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Lift Pump Problem

97duallydiesel

97duallydiesel

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I was having stalling issues so I ordered a new PMD relocate kit with new PM. I installed it and everything was working fine when I took it for a test ride.
But when I returned home and was going to attach my plow it started to act up . The idle was fluctuating ,going from normal just under 1K to 500 and started to blow black smoke . Also I had no power so I pulled her back in the garage thinking maybe something came loose . I'm not sure if I goofed by putting some dielectric grease in the connectors prior to installation so I pulled everything apart and cleaned the majority of the grease out.

When I cranked her over she started right up and ran for as long as the fuel that was in the FM bowl then died. the reason I know this is because i removed the filter and there was very little fuel left in the bowl. I tested the fuel lift pump on the frame rail by turning the key and it didn't appear to be working... No humming or bowl fill up. Off to Advance Auto for a new one and a new relay while I was at it..didn't want to take anything to chance.

I replaced the pump even tho it was replaced new 3 months ago . The relay was a different size and color but had all the right numbers and prongs.

The pump is still not working .... Is there another relay or fuse ( The fuse in the relay center is OK) that I missed ?? I don't think the PMD has anything to do with it right??

Please help Me :sad: The truck is stuck half in and out of my garage..And it's gonna get cold tonight...Steve
 
unplug the pump and verify your getting voltage or not. I've heard both arguments about the ops not being necassary on obd2 but I certainly don't know. I have a relay on my ops and don't have any problems with mine just the pump. If you don't have voltage at the pump I'd probably try a new ops just to eliminate that.
 
ak diesel driver said:
unplug the pump and verify your getting voltage or not. I've heard both arguments about the ops not being necassary on obd2 but I certainly don't know. I have a relay on my ops and don't have any problems with mine just the pump. If you don't have voltage at the pump I'd probably try a new ops just to eliminate that.
Click to expand...

AK what's a OPS?
 
Oil Pressure Sending Unit. On the older rigs the lift pump is run thru the OPSU to opereate the lp and is a frequent problem. Some say on OBD@ that it doesn't need the OPSU others have said it does. Don't know for sure myself. You could be a good guinea pig to find out.
 
ak diesel driver said:
Oil Pressure Sending Unit. On the older rigs the lift pump is run thru the OPSU to operate the lp and is a frequent problem. Some say on OBD@ that it doesn't need the OPSU others have said it does. Don't know for sure myself. You could be a good guinea pig to find out.
Click to expand...

I read Doc's sticky and the OPS is located in the rear of the engine near bell housing correct? He also states the OPS and the PCM has to malfunction for no LP power.. The only problem is its almost 6pm here and all the auto stores are closed and not sure if there open tomm.. probably . Might have to push truck out of garage for tonight which isn't a pleasant thought seeing how my driveway is inclined and covered with a light cover of snow..

He also states there is a point where you can jump the LP by attaching a 12V source to a test wire in the rear of the engine.
 
Run a hot wire right to your LP (located on the frame rail under your drivers' door), make sure it is pumping (should prrrr like a cat), then go up and see if you have fuel coming out of the water-drain by the brass T-handle. If so, your FM should fill up and you can get into the garage. THEN we try to figure out what's wrong with the truck. DO NOT leave the hot wire hooked up to the LP and try to drive the truck.
 
JiFaire said:
Run a hot wire right to your LP (located on the frame rail under your drivers' door), make sure it is pumping (should prrrr like a cat), then go up and see if you have fuel coming out of the water-drain by the brass T-handle. If so, your FM should fill up and you can get into the garage. THEN we try to figure out what's wrong with the truck. DO NOT leave the hot wire hooked up to the LP and try to drive the truck.
Click to expand...

Thanks . Only problem is the Beasts to long to fit into garage .. I diffinitley wouldn't leave the hot wire attached. :thumbsup:

And when you mean hot wire should i run it directly from the positive side of battery?
 
My opinion? (note that it's still an opinion because I need to take one apart someday to find out) I think the ECM on the OBD-IIs passes the LP power back through the relay on the power side. I further hypothesize that if the relay burns those contacts, then the signal doesn't get through.

Why do I think this? Because this same question seems to come up every time somebody fries a NON-ACDelco OPS, and we already know the aftermarket guys build 'em too light. I haven't seen this discussion with an ACDelco OPS (failing the first time).

But it's really just a guess that seems to fit the data...
 
where 's the best place to find the OPS on my rig ? looking over the top of the motor in the engine compartment or from underneat..
I 'm just waiting on a buddy to help with the LP jumping .. safety first.. I'll let u know how it works out...
Obviously I need to get a acdelco OPS replacement correct?
 
In OBD-IIs, with OPS unplugged lift will continue to run, been there done that just test the theory if it's really needed or not, test condutcted at GMCTD's place both of us learing the ins & outs of the lift powering routine of a OBD-II, unplugged the PCM feed lift still runs, unplug both or the common gnd and lift loses power.

OPS on a 97 I suspect would be under driver side rear corner under intake, just fwd of fuel filter mgr.
 
If you remove the 2 nuts holding the glowplug controller on the back edge of the intake,, you can schooch it aside, to get a better shot at the OPS, I'm sure theres a socket to use for it,, but when I did mine,, I just stuff'd my hand back there and hand tightened it,, then used a set of pliers to tighten it the rest of the way.
 
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