2nd Gen Non-Engine/Transmission Air In Fuel Help

[rchilders]

I know there are lot of postings on this subject but hoping for some one with

the exact symptoms for a cure if i start Truck every day every thing ok but

if i let it sit for more than one day it starts runs about one minute then here comes the air and it dies have to pump the plunger get air out then it is fine no problems when driving.





97 2500

 

[fest3er]

I changed my lift pump recently. The air problem started for me at that time (symptoms similar to yours). Now it's gotten to where it doesn't want to idle at any time; it seems the air sucking problem has gotten worse. I made it a little better by redoing the fitting on the lift pump's intake. For a little while. Now it don't wanna idle, and boost is limited to 20 PSI or so, so I *know* there's a fueling issue.

I think it's going to come down to disconnecting the supply and return lines to/from the tank at the firewall and see if the list pump/filter/P7100 work 'properly' and can hold fuel. Then maybe I'll try a long clear line between the prescreener and the LP and see if air is there. Then bypass the prescreener.

Your problem may be in one of three areas:

• The rubber fuel return line behind the fuel filter.
• The fuel connections at or in the tank.
• The fuel lines on/near the lift pump and filter.

There are more, but these are a decent start.

Basically, given the age of my truck, I should simple replace all fuel lines and seals and connectors that are not new within the past few months. That includes dropping the (now full) tank and replacing the innards there, too, which I know are faulty. I happened to purchase a 400# ATV lift for my Suksuzi DP bike; it ought to be enough to hold the tank if I ratchet-strap them together. And be prepared with a floor jack, if necessary to stabilize the load. Maybe even make a plywood platform between the lift and the tank to spread the load.

It's been suggested to apply vacuum to various parts of the system until I find the part that has the leak. But that would mean spending more money I ain't got.

Hmmm. 250# of fuel. + tank. The suspension should rise at most one inch or a little more. (Don't need any surprises when the tank strap bolts are released. )

Now, add to that the tail pipe is rotted out (Jannetty aluminized, 8-9 years old), the A/C don't want to work, there's too much blow-by and oil leakage, and the front end eats tires. I might as well tear the whole thing apart and rebuild it; if I had a garage and the space, I'd consider doing a frame-up rebuild, it's that bad. It's finally gotten to the condition where it needs a lot of attention. Alas, cash is real tight. Oh, well. That's life, I suppose.

 

[scotmartin]

My truck had to have both flexible fuel lines replaced. They are near the bell housing. Exact symptom you describe.

 

[GAmes]

fest3er, I'm 99% sure this is your problem. Go to post 19 and 20 if you don't want to read the whole thing. https://www.turbodieselregister.com...ion-1994-1998/204958-lift-pump-failure-2.html This could be the OPs problem as well, but the ones you listed are more probable if he hasn't replaced the lift pump.

 

[Joe G.]

It's more likely that it's the fuel heater than the lift pump.

Email me at -- email address removed -- for my writeup on the 12 valve fuel supply system, how it works and how to fix it.

 

[fest3er]

fest3er, I'm 99% sure this is your problem. Go to post 19 and 20 if you don't want to read the whole thing. https://www.turbodieselregister.com...ion-1994-1998/204958-lift-pump-failure-2.html This could be the OPs problem as well, but the ones you listed are more probable if he hasn't replaced the lift pump.

Yeah, mine's been sucking more and more air 'til it seemed like there's more air than fuel in the line. At least it ain't sucking seed, as Curley might've said.

I coulda swore I tightened that nut when I put it all back together. But that's the nature of such failures: age and heat (and how they affect the part, not the owner ). And replacing the LP could easily have disturbed that seal. I probably should still replace that bit of hard-line, as rusted as it is.

Thank you for that extra bash upside me noggin!! I forgot about that measly part. Cummins will have it tomorrow. Even with the overnight premium, it's still cheaper than renting something to head to Minn. next week for a family reunion.

The moral of this story is, "LISTEN TO YOURSELF!" I shoulda listened to me when I told myself, "Self? Replace everything while yer in there. " But no. I had to be clever. And miserly.

 

[rchilders]

Ordered hoses from Larry B"s today going to change those and remove fuel heater and see what that does ,already replaced the 90% hose pump to pre filter changed return hose last year should of done both.

Rick C.
97 2500 130,000 Stock 4in Exhaust

 

[KYOUNG]

I had the fuel heater unplugged and did not notice the little green seal that went around the plug had fallen on the ground. I had all kinds of air problems, found that seal laying in the drive and figured out it was for the plug. put it back in and cured all problems.

Check out your fuel heater real well, and loose the hocky puck heater out of it, you will never miss it!!

 

[fest3er]

I replaced the square o-ring to no avail. No difference.

Next I will replace the fuel filter. Again. I noticed the big o-ring on the top of the filter is just flopping around (it's now 1/8" too long). Question: What's the effect of not having a good seal there on the filter? Crunching... Hmmm. Seems to me the LP should push fuel past the filter directly to the p-pump if that o-ring is no good. And that ain't good. Is there a check valve in the filter or assembly that keeps fuel from flowing backward out of the p-pump?

If that don't do it, I'll take the prescreener off again, since that's the only other thing I messed with when I changed the LP.

 

[Joe G.]

Have you removed your fuel heater? It's part of the pre-filter/fuel heater assembly. It's that part that looks like a hockey puck that has an electrical connector to it. Remove the bottom of the assembly where the pre-filter screen is. Then remove the screw in the middle with an 8mm allen wrench. Then put the pre-filter up where the fuel heater was and screw it where the screw you removed was.

