Well, My 1994 Chevy 2500 6.5L turbo diesel did it to my daughter this time. Stranded her at a friends house. I thought I had it fixed bt I guess not.

There are three things that are wrong with my truck at this time. I will list them out here - the only one that really has me frustrated is the third one.

After reading this please offer suggestions, comments on how to fix #3 or...move the truck on to someone else.

1) The A/C does not work - I beleive I can fix this - just needs to be vacuumed down and recharged.

2) The truck hesitates at low speeds - like if I am pulling out of the driveway and give it just a little gas and then let off I get a slight surge and then a hesitation - probably need a TPS.

3) I keep getting air in the fuel line and it strands me until I open the t-valve, turn the engine over till fuel comes out, close the t-valve, open the bleeder on the fuel filter, turn the engine over till fuel comes out, close the bleeder on the fuel filter and then start the truck up.

#3 has been happening now for about 6 months. I have relpaced the lift pump (which was bad - because the truck was not pumping fuel - replaced it and truck pumps fuel again) so that's not a problem. All I have to do is the procedure above to get all of the air out of the system and the truck runs fine.

Any ideas?? or should I send the truck on down the road?

Thanks fo rthe help,

Paul

You have a 94, chances are your OPS is also bad. OPS controls the LP during run as soon as it finished cranking. Make sure you don't have vacuum caused by the fuel cap. There may also be leaks along the fuel line.

Another possibilities will be the PMD.

x2, This problem is not bad enough to send the truck down the road! Fix her and drive the beast till she dies! That "could" be a very long time with very little cost in repairs and maintenance. She's not worth much on the market and somebody that subscribes to these pages may get her from you at a bargain unless you hang on.

You have a 94, chances are your OPS is also bad. OPS controls the LP during run as soon as it finished cranking. Make sure you don't have vacuum caused by the fuel cap. There may also be leaks along the fuel line.

Another possibilities will be the PMD.






Where is the best place to buy AC Delco Parts?

Are you saying I should NOT have vaccum at the fuel cap?????

I Don't see any leaks along the fuel line.

Why would the PMD cause this?? How much is that gonna run??

Thanks,

Paul

Forgot to add another symptom. Seems like when I was pulling an empty trailer yesterday the truck was "sputtering or bucking"

Any new Ideas?

classic pmd and ops. just remote a new pmd to the bumper and either replace the ops of hard wire the lift pump to 12V. Had the same problems as you do.

classic pmd and ops. just remote a new pmd to the bumper and either replace the ops of hard wire the lift pump to 12V. Had the same problems as you do.

Jason 2500 - which symptoms - having to bleed the fuel system or the sputtering?

all of your symptoms. the sputtering can be from the pmd or the ops not giving power to the lift pump all the time. it can show power at idle but as soon as its under a load and giving fuel to the ip the ops goes bad. there is no test for the pmd but its better to replace it and remote it out of the engine on a heat sink. i would always get stuck at some walmart or someplace like that and i would bleed it and then she would buck. the pmd takes 15 minutes to fix and the ops either way you go isnt that bad either

Sure sound more like a fuel supply prob than PMD trouble
As been said,the OPS could be bad. When you shut the engine off you should hear the LP still run for a few sec till oil press is bled down.
If it does,the OPS is still working,if not,OPS is shot.
To much vac in the tank or plugged sock will cause poor or no fuel supply too

OK - Before I sell I am going to buy a PMD relocation kit off of ebay and try the AC Delco OPS.

Wish me luck,

Paul

did you get air in the lines before changing the lift pump ? There are O-rings on the line where the lift pump connects, one might be damaged.
Other than that, you may have rotten hoses or loosen fixations...
Carefully check, when under pressure if you see air in fuel, that means you're sucking air inside, that doesn't mean you're loosing fuel, so you won't see any fuel leak probably

did you get air in the lines before changing the lift pump ? There are O-rings on the line where the lift pump connects, one might be damaged.
Other than that, you may have rotten hoses or loosen fixations...
Carefully check, when under pressure if you see air in fuel, that means you're sucking air inside, that doesn't mean you're loosing fuel, so you won't see any fuel leak probably


how would you check to see if there was air in the fuel???

