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Studded/miss/slip from 65mph and up

P

PSnewbie

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Mountain Home Idaho
So I bought a truck today. 1999.5 f250 7.3 and that should be studded not studded. Took it in the freeway but was only able to get upto 60 due to construction. So on the way home and out of town when I got to about 65mph the truck started to lurch really hard kind like it was shifting down then back up. Tach does not flutter. And when I get to over 75 it calms down but can still feel a tiny slip or lurch I don't know how else to describe it. Kinda worried I bought a lemon now. Runs fine other than that. Any help would be awesome and appreciated.
 
I'm not too sure really. Really just hoping to get a couple ideas of what it could be. But being that it only happens above 65 mph I'm not sure how fuel delivery would cause it. But I'm new to owning a diesel so im very open to whatever anyone suggests
 
Try putting it in 3rd and see if the problem still happens at the same speed, or if it follows engine RPM. This will help to isolate the problem to engine/trans or drivetrain.
 
By fuel delivery, you need to get a fuel pressure gauge (that also reads vacuum) on it just before the Injection pump. There might not be enough pressure at that load. If you get zero or a vacuum when it occurs replace the fuel filter(s). If it still occurs- replace lift pump.
 
Will L. said:
By fuel delivery, you need to get a fuel pressure gauge (that also reads vacuum) on it just before the Injection pump. There might not be enough pressure at that load. If you get zero or a vacuum when it occurs replace the fuel filter(s). If it still occurs- replace lift pump.
Click to expand...

Theres no injection pump on a 99.5 7.3L. Fuel filter is a possibility, but it would rear it's head under load more so than at a steady cruise. It uses somewhere around 50-75 PSI fro mthe electric supply pump that feeds the fuel passages in the heads, a high pressure oil pump that supplies upwards of 2500 PSI high pressure oil to the injectors, and the electric solenoid that fires the injectors. HEUI is an oddball injection system IMO.
 
Also I went out and started it today and it ran fine for about two minutes. I gave it a little bit of gas and then it started to idle very rough and sounded like it was going to die so I shut it off. I tried to restart it and it took about ten seconds for it to start. And even then it ran rough. Boy I sure hope I didn't make a mistake with this truck.
 
Sounds like a high pressure oil control issue to me. There is a solenoid thta controls the high pressure oil pressure, and when it goes it will do all kinds of wierd things. I think they call it the IPC valve.
 
It would cause it to be hard to start, and idle rough. If the high pressure oil pressure is off, it will cause all kinds of problems with the way it runs. HEUI uses high pressure oil to work like a hydraulic press basically. When the solenoid opens it lets high pressure oil into the inejctor which causes the injector plunger to inject the fuel under high pressure. Think if like a hydraulic press where the oil is the jack handle, and when the jack handle is worked it forces the ram to put pressure on whatever it is your pressing(the fuel in the case of HEUI). So if the pressure is low, then the fuel will be going in at to low of a pressure, but if the pressure is high it will be inejcting more fuel than it wants to. Another failure prone area on 7.3's is the high pressure oil pump pressure sensor. The 7.3L is a good engine when it's running right, but when it's not it is a nightmare to deal with. I've only messed with a few of them, and decided real quick I didn't care for messing with them.
 
Check the oil. Seriously, is it low? The HEUI will run out of oil before the engine oil pump. Smell like diesel fuel? The oil is very important in this system.


Never run out of fuel with this truck, NEVER EVER!!! Unless you want to change injectors... The later years ECM's are even programmed to simulate a "miss" to let you know you are running low on fuel. Fuel filters are also critical as with any diesel.

Worst case: Check your fuel for water. If you find any unload the truck ASAP taking whatever loss is necessary. In my experience the HEUI is damn near impossible to get running properly after eating water. And next time get the truck up to speed before you buy.
 
I hooked up a scan tool to the truck and could not get a response from the pcm could this be the issue I'm having with hard to start and running like crapp
 
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