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I'm leaning towards the IDM with these symptoms

64K views 11 replies 4 participants last post by  hayjayhorses 
#1 ·
I have a 2002 F350 7.3, Manual transmission, 4x4 ESOF, 198K Miles.

The truck has a very regular knocking and shaking at idle that stays constant as the throttle is depressed. The truch has no power. The Check engine light is not on, and I don't have any DTC's showing up.

The injector buzz tests completes without issue, and all 8 injectors sound good.

The cylinder contribution test consistently shows low contribution from Cylinders 1, 2, and 3. Occasionally Cylinder 4 shows up on there as well.

The problem onset all of the sudden. I replaced the driver's side (even number cylinders) UVC harness, and it made no difference. The old one didn't look bad.

Due to road closures, I was taking a very bumpy dirt/gravel road to and from work each day that is 10 miles long. I had been driving this route for a month. Often there was considerably sized puddles on the road.

Early on in diagnosis, the alternator went out, and the batteries were about due for replacement, so I replaced the alternator and both batteries. I fired up the truck and the problem went away for about 2-3 minutes, then started acting exactly as it had before.

Do you think it is a safe bet that I've condemned my IDM with this data? Has anyone ever seen one fail without giving the P1298 code?

Thanks in advance!
 
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#2 ·
I have checked the fuel pressure and it is very steady and within specification. Control oil pressure as read on the my scan tool didn't waver too much either. The engine has a very predictable, repeating knocking style sound that it makes and the truck shakes pretty well side to side from the misses.
 
#3 ·
That's a tough one. I guess the IDM could be the culprit. It would be better if you could swap with a known one before having to go out and buy one. If that doesn't do it, it may be time for injectors.
 
#4 ·
:stupid

you don't have to remove your old IDM just unplug it and plug another one in and see if it is any different. The 2nd IDM will stay there.

I would also check the wiring harness on the chassis side of the 42 pin connector. I had this issue with my '00 F550 and found a few broken and chaffed wires.
 
#5 ·
Well guys, My symptoms led me astray on this one. I thought the frequent reproducible test results indicating a problem with the same cylinders was an issue with those circuits, but the real issue is that my truck was parked at an incline where the front of the truck was higher than the rear.
The issue was that on the bumpy road I think my pickup tube broke off in the fuel tank, and the truck is acting like it is running out of gas.
Thank you for taking the time to try to help me out, and Jay, I agree with your information in red and blue...
 
#6 ·
This is now the 3rd truck with similar issues like mine. I still have not figured out my problem as all AE tests come back normal, fuel pressure is steady and clear. I will be pulling both valve covers soon and looking for anything out. Real curious now why in the last several days more trucks have same issue??

Mine missed at about 1500 RPM now cannot pull a load or accelerate without severe missing and a metalic knock. Idle it purrs but occasionally misses without the knock.
 
#7 ·
My fuel pressure was steady and clear as well, it led me on a wild goose chase for a couple months.
When you say "All AutoEnginuity Tests come back normal", can you elaborate on that?
I found it easier and more comfortable to test the UVC harnesses through the IDM connection with an ohm meter.
I'll tell you what, after this experience the next time I have a funny issue with the truck and no MIL, I'm going to get 5 or so gallons of diesel in it and try again.
 
#9 ·
Here are some basic numbers I got;

RPM;........IDLE 654.....3100.....NORM RANGE
ICP;................487.....974.....480-550 IDLE 1800 MAX
ICR DC%.........7.42.....9.77....10-15% WOT 65%MAX
ACCEL POSIT;..10.2.....29.41...10-15% IDLE
EXBP;...........11.89.....21.01....10-15%IDLE 45%WOT MAX
ICP VOLT........0.83......1.73
ENGOILTEMP.....154.....162
VOLFUELDESIRE; 4.9.....13.4
FI PULSE...........1.98....1.55

I do see the ICP get as high as 2400 on spikes with WOT hill climbs but it drops quick to norm. Fuel delivery pressure is rock steady at 60psi under load or idle wot or soft acceleration. When charted the numbers track each other well. I cannot change the sample rate to less than 2 seconds apart and the misses probably are not well shown if erratic electrical shorts.

BTW I started with less than 1/4 tank and assumed it would be a fuel issue. THe steady pressure at idle and wot removed that suspicion. If the pressure is there no matter the demand I am sure the flow is OK.
 
#10 ·
did you get this data while under a load? If not you need to hook a trailer up to it and pull some hills (or simulate a load by applying the brake) if your just siting in the parking lot reving the engine it will not drop fuel pressure.
 
#12 ·
Have you been able to take the fuel and HPOP pressures when hauling your gravel.

I have had week fuel pumps that only caused problems only when pulling a load, no issues empty.
 
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