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Old 07-24-2017, 02:04 PM   #1
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Ford Lehman injector bleed off pipe (return pipe)

Having trouble locating specification on leakdown pipe test.

Thought it was a few psi over 10 minutes, but cant find it in my files or numerous searches.

Anyone know what it is please?

Thank you.
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Old 07-24-2017, 11:21 PM   #2
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Old 07-25-2017, 02:01 AM   #3
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I have spent the last couple of hours reading about diesel fuel system design trying to understand what you are looking for.
As usual, the more I read (found a great discussion/manual by Bosch) the more I realize just how little I actually know.
This brings me back to your query, what exactly are you looking for? Are you simply pop testing injectors or something else?
Just curious...
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Old 07-25-2017, 05:27 AM   #4
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It is the pipe on top of the injectors that returns unused fuel to the tank.

Looks different for different injectors and different engines.

If it leaks inside the valve cover, you get fuel dilution.
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Old 07-25-2017, 05:52 AM   #5
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I just run it with rocker cover off and wipe the top of injectors and rail with paper towels. Any significant leak will be obvious. A tiny leak would be caught by advising the operator to carefully monitor oil level and note any rise.

If you want to pressure test it, get one of those portable air tanks and fill it to say 10psi and hook it up to return line at head only, do not include any fittings tied to inj pump (if any). Put pressure to rail and dribble fuel on all fittings and brazes under cover and check for bubbles.
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Old 07-25-2017, 06:17 AM   #6
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Thanks Ski,

Already found the leak, stripped threads in one injector for the banjo fitting bolt .

When I talked to American Diesel they suggested someone local put in a helicoil.

The guy who did my head said bring it by.

Was suprised at the stripping. That injector was a rebuild installed last year....only torqued once. American Diesel said they never and dont suggest using a torque wrench...that suprised me A LOT.

Also had a retaining bolt break, but thst could have been from a previous overzealous mechanic.
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Old 07-25-2017, 07:00 AM   #7
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Quote:
Originally Posted by psneeld View Post
It is the pipe on top of the injectors that returns unused fuel to the tank.

Looks different for different injectors and different engines.

If it leaks inside the valve cover, you get fuel dilution.
That makes sense now. Poor David H.'s Cummins comes to mind...although his is a common rail system, I believe that this is what destroyed his engine.
Most or actually all of the injectors that I felt with in my past life were of the type that used 3.5 mm braided hose on barbs. My Japanese engines all used similar barbs with hose too come to think of it. Any fuel return leaks happened outside of the engine.
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Old 07-25-2017, 07:14 AM   #8
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Quote:
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... American Diesel said they never and dont suggest using a torque wrench...that suprised me A LOT...
That surprises me to. When we had our 135 rebuilt, we had one of the six that leaked. I used a torque wrench as per the book. It was easy to find the leaker and the other 5 were in spec.
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Old 07-25-2017, 07:33 AM   #9
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Still wondering if anyone remembers the acceptable pressure leakoff ...or where to find it, not in my manuals.
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Old 07-25-2017, 12:07 PM   #10
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If return rail does not show any evidence of leakage visually when under pressure, it is good enough.
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Old 07-26-2017, 10:47 AM   #11
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I used a clear tube before the return line to view the returned fuel. Even at 2800 the tube never filled with diesel, so I would assume a couple of pounds at most depending on return line size, number of bends, and distance.
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Old 07-26-2017, 12:12 PM   #12
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I used a clear tube before the return line to view the returned fuel. Even at 2800 the tube never filled with diesel, so I would assume a couple of pounds at most depending on return line size, number of bends, and distance.
I would guess that would be good enough.

Last year I pressure checked to 15psi and it held overnight...which is overkill, but it was charged at the end of the day so I just went with it the next morning.

This time, it dropped 10 psi in about an hour and when I went back to tighten everything up, i discovered the stripped banjo bolt.

While a minimal leak/weep might be acceptable, if everything meets spec, zero leakage shoukd be easily obtainable.
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Old 07-26-2017, 12:45 PM   #13
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Keep it simple, it's simply unused fuel being returned to the fuel tank, any pressure is from resistance in the line. Frankly it doesn't matter as long as there are no leaks.
Ford Lehman injectors are under the rocker cover, periodically remove the rocker cover, run the engine at idle and check for leaks at the brazed pipe connections.
A symptom of a faulty leaking diesel fuel return line is a rising oil level on the dipstick. Another possible cause of this would be a a faulty diaphragm in the lift pump.
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Old 07-26-2017, 12:55 PM   #14
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A lot of reasonable suggestions, but like looking for the horse after it left the barn.

It is easier to check for leaks prior to the fuel line ever receiving fuel.

Thanks, without the spec...I can figure it out easy enough like suggested...just wanted to know what Ford or someone in the past thought was a good precheck.
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Old 07-27-2017, 07:21 AM   #15
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Ford Lehman injectors are under the rocker cover, periodically remove the rocker cover, run the engine at idle and check for leaks at the brazed pipe connections.
I would add to that and suggest a valve lash check/adjustment. Mechanical valve trains do wear, and just a bit out of tolerance and the old bird gets noisy fast.
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Old 06-18-2018, 03:55 PM   #16
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Found this in the 2720 Service Manual:

2. Remove the external leak-off pipe banjo connection at the rear of the cylinder head and fit a single outlet banjo connection securely in its place.

3. Connect a cooling system pressure tester to the banjo connection and pressurise the leak-off rail to 0.7 bar (10 psi.).

If the pressure remains constant for 10 seconds or longer, the system is satisfactory - proceed to step 8.

If the pressure cannot be maintained or begins to drop in less than 10 seconds, a leak is indicated - continue with step 4.

A little late, but I hope this helps...

Cheers!
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