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Hi, I have a 1994 F350 7.3L IDI turbo with 125,000 miles.

Runs great except for starts when warm. IE. I start it cold and it starts fine. gives a quick puff off white smoke and idles nice.

If I drive it for say 20 minutes and then shut it off and let it sit for an hour or two, it will start up but idle rough and produce a bluey white smoke. It helps if I give it some fuel. It will then even out after 10-15 seconds and run fine. This issue has slowly been getting worse the last few months.

I've had the truck for three years now and tow a fifth wheel with it. Power still seems fine, even when pulling the load.

Anyone else seen this problem?
I'm thinking maybe it is a wearing out Injection Pump?

Thanks Ray
 

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I had a very similar problem as you described and what it turned out to be was a clogged filter in my Racor water separator unit. The engine would start up fine cold, and run well all day, it was only sometimes after starting it up when it was warm it would run rough for 10 seconds. The most likely cause of the problem you described is that either the fuel system is sucking in air somewhere or you have a clogged filter or some other type of obstruction limiting the flow of fuel.

My theory about why you could have this symptom only when warm is that when the engine is cold and the fast idle is engaged, it keeps the engine running at a speed where it's not going to run rough at all. I have never had my truck run rough when the fast idle was on. When you start the engine warm, it is going to be running at its normal idle speed and at that idle speed is where it tends to run rough like that. If you ever have the engine start running rough, just by putting it in neutral and and giving it a tiny bit of throttle tends to clear it up.

When I was having the type of trouble that you described, I did an experiment, and that was to start the truck cold without the fast idle engaged. Interestingly, it started running rough right away, which it would normal never do if the fast idle was on.

Before worrying about your IP, check for any air intrusion in your fuel system, make sure if your fuel filter is old to change it out. That can also be a problem with the injectors as well, but like I said, check for the simple stuff first.
 

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Thanks for the advice dieselnoob4, appreciate it.

The fuel filter was replaced about 4000 miles ago. But is suppose something could be clogged, we are snowbirds and travel quite a bit filling up at many different fuel stations, some in tiny towns. I wonder sometimes about the quality of the diesel. I think I'll try a few tanks with an diesel injector cleaning additive.

Thanks Ray
 
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