Need fuel HELP! W/ 6.5l

[ironnut]

So I decided to change my fuel filter today. Thought it might be a little clogged because when I accelerate onto the freeway it will miss/stumble for a quick second occasionally. It's a 5 speed manual and it only occurs in 4th/5th under acceleration, and a little load. So i changed filter, then tryed to prime the system, but i could never get any fuel to come through the air bleed cap on top of the filter. Tried cranking it 7-8 times w/ 2 minutes rest between but nothing. Took the filter out to try all over again, and noticed a good amount of sediment in the filter housing. So I called the chevy dealer asking for some advice. Couldn't really help me out, just told me that if I need a new PMD or pump they will only replace it under warranty if the fuel filter is clean and the fuel system flushed. Which cost 450$. But could save me $2000. This seems strange becasue the truck ran great except for an occasional stumble. Maybe i should have left the filter alone. Either way looks like in gonna be spending some bucks, anyone got advice as to what I should do? Now the trucks just sitting outside, and I need the dang thing running! It's a 98 6.5L 5 speed w/ 116,000 miles. Any the original engine was replaced at 60,000 miles.

 

[tRustyK5]

From Casey's fuel pump post:

Now you have to bleed the fuel system. First, if you haven't recently replaced the fuel filter, go ahead and install a new one. Just undo the clasps and pull straight out on the filter. Put a little oil on the o-rings of the new one when you go to install it. The new just pushes back on.

Close the drain valve on the bottom of the fuel filter assy, but leave the air valve on top open. Next, disconnect the fuel cut-off solenoid on the injection pump. This is the pink wire right on top of the pump itself. We want to avoid pumping any air into the injection lines when we start cranking the motor, and by removing this wire, the air can't get into them.

To save battery power and the glow plugs, disconnect all 8 wires going to the glow plugs. (that is if you have an automatic glow system...if yours is manual, then just don't glow!)

If you can, install a piece of clear tubing over the small barb on the top left of the fuel filter assy. I usually run this clear hose into a container sitting on the cowl of the vehicle so I can see it from the driver's seat.

Start cranking the motor over. We're not trying to start it, we're just priming the system. What you're doing is pumping fuel from the tank, into the pump, up to the filter, and back through the return lines. Since the injection pump is disconnected, it won't get any air in it and get air-locked.

Only crank the motor for no more than 30 seconds. I have personally burned up a starter by cranking too long. Let the starter cool for 2 minutes before cranking again.

When you see clean diesel fuel coming out the hose at the top of the fuel filter, shut the air bleed valve off, disconnect the clear hose, reconnect the pink wire to the injection pump, reconnect the glow plugs, and start it up. I guarantee it start up on the first try with this technique (as long as the injection lines didn't have air in them to start with).

I know this seems like a lot of steps, but you should be able to get this all done in under 2 hours. I can do it now in under one hour. Using these steps makes it very easy to change the pump and bleed the fuel system.

BTW...you can use these same steps to change the fuel filter. Just skip the part about changing the pump!

Did you disconnect the power wire to the injection pump before cranking it? If not, it is now airlocked.

To fix an airlock situation leave the power wire attached to the IP, and loosen all the injector lines at the injectors. Even if you only get 6 or 7 of them that should do. Now crank for 15-20 seconds while a helper watches (or have the helper crank the motor while you watch) As soon as a line begins to drip fuel tighten it up, until all the lines you loosened are tight again..

Rene

 

[ironnut]

I didn't undo the Injection pump connection because first off i didn't know what it was and second because in the factory GM manual it doesn't say to do that. I'm just debating now where i want to try to fix it myself or just spend the money to have it done.

 

[jac6695]

Sounds very similar to how my IP in my 97 failed last year. The occasional stumble followed by failure. Check with different dealers regarding the policy to warranty the IP and PMD. The dealer I took my truck to wanted to do the fuel system procedure, but I found another that didn't need to. BTW, when I change the fuel filter in my truck, I never need to bleed air out (lift pump pushes it through). Just a little cranking and it will fire up. Same when I run out out of fuel, fill the tank, and crank over for a bit. Good luck!

 

[ironnut]

Well it turned out my lifter pump which is down along the frame had failed which is why I couldn't prime the engine, and it also solved the freeway stumble! ​

Runs great again.​

​

Thsnks for the posts​

 

[arveetek]

I just saw this post and thought I would comment.

My tips given above for changing the fuel filters won't apply to the newer trucks, especially his '98. The newer trucks use a completely different kind of fuel filter, and I don't believe that there is a fuel cut-off switch wire on the DS4 pumps, at least not one that I can recall. Plus, the newer trucks have an electric lift pump mounted on the frame rail instead of a mechanical pump bolted to the engine. As Ironnut found out, this was his problem.

The EFI 6.5L are known to have problems with the fuel pump and with the oil pressure switch which energizes the fuel pump. Either one are prone to fail, causing these kinds of symptoms.

Casey

 

[tRustyK5]

Thanks Casey, good to have that cleared up in this post for future reference.

Rene