Anybody familiar with the IH version of this engine?

Booyah45828

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I'm looking to bounce some ideas off someone's head.

I have an IH school bus with a 6.9. The bus is a 1984, engine is a jasper reman, unsure of the year or when it was installed. It definitely has the ford rpm governed pump fwiw.

I'm having what I believe to be air intrusion issues. Glow plugs are on a manual switch, and were replaced last year. They all are working fine. The engine will start, run for a second or two, and then die. Crank it for about another 10 seconds and it will start back up and run normally. Stereotypical air intrusion issues right?

Well, I've replaced the O-rings, caps, and lines with a delphi kit, so I don't think I have issues there. They were originally leaking fuel last year, and dumped a bunch of fuel into the valley, so I replaced them. All the o-rings were shot and broke upon removal, so that was definitely an issue. After replacement, there is no more fuel leaking, but I know that doesn't necessarily mean that air isn't leaking.

I also installed a check valve by the tank, because the onboard generator, that shares the same fuel pickup with the engine, was drawing air back through both engine filters. There is a check valve in each supply line now, and running the generator no longer pulls air back through the primary or secondary filters, so I don't think my air issue is on the supply side of the fuel pump either.

What I don't know, is that there is a hose that runs from the #2 injector cap to what they call a "bleed orifice elbow" on the filter head. I assume this is to bleed off air in the filter head similar to what is done on certain idi equipped ford trucks. This elbow is on the outlet of the secondary filter and is connected to the line that supplies fuel to the injection pump. My question is this. Is this "air bleed elbow" nothing more then a metered leak from the fuel filter, or is there a check valve of some sort in there similar to what is found on the 7.3 filter head?

I'm thinking that it's supposed to be some sort of check valve, otherwise what would prevent that from letting air from the return system into the filter head when the engine isn't running?

So IH experts(if there are any here) what say you? I'll eventually figure this out come spring time, but I figured we could discuss it before then.

*I'm not installing an electric or eliminating the mechanical lift pump. I considered installing a smaller cube type primer pump parallel to the mechanical pump, or installing a different filter head equipped with a primer pump, but I'd rather fix my issue then mask it with either of those option.
 

riphip

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This is just one of the reasons I & others have moved to electric fuel pumps. The IHC 6.9s are basically the same with maybe different filters, IP, exhausting & accessories, etc
Check valve will have to be added, not a factory supplied item.
 

chillman88

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Check valve will have to be added, not a factory supplied item.

Actually he's referring to the line that goes from the filter head to the injector return lines. On at least the 7.3 there is a check valve built into that hose barb. Might not work reliably, but it is there.
 

TahoeTom

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Another source of air intrusion can be the "olives" at the hard line ends. They are like a short section of fuel line compressed by the fitting. There are olives in the line from the filter to the IP and at the fitting at the back of the engine where the return line goes back to the tank. I think there may be 5 total of these. If your O-rings were bad chances are you need to replace some olives. You can source them from McMaster Carr, or some of our vendors here offer return line kits that include them.
 

Cubey

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If your O-rings were bad chances are you need to replace some olives.

Hard to say. My RV's injector o-rings were no olives are leaking (yet). I carry a set I bought for the F250 but never put in, since just loosening and retightening the fuel supply line at the IP with a bad olive (or a self loosening line) once a year always solved the problem, the two times I found it leaking and causing air intrusion. By no means a permanent fix, but it stops the air intrusion instantly, so it's easy to ignore for another year.
 

hce

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I would bet the bleed orifice is just an orifice, check valve would only be needed to mask for another problem.
Is there a return on the generator, is hooked into the engine return?
The electric fuel pump comment got me thinking. How many mechanical lift pump have been replaced by electric when it was the lift pump causing the air intrusion. Really there is no better component on these engines that could allow air in with little to no diesel being leaked out. A thin 3 inch rubber diaphragm sealed on the perimeter then also steel plate on either side in the center riveted together though a hole. One whole side of that diaphragm is exposed to the atmosphere through that 1/4" weep hole.
Also check that the return is submerged in fuel.
 

