Last week, I bought a '94 6.5T truck. It wasn't running. After putting two new batteries in last night, it still won't start. The PO said that he opened the valve on the top of the fuel filter housing and nothing would burble out. I confirmed that today. I looked in the fuel filter housing and there is fuel in there but not a lot, maybe an inch or so. The truck did cough/burble a little this morning when I tried to start it.

Does this sound like a lifter pump replacement? And, how do I eventually bleed the fuel system. I bought a factory manual and I looking through it... I am obviously new to diesels, but not gas trucks and vintage motorcycles. Thanks for any help!! Oh, the truck has 218,000 miles on it.

Either the LP or OPS since OPS controls the LP during run.

Try jumping the LP with a 12V source directly.

How to should be in the FAQ which the grey part on the top of this forum.

on a 94, I have found the easiest way to check OPS /Lift pump is to take a short piece of wire and bridge the 2 outside contacts in the OPS harness. The lift pump should come on,regardless of key. If it doesn't, the lift pump or fuse is done. If it does, it is the OPS or the harness

UPDATE:

Thanks for the help so far!

I went ahead and pick up a LP from NAPA, Carter brand. I installed it, no problem. Truck still won't start and nothing comes out of the fuel filter valve. Also, a friend came over and when he tried to start the truck. I got under the truck and tried to listen if the new LP was making noise - none.

Where is the OPS located and what does it look like?

I'll try the test mentioned above.

Oil Pressure Sender is located at the rear of the engine, on the left hand side, behind the cylinder head. In order to get access to it, unbolt the fuel filter body from the intake manifold and slide that over to the right side of the engine.

When I changed my OPS, I puchased the OPS socket at my local auto parts store ($12.00), but some guys use kitchen faucet wrenches...

Even with the fuel filter moved over, clearance is tight, you'll skin your knuckles...LOL

Oil Pressure Sender is located at the rear of the engine, on the left hand side, behind the cylinder head. In order to get access to it, unbolt the fuel filter body from the intake manifold and slide that over to the right side of the engine.

When I changed my OPS, I puchased the OPS socket at my local auto parts store ($12.00), but some guys use kitchen faucet wrenches...

Even with the fuel filter moved over, clearance is tight, you'll skin your knuckles...LOL

Thanks! A couple of questions:

What are faucet wrenches?

Any idea what these OPS units cost?

my OPS was a new unit from GM, about $50 if I remember correctly...look at my older post...

if you don't know what a faucet wrench looks like, that's because you probably don't have one in your tool box ;-), go buy the socket at the store, it's a lot easier to work with, and if you keep the truck, you'll use it more than once!

;)

OPS get an ACDelco brand. It is about $30 to $40 depending on where you are, US or Canada. The part store can order it for you.

FIRST, check the LP fuse on the passenger side firewall. Its behind a plastic cover unless the cover has been removed.

You can power the LP simply by pushing the tip of that LP fuse up against one of the battery junction posts next to it. Thats the easiest way.

Also check that the crank fuse under the steering column isnt blown, it powers the LP during crank. Also check the ECM fuse and the F/Sol fuse under the steering column. Either of them will keep you from starting.

For the LP, near where the LP fuse is, there is an LP relay on the passenger side firewall. That is what powers the LP during cranking.

The OPS might start sending power eventually, which might be why you eventually get some fuel to come up after cranking a lot. The OPS starts sending power to the LP when it gets over 4psi of oil pressure.

When the engine is running you can verify the OPS is working by checking voltage on pin G of the OBD1 port, which is the bottom left contact. There should be battery voltage. Any less and the OPS is failing for sure. If you are getting voltage there while cranking it probably means your crank fuse is blown or the LP relay is not working.

FIRST, check the LP fuse on the passenger side firewall. Its behind a plastic cover unless the cover has been removed.

You can power the LP simply by pushing the tip of that LP fuse up against one of the battery junction posts next to it. Thats the easiest way.

Also check that the crank fuse under the steering column isnt blown, it powers the LP during crank. Also check the ECM fuse and the F/Sol fuse under the steering column. Either of them will keep you from starting.