Best place for AC delco parts is rockauto.com

could possibly be a dirty fuel sock in the tank

To check for air in the fuel, replace the short length of fuel line coming out of the top front of the IP with a piece of clear vinyl or Tygon fuel line. Crank the truck, OR run it at idle and watch for bubbles going through the line.

What you do for no 3 in your original post is a sign of air. If you have to bleed air from the system means that LP/OPS is not working. IP has to suck the fuel all the way from tank. Hence, air in the fuel system.

Replace/bypass your OPS and remote mount your FSD/PMD. Even if it isn't your problem now, it eventually will be. Both are known to be a cause for reliablity issues in the 6.5s. Get those sorted out and you should have very little problem with reliablity in the future.

I agree with the above, it sounds like a bad ops causing your injection pump to suck the fuel from the tank.

Keep your truck. You will never find a cheaper or easy to work on full size diesel IMHO.

ok - so I replaced the OPS this evening with an AC-Deloc replacement one AND did the OPS relay mod.

Once I finished with it all I started the truck and took it for a test drive. Along the way (I live in the country) I stopped the truck and shut off the engine and low and behold I heard something runing for 1 to 2 seconds after the ignition was shut off ( I assume this was the lift pump). I did this twice and heard something running - on the third time and every time thereafter - no more noise.


did I do something wrong? Am I supposed to hear something after I turn off the ignition?


Still Frustrated in Illinois

is the noise from under the seat?? if so it is the lift pump. i have not done the ops mod but it sounds like a relay delay shut off issue (may be normal).
if noise is under the dash it may be a heater stepper motor stepping off.

are you still getting air at the filter assembly?? if so most likely it is a bad fuel pickup assembly they are know to rot at the line as it exit out the top of the tank. the only real way to check for issue is to watch as stated a piece of clear tubing as it feeds the fuel filter. if there is any air at all you NEED to fix the problem or you will end up being stranded.

the reason you do not see the (fuel leak) problem is is a suction issue it is sucking air when it is sucking air fuel does not flow properly. it only takes a very small pinhole to cause bucking and stalling issues.

wes
houston, tx

Wes,

Noise seemed to be coming from the engine compartment. The air at the fuel filter was an intermittent thing and haven't driven it much since it stranded my daughter.

I will have to get a clear piece of tube to check for air in the fuel.

is the LP supposed to run after ignition is shut off?

generally no but if the ops is slow to shut off (bleed down) oil pressure it can cause your symptoms.

the 2 outside pins on the ops are for 12v supply and 12 v supply to the lift pump. center pin is for the oil pressure gauge.

i have replace my bwd ops 4 times in the last year (lifetime warranty) oriley hates it when i walk in as i have my tickets back from 1982 when i started using them. lifetime is a REAL long time. acdelco ops's are much better.

the other thing that makes noise is the hydroboost it may be bleeding down also but again not normally after the motor is turned off.

wes
houston, tx

The LP runs after it turns off is fine. It will run till the Oil Pressure is not detected anymore.

Sounds like it is an OPS issue.

5/16 inch vinyl line from the hardware store can be made to streach over the fitting on the filter just pick up a 5/16 double barb fitting to connect to the origional hose and the vinyl line

wes
houston, tx

To check for air in the fuel, replace the short length of fuel line coming out of the top front of the IP with a piece of clear vinyl or Tygon fuel line. Crank the truck, OR run it at idle and watch for bubbles going through the line.


This sounds like it is easier to check for air in the fuel this way. Can someone take a picture to show me exactly what getheledout is talking about?

As I said, drive it first before getting the trouble of checking for air. Eliminate one problem at a time. Sounds like you can get it started and stay on with new OPS. As I said, in-op OPS cause in-op LP cause air. If you eliminate the cause, then you are probably free of air. Just try to bleed it again now and see if the problem goes away.

You might have fixed your problem with replacing the ops. You said you heard the lift pump run when you shut the truck off? Then when you ran the truck alittle longer you didn't hear the lift pump once you shut it off? When I wonder if my lift pump is working or not I start my truck up in the morning, after it sat all night and got a chance to let the oil cool off. See the oil is thicker and the engine will take longer to lower the oil pressure once you shut it off, therefore allowing the lift pump to run until the pressure drops.

Once you drive the truck down the road alittle longer the oil heats up and the oil pressure drops fast and you probably won't hear the lift pump run once you shut the truck off because the lift pump will shut off almost at the same moment you shut the truck off so you won't hear the lift pump run once the oil is warmed up.

