99' 7.3 powerstroke pulsing at very light throttle in cruise only, starting hard morn - Diesel Forum - TheDieselStop.com
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99 & up 7.3L Power Stroke Engine and Drivetrain Discussion of the 99 & up 7.3L Power Stroke diesel engine and drivetrain in the 1999-Up Super Duty trucks and Excursions. No gas engine discussion allowed except on transmissions and drivetrain that pertain to all models. Please confine discussion of topics in this forum to those items that are specific to the 7.3L Power Stroke engine.

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Old 01-04-2013, 11:46 AM   #1 (permalink)
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Question 99' 7.3 powerstroke pulsing at very light throttle in cruise only, starting hard morn

I have a 99' PowerStroke, first noticed this in (cruise control) doing 70+mph. OK, so you're driving down the freeway- you go up hill, start down the other side. . . the truck reduces throttle, not quite completely, the entire truck begins to pulse forward/backward like you're playing a tap dance on the accelerator. If it takes throttle completely off, it does not do it- it is only at that very light throttle spot. if you take it out of cruise and drive it the same exact way, it will not do it. Also it is now doing it at 35mph, in cruise, taken out of overdrive, again very light throttle only. it was getting worse, especially after warming up good, and i changed the Cam Sensor. (ford part) that seemed to take care of it at low speed for a while, but it started again.

I am also having trouble starting it if it sits overnight. (it has been cold) It will crank 3 - 4 times, then runs great. it cranks fine(possibly a tad long) and starts fine all day long.

I am running RotellaT with 20% Lucas
I have replaced:

CPS
VSS
fuel filter, TWICE
GPR
all 8 Glow plugs
*brand new batteries
*brand new starter
*I have fuel in the bowl

What could be causing this? Thanks so much!
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Old 01-04-2013, 08:44 PM   #2 (permalink)
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Do you have it chipped?

If you have a hot program on it, it will be touchy on cruise control and surge like you're describing.

The other possibility is if the Exhaust Backpressure valve (which closes off the exhaust to warm the cab up quicker when it's cold out and the oil is below about 140 -150F) is malfunctioning and hunting (cycling open and closed). If the engine is fully warmed up (over 7-10 highway miles), then the EBP system should be disabled and that wouldn't be the issue.
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99.5 F250 PSD Supercab LB 4x4, ZF-6 w/SB Con OFE, 3.73LS, Boost & pyro gauges, Swamps S175/146 injectors, DP 80 HP Econo PCM (classic version), AIS, coolant filter w/"hokum" bracket, regulated return, heated mirror mod, lighted cupholder, Marinco heater plug-in.

Hard or no-start? Check Here
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Old 01-05-2013, 01:33 PM   #3 (permalink)
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Thanks Well i do not have it chipped, it is all stock. I can drive well over an hour freeway, it will still pulse. I don't know if this is related, but it will kinda stumble or stutter lightly at take offs when engine is cold.
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Old 01-07-2013, 02:06 PM   #4 (permalink)
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Surging like a Bucking Bronco

I think I have the same problem. 2000 F250 6 speed manual--all
stock--110K. Between 16 and 1800 rpm with a feather touch on the
throttle, it feels like the fuel is shut off and on, resulting in a bucking sensation. If I put my foot into it, I think it is less likely to
happen. Warm or cold, it'll happen in this rpm range without a definite pattern; it's intermittant and I'm unable to figure out all
the conditions which causes this. It's a California truck that I bought
at 107K miles and this phenomenon has just started in the last
1000 miles-back in Minnesota. Anybody have a clue?
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Old 01-07-2013, 03:19 PM   #5 (permalink)
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Camrhien, you might have a problem with the accelerator pedal assembly. It's a potentiometer that can develop bad spots in it. If it doesn't do it with cruise engaged, then it's most likely the AP position sensor.

JBoy's problem sounds like something else, because he's seeing it with cruise engaged. Might be a sensor issue or a problem with the IPR. If the IPR coil isn't snug on the back of the IPR, then it may cause issues, because the coil can slip instead of regulating the valve inside like it should.
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First truck -- 1929 Model A Ford pickup, restored from ground up. Wish I still had it!
99.5 F250 PSD Supercab LB 4x4, ZF-6 w/SB Con OFE, 3.73LS, Boost & pyro gauges, Swamps S175/146 injectors, DP 80 HP Econo PCM (classic version), AIS, coolant filter w/"hokum" bracket, regulated return, heated mirror mod, lighted cupholder, Marinco heater plug-in.

Hard or no-start? Check Here

Last edited by klhansen; 01-07-2013 at 03:22 PM.
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Old 02-11-2014, 03:07 PM   #6 (permalink)
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fixed

Old post but i may have your culprit. Mine was doing the same thing for months, Turned out it was the square connector on the inner fender well from the engine harness. The pins inside were corroded and funky looking. We took a small piece of braided copper wire and cleaned each one, sprayed the crap out of both sides with contact cleaner and then reapplied new dielectric grease. Problem went away and truck never ran bad again.It was a light throttle surge between 12-1500 rpm. Truck scanned fine before, no codes.

Im making it a mission to get on here and post the info for future searches. I searched for hours and found people with the same symptoms that never found the issue. This connector handles all the injector wires etc..

Jake
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Old 02-12-2014, 11:43 AM   #7 (permalink)
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Okay Great! Really appreciate the thoughtfulness, bigjake1! I never did find the problem, so I'll be checking that ASAP. THANKS SO MUCH!!
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Old 02-25-2014, 06:57 AM   #8 (permalink)
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More Info UPDATE!!

Quote:
Originally Posted by bigjake1 View Post
Turned out it was the square connector on the inner fender well from the engine harness. The pins inside were corroded and funky looking.
Well, I did some checking. The wiring harness must be different in a '95 vs a '99, because I do not have a connector as you describe.

some info: I have an identical truck; I have swapped the PCM and the IDM out, made no difference. painstakingly checked all the connectors, including UVCH.

I did finally get to check the fuel pressure. When I turned the key on, it was moving from around 25 - 50 psi, going up and down some. (running, it was around 50 psi, varying about 5 psi either way) I took the regulator/relief (FPR) apart on the top of the fuel bowl, and I found the small rubber washer on the "plunger" had swelled, and was very loose on the plunger. I swapped it out with my other truck, it is now back up to a steady 70 psi, seems like it has helped.

I am still getting an lightly erratic idle though, and can still feel some pulsing going down the road at times. It seems most pronounced after the truck has been driven and allowed to sit a little while, not totally cool off.

I have an original black (new) CPS in this truck. Buzz tests, cylinder contribution tests, all show up ok. I physically checked the clearance on all eight injectors, they were all almost identical, around .003-.0035 clearance.

(early '99 f350)
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