7.3 IDI Non Turbo- Only Front 2 Injectors getting fuel?? - Diesel Forum - TheDieselStop.com
7.3L IDI Diesels (Not Power Strokes) Technical discussion of topics related to vehicles powered by the 7.3 Liter In-Direct Injection Navistar engines.

 
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post #1 of 14 (permalink) Old 08-30-2019, 06:51 AM Thread Starter
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Unhappy 7.3 IDI Non Turbo- Only Front 2 Injectors getting fuel??

I picked up a 1991 F250 with the 7.3 IDI, I am familiar with diesels and have owned multiple 12v Cummins which seems relatively similar. The truck I was told was a daily driver then one day it just wouldnt start, turns over just fine but wont catch. Bought it cheap and have researched A LOT and swapped out many parts, new fuel line from tank to new lift pump, bypassed filter housing directly to new (remanned) injection pump. The motor as always still turns over very smooth but since I swapped out the new IP only the front 2 fuel lines are getting fuel to bleed then the back 6 are dry no matter how long i turn it over or let the LP prime. Very weird and after all this I am just baffled as to what would cause this No fuel/only fuel to select cylinders...Any help would be Awesome
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post #2 of 14 (permalink) Old 08-30-2019, 04:27 PM
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I would take the IP to a rebuild shop, and have it tested for output. It sounds like something isn't right there.

1993 F-350 crew cab non-turbo 5 speed transmission
35 years a mechanic on large stationary engines natural gas and diesel fired, and other industrial equipment.
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post #3 of 14 (permalink) Old 08-31-2019, 06:21 AM Thread Starter
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I dont think at this point it is the pump ( plus if there was a shop around me that would work on it I would have brought i tto them a long time ago) so the IP that was in it I assumed was bad, I got a spare "running" motor with the truck so first thing i did was swap the pumps from that one and it did the same thing that this new Re-manned one is doing now only fuel to the front 2 injectors which is why it seems like it is something else I am missing
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post #4 of 14 (permalink) Old 08-31-2019, 11:45 AM
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Do you have enough flow to the IP? The only thing between the filter and the injectors is the IP, it is what delivers to the injectors under pressure. Nothing going through the injector lines means nothing coming from the pump. The only thing that would prevent that would be supply to it. The fact that it gets fuel to the front two means that it should be going to the rest of them...unless it isn't getting enough fuel to supply it. Fuel shut off valve maybe not opening up all the way, delivery pump weak, supply to the delivery pump restricted. The only thing common to two pumps would be on the supply side. Maybe start by checking fuel pressure at the filter (Schrader valve) should be around 4 PSI with a good flow. Mine will fill a pint jar in maybe 30 seconds. Doesn't take it long. I would make sure I have good flow all the way to the IP. If it has good flow then the only thing left is the IP itself. At that point I would check the fuel shutoff and make sure it operates the way it should, any deeper than that I would go to somewhere to get it rebuilt, or find somewhere reputable to get another one.

1993 F-350 crew cab non-turbo 5 speed transmission
35 years a mechanic on large stationary engines natural gas and diesel fired, and other industrial equipment.
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post #5 of 14 (permalink) Old 09-01-2019, 08:35 AM Thread Starter
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I thought the same thing, so currently the setup is filter housing completely bypassed so fuel hose straight from LP to IP, have tried pulling fuel from tank And from a 5 gal bucket. The pump is new so assuming everything works on it the pump shoudnt be the issue and a did check the FSS just incase. But same thought if 2 fuel lines are getting fuel the rest "should". It could possibly be the LP but again that is also brand new and rated for bigger engines, I believe somewhere around 75gph and 7+psi.
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post #6 of 14 (permalink) Old 09-04-2019, 08:42 PM
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It sounds like you are running an electric delivery pump. You say the pump will put out 75 GPH @ 7 PSI That is a lot, way too much for an engine that takes about 4 hours to use 40 gallons @ 4 PSI. If that pump has a built in relief valve, it might be relieving and not getting a low enough pressure to reset...no or very little fuel out its discharge until it does. It might help to get a smaller pump, or go back to the old mechanical one that is mounted on the passenger side block, and driven by a camshaft lobe. Same pump that the old carburated engines used. You can also build a bypass and regulate it so that it maintains about 4 PSI back pressure to the filter, and only lets out enough to maintain that pressure. A lot of trouble when you can get another electric pump with the proper pressure and flow on Amazon for around 12 bucks