 

[Joe Mc]

I know we're talking 12 valvers here, but I found a pin hole in the metal supply line that comes out of the fuel tank just before the quick disconnect fitting. Mine would be fine if I started it every day, no leaks or anything, but if I let it sit over the weekend it didn't want to start. I'd have to crank it like 3 - 4 times till it regained prime. Once I installed the Vulcan Draw Straw problem gone.

 

[Missouri Mule]

Yes there are check valves in the lift pump to keep fuel from running backwords.

 

[fest3er]

I fixed my problem, and figgered I'd share what I found wit'chy'all.



'Tweren't nothin' in the fuel tank.



'Tweren't no fuel lines, supply or return.



'Twasn't the list pump or its connections.



'Tweren't any of the banjo seals.



'Twasn't the prescreener.



'Twasn't the square-cut o-ring on the prescreener's input, nor the little o-ring on the filter, as shown in the first picture.



It was the middle o-ring on the filter, the o-ring that separates the gazinta from the gazoutta. See the second picture. Wix (from NAPA) are a competent filter manufacturer; this o-ring happened to slip past them. Dunno if it was the wrong material or simply the wrong size. It sure seemed OK when I installed it. Found it last night after I changed the square-cut o-ring and told myself, "Self, that don't look right. " It must have slowly stretched, worsening the problem gradually.



Bought a new filter from Cummins Atlantic and, after cranking to get fuel in, it runs and idles just fine.



The moral of this tale is to stop, write down everything you futzed with before the problem appeared, then go back and triple-check those things before expanding the search. I changed the LP and the filter at the same time.



Of course, the other old saw also applies: you'll find the problem in the last place you look.

 

[fest3er]

After a test drive, it's better, but still ain't quite right. Under 1250 RPM, it starts getting rough, like a cylinder or two aren't firing right). At idle in neutral, it'll be smooth, then ease down to 500 RPM, then work its way back to 800; after maybe the third time, it eases down to 500 and soon quits.

At 1375 RPM in neutral, there's an occasional miss. At 1500 RPM and higher it's smooth as a top.

It's also not fueling as well as it used to. Or should I say as 'easily'. Sometimes it'll get right up to 20-28 PSI boost. Other times it acts as though the boost feedback to the AFC ain't working. But then it does pick up after a while. This, too, comes and goes.

What's the likelihood guck got past the filter (due to the bad o-ring) and into the injectors? Or into the pressure regulator (keeping it from maintaining proper pressure at lower RPM)?

This is *really* starting to get old.

 

[fest3er]

Finally had a chance to park the truck aimed downhill. Came out later and saw a small puddle of fuel underneath. Sure looks like the supply line (to the prescreener) is leaking right near the quick-connect fitting near the firewall.

I might expect the new lift pump hastened the demise of those old lines and fittings.

I really shoulda listened to me when I told me to change everything while I was there the first time. I'll never learn.

 

[WDaniels]

Just perused the post very quickly but didn't see in it what was causing mine to suck air. The metal line from the lift pump to the fuel filter housing has a "Gasket" on the bottom of the line where it goes into the lift pump. Mine was old and had a piece missing out of it allowing air into the system and eventually allowing the filter to be drained while running causing it to start hard and quit. I replaced the rubber elbow which was cracked and bad, the lift pump and the fuel heater which ended up being good all to no avail. Then I checked out the gasket that is under the "B" nut on the bottom of the line. Presto el fixo!

Hope this helps.

WD

 

[WBodine]

Well I just read through your post. Just a thought I had a simillar problem took me forever to find it. I found a hole in my fuel line between the fuel tank and the frame rail. The years of vibration of a plastic tank on a steel line wore a flat spot with small pinholes in the line. I never had a puddle of fuel or even a wet spot. When I finally found it I had droped my tank to install a Vulcan Draw Straw. The aera was bearley damp. Might be worth a quick look with a flashlight I believe you can see where the line comes out of frame rail about mid tank. Keep us posted on what you try and what you find. WBodine

 

[fest3er]

... I really shoulda listened to me when I told me to change everything while I was there the first time. I'll never learn.

Yup. I think I finally found the problem. Pinhole in the steel line into the prescreener, about an inch away from the quick connect fitting, and an inch before where the dipstick tube has been rubbing that line for years. I shoulda replaced it the first time 'round.



Quick connect fitting sure wasn't quick disconnect, especially with almost 12 years of rust. Short length of 5/16 EFI line is installed, but I know it ain't gone stay on their very long. The plastic flex line really didn't want to go in the hose. I need to get a length of new steel line and insert that into the plastic, then connect that to the prescreener input line.



Listen to yourself. If you determine everything should be replaced, replace it all. At one time (unless you have nothing else to do with your time). Don't cheap out. Rusted lines will fail. And they will fail faster once disturbed. They'll also fail faster once the pressure differential changes (like after installing a new lift pump.



If steel lines look badly rusted and corroded, replace them, whether they are trans coolant lines, fuel lines or brake lines.



Now to make it a more permanent fix.

 

[rchilders]

Well think i got my air problem fixed for know removed heater and replaced both hoses

let it sit for a day and half seams to OK know ,Happen to have my brake booster off

to replace it it was leaking sure made it sweet to change those hoses and fuel filter anyway thanks for all the great ideas sure helpful.