For the LP, near where the LP fuse is, there is an LP relay on the passenger side firewall. That is what powers the LP during cranking.

The OPS might start sending power eventually, which might be why you eventually get some fuel to come up after cranking a lot. The OPS starts sending power to the LP when it gets over 4psi of oil pressure.

When the engine is running you can verify the OPS is working by checking voltage on pin G of the OBD1 port, which is the bottom left contact. There should be battery voltage. Any less and the OPS is failing for sure. If you are getting voltage there while cranking it probably means your crank fuse is blown or the LP relay is not working.


UPDATE 10/04
I checked the LP fuse on the firewall, looks good.

Crank fuse looks good.

ECM/ IGN fuse looks good.

The F/SOL fuse looks good.

When I got the truck, both batteries were dead (since replace with new batteries). I wanted to check the various electics before replacing the batteries, so friend hooked up some jumper cables to one of the batteries. I went ahead ant tried to start the eninge. It turned over but we noticed a wiff of smoke comong from the large cable running to the right side of the OPS. Don't beat me up too bad for this... So, maybe I fried the unit last weekend?

Also, the PO told me that the truck was difficult to start if it sat very long and then one day, it wouldn't start at all and that is how I bought it.

And, to horor, I just discovered a 2 Pac CD in the CD player - I hope it hasn't done too much damage to the truck... :)

So, what's next? OPS replacement? Oh, how much fuel should be in the fuel filter canister? Full?

How is the fuel filter? Did you change it?

Now I get it, your glo plugs arent working most likely. You fried the glo plug controller, possibly by running it off of 14V, or it was on its way out already sounds like.

Do you get a glo-plug light and SES light when you turn key to on? How long doed GP light last? Check to see if voltage is getting to the GPs during the GP light. pull out some of the drivers side GPs and see if they work.

The unit you are referring to is the Glow plug controller, not the OPS. The OPS is behind that controller, on the back edge of the block. It is round, and looks pretty much like any Oil Pressure sender, except it has 3 wires going to it instead of 1.
a blown glow plug controller would keep it from starting, also.....

Now I get it, your glo plugs arent working most likely. You fried the glo plug controller, possibly by running it off of 14V, or it was on its way out already sounds like.

Do you get a glo-plug light and SES light when you turn key to on? How long doed GP light last? Check to see if voltage is getting to the GPs during the GP light. pull out some of the drivers side GPs and see if they work.

The glo plug light comes on for about 6 seconds, then goess off. The Service Eninge Soon light comes on and stays on.

I took out the front two glo plugs on the drivers side. Neither got hot with them dangling out of the engine. I checked voltage, but I checked it after the light would have gone off in the dash, since I am here alone.

I screwed the front glo plung back in, turned the key till the glo plug light went out, tirned the key off and pulled the glo plug and it was hot.

So, where does this leave me?

Thanks to everyone that has helped this babe in the woods so far!!

The lift pump will not be running when key is on, unless either you have more than 4LBS oil pressure or the Key is in the crank position in a working OBD1 system. If you jump out the OPS ( as explained in earlier post) it will run, regardless of the key position, if Lift Pump is working and fuse is OK.
The faucet wrench referred to above is properly called a Basin Wrench. It allows you to reach in a tight area and has a jaw that self closes, and a long shaft to allow you to turn handle outside if the tight area. It was designed to reach up from below a sink, between the wall, and remove or tighten the plumbing connections at the faucet.

the glow plugs will not heat dangling in air, they have no ground there, they would have to be touching the block to heat. You could use a jumper cable to the body of the glow plug, and ground the other end.

Change that IT RUNS!

I hooked power directly to the LP via a good battery and its running now.

So, are we back to replacing the OPS?

A huge THANK YOU to everyones' help!!!

Something other than the OPS runs the LP during crank......it or both could be bad.

And figure out what smoked when you tried jumping the truck, that doesnt sound good. Maybe theres an exhaust leak.

Something other than the OPS runs the LP during crank......it or both could be bad.

And figure out what smoked when you tried jumping the truck, that doesnt sound good. Maybe theres an exhaust leak.

Ok, so go ahead and order an OPS since once the LP was powered with a battery hooked directly yo it the truck ran fine?