1993 F-350 crew cab non-turbo 5 speed transmission
35 years a mechanic on large stationary engines natural gas and diesel fired, and other industrial equipment.
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post #7 of 14 (permalink) Old 09-05-2019, 10:07 AM Thread Starter
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Well its might be a bit high I think its like 5-7psi but the filter housing has pressure gauges on it and they read about 5 psi getting to the filter, it wasnt just some pump that i thought sounded good it was one that was recommended by someone else with the same engine. But if you have another pump i should try cheap that you can link me i will definitely try it because im out of options
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post #8 of 14 (permalink) Old 09-05-2019, 05:16 PM
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What happens when your existing pump hits that 5 PSI? Does it stall out, or does it keep on running? If it stalls out then look elsewhere for your trouble, if it keeps running, then there is a relief valve that might be causing your trouble. What kind of flow are you getting @ the injector pump? Not just at the filter, down the line to the IP itself. Are you still running the steel line with the rubber ferrules, or did it get changed to a hose? If it is a hose, it could be peeling on the inside and causing a serious restriction.
The link I spoke of earlier is amazon.com search electric fuel pump. They have a whole lot of choices. A fuel pump that would work on an old carburator is all you need. They used to use them all of the time when they changed their engine over to run the Holley double pump carb. for racing (flooding) purposes. Overkill sometimes hurts, as bad as under-kill

1993 F-350 crew cab non-turbo 5 speed transmission
35 years a mechanic on large stationary engines natural gas and diesel fired, and other industrial equipment.
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post #9 of 14 (permalink) Old 09-06-2019, 05:51 AM Thread Starter
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The setup the previous owner had was a gauge on the front side of the filter coming in and a gauge on the back side of it going out to the IP so both gauges usually read about the same while cranking i believe around 5ish psi. The pump does "bog down" when in seems the system is primed but does not stall out it keeps running, and yes still a steel line from the filter housing to the back of the IP and all the fuel lines up to that point are new.
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post #10 of 14 (permalink) Old 09-06-2019, 05:09 PM
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Then the only thing left is the IP. I hate to say it, but new/rebuilt doesn't necessarily mean good. It might be the metering valve stuck, but I would hesitate to go that deep without a way to bench test it. Runaway engines are NOT a pretty sight.

1993 F-350 crew cab non-turbo 5 speed transmission
35 years a mechanic on large stationary engines natural gas and diesel fired, and other industrial equipment.
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post #11 of 14 (permalink) Old 09-07-2019, 07:22 AM Thread Starter
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Right and its not that it couldnt be but the thing that throws me off is the way things went down is, the IP that started on the truck was told it was a daily driver then one day they went to start it and it would only turn over. I replaced the LP before swapping it and was able to bleed all 8 fuel lines. Still wouldnt start thats when I swapped it out for the Spare IP and that one only let fuel to the front 2 injectors. With that i assumed O this IP must be clogged or bad, thats when i ordered the Remanned and now this remanned is doing the exact same thing...
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post #12 of 14 (permalink) Old 09-07-2019, 11:24 AM
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Do you still have the one that put fuel to all 8 cylinders. If you do, then put it back on, and test all of the glow plugs. Glow plugs will make it not start, sometimes even in the summer time. Old engines with lots of wear will still run fine, but they need a little help starting....just don't use ether for that help.

Send the reman one back and tell them it only gets fuel to two cylinders.

1993 F-350 crew cab non-turbo 5 speed transmission
35 years a mechanic on large stationary engines natural gas and diesel fired, and other industrial equipment.

Last edited by oldrebuiltdodge; 09-07-2019 at 11:26 AM. Reason: addition
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post #13 of 14 (permalink) Old 09-08-2019, 06:37 AM Thread Starter
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Yes I sent in the other one for the core swap, is there a simple way to bench test not to check pressure through the pumps but just to see that fuel is coming out of all 8 lines? I had an idea but im just not 100% sure it would work. Also do you think it is the injection pump it seem to coincidental that 2 pumps back to back did the exact same thing.
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post #14 of 14 (permalink) Old 09-08-2019, 10:46 AM
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If it has fuel in it, and you rotate it by hand, it should give a little squirt at each port. It is after all just a fancy positive displacement pump.

1993 F-350 crew cab non-turbo 5 speed transmission
35 years a mechanic on large stationary engines natural gas and diesel fired, and other industrial equipment.
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