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My truck, 99 F-250 SD 7.3 PSD, has been doing this surging/misfire since I bought it in October of last year. It only does it when i'm at a steady speed going down the road. It tends to get a little worse when I come to a slight grade also but if I give it more fuel or back out of it a little it goes away. I also have a superchips programmer and the higher that I put the settings the worse it gets. Other than this issue the truck seems to run great and has plenty of power for whatever I want to do with it. There is no check engine light or codes stored in the computer. I did a buzz test, with a scanner at my work, and they all sounded normal. I also tried to do a cyl contribution test but for some reason it wouldn't do it.:dunno: Wondering if anyone has ever run into this before or might have an idea on where I should be looking. I was thinking of getting a fuel pressure gauge and watching that going down the road..What is a normal fuel pressure reading for a truck like ours.. Thanks
 

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Normal fuel pressure is 58 psi, doubt that’s your problem.


Just some wild guesses;

Could be a loose or faulty IPR (injector pressure regulator) I’d make sure the solenoid is snug and/or remove it and check the O-rings. You can also watch the ICP (injector control pressure) with the scanner.

Also could be the gas pedal, You can watch it with a scanner and/or remove it and soak the pot and micro switch on the back of the pedal with WD-40.

Might could be the UVC (under valve cover wiring harness and valve cover plugs) but they usually don't last a long time without getting worse after they first start acting up.

Also just might be the CPS (cam position sensor) I keep a spare with me all the time, cost $20, easy to change so I always try that when I have run-ability problems.
 

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Does it only do it in a certain rev. range? Could be turbo surge. Usually happens around 2000 - 2200 rpm. What other mods do you have?
 

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I believe 10/98 would be considered an early 99 so it should have the wicked wheel in the turbo from the factory so it shouldn’t have much turbo surge unless chipped out pretty hot.
 

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Discussion Starter #5 (Edited)
Normal fuel pressure is 58 psi, doubt that’s your problem.


Just some wild guesses;

Could be a loose or faulty IPR (injector pressure regulator) I’d make sure the solenoid is snug and/or remove it and check the O-rings. You can also watch the ICP (injector control pressure) with the scanner.

Also could be the gas pedal, You can watch it with a scanner and/or remove it and soak the pot and micro switch on the back of the pedal with WD-40.

Might could be the UVC (under valve cover wiring harness and valve cover plugs) but they usually don't last a long time without getting worse after they first start acting up.

Also just might be the CPS (cam position sensor) I keep a spare with me all the time, cost $20, easy to change so I always try that when I have run-ability problems.
Okay i'll have to hook the scanner back up and have a friend ride with me so I can watch that stuff. Thanks.. :thumb:
I just had the cam sensor changed under the recall about a month or so ago and it made no difference..
 

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Discussion Starter #6 (Edited)
Does it only do it in a certain rev. range? Could be turbo surge. Usually happens around 2000 - 2200 rpm. What other mods do you have?
It dosen't matter with speed or RPM's. It will do it pretty much at any rpm as long as i'm at a constant speed... I have also been rolling at 55mph in OD and it started doing it so as another test I hit the OD button to turn it off but it didn't make a difference either.

The only mods I have is the superchips programmer that came with the truck and I eliminated the muffler, plus a boost gauge but thats not really a mod. I also replaced the torque converter about 4 months ago because it was making noise. Everything else is stock as far as I know. O ya I changed the fuel filter not too long after I bought it, mainly because the seal was leaking and also partly because I was hoping that might change something, but it made no difference either.
 

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Any fluctuation on the boost gauge when it acts up, or does it remain steady?
 

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Fuel filter should be changed every 8-10k miles. The main gauges to have are the EGT and the tranny temp. I think I would invest in adding those gauges before it winds up costing big dollars in repairs. Even the SCMT you have needs to be monitored with gauges.


You know, on second thought fuel pressure could cause concerns that lasted a long time if you got a crappy load of fuel and partially clogged the system. I have a fuel pressure gauge in the cab but if I didn’t then I’d probably check that too, just make sure you rig a gauge so you can check it under load at highway speeds. Wish you lived closer, we could spend a couple hours with a scanner and some gauges, I love troubleshooting equipment lots more than working on it.
 

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It is possible there is a bad spot in the throttle potentiometer. If it doesn't do it with the cruise that could be your problem. Just a thought.:: Edit:: sorry just saw that was addressed in the second post.
 

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I am experiencing the same problems.....steady speeds = fluctuating rpm's/turbo??? guages don't move, happens at any speed as long as it is steady...

What is really weird is that one day it will happen alot and the next day it won't flutter at all?:dunno:

Any help would be great.
 

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Try changing the oil. I ran Rotella synthetic in mine for awhile and it started doing that. After lots of arguments finally changed back to dino oil and it quit doing it. Till recently, it has been ever so slightly starting again, running valvoline blue at present, it it gets worse, the first thing I'll do is change oil maybe try that new Castrol. Mine has 260,000 miles now, had about 190,000 the first time it started doing this. Also just had CPS recall performed, no change. Mine is also throwing code P1298.
 

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if you change your ipr orings your problem will go away i almost bet on it.if the orings are even a little bad it will make your truck idle bad and miss.the ipr is a regulator for the injector pressure just call ford and they sell a ipr oring kit for like 40.00
 

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All it would take is to be able to watch the ICP whilst it’s doing it with a scanner. With that many miles if it were me and if I didn’t have my Predator then I’d just change the IPR o rings and hope for the best. I think they even sell kits on eBay.
 

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ipr location

sorry to but in but where is the ipr located, i'm having some rough idle/hard cold start issues and can't find the ipr in the chilton's manual anywhere. thanks in advance!
 

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Located below and behind the fuel filter slightly to the drivers side. It has a large tin nut that holds the solenoid on it.
I got a complete Ford factory service manual on eBay for $12, its great and I recommend getting one, everything is in there. Just make sure it’s a factory manual and not an aftermarket generalized manual.
 

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Located below and behind the fuel filter slightly to the drivers side. It has a large tin nut that holds the solenoid on it.
I got a complete Ford factory service manual on eBay for $12, its great and I recommend getting one, everything is in there. Just make sure it’s a factory manual and not an aftermarket generalized manual.
Just to add, it is mounted in the HPOP housing, below where the hpop lines connect.



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