Case Study #1, 1995 PowerStroke Options

[Ryan H]

Vehicle: 1995 F-250 7.3L PowerStroke with an automatic transmission and 230,000km.

Complaint: Surge on startup and poor fuel economy.

History: Issue has been present since the owner purchased the vehicle 5 years ago. At the time the truck had 90,000km on it. Vehicle has been worked on my multiple shops including the local Ford dealer. Parts that have been replaced in the past include high pressure oil pump, IPR valve, 8 injectors, PCM (from a 1997 Truck), IDM, CMP sensor, valve cover gaskets and harnesses with no change to the original issue.

Diagnosis: The fault was verified and the surge is present at all engine temperatures just after start up for about 4 seconds. Once running a rough idle is noticed but sets no fault during a contribution test. No exhaust smoke is noted but while approaching a stop the RPMs drop below idle speed and sometimes causes a stall. Initial inspection of the vehicle retrieved no codes. Watching the PIDs in the datalogger revealed an interesting trait. At operating temperature the injector pulse width is 1.5ms and MFDES is 18 mg. Usually these figures are around 1.0ms and 10mg.


Where to go from here?

[Ryan H]

Here is a snapshot of the vehicle at start up.



At this point it looks like the engine is either under load or not receiving enough fuel into the combustion chamber to properly idle. From experience the PCM out of a 1997 F-series Federal Emissions engine should not be causing this issue in a 1995 truck.

Fuel Pressure is good at 47psi @ idle
Engine Oil Pressure 22psi @ idle
Injection Control Pressure (High Pressure Oil) 650psi @ idle verified with a manual gauge.

The Injectors appear to be supplied with correct fuel and oil pressure.

[Ryan H]

This is where I ran into a bit of a block. With the lists of parts that have been changed in the past with no effect on the original symptom, I was stumped. I kept looking at all the information that I had collected but couldn't come up with the next logical step.

[John Thompson]

This is where I ran into a bit of a block. With the lists of parts that have been changed in the past with no effect on the original symptom, I was stumped. I kept looking at all the information that I had collected but couldn't come up with the next logical step.

Hi Ryan,

I have never been (or really wanted to be) a deisel diagnostic tech...but I l do love to learn . Even though I know very little about your powerstroke system, I can relate to "next logical step" in gas engine diagnostics so here goes...

Vehicle: 1995 F-250 7.3L PowerStroke with an automatic transmission and 230,000km.
PCM (from a 1997 Truck

That would concern me...

At operating temperature the injector pulse width is 1.5ms and MFDES is 18 mg. Usually these figures are around 1.0ms and 10mg.

I would assume that an abnormally high ipw would be a command not an injector fault issue....unless the "wrong" injectors (different nozzle or flow than oem) had been installed on the truck at some point?

At this point it looks like the engine is either under load or not receiving enough fuel into the combustion chamber to properly idle. From experience the PCM out of a 1997 F-series Federal Emissions engine should not be causing this issue in a 1995 truck.

How about California Emmissions?

[Ryan H]

Hi John,

I did some investigation into the mismatched PCM in this truck. This was also my concern initially because 1997 E-series vehicles and 1997 California Emission F-series have different injectors than the truck in our shop, but both the engine and 1997 PCM are from F-series Federal Emission vehicles.

I should say that after my first brief inspection of the vehicle, I too felt the injectors may be the cause of this issue, but the history of the vehicle didn't point in that direction as the injectors were changed with no difference to the problem.

Of course the one big down side to diagnostics is time. My customers rarely give me an hour to find the issue which was the case with this truck. Luckily there were three dead glow plugs and the customer had rescheduled to have them replaced a week later, so I would see the truck again.

[Ryan H]

I just want to take a closer look at the injectors to help with explanation. There are several different injectors used in 1994-2003 Ford 7.3L PowerStroke engines. I will just key on the one difference between the early and late injectors. This is the split shot injection. As you can see below the injector actually injects twice in an effort to rate shape the injection event. This is done to reduce emission and the diesel "knock".



You can see the differences in the two injection evens in the above image. The one thing that isn't illustrated is the injector on time is almost double in the split shot injector. The injectors that should have been in this truck would be code "AA" non split shot. Codes AB and AD are split shot injectors. So with the valve cover remove this is what we saw.

[Ryan H]

In conclusion this customer spent close to $7000 trying to fix this truck over a 5 year period. I suspect his original issue had changed over time but whether he failed to inform us or notice it, his history of the vehicle was not correct and added to his problems.

The wrong injectors had been supplied to the customer from an online source and the mechanic who did the installation did not notice the different part numbers.

Two things I took away from this case were that a costumers description of the issue can be seriously flawed and never rule out previous work done on the vehicle as being the cause of the fault.


“Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth.”

Sr. Arthur Conan Doyle