7.3 hard to start under 1/4 tank? - Ford Powerstroke Diesel Forum
7.3L IDI (Non-Powerstroke) Diesels 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 17 Old 01-31-2010, 09:36 PM Thread Starter
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7.3 hard to start under 1/4 tank?

I have a 90 7.3 I use for my work truck, it's a great running truck..... Except A couple months ago I noticed it chugged and reved up when I started it. Thought that was kind of weird, drove it that day and went to went to start it the next morning, it started then died. I cycled the plugs and cranked on it and it finally started. Now the truck had just under 1/4 tank of fuel. I filled it that day and it started fine the next moring and did so until it got down around 1/4 tank again. Once it starts it runs fine and starts all day untill it sets. The IP was rebuilt 4yrs ago, I run off the front tank only as the rear tank leaked when I got the truck and I haven't fixed it yet. Any input I'm wondering if it has a check valve inline somwhere, maybe pickup tube?
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post #2 of 17 Old 01-31-2010, 09:39 PM
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Sounds like you got some gunk in the tank maybe... I don't really know these older motors though.

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post #3 of 17 Old 02-01-2010, 06:55 AM Thread Starter
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I would of thought that but it is so consistent, I've had it under a 1/4 tank numerous times and that is when it happens. I changed the fuel filter last oil change it didn't change it at all. I'm wondering if it has a check valve somewhere and when the fuel level gets low it loses prime?
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post #4 of 17 Old 02-01-2010, 07:05 AM
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No, it will run the tank bone dry... im wondering if your fuel pump in the tank is getting weak.

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post #5 of 17 Old 02-01-2010, 11:52 AM Thread Starter
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It has a mechanical lift pump on the block, that was the first thing I replaced. Forgot I did that until I read your post, I was thinking maybe it had a hole in the diaphram or just weak like your saying. It's more like the injector pump has fuel, it starts then dies and you have to crank it for awhile before it fires. Once it starts it belches for a second clears up and will run fine and start perfect the rest of the day. Anything over 1/4 tank it starts perfect even in 20 degree weather, so I know my GP's are good?

Thanks for the help, giving me different angles to think about.
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post #6 of 17 Old 03-19-2010, 08:26 AM
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same problem as you?

hey man wondering if you have figured anything out on your truck yet? Mine seems to be doing the exact same thing. I have a 94 idi. I am thinking its a leaky return fuel line on mine that was causing it to lose prime after sitting for a while, but didnt know if you were able to diagnose anything on yours that might point me in the right direction.

thanks
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post #7 of 17 Old 03-20-2010, 04:33 PM
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A lot of times the fuel pickup tube in the tank will break off around the quarter tank mark. So it cant suck up any fuel past a quarter tank cause it doesnt go down far enough. Only way to tell is to pull out the sender/pickup assembly and inspect.

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post #8 of 17 Old 05-15-2010, 01:53 PM
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This is an older thread BUT Justin is 100% correct. I write this to help those that may do a search!!!! I spent a year fussing with this issue on my 94.....

Pull the sending unit out. Fish all the broken pieces out (Be thorough, if not this will haunt you down the road at -30F in South Dakota in a Blizzard, ask me how I know). Put some rubber hose on the end. Cut a v in the end to avoid sucking on the bottom of the tank and replace the sending unit. It not hard.

Thad

PM me with questions. I removed the sending units several times and can guide you throught the process if you desire!


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post #9 of 17 Old 05-17-2010, 08:59 PM Thread Starter
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Thanks for the tip Dakota I'll pull the sending unit, I still haven't even messed with it yet. I do have a question if the pick up tube is broken why will it still run under 1/4 tank it just won't start after it has sat awhile unless I crank the hell out of it?

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post #10 of 17 Old 05-17-2010, 10:04 PM
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it may not be broken all the way, but it may have a small hole in it, small enough to allow it to work, but large enough to give you problems. alllows air to enter the system until a strong enough vac is pulled.

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