I have a 200,000 mile 1996 ford F250 with the PS 7.3. The truck was running perfectly. While driving it a few days ago I noticed an immediate rough running motor, and at idle it was like a gasser missing on one or two pistons. It will barely start. Runs really rough. I drove it for about 2 miles and it did not clear up. It barley starts, runs terrible and can hardly be driven.

To complicate this matter a bit, I have only had the truck for a week. Old owner did supply much information on past repairs and has no idea why it would be running rough. It was running perfectly when I picked it up.

Here is what I know:
Hooked up scanner and there are no codes. It is clear
No check engine light
Fuel pump was replaced about 60K ago
Fuel Filter was replaced about 10K ago and still looks good
Engine oil is clean but was supposed to be changed about 3K ago, looks to clean for a diesel.
Oil pressure appears normal
There is a faint smell of diesel but I cannot see any leaks or fuel sitting on top of the block
CPS was replaced at 150K
After running the truck, although I dont do it for long with it running so rough, there is a very faint air hissing noise near the top of the motor. Not sure exactly where it is coming from.

The truck as 2 fuel tanks. I did switch to the front tank and ran fuel through it over the last few days. It has well over 50% left in the tank. Was running on the rear tank when I bought the truck.

I think its fuel starved, and have not checked fuel pressure yet. I don't have a gauge and I am not sure of an easy way to test fuel pressure from the pump to the injectors or if I should also be looking at the push from the tanks to the fuel pump up front.

What I think should be done (but of course asking for your assistance), is to check the fuel pressures with a pressure gauge. Looking for help here on how to get this accomplished.

Check for any noticeable leaks.

Maybe change the oil to a known diesel oil to make sure there is no issues there? (I cannot see this being an issue, the guy I got the truck from was particularly good about using Rotella for the oil changes).

Any help for this beginner is greatly appreciated. -

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and seconly do a injector buzz test sound like an injector going out -

hotcummins's Sig:

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Yeah... I thought the same on the injector. But I would hope that there would be an error code for the injector. Heard I should pull the valve covers and unplug one at a time to find the faulty one.

I know the ford harness can be disconnected outside the valve cover, but that would kill 2 injectors I think... -

what kind of scanner did you use??? most generic scanners wont pick up the codes on our trucks....

you can hook a temporary gauge into the back of the fuel filter bowl on top of the motor... should be 55-75 psi at idle...

if you smell fuel out of the engine bay, check closely for leaks... that very well could be your problem.... a tiny bit of air can really cause a problem.... my truck was leakin around the filter cap and was causing a real rough idle when cold....

check there before you start pullin Valve covers or injectors... oh when you disconnect the harness on the outside of the VC, it shuts that whole bank off... it will still run but your problem will be worse feeling...

also, get the truck up to operating temp and run a Buzz test and a cylinder Contribution test... then report back... -

blk99's Sig:

early 99 CC LB Dually 2wd, slush box, PHP Tunes, late 99 conversion, AD's, Termy modded 17* hpop and Termy Scan Gauge, exhaust brake, little bit bigger IC, gauges, intake, exhaust with 6" tip, and some other stuff that is irrelevant........ oh yea and it has 480K original miles...

this is going to sound odd but call the ford dealership. i have a 97 and there was a recall on the cam position sensor. i dont know if your truck falls into the recall range but if it does this could be your problem. remember recalls are free!!!! mileage does not apply. i took mine in at 145k. a phone call is free and if it is your problem they might tow it for free. i work at an acura dealer and we actually have to tow cars over 800miles sometimes. -

I assume you don't have a fuel filter light coming on. Could be a valve cover gasket or the pig tails running from there to the injectors. I agree to start with an injector buzz test. A professional scanner will do that well. -

robammerman's Sig:

1996 Ford F350 4X4 4dr long box. Bully Dog Six Pack chip, Stage II injectors, hybrid turbo, retrofitted 6.0 intercooler, Bank 4" turbo back exhaust, K&N intake, Snow Performance Stage 3 MPG max, South Bend clutch, 4.10 gears and a spool in the rear. 247,000 miles.

This is a little late, but thought I would post an update at this point.

the truck is back to running very well. I did get a preasure tester and tested off the shraeder valve just left on the left side of the fuel bowl. (not sure if that was the correct place). Was getting 12PSI at idle and 40PSI+ at WOT. after about 2-3 tests, the truck suddenly started running right again. (I also replaced the fuel filter for the heck of it and made sure the surfaces where clean at the fuel filter gasket area and threads.)

I also changed the oil to make sure that was not an issue, but after the truck was running better.

It seems there was air in the lines, fuel system. I think it has something to do with the dual selector between the 2 tanks... Checking that out this weekend.

I do have a new fuel pump, but wanted to do a bit more testing before spending half a day changing it out.

Thanks for all the advice again... I am really getting to know the 7.3 quickly! -