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'95 with no power to LP

D

D2 Cat

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Location
south of Kansas City
I just acquired this truck with 226,000 miles on the clock, 1/2 T, Z-71, 4x4. It has not ran in at least two months.

PO said the engine was replaced 40,000 ago, replaced PMD recently, changed fuel filter and lift pump last fall. They said it ran fine until the weather started getting colder (in Nov) then it seemed to b losing power, and then stall. They thought it was a fuel delivery problem, because it was running perfectly until the moment it cut out. That's when they replaced the LP and fuel filter. It would then start up, it warmed up for about 15 minutes, then about 5 minutes into the drive it stalled and cut out again. It would turn over and start and not stay running long enough to drive. They gave up. They want a gas truck!!! I have to assume all the claims of a different engine are just that, I have no receipts.

It turns over good, just won't fire. I checked the LP and no power there. I jumped a battery to the LP and it pumps fuel. The fuel tank was empty when I tried the LP, so I added 5 gals. When it pumped there was a lot of air, but I expected that. I tried to bleed it, but never succeeded. Later that day I could smell diesel and see in the moisture in the driveway there was some diesel running off.

I removed the fuel monitor and cleaned it. It was filthy. It had a new filter in it (by PO) and I think the screw on cap was not tight. It was also leaking at the WIF sensor. I replaced that O-ring. I removed the fuel heater. That gasket seemed OK, but I did add a touch of permatex #2 on both sides for good measure. I will replace the hoses coming out of it when I install it.

I replaced the OPS and the fuel relay. I ran 12 Volts from battery to "G" connection on OBD terminal and still had no power to LP.

What do I need to do to check power to the LP? Is new OPS not functioning properly? Wire at OPS connector not working? Can I jump past the OPS to get fuel to see if this thing will come to life?

All these things I have done are things I learned snooping here are critical points on these trucks. I am not a mechanic, just an eternal optimist!
 
Run a hot wire directly to the LP. See if you can get it to run then it will be easier to tell what's working and not working.
 
Run one postive and one negative staraight from the batt to the LP.

If it dosent pump when you hook a wire to the G terminal than it is probably a ground on the left fram rail farther back.
 
OK, that makes good sense. If I went to a salvage yard, did GM use the same connector on other applications as the one on the LP? I'd like to not tie into the existing wiring, but that connector is quite deep.

Do you guys know a simple way to get power to the connector on the LP?
 
I see you made it here. That is good. All the masters are here.

I am not sure if you get my last PM in the other forum:
another way is to use the OPS plug. Unplug it and jump between the 2 end pin. You can use a paperclip (the greatest engineering invention) as guybb3 suggest.

If it does not run, I got the feeling that your LP may be bad.
 
I accomplished nothing but purchasing some fuel line today. I plan or replacing the 1/4" lines coming from the fuel monitor.

I'm working outside on this so I waiting for a warmer day! If I need to replace the LP what's the possibility of using a factory Carter LP from a 2nd gen. Cummins? Those pumps are considered failures when they get DOWN to 5 PSI. Other then the connections, anything negative about using them? I've got a couple of them as spares and I have considered replacing the fuel line to the fuel monitor with some hose I have from one of those trucks. I think I would have to have a fuel gauge or a fuel indicator light because I don't think those pumps would allow the fuel to flow freely through upon pump failure. I guess you'd say it's not a fail safe pump! What you you guys think?
 
LP suggestions:

1. 93 model year LP, plugs right in. Exact same housing with slightly higher pressure and volume rate.
2. Walbro FRB-5, takes a little bit of retrofitting.
 
You can use any pump for diesel that will put out between 5 and 15psi. As long as it will stay above 2psi at WOT. I have cut the steel lines that go into the LP and just slid 3/8" hose over and clamped down, been that way for years with no trouble.

Have you looked for a fuse for the LP? And is the LP relay there? In a 95 should all be in the fuse center under hood. Otherwise you have a broken wire or ground. Just check the ground on it, see if it looks good or just put a meter to the ground in the connector and ohm it to the frame, should be less than 1 ohm.

The fuel filter housing is know as the fuel filter manager. sounds like you are doing well fixing it up and replacing lines. If interested it may be a good opportunity to perform the "Feed The Beast" (FTB) modification to upgrade the 1/4" line to 3/8" from the filter manager to the IP.
 
D2 Cat said:
I know AC Delco is recommended for the OPS. Is brand as important on the LP?
Click to expand...

AC Delco is good way to go. However you also need to add a relay, or what is know as the OPS relay mod. You dont want the LP to get its power through the OPS, only to run while the OPS sees oil pressure. So you run the OPS output to a relay coil, and run battery power through the relay to the LP.

Also, while youre at it, throw on a grease hose so the OPS sticks up from behind the firewall. A 6-9" grease hose is good with 1/8" to 1/4" fittings on each end and a ground on the OPS side of the hose. Otherwise PMDcable.com sells one that grounds it with steel through the hose, its more robust than a regular grease hose.

The OPS not only controls the LP but is your instrument panel gauge Oil Pressure Sender. The non Delco units are not as reliable for being accurate.
 
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Is there a writeup on this modification of more fuel to the IP? Would you remove the existing hose barb and drill and tap a larger one? Much noticeable difference on a stock truck?

I installed a new relay for the LP and checked the fuse with ohm meter. It's probably a broken wire and lack of ground as you mentioned.

I will definitely do the relay mod. after I get it to make constant noise!!

You mention the OPS controls panel gauge. I notice my fuel gauge seem "upside down". Yes, the needle is pointing past full 30 degrees. But I think the different times I turned the key on it went to different positions. I only added 5 gal. I'll have to study that more before I can really comment correctly on it. What controls the fuel gauge?
 
1995 lift pump problems

D2 Cat check pin F on the DLC. On my 95 this is the correct pin for the LP.
See the attached pic from the 95 Helm manual.
I can power the LP by jumpering 12V to pin F.
 

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Desert, That's good to know. I appreciate the schematic. I tried the "G" pin for 12 volts to the LP and didn't get it. (I think I got that info. on a forum I was snooping on) It looks like I was at the wrong location. "G" is in the lower left spot, if I remember correctly.

I also see that gray wire at the LP goes directly to the OPS.
 
D2, Pin G is referred to all the time but my 95 is pin F like the manual. You can see how the LP is powered through the relay during crank and then through the OPS after the oil pressure builds. Put a volt meter on pin F and look for 12V during crank, if 0V than check fuse and relay. If 0V while running than OPS is bad. Jumper 12V to pin F with engine off and LP should purr.
 
It is pin G in the 94 GM service manual. It is the bottom left contact. F is the top left contact. I have found errors in some of the manual schematics. but yours actually works going to the top left pin? or is pin F on the bottom row of yours?
 
well, is it just that no one with a 95 has ever realized this, or are all of them not the same? That is the schematic for C/K trucks? And what does SIR stand for, is that something that locks the doors or something when you crank? 93 also goes to pin G. You would think for scanner software sake and configuration it would remain the same. Scanners I believe show LP power during operation.
 
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