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My C15 has hesitation/miss/shudder on hard pulls & acceleration why?

Motor mounts replaced

ECM bypassed and tested

injectors replaced

Remember listening to Kevin Rutherford show there was a driver with similar issues and they thought it had something to do with the wiring harness/sensor on front side of the motor? Could this be the same issue or does anyone have any suggestions?

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Have you had the fuel pressure checked? It almost sounds like the motor might be starving for fuel when under a heavy load.

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The fuel psi on my 2006 c 13 was 10 psi out of spec and caused all kinds of very scary stumbling, miss, rough run under pull issues.

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First inclination is fuel lines, but my neighbour just went thru this and in his case it turned out to be a bad cylinder liner, now he's in for an in-frame.

But always worth checking out the cheap stuff first.

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Have the actuators checked, I have never experienced that when accelerating with my c15 after it has gotten up to operating temp but have had similar problems on hard pulls. if you are experiencing it when you are first getting started or after the truck has been turned off for a while it may be do the the engine being cold, I was told that the injectors are not all firing until the engine gets to operating temp causing hesitation, smoke blowing out the stacks and loss of power

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I just had similar symptoms with my Cummins. They diagnosed and replaced defective timing/metering actuators. Motor hasn't run this good in a long time.

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My 2003 C15 6nz has same issues.

Changed frame mounted fuel filter head (Peterbilt said was sucking air)

Next they said it's a bad fuel line between fuel pump and tanks. I changed all fuel lines. Next they said it's a bad fuel pump, they changed it.

The list is endless. Still it pops and stumbles under load. 3X CAT drove with me, cutting out injectors with no resolve.

Here's my unique symptoms.

I'm 19 months into a platinum rebuild by CAT. New Tranny (18) behind it.

2 new diffs. Balanced driveshaft. New

Ujoints & hangar bearing. New load leveling valve.

Pops, stumbles and power goes down under load or pulling empty trailer.

Ease my foot off accelerator but still maintaining road speed on a flat surface and all is fine. Press down a touch to increase speed and pop...shake and shudder.

Here's the clincher...

Idle for a few hours and head out loaded and my engine runs smoothly and perfectly , for 2 to 5 minutes.

Last week I had a entire day of perfect smooth powerful engine running, for unknown reasons.

Tried using another fuel supplier for 2 tanks but no change.

Thought perhaps a cracked drop tube in fuel tank sucking air at top. Nope!!

I made up a brand new fuel line going from my new fuel pump directly into the fill hole on top fuel tank. Still no resolve. Pulled all 6 injectors to check for compromised O rings. All good. Did top set and closed her up. Still the same.

Shaking/popping/heavy low pitch bang under load or pressing down on accelerator slightly to maintain road speed on flat roadway it starts, back out of acceleration and all good.

On a highway when I'm exiting and slow going around a exit ramp, followed by hard acceleration to bring my rig up to highway / road speed again and for unknown reason the truck runs / pulls great again for....5-8 seconds, and thereafter it's "pop...pop...pop" as usual again.

I need help. If anyone has any ideas , even if I have to pay, I gladly will.

Again, 2003 CAT C-15, 6NZ

CAT warranty still applies but they are at a loss as to what's happening, as is Peterbilt and another local shop.

PLEASE PLEASE HELP.

Text me at 905 746 5505

I assure you that I will be grateful !!

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Did you figure it out? I'm having the same issue.

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Had the same issue on 03 6NZ, changed from CAT to Donaldson fuel filters and it runs perfectly now.

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I have 99 pete 6nz starts to stutter in 4th gear on in the first 3 to 5 seconds of the pull in most gears then clears right up plenty of fuel pressure changed fuel lines trie pulling from separate fuel tanks etc . any suggestions???

???????

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i FOUND OUT ACCIDENTALLY THAT THERES A UPGRADE TO THE FUEL PUMP SPRING. i BOUGHT IT, INSTALLED IT IN MINUTES AND IT BOOSTED MY FUEL PRESSURE TO THE POINT WHERE MY ENGINE IS RUNNING CONSIDERABLY BETTER. i HAD THE SAME THING GOING ON WITH MY C15 6NZ.

Parts guy at CAT said alot of guys with 6nz engines are being wrongly told the fuel psi should be 95 psi, when in fact it should be 115 psi for a 6NZ. Now im running 125 PSI and its much much better.

The spring is hugely over priced, its a darn spring the diameter of a pencil under 3 inches long (but it comes with a new cap plug….WOW.. NOW ITS WORTH THE $93… “ NOT”…. (but it works..try it )

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DeWayne Woodall will be eternally grateful.
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