air in the lines???

[fastasu]

A little direction please. I've trying to figure out my small fuel issue for a while now. Where to start checking for the culprit? Lift pump or...

History on the matter. I purchased a 2000 Chev 2500 with the 6.5 a while back. On start up, if it's been sitting for a few hours or longer, it will be pretty sluggish for the first 10-15 minutes then perk back up. A few months ago, I parked it and drove my other truck. After a couple of months, I went back to get it, and the fuel system had to be bled as if I just changed the fuel filter. After I bled it, it ran like a top from that moment until I parked it and let it set all day while at work, Then when I started it up after the end of the day, back to sluggish for the 10-15 minutes again. My last diesel (duramax), I never had any issues like this. I never thought about air until in the system until it was parked for a couple of months and had to be bled....

 

[Paveltolz]

Welcome to The Truck Stop Fastasu.
Yeah, sure sounds like air is entering into the fuel system. Especially if you had to bleed the system and it started and ran fine immediately afterwards. When you bled the system, did you do that at the Filter’s bleed screw or through the T-Valve at the thermostat? Just curious.
I’ll let Will L. tell you the virtues of replacing the short fuel return line on the Injection Pump (IP) with a length of clear line to observe the amount of air leaving the IP. While a few bubbles are normal, you shouldn’t have more air than fuel pushing back to the tank.
Working from front to back (which is probably the reverse order but, easiest to do):
The heat under the lower air intake can adversely affect the fuel lines and cause them to fail. Typical at the connection points to the IP from the FFM, to the T-Valve from the FFM, and to the FFM from the Lift Pump. Sometimes one can trim a 1/4” of the ends and reuse the hoses. Being 24yrs old, IMO, better to just get new lines and replace them under the lower intake.

Another area to check would be the Fuel Filter. Either the Bleed screw or O’ Ring although those would usually leak fuel… you never know.

Depending on where you’re located, the steel fuel lines from the tank to the Lift Pump and from the LP to the rubber transition to the FFM could be suspect as well as the rubber lines from the tank’s sender unit. Someone found rust had created a pin hole at the Sender Unit’s steel lines. That’s a fun job…dropping the tank (pump it out as best you can first. Ask me how I know).

I’m sure I’ve missed something so other’s will share their insights, techniques etc. as well as fuel line diameters (I’ve replaced everything with 3/8” from tank to IP and removed FFM etc.).

Don’t envy you the detective work but, you’ll sort it out with patience.

 

[Will L.]

Normally I recommend against just throwing parts at something when diagnosing.
So yes I am going to start with the diagnostics side of replacing the 1/4” diameter return hose that comes out of the front top area of the ip (injection pump). Factory it is a black rubber hose in an upside down “U” shape.

You can get clear 1/4” line sold by the foot at hardware stores like Home Depot, Ace, Lowes. It is NOT fuel line, it is clear pvc tubing. It will last about 3-5 years depending on your environment. Buy 2 screw style hose clamps because the factory clamps won’t fit. A better choice is buying a foot from fuel-line.com because theirs is rated for ethanol that is in modern diesel fuel. We don’t know how long it lasts, but of a couple guys running it so far it is ok for 5 years.

If not familiar with which line, ask and we can post pics.
As mentioned watch for a trail of bubbles or other contamination. You should have clear line at this location permanently imo because problems always pop up and at an instant you can pop the hood and see.

If there is bubbles- then you have to chase back the connections and line looking for the source. If the LP (lift pump) is working then from tank to LP any opening will suck air in and create this problem.
Any openings after LP will cause a leak of fuel.

A common mistake is people hear the noise of the LP and assume it is working. Huge error. I always promote adding a metal T adapter at the ip inlet and installing fuel pressure sensor there and permanently mounting fuel pressure gauge somewhere in your dash. Low incoming fuel pressure wears out the ip sooner and not working at all has ruined brand new ip in less than 10,000 miles. So the investment is worth it. Staying above 1psi at all times should keep it running but as mentioned causes damage. Desired pressure is 8-14psi according to Stanandyne who makes the ip. Factory LP will not supply this.
a non working LP will cause aeration (air bubbles) even if there are no leaks in the fuel line. But when this occurs it is normally freeway speeds problems get noticed first. If yours was weak since you bought it, you might not realize it is running weak at higher speeds.

Your 1/4” return line that comes from the ip, ties in all the 1/8” return lines together, then as 1/4” size returns fuel to the fuel tank: this line needs to be sealed the entire way and stay submerged in fuel in the tank. Having the line open at all can allow air to travel backwards to the ip and cause this as well. But it is normally noticeable as a liquid fuel leak when the engine is running.

If/when (highly suggested) you replace all the rubber lines- you need it to be SAE30R9. The only exception I do from this is the tiny clear piece previously mentioned. It is so cheap and easy to replace that the advantages of always clear is worth replacing it every 5 years imo.

Factory-the line from tank to FFM (fuel filter manager) is 3/8”. From FFM to ip is 5/16. Return line on injectors is 1/8” (get factory GM with clamps or Mercedes Benz FROM A DEALERSHIP) the rest of the return line is 1/4”.

A frequent upgrade is to enlarge the line from the FFM to the ip with 3/8” known as FTB Feed The Beast modification.

Imo replacing the FFM system and getting something like the FASS LP with filters is a worthy investment. You can have great fuel pressure, the filtering is far better for cleaner fuel as well as completely stop water from getting to the injection system. Then run 3/8” line the entire way to the ip. The only drawback is initial cost.

If you find the factory LP is bad and don’t want to upgrade, the best version of that pump is the AC Delco EP158. Only a few places to be trusted selling it because there is a lot of Chinese knock off parts that have been discovered.

Hope this rambling helps more than hurts.

 

[Big T]

Having been through this twice and recently, Will L’s dissertation can be boiled down to this:

“If the LP (lift pump) is working then from tank to LP any opening will suck air in and create this problem.”

In my experience, the o-ring seals at the connection to the sender unit go out and you suck in air there. So run or drain the tank down, drop it and get those seals from Napa for like $10. Replace any suspect lines between tank and LP. Given the age of the truck, I would throw parts at it and replace it all between the tank an the LP and as Will L said, replace the LP with a Fass or Air Dog Raptor while doing all of this.

Welcome to the 6.5 forums here. We are a needy bunch.

 

[fastasu]

Appreciated!!! Lot's of good info! I'll get everything together over the next week and try to get it all done on the weekend of the 25th. I did purchase a heavy duty lift pump from DieselSite a while back and haven't had a chance to install it. I guess now is the perfect time. I'll look into the FASS LP as well. I was wanting to do the glowplugs and ip just for piece of mind. I have no clue the history of the truck. I acquired the truck for $900. So I can invest a little bit, and still be sitting decent (I think lol).

 

[jrsavoie]

Appreciated!!! Lot's of good info! I'll get everything together over the next week and try to get it all done on the weekend of the 25th. I did purchase a heavy duty lift pump from DieselSite a while back and haven't had a chance to install it. I guess now is the perfect time. I'll look into the FASS LP as well. I was wanting to do the glowplugs and ip just for piece of mind. I have no clue the history of the truck. I acquired the truck for $900. So I can invest a little bit, and still be sitting decent (I think lol).

I'd check a glow plug or 2. If they're AC Delco and 60G and look & test good, I'd just run them. I used to pull mine periodically just to give them a visual and a fresh coat of anti seize on the threads.

I forget the torque spec, but it isn't much

 

[Will L.]

Glow plugs- yeah pull and check. Ip- nopers.