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Hard cold start on 1999 6.5 chevy. p0251 code

100% you are sucking air. Not a fuel leak. Sucking air in the fuel line somewhere.

It also could be bleeding off through a bad liftpump check valve. But even if the check valve is bad, that can not allow air in the line unless there is a open section of line. So still first fix is new sae30r9 fuel line.

If you have a 100% filled tank and that solves the problem, then it is in the tank. Drop the tank and replace the 20 year old line inside.

If the full tank does not solve it, replace the rubber lines ontop of the tank, and the lines at fuel filter and injection pump.

The best answer is do inside the tank at the same time so that everything is good for the next 15 years.

Now you need to know about fuel pressure. When replacing the fuel line from ffm to ip, install a “T” for the new fuel pressure gauge. I like mechanical gauges, but electric is easier. Max 15 psi gauge so you can read the lower levels accurately.
 
Does not seem to make a difference with the level of fuel in the tank. This is a dump truck with dual tanks. I believe it lifts from the back tank to the front tank then lifts to the FFM. I had read about pressurizing the fuel system with 3-4 psi through the tank fill to force the leak. Anyone try this? or just replace the lines? We were also thinking of disconnecting the rear tank and pressurizing from there. If it's likely pre lift pump this should show with pressurizing?
Thanks
 
just started it parked up hill . We could see air bubbles in the clear tube we installed. it was empty before start then bursts of small air bubbles every 10 seconds for about two minutes. then engine engine smoothed out. Is there a way to pressurize the system or put dye in the fuel?
 
What does this truck have for a lift pump ?
If it has hose clamps at the lift pump, tighten the clamps then check again for air bubbles in the clear hose.
That's what fixed My air leaks anyways. LOL
Also, be sure that the lift pump is functioning by opening the water drain above the front of the engine, then put the end of the hose into a container, turn on the ignition switch, wait for lift pump to quit running, turn of ign switch and look and see if there is fuel in the container.
Welcome to the truck stop John.
 
john aquina said:
just started it parked up hill . We could see air bubbles in the clear tube we installed. it was empty before start then bursts of small air bubbles every 10 seconds for about two minutes. then engine engine smoothed out. Is there a way to pressurize the system or put dye in the fuel?
Click to expand...

Your fuel system is completely draining back to the tank. Overnight the lift pump valves don't seal that well and frankly don't have too. Fine tooth comb over the system esp. behind the FFM where the hoses flex to the body fuel lines. Any damp spots are trouble. Air leaks may not leak fuel so - good luck. Many places to look already suggested. The good news is you found the problem: air. The bad news is "where is the air leak?"
 
Was able to pressurize the system with a few pound of air in the filler neck and noticed a few damp spots on the return back to the tank. Finally found something that may point to the problem. Looks like the line has started to rust through where the factory hold downs are. Would this cause our problem. Does it act like a siphon and allow the fuel to flow back to the tank? Am I looking toward a bad lift pump also?
Anyone know where to get lines? this is a 3500 dually standard cab dump Cab and chassis model) I think. GM(which I use just to source part numbers) says the lines are discontinued by gave me the part numbers. 15026040 and 15025278.
Thanks
 
Good start. Any air leaks lets fuel drain back. Can you see the top of the fuel tank? The pickup assy also rusts through. Note the return line is submerged in fuel all the way to the bottom of the tank to prevent syphon.

Your lift pump has good flow and PSI? Drain back through it overnight is normal and ok. The valves don't have to seal perfect to work. IMO they don't even new.

You may have to make new fuel lines. Nothing wrong with hose...
 
It's a dump so seeing the top of the tank is the easy part. The sending unit does look good. The concern I have with making lines is that they are crimped flex lines to the steel hard lines.
My question regarding the siphon was to try to understand how the return line leaks would cause air to get in the supply line and cause the starting problem or maybe we haven't found the root cause yet.
 
In a loop of hose to syphon fuel out of a tank... It doesn't care where the air comes from. Forget about "fuel flow" with the engine running. It has all night to drain out. So any air leaks allows fuel to drain back to the tank in both the supply and return. The rotory pump in the IP and check valves leak slowly, but, given all night they give you the issue by allowing fuel slowly through them.

Any dampness on the FFM or IP?

If it is easy pull the tank pickup out and check for rust through at the top. Maybe the return hose to the bottom fell off.
 
Now where to find the lines? I think it's a little tricky because it's a "cab and chassis model" but is standard cab 135.5 wb. any help would be appreciated. I see dorman makes something that s says Rear; Standard Cab Pickup; Return and another that says feed but I am not sure. I was also thinking of trying it and adding an extension if needed.
Any help would be appreciated
Thanks
 
Last time I needed a fuel line for a 6.2 the GM dealer manual said to make it as there was no part number for that section. This was for a 1988 MY in 1993. No reason to go stock just make one. Try the dorman if its cheap enough.
 
It also would be worth getting on Leroy Diesel web site and get that fuel pressure gauge fitting that He sells, comes with the plastic tube to hook to it, I got a cheap MrGasket fuel pressure gauge and installed it under the dash, that takes all the guess work out of if the lift pump is functioning. That alone is a huge repair bill if the LP does fail.
 
UPDATE: we changed the fuel and return lines they showed leaks when we pumped air into the gas tank. It now starts immediately! It drives good, but i think i feel a slight miss now. I do have a small leak in the new line which we will fix Saturday. We had to make the lines because no one had them
 
Address the known problem first. Then any issues, start diagnostics pattern from beginning- clear line on return ip and fuel pressure gauge on input. Then check for volume of flow and test for contamination.

Then bleed all injectors. While bleeding see if you can determine which cylinder is a miss
 
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