If the lift pump wasn't working because you had a bad ops you could have been sucking some air via. a loose connection. But the connection might not have been that bad and you might be just fine now that you got the lift pump working because now you should have a positive fuel pressure instead of having a negative pressure from having the injection pump suck fuel from the fuel tank.

Being you know how to purge the line, if it doesn't start, to get it running again I would drive it without replacing more parts and see what happens. I always feel that if you try alot of things at the same time you don't know what worked and didn't work. Also you could open yourself up to creating another problem when you are changing other parts and you won't know where you are at. Just trying to help here and saying what I would do but I am sure others would do it differently. But that is just me I guess.

By replacing the IP return line with clear tubing permanently one can allways tell if air gets in. That and a fuel press gauge is the best mod one can make.

Yep replacing the line is a great idea. I should probably change mine also. Bison is a very very knowledgable person and has helped me out alot. Thanks.

What kind of clear tubing that can withstand diesel fuel with a possibility of biodiesel for a long period of time? I know regular food grade clear hose from hardware store will not withstand diesel fuel. Heck, those tube will not even withstand our chlorinated water for more than 6 months. Plus it should be able to handle more than 200F. Regular pvc type plastic that I used for my air intake will soften up at that temp. Then when it soften up, your fuel will be contaminated with soften plastic materials.

Any suggestion? Bison.

By replacing the IP return line with clear tubing permanently one can allways tell if air gets in. That and a fuel press gauge is the best mod one can make.
were is the best location to tap into/read fuel pressure?

I tee'd in with a 1 piece brass 1/4 T (i got a mech gauge with snubber)in the short horizontal section of the fuel hose just pre IP inlet.There is where you want to read the pressure.

For Clear return hose i just use reg tubing avalable at any auto supply store,itll last for years although it gets hard over time.replace it once a yr if you're scared it'll pop or becomes yellow(hard to see trough),its cheap.
Chainsaw fuel line may be a better option.

Attached are a couple pics of my Tygon fuel return lines that I installed as part of my recent engine rebuild. I did not have to use any clamps on this stuff because it holds so tight. It does get soft when the engine gets hot and I have not yet tested them in the summer heat. But, I got it from my local ATV dealer who uses it exclusively over clear vinyl line. Its also used for chainsaw applications so it 'should' stand up to the heat well. I read one post from another diesel owner who used it on his truck without experiencing any problems. Note that I sleeved the Tygon injector return lines with regular fuel lines on those two or three sections that lie almost right against the the Turbo heat shield on the P side of the engine.

The pictures really help - THanks!!!!

The pictures really help - THanks!!!!IMO clear tubing on the injector return lines are not needed for spotting air in the system,just on IP return is good.

ok - so I replaced the OPS this evening with an AC-Deloc replacement one AND did the OPS relay mod.

Once I finished with it all I started the truck and took it for a test drive. Along the way (I live in the country) I stopped the truck and shut off the engine and low and behold I heard something runing for 1 to 2 seconds after the ignition was shut off ( I assume this was the lift pump). I did this twice and heard something running - on the third time and every time thereafter - no more noise.


did I do something wrong? Am I supposed to hear something after I turn off the ignition?


Still Frustrated in Illinois

my lift pump ws still running for a few seconds at shut off after i did the relay mod...
The relay being powered thtrough the OPS, this is normal, the relay stays on till the oil pressure has decreased enough to release the OPS switch.

Well, after the new OPS and OPS relay mod I drove the truck three different times yesterday with no problem -I am ready to say cautiously that the fuel delivery problem is fixed - I will keep you posted.

There is still the problems with the engine idling rough from time to time and the bucking. I have a used (but tested good) PMD and relocation kit on its way from ebay. hopefully, after that mod my issues will be solved for now. Again, I will report back when I know more.

I can't thank you all enough for your help and support - if your ever in Illinois near St. Louis, I'll buy the beer! Now - while I am waiting for the PMD - its on to the AC - but that is another thread.

Thanks again,

Paul

Used tested PMD's can throw you a curve...don't throw in the towel if your issues come back in short order. The used PMD's come in with returned IP pumps and have been exposed to the same conditions that cooked the one you have on yours now...