Engine/Transmission (1994 - 1998) Bad Injection pump?

[SLangegger]

At first I thought this was a fuel supply related issue, but now Im not so sure... . Once the truck gets warm, it acts like its out of fuel. I let it idle for about 20 mins in the driveway, and the truck actually died. Its hard to restart, and once it fires, its very sluggish, and wants to lope. The fuel pressure dosent drop before it dies. When it dies, it "ticks"(like a lifter tick). It has exhibited the same symptoms at all driving conditions. Gage says 18-20 psi at idle, 20-23 at 2500 rpm free rev.



Here is a list of things I have checked/replaced... .

New overflow valve

New lift pump

Removed fuel heater

Replaced all lines from tank to pump

Removed/inspected/cleaned pickup in tank

Pressure tested all feed lines for leaks

New fuel filter

Tried Cummins fuel conditioner

Inspected FSS for full travel

Lashed valves



Im out of ideas. The only thing left I can think of is the P7100. Is there any test I can perform to check the pump? What are the signs of a bad IP?



Thanks for any ideas.

Steve

 

[JGK]

The fuel pressure seems a little low. It shouldn't really ever drop below 20 lbs and at 2500 rpm free rev its not unusual to see 28 lbs or more. Where's your gauge plumbed in?



When its running, check that the fuel shut-off solenoid is fully up.



Any mods done to the pump (AFC changes, plate, goveror lever adjustment, etc. )? How many miles and on what injectors?



-Jay

 

[SLangegger]

Jgk,



The gage is plumed at the feed port on the pump. (As shown in faq section) I thought it was low too, but members have said they have "limped home" on as little as 4-5 psi with no problems. The lift pump is a new unit, direct from Cummins, with only a few hours runtime on it.



I checked the FSS. It is all the way up. I cant move it in any direction when I push, pull on it. It feels SOLID.



145000 miles, stock injectors. Only mods are #6 plate and 3kgsk.



Thanks

Steve

 

[Joe G.]

If you think that you have P7100 problems you should take it to a pump shop to make sure before you buy one.

 

[fest3er]

... Pressure tested all feed lines for leaks ...

Did you check all the return lines as well? There is the notorious rubber line 'behind' the fuel filter that is known to age and crack. Did you also clean the fuel pre-screener (between the tank and lift pump, near the starter)? Since it's not the dead of winter and -20F, I won't suggest that your fuel tank has gelled solid.



Also, what fuel has been run through it? If it's ULSD that hasn't had enough lubricity enhancer added, the pump might have worn out. Houston, TX, had a rash of failed pumps last year; and Blue Ridge Injection (local shop) keeps getting worn-out pumps in for repair (on and off-road, and ag), from all 'round the country, due to inadequate fuel lubricity.



Food for thought.



N

 

[tp0d]

You probably have tried it, but try running with the filler cap off and see if it still happens. .

Are these the original stock 160hp injectors? Might want to try a different set, mebe someone here has an old set of 180's or even 215's to try... ?

I guess it still could be the inj pump, but definetly get a rebuild price from a good pump shop before spending on a new one. . Unless you're buying a 215 pump that is hehh

good luck

-j

 

[SLangegger]

fest3er,



All return lines have been replaced/inspected also. If your talking about the screener in the fuel heater housing, yes I cleaned that as well.



tp0d,



Yes, stock original injectors... . I will run it with the filler cap off. If that ends up being the problem, I will feel like a real dumb @$$.

 

[DonFitzwater]

Filler cap? I'm thinking a piece of clear fuel line before the lift pump to eliminate hard line issues from chafing, etc... ... ... ..... heard about somebody having problems with the lines rubbing near the firewall... ... ... . the clicking or ticking sound sure sounds like a fuel system going dry. . ?

 

[Joe G.]

If it's the lift pump clicking it will click if fuel flow is restricted because that prevents the spring in the LP from keeping up with the push rod. If it's "going dry" the spring has no problem keeping up so it won't click.

 

[SLangegger]

Its not the filler cap. The truck still died after about 15-20 mins of idling with the cap removed.



Joe,



Where would the fuel flow be restricted at? On the intake side of the lift pump or on the output side of the lift pump?

 

[Joe G.]

With low fuel pressure I would think the restriction or air leak would be before the lift pump. If it was after you should see more fuel pressure. How did you "pressure test" all the lines? Remember, you can't see an air leak so if you put air pressure in the lines you are not going to see a small air leak in spite of having a lot of pressure in the lines.

 

[SLangegger]

I used a blow gun in the filler neck. I stuffed a rag around it to form a seal, then had a friend hold the rag/ squeeze the trigger while I looked for fuel leaks.

 

[Joe G.]

I doubt that would reveal an air leak.