Booyah45828

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Actually he's referring to the line that goes from the filter head to the injector return lines. On at least the 7.3 there is a check valve built into that hose barb. Might not work reliably, but it is there.
Yeah, there is definitely a check valve on the Ford 7.3. I replaced one once that caused a similar situation as to what I'm having. Clear hose showed the situation, which is something I'm likely going to try.
every IDI needs a fuel pressure gauge on the filterhead IMO
That's in the plans.
Another source of air intrusion can be the "olives" at the hard line ends. They are like a short section of fuel line compressed by the fitting. There are olives in the line from the filter to the IP and at the fitting at the back of the engine where the return line goes back to the tank. I think there may be 5 total of these. If your O-rings were bad chances are you need to replace some olives. You can source them from McMaster Carr, or some of our vendors here offer return line kits that include them.
I didn't think about that, I'll have to check those out.
I would bet the bleed orifice is just an orifice, check valve would only be needed to mask for another problem.
Is there a return on the generator, is hooked into the engine return?
The electric fuel pump comment got me thinking. How many mechanical lift pump have been replaced by electric when it was the lift pump causing the air intrusion. Really there is no better component on these engines that could allow air in with little to no diesel being leaked out. A thin 3 inch rubber diaphragm sealed on the perimeter then also steel plate on either side in the center riveted together though a hole. One whole side of that diaphragm is exposed to the atmosphere through that 1/4" weep hole.
Also check that the return is submerged in fuel.
The generator tees into the pickup and return for the engine. The fuel return is submerged in the tank? I was under the impression it wasn't. I'll have to look at the generator fuel system to make sure it's return isn't leaking air and causing the problem.
 

IDIBRONCO

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The generator tees into the pickup and return for the engine. The fuel return is submerged in the tank? I was under the impression it wasn't. I'll have to look at the generator fuel system to make sure it's return isn't leaking air and causing the problem.
The way that the generator is hooked into the fuel system sounds like trouble to me. It may have been the easy way to do it at the time, but I think it would cause issues down the road (like maybe now?). If it was mine, I think I'd probably give the generator it's own fuel tank. That would ensure that a fuel issue with the generator couldn't affect the truck engine.
 

Booyah45828

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The original plan was to install a separate pickup/return in the tank for the generator. I plumbed it to share pickups/returns just to see if it would work. It did great for a year or so and then spring last year it had trouble, sucking the engine fuel filters dry and then the return caps all leaking.

The tank on the bus is like 80 gallon, and having the generator draw from the same fuel source was the one of the main goals for the generator. I'm not installing a separate tank for it. If the worst comes to the worst I'll go ahead and install separate pickups and returns. It's just odd that it worked trouble free originally.
 

IDIBRONCO

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If the worst comes to the worst I'll go ahead and install separate pickups and returns. It's just odd that it worked trouble free originally.
That would be my second choice. Maybe something at a T worked itself loose enough to let some air in? Maybe something shrank slightly in the cold?
 

dgr

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Why can't you have a small enough leak on the supply side of the fuel pump to suck air but not leak fuel? Placing a check valve in that line is going to lower the flow available for the mechanical pump.

Put a clear line on the return to the filter head and look for bubbles. Then plumb from a 5 gallon can to the supply side of your fuel pump, run until no bubbles, shutdown and come back the next day and see if you've got air intrusion.
 

Booyah45828

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That could be possible, and if correct, will be found with clear hose come spring time.

The check valve is 3/8 npt, has a flow coefficient of 1.6 gpm at 1 psi. That's more then what the stock pump is supposed to flow, So I'll assume it's not a restriction. Fuel pressure at the filter head will tell the tale though. This is it here. https://www.mcmaster.com/7768k69

It might have made a small difference in fuel pressure, only a gauge and a before and after would tell though. It seems to run about the same before and then after. I thought the pitch might have changed slightly but that might just be my imagination.

If I find that there isn't air on the supply, then the next step is putting the return in a 5 gallon bucket to see if it's leaking air on the return side.
 

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