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Diesel Fuel Injection puzzle.

Diesel Fuel Injection puzzle.

Diesel Fuel Injection puzzle.

6.9L International Harvester in a Ford 1-Ton.

Trying to troubleshoot a fuel/starting issue. It will always start in less than a single revolution. Next day, 3 months, matters not, except, if it's been more than 2 days it will run for 3 seconds only then die. It will then take approximately 2 minutes of constant floored cranking to start the second time.

This engine has the typical cam driven fuel pump => spin-on fuel filter => fed to center of the fuel injection pump => distributed to each injector => injector cooling/leakage collected at each injector to gravity flow back to the selected tank.

While trying to puzzle out the starting issue I see this baffling fuel line. I don't see it in the factory manuals.
Why would the pressure supply be tapped to the return?! Could this be part of the starting issue?

Keith Cress
kcress - http://www.flaminsystems.com

RE: Diesel Fuel Injection puzzle.

The first thing to check for is fuel drain back.
There may be a small leak in the fuel suction line.
Too small to affect driveability, but enough to act as a vacuum break and allow the fuel line to drain back over time when the vehicle is sitting idle. The red-neck approach is to apply some air pressure to the fuel tank. Judgement is required, don't blow up the fuel tank.
Let it sit for a while with pressure applied. Then inspect your fuel suction line for signs of leaking fuel.
My buddies old Kenworth ran well but would quit after idling for awhile. We put pressure on the tank. No joy. We got distracted for awhile. Then we noticed the floor of the cab was wet with fuel.
Examination revealed that the fuel ws leaking from the tachometer.
Turned out that the tack was cable driven from the injection pump/distributor.
A tiny O ring had failed allowing air to break the vacuum and let air into the suction line. Under load the fuel flow would keep the air flushed out of the line. At idle, it would draw in enough air to cause a vapour lock.
Another possibility is a leak in the fuel pickup tube inside the fuel tank. seen that also.
Not enough to bother when driving, but too much when idling while being loaded.

"Why not the best?"
Jimmy Carter

RE: Diesel Fuel Injection puzzle.

What year? Fuel solenoid? Look for normal air leaks in the fuel lines? That hose someone likely added it to bypass?
Bleed everything good, that hose looks like it would keep feeding air back into the system to me.

RE: Diesel Fuel Injection puzzle.

Interesting suggestion Bill. I'm considering it. I don't see any overt leaks hitchhiking dirt etc. but under pressure might show something.

enginesrus; '85' Once it runs it runs very well so I'm not betting bleeding will help. Your comment about the hose really has me thinking that I'm going to pull it and see what I see. I'll get back with results when it stops raining.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Diesel Fuel Injection puzzle.

I wouldn't worry about the return line that you can't figure out.
When I was young and chasing whistles in a mill an old timer gave me some advice which may be applicable here.
"If something was working, don't worry about the wiring. Gremlins DO NOT change the connections.
Look for loose connections and faulty devices."

I'm guessing that that engine is 30 or more years old. A corrosion leak in the pickup tube inside the tank is a distinct possibility at that age.
If the motor runs well, the probability of a problem with that return line is slight.

"Why not the best?"
Jimmy Carter

RE: Diesel Fuel Injection puzzle.


Do liquids in connectors, corrosion, dissimilar metals, and hungry rodents qualify as gremlins?


RE: Diesel Fuel Injection puzzle.

No Rod, but a reasonable question.
Lines disconnected and then connected to the wrong place is the work of Gremlins.
When you are the first to approach the issue, you may discount Gremlins.
If you are the second or third (or in one case possibly the 9th) person to approach the issue, Gremlins may have been invited in by previous attempts to solve the symptoms rather than solve the underlying issue.
I made an assumption that the engine in question is Keith's personal ride and that he is the only one under the hood.
Hence no Gremlins.

"Why not the best?"
Jimmy Carter

RE: Diesel Fuel Injection puzzle.

Stanadyne fuel pump? The throttle shaft seal is bad, that is all. It's allowing air into the pump which allows the pump to drain back to the tank.

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