Fuel surging problem - 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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Old 08-14-2010, 12:21 PM
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Fuel surging problem

I have a 94 IDI with factory turbo that is surging just after take off. Say when i take off from a light, with average acceleration its like the throttle is mashed to the floor for just a second. It only does it shortly after take off. The other thing that happens since this first started is a rough idle. But only very occasionally. If i tap the throttle it goes away.
I originally thought it was the trans prematurely down shifting, but i can get it to do it In the driveway in park. I rev it and about 1500 rpm it spikes, but only for a second or two. Not WOT just a bout 500 rpm's or so more.
Its freaky when you pull out somewhere and it just takes off on its own.
I've owned the truck for about 6 months now and after a little work here and there it runs great. Other than this new problem.

The last owner gave me receipts for a tranny rebuild and injection pump. Im not sure the tranny was rebuilt, but the IP looks new. On the other hand he lied to me about several other things. He said it had all new glow plugs, brakes and injector o-rings. Glow plugs were shot, O-rings were shot and the brakes were only new on the driver side. LOL I did new glow plugs and orings with New caps and hoses.
Im a pretty good mechanic but have limited experience with diesel's. So im learning as i go here.
Any thoughts???
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Old 08-14-2010, 07:18 PM
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Based on my experiences with these engines, I would say that its a fuel delivery issue combined with an air intrusion issue.

Mine would do this when it was slightly starved of fuel. It would rev high for just a second or two until the fuel was fully flowing again.

What you should do is check the fuel return lines since they are a known culprit for air intrusion. Its not a bad idea to just replace them all anyway UNLESS it was recently done. Its not very expensive and you can pay someone to do it if you arent confident in yourself to not screw it up.....its really about as easy as changing spark plugs....not real hard.

Besides this check to make sure your lift pump is functioning properly.....might not be keeping up the demand if it is failing. I think it is more than likely the return lines (at least I would bet $100 it is)

Thad
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Old 08-14-2010, 08:17 PM
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Just to clarify, Your referring to the rubber hoses that run between the injectors correct? If so I have replaced all those along with new plastic caps and o-rings.

In the meantime i will do some research on how to check the pump.
Thanks for your help....
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Old 08-14-2010, 10:38 PM
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Alright, I am guessing now that your engine mounted fuel filter is losing prime somehow......I would check the pump first though. I cant remember the procedure for checking the pump. You disconnect the fuel line running to the filter head, route it to a jar and have a buddy run the starter. But I dont remember off the top of my head how long to run the starter and how much fuel should be in the jar......

Thad
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Old 08-17-2010, 07:43 PM
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Your air intrusion comment got me thinking. I recently switched to the rear tank and have ran it down below 1/8 tank of fuel. I have never ran either tank that low before. This is the first time i've used the rear tank at all.

Yesterday i moved it and it would barely run. (on the rear tank). Today i took it to fuel it up and switched to the front tank which has about the same ammount of fuel. Ran fine to the fuel station, filled the front tank and not the rear. Drove it to a couple places on the front tank and never had an issue. On my trip home i switched to the rear tank and had the surging a couple times. Switched back to the front and it only did i 1 more time. Im guessing residual air from the other tank.

I need to drive it around some more to make sure its only doing it on the rear tank and not just a fluke, but it may just be the pickup tube or the fuel switch.
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Old 08-17-2010, 08:14 PM
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WOW! I cant believe I missed that! Epic failure for me.

These rigs are extremely prone to having issues when below a 1/4 ish or so of fuel. The problem is that the end of the fuel pickup tube in the fuel tank is shaped like a shower gead. They are plastic and get extremely brittle over time and break/shatter into a million pieces.

So there are two options:

1. Keep it above 1/3 or so of fuel in the tanks or

2. Drop the fuel tank, remove the pickup tube from the tank, clean out the pieces of the "shower head" and put a piece of fuel line on the end to ensure you can get fuel from the bottom of the tank. I recommend that you cut a v ito the bottom of the tank to ensure the fuel hose doesnt suck on the bottom of the tank. I put some screen on the end also to prevent large particles from getting into the fuel. (I am pretty adament on putting screen on the fuel hose.....read below why)

When this happened to me I tried to get most of the pieces out of the tank but wasn't as thorough as I should have been. This came back to haunt me for a year or so. Since originally I did not put any screen on the fuel hose I used it sucked the pieces of the "shower head" that I missed and clogged up my fuel tank selector valve (FTSV) and caused a fantom fuel starvation problem that left me stranded several times in the middle of the midwest. Not fun when there is a blizzard and its well below zero outside. I replaced one FTSV only to have more fuel issues. Eventually I bought another FTSV and put screen on the end of the fuel lines that I put on the fuel pickup tubes.

Basically, I wasted tons of time, money and frustration on something that could have be prevented by spending five minutes and $2 dollars on.......really frustrating.

The point is do it once and do it right.

I am absolutely certain that your problem is the pickup tube. From presonal experience if you can take the bed off the truck since it gives you better access to the tanks and doesnt include laying on the ground.

Thad
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Old 08-21-2010, 11:40 AM
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Just to update. I've run around a little more on the front tank with no issues at all. So im positive its the pickup tube. I still havent pulled it to fix it yet, but i will do that soon. I plan to add a screen too.
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Old 08-21-2010, 06:10 PM
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Sweet! Again I recommend removing the bed if you have a come along or two to use as a hoist. Otherwise its a pain.....I have done it both ways.

Thad
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