7.3 idi cold start

[88f3507.3idi]

I have an 88 f350 with the 7.3 idi non turbo. It's hard to start when it sits for a little while. I replaced the rerun line caps and o rings and replaced the 1 glow plug that is bad. I wired up a push button for the GPS and put vinyl clear hose on return line from fuel water seperator to return cap on passenger side and from left rear bank to the tee that goes into return to fuel tank I also ran clear line from ip to the metal return line that goes into tank. I noticed that it has air in the line at the rear left bank at the tee and in the line from ip to metal return line. How can I fix this air in the lines? I'm thinking that's causing my hard starting any suggestions will be greatly appreciated as I'm scratching my head to figure this out

 

[ironworker40]

Manual says to run at 1500 rpm for to three minutes to clear air after you install clear lines. Then run at 3000 rpm for 2-3 minutes and watch for air in lines.
1-Is this what you did?
2- which direction is air traveling?

 

[88f3507.3idi]

From fuel water seperator to right bank return cap towards back of engine to metal return line. The line from IP runs toward metal return line on left bank and from left bank return caps its running towards bad of engine at the tee in the metal line. I've had it running and cracked injectors lines open and air still hasn't pushed out. After running for lil while the engine acts like its starving for fuel and it dies then I notice the return line from IP to metal line will be empty. Makes me wonder if there's a restriction in fuel flow from the fuel line off the fuel water seperator

 

[ironworker40]

In your first post you only stated you had air in the line from ip pump to tee and at the tee. So you have air in all of the lines? Or are you explaining the routing of the lines? How old is lift pump? How much fuel is in the tanks? And again did you run at 1500 and 3000 rpm and which direction is air flowing.

 

[88f3507.3idi]

The flow is running towards the tee on both banks it has air on left bank at the tee and after engine dies I notice no fuel in line from IP to the metal return line. It usually flows from return line at fuel water seperator then I will notice air in that line too

 

[ironworker40]

Okay Air traveling toward the tank means flow is in the proper direction this is important because opposite flow means fuel system restriction as per service manual.
1-Fuel level must be 1/2 tank or higher. Full tanks would be best.
2- you must check bolth tanks for 5 min at 3000 rpm
3- next step AfTER above conditions are met check rubber hose at lift pump.

Did you check to see if filter is full when it dies? I would replace lift pump if it is old. If you remove outlet line on lift pump and crank fuel should squirt out of pump a couple of feet. If you have a gauge you could pressure test the lift pump.

 

[ironworker40]

As per manual next step is to put clear line in the inlet and outlet lines on fuel filter and run at 3000 rpm for 5 min checking both tanks. This will be tricky to do , you will need fittings to make that work. They are trying to isolate the problem by doing this. If air is in inlet to filter then you check lines back to lift pump and then to tank. If air is in filter outlet only then problem lies in filter or filter housing. Is the O ring on fuel heater okay? Sometimes the water drains on the filters leak. I have also had bad brand new filters, Have you changed the filter recently? There is more test to do at fuel selector valve if none of this works.

 

[88f3507.3idi]

Okay that's good advice. The fuel heater isn't leaking fuel so I'm assuming the oring is good

 

[Agnem]

From fuel water seperator to right bank return cap towards back of engine to metal return line. The line from IP runs toward metal return line on left bank and from left bank return caps its running towards bad of engine at the tee in the metal line. I've had it running and cracked injectors lines open and air still hasn't pushed out. After running for lil while the engine acts like its starving for fuel and it dies then I notice the return line from IP to metal line will be empty. Makes me wonder if there's a restriction in fuel flow from the fuel line off the fuel water seperator

Don't worry about air in the return lines. FIX THIS FIRST! if you have a fuel starvation issue, you can bet there is a chance your other problems are related to it. Put a fuel pressure gauge on the line from the filter header to the IP and go from there. You need 5 PSI all the time.

 

[ironworker40]

Mel Can we pressure test at the shrader valve? Will this give us the same reading as on the pump outlet?

 

[ironworker40]

Mel Can we pressure test at the shrader valve? Will this give us the same reading as on the pump outlet?

Okay so I answered some of my own question. I used my homemade old persons tire pressure gauge. I just pushed it on the shrader vale at the filter and got 6 psi at cold idle. It would be more accurate with a smaller gauge like say 15 psi but its too cold to be messing with it.

 

[Agnem]

That gives you lift pump pressure, but post filter readings would be more meaningful.

 

[ironworker40]

That gives you lift pump pressure, but post filter readings would be more meaningful.

Okay so that will tell us lift pump psi without removing lines and can quickly eliminate lift pump being weak or failure, and that's what I was looking for because I suspect op has a weak lift pump as some of his problems.

 

[Agnem]

Keep in mind that often pressure is not the issue, but volume is. Pressure will drop when volume decreases, so having a way to monitor it when the truck is under load is important.

 

[88f3507.3idi]

I think the problem with my truck is it loses prime on the fuel when it sits for little while and takes a bit to start back up. Return line from filter head flows fuel before engine is even started. Maybe clogged fuel filter? Or pick up tube on sender inside fuel tank? I will drive little ways then it runs rough for a second then dies. I notice the return line from IP to metal line will be dry after it dies and if I crank on it for few minutes it starts up.