I've checked the fuses mentioned in other posts and they are fine? I don't know what else the problem is other than the OPS.

Let's change the OPS first.

After that we can see other things:
Sounds like your Check Engine Light is on, may want to check the code.
It is a 95, all you need is a paper clip.

Then clear the code and see if it comes back.

Let's change the OPS first.

After that we can see other things:
Sounds like your Check Engine Light is on, may want to check the code.
It is a 95, all you need is a paper clip.

Then clear the code and see if it comes back.

In fact the SES light goes off with the truck running.

I would still check and see what codes are set. Just because the light isn't on doesn't mean there isn't so pertinent info you want! Write down the codes, then clear the codes.;) Since the truck is new to you,You just might be glad you did

I would still check and see what codes are set. Just because the light isn't on doesn't mean there isn't so pertinent info you want! Write down the codes, then clear the codes.;) Since the truck is new to you,You just might be glad you did

Gret! Now, how do I do it? :)

Everything is in the FAQ on the sticky at the top of this section:

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

This is one of the few forum that has nice FAQ for almost everything you want to know or do.

You can power the LP simply by pushing the tip of that LP fuse up against one of the battery junction posts next to it. Thats the easiest way.

For the LP, near where the LP fuse is, there is an LP relay on the passenger side firewall. That is what powers the LP during cranking.

The OPS might start sending power eventually, which might be why you eventually get some fuel to come up after cranking a lot. The OPS starts sending power to the LP when it gets over 4psi of oil pressure.


You may need to do some more process of elimination. And does the LP work if you just press the tip of the fuse against the battery junctions next to it?

You may need to do some more process of elimination. And does the LP work if you just press the tip of the fuse against the battery junctions next to it?

I pulled the fuse on the back of the firewall and with the key in the ignition, all the way forward (just before you'd be turning the engine over), I touched the 20 amp fuse to one of the battery posts next to it and was delighted to hear the fuel pump clicking away. I have not swapped the OPS yet. So, does the point to the relay, next to the fuse as the culprit?


Thanks again from everyone, you guys have been a huge help!

UPDATE 10/06

Since NAPA is close by, I went ahead and replace the fuel pump relay, mounted on the firewall. Truck fired right up. I let it idle for a few seconds or minute and put ot in drive and moved about 2 feet before it died. Now its hard to start.

So far, here is what has been replaced:

FP
Fuel pump relay.

I have checked all the fuses and they appear to be fine.

The fuel filter looks good.

I tested the LP fuse on the fire wall by touching it to a battery post, and it powered up. Since that test, I have replaced the fuel pump relay, mentioned above. However, when pushing the key forward and the glo pulg light goes out, I do not hear the fuel pump "clicking".

Is this an issue of cracking open the fuel filter valve and pumping air out? Or, is there still something I need to fix?

I am closer, but still not over the finish line...

UPDATE 10/06

I tested the LP fuse on the fire wall by touching it to a battery post, and it powered up. Since that test, I have replaced the fuel pump relay, mentioned above. However, when pushing the key forward and the glo pulg light goes out, I do not hear the fuel pump "clicking".

Is this an issue of cracking open the fuel filter valve and pumping air out? Or, is there still something I need to fix?

I am closer, but still not over the finish line...
OK, so you know lift pump is ok, but it will only run when the key is in the start position, not on position, unless you have Oil Pressure and a functioning OPS. As soon as you let the key back to run from start, the lift pump will shut off without an OPS that works.

OK, so you know lift pump is ok, but it will only run when the key is in the start position, not on position, unless you have Oil Pressure and a functioning OPS. As soon as you let the key back to run from start, the lift pump will shut off without an OPS that works.

Ok, so, according to my oil pressure gauge on the dash, I have oil pressure. I bought a new OPS, but I have not installed it, so, considering everything else thats been replace/tested, its time to install the OPS unit I bought yesterday?

Yes, it can still show proper oil pressure but it does not send enough amp to the LP.

The OPS has 2 separate functions, they work independently of each other, One sends signal to gauge, the other controls lift pump. One can fail while the other still works.
Yes, swap it out with an A C Delco OPS