1996 7.3 Running Really Rough - Diesel Forum

phlorit · 10-07-2009, 03:48 PM

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.

94strokerace · 10-07-2009, 04:00 PM

The air hiss may be the ebpv. normal until warmed up, then the butterfly opens. Recommend making the butterfly fly away.

To check fuel psi, look on the left side of the fuel bowl. There is a schrader valve, use a tire psi gauge. A little messy, but will work. 1/8npt if you want to install a guage at that port.

I think you have a burned uvch (under valve cover harness). the injectors wiring/glow plug wiring and grounds run through the core of the gasket via connectors. Open the oil fill cap and sniff for burnt plastic. If you smell burnt plastic, post back and we will then point you towards the next step.

phlorit · 10-07-2009, 09:30 PM

First, thanks 94Strokerace.. Your guidance helped a bunch. I cannot smell any burnt plastic inside the valve cover.

Next, went and got a US General fuel pressure gauge. Just a basic injector pressure tester. Had the correct schrader female end for the test.

Tested as it sat from my previous notes. The needle did not move from Zero. Thought I had something setup wrong. Truck was running rough as it was before.

Took off gauge and checked it. THere was diesel in the gauge, so it was getting fuel.

Then I, for the sake of doing it, changed out the fuel filter. New gasket of course as well. Started the truck and ran the throttle up to WOT. Now the gauge was sitting at 10PSI at idle, but after the new filter, it was running somewhat normal. Let it idle for a while and then did some WOT 5 second pulls. It was heading up to 30-40 PSI and back down to 10PSI at idle.

Took the truck out.. and ran it around and it felt back to what it was before the issue. Ran well, smooth.

Brought it back and tested the pressure again. 10PSI at idle and 30-40PSI at WOT.

Checked all harness connections and they are old, but look ok. I know this does not matter much.

So, a few thoughts...
1. Bad fuel in the front tank that clogged up a 10,000 mile filter?
2. Bad fuel pump at those pressures?
2. The pressure is still bad, but with potential junk in the filter it just could not push enough fuel?
3. Fuel filter was just bad.

I am not sure what the pressure is supposed to be, but I think it should be up around 60PSI.

I will change the oil for the heck of it and see if that improves the pressure...

Thanks in advance for review of this information....

BiodieselPlace · 10-07-2009, 11:08 PM

Quote:

Originally Posted by phlorit

First, thanks 94Strokerace.. Your guidance helped a bunch. I cannot smell any burnt plastic inside the valve cover.

Next, went and got a US General fuel pressure gauge. Just a basic injector pressure tester. Had the correct schrader female end for the test.

Tested as it sat from my previous notes. The needle did not move from Zero. Thought I had something setup wrong. Truck was running rough as it was before.

Took off gauge and checked it. THere was diesel in the gauge, so it was getting fuel.

Then I, for the sake of doing it, changed out the fuel filter. New gasket of course as well. Started the truck and ran the throttle up to WOT. Now the gauge was sitting at 10PSI at idle, but after the new filter, it was running somewhat normal. Let it idle for a while and then did some WOT 5 second pulls. It was heading up to 30-40 PSI and back down to 10PSI at idle.

Took the truck out.. and ran it around and it felt back to what it was before the issue. Ran well, smooth.

Brought it back and tested the pressure again. 10PSI at idle and 30-40PSI at WOT.

Checked all harness connections and they are old, but look ok. I know this does not matter much.

So, a few thoughts...
1. Bad fuel in the front tank that clogged up a 10,000 mile filter?
2. Bad fuel pump at those pressures?
2. The pressure is still bad, but with potential junk in the filter it just could not push enough fuel?
3. Fuel filter was just bad.

I am not sure what the pressure is supposed to be, but I think it should be up around 60PSI.

I will change the oil for the heck of it and see if that improves the pressure...

Thanks in advance for review of this information....

Have you checked for fuel leaks in the valley?
I thought you mentionned are smell of diesel.
Those lift pumps are prone to fail.
10 psi at idlle is not enough. 60 psi is about right at higher RPMs.
Something wrong with fuel delivery.
Could be pump, or could be related to pressure regulator, maybe even cloged up strainer on your regulator.

