic process to know when codes are setting, particularly if there is more than one. Hence, clearing the codes is something you may wish to do. Clearing the codes may be accomplished by simultaneously depressing the brake and accelerator pedals fully while the PCM is in diagnostic mode (terminals A and B connected). It will not appear that you have cleared the codes until the next time you power up in diagnostic mode, however.

Clear codes by disconnecting the battery for a couple of minutes.

Ok, I cleared the codes by depressing the brake and accelerator fully, and then turned it all back on the see the codes, and the only code that flashed was 12 three times, then it flashed 12 three times again. So I guess all the codes are "soft" codes? So should I just try to replace the PMD first?

Take it for a ride around the block and recheck codes.

Ok, took it around the block for a drive and now instead of 9 codes, there are only 3, and they are 18, 35, and 54. What should I replace first, the PCM or the PMD? Cause these codes are refering to the IP and the code 54 for the PCM.

Is the truck behaving now, or still displaying symptoms that something isn't right? What are the symptoms?

An IP is a lot of money to dish out, especially if that doesn't solve the problem.

Now it runs like a champ, I didn't go far, but the little distance I did go, I couldn't ask for a better running truck. But it still has those three codes. Should I just replace the PMD and see if that helps with some of the codes?

Now it runs like a champ, I didn't go far, but the little distance I did go, I couldn't ask for a better running truck. But it still has those three codes. Should I just replace the PMD and see if that helps with some of the codes?Are you in a hurry to make this truck reliable, or can you take your time tinkering with it till you get it right without wasteful spending? ;) In my experience, I'm always in a hurry but don't want to spend any extra.

If you have time, drive it for a few days to see if any symptoms of a problem surface. Others here may have a better idea of the underlying problem based on the codes?????

Thank you for your advice huisman, it helped alot, and I don't really have the money to be in a hurry):h . So I will try what you advised, thanks. I will keep you all updated if the symptoms start back up.

Unfortunately, I think you are beginning to realize these trucks are only for the patient optimist:( . Take your time and don't get frusterated. They are wonderful and fun once you understand them a little better and get all the kinks worked out!! Hope she is still running well.

All 3 of those codes seem to point at the same thing...the injection pump. I say buy a rebuilt one, to get rid of the problem and to have a warranty put on it just in case.

Does anyone know where I can get the best deal on a IP? And also, I have seen other threads about someone checking their codes and that it should flash code 12 to start and again when it is done, but mine doesn't do that, it only flashed code 12 after I cleared the codes, but after I drove it, and the regular codes came back, it doesn't show code 12 before or after?

was the engine running when you tried it? Absensce or presence of Code 12 doesn't tell you anything anyway.

only has code 12 if there is no other codes just to show you that the system is working but there is nothing to tell you

No the engine wasn't running when I checked the codes, should it be? And thanks for the replies on my situation.

was the engine running when you tried it? Absensce or presence of Code 12 doesn't tell you anything anyway.
No the engine wasn't running when I checked the codes, should it be? And thanks for the replies on my situation.
TDG wants to know if the engine was running when you tried moving the wastegate actuator arm. Not if the engine was running when you pulled codes. :slapforehead::lol:

how come my pump always runs when i turn the key forward? it has always done it since i put that carter pump on.





The pump won't kick in till after you turn the engine over, if it's still wired as GM intended.

96 and later are supposed to do that. ;)

cool. another question. is there a better place to hook up a permanent fuel pressure gauge other than the water drain outlet?