Good luck.

phlorit · 10-08-2009, 12:42 AM

Quote:

Originally Posted by BiodieselPlace

Have you checked for fuel leaks in the valley?
I thought you mentionned are smell of diesel.
Those lift pumps are prone to fail.
10 psi at idlle is not enough. 60 psi is about right at higher RPMs.
Something wrong with fuel delivery.
Could be pump, or could be related to pressure regulator, maybe even cloged up strainer on your regulator.

Good luck.

Yeah.. I think next steps are to replace the fuel pump, change the oil (making sure there is a good diesel oil in the case), and clean out the regulator and screen very well...

It will be this weekends project.

Took the truck for a drive and it seems to be running ok. Wonder how it will fell with better pressure? Anyway.. I'll update the post after the next actions and let everyone know how the old beast is doing..

**Excavator** · 10-08-2009, 04:16 AM

pull off oil filler cap and smell in the valve cover. If the harness is burnt under the cover it will smell like burnt wires and you will needd to pull off valve covers and replace the harness's as well as check the connectors outside the valve covers for melted and burnt pins and plastic connectors

mcr96 · 10-08-2009, 10:53 AM

Had the same thing happen 2 weeks ago on my '96,..... did not smell burnt wires at all, ... replaced the V/C gasket and harnesses, one was burnt, replaced the glow plugs while I was into it, after all that, no difference, called Bean Diesel picked up one of there IDM's, plugged it in and now runs better then new! ....... Basically the burned out harness fried the IDM.

phlorit · 10-08-2009, 09:45 PM

Thanks for the feedback... For preventative measures, I will replace the harnesses soon. After running a new fuel filter, and on the back fuel tank, its running pretty good.

Bought a new fuel pump and will be replacing this weekend, changing the oil and testing again.

Next weekend I will replace the 4 harnesses just to make sure. I'll keep everyone posted on how it goes for both.

Pressure right now is 10-12PSI at idle and 40PSI at WOT from the schrader valve on the fuel pump although the truck is running smooth.

whyndell · 10-31-2009, 08:33 PM

What is an "IDM"?

Also how much trouble to change the harness and glow plugs, I have a 96 F350 7.3 Powrstroke, 198,000 miles.

BiodieselPlace · 11-01-2009, 03:47 PM

Quote:

Originally Posted by whyndell

What is an "IDM"?

Also how much trouble to change the harness and glow plugs, I have a 96 F350 7.3 Powrstroke, 198,000 miles.

IDM = Injector Driver Module.
It is controlled by the PCM and provides power to drive the injector solenoids. Mounted under the hood on the drivers side. It's a metal box with a large connector bolted to it.
If you find burnt pins on either the harness or the UVC gasket connectors, I would just replace the gasket(s) and then you have to splice in a new connector(s) on the hardness side since most likely the connector is burnt. You can get the kits from Ford or Napa.
And, yes, it would be wise to replace all 8 glow plugs since your have the valve covers removed and since you don't know when they were put in.
One more comment that has been brought up already: glow plug shorts, harness short, burnt pins can dammage your IDM. That's exactly what happenned to me a couple months ago...

Good luck

whyndell · 11-02-2009, 03:54 AM

Thanks BiodieselPlace

This will give me a place to start. I'm a new deisel owner bought the truck to pull my 5th wheel.

BMAC123 · 11-03-2009, 11:36 AM

I was not able to get a new gasket kit from NAPA. I had to goto FORD. 80 bucks later my truck ran like a champ. It didnt show anything on the computer either till I did an injector vibrate test. Then it only showed the #2 being bad connection. No plastic smell... Just burned wires. Make sure you plug your glowplugs back in all the way. They can be a pain.

95FORDBOY · 11-06-2009, 01:34 AM

i had a simalar prblm with mine changed the V/C gaskets that didnt help checked all the same things u have and it ended up being my IPR valve

7867111 · 11-06-2009, 01:46 AM

my f350 disel is leaking disel inside the radiator and it is coming out of the water resibore i dont know what is wrong but the truck is runing perfect

94strokerace · 11-06-2009, 03:50 AM

That sounds like injector cups. A couple of special tools will be required and a specific loctite as well. There used to be a set floating around from member to member as needed, but have fell off the radar, not sure what has happened to them, but maybe they will resurface if you ask....

The cups can be had from powerstrokeshop.com