8.1 losing power like ignition cutting off and on

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R JONES

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Oct 14, 2018
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2004 8.1 workhorse started cutting out when going up a hill. then got to where it would cut out on flat ground. its like turning key off and back on.  you can stop and turn ignition off and restart it and it will run OK for awhile then start doing it again. replaced fuel pump and filters before this last trip. took a 400 mile trip and a got a knock sensor light. cleared it and finished the trip. on the way home about 150 miles in the trip check engine light came on again for knock sensor. cleared it and headed on home about another 100 miles is when problem started and no codes. need fixed headed on another trip next month
 

Isaac-1

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Please keep us updated on this, I think mine may be starting to do the same thing, just now having bit of stuttering hesitation going up hills, just barely perceptible in my case.
 

Alfa38User

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Oct 4, 2007
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Check and replace any fuel filters, the check engine light message could be a red herring!!
 

R JONES

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Oct 14, 2018
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when it happens its like you just turned the engine off  and comes right back on  but rpm's never change.  kinda like it wants to go into limp mode but doesn't
 

SpencerPJ

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I'm not sure...  You also might find a 8.1 forum and check for advise.  It also sounds like an ECM. 
Modern electronics can be tough to diagnose without the right equipment.
Good Luck
 

Isaac-1

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I can't think of why hills would effect it, but has the ignition relay mod been done to yours, (I don't think the relay kits are still available, though it should be easy to roll your own with off the shelf parts).

www.oemys-performance.com/media/wh%20ignition%20relay.pdf
 

richardhufford

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Apr 11, 2016
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San Jose, AZ
This may be silly, but if it acts like you're turning the ignition switch off and on, maybe it's the ignition switch.  I had a car that was cutting off and on, and replacing all of the electronic ignition parts I could think didn't make a difference.  One day I noticed that the dashboard idiot lights were turning on and off, like when you first start the car and I realized that it was simple vibration turning the ignition off.  A new ignition switch fixed the problem.
 

Isaac-1

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The relay mod was added to prevent the ignition switch from over heating and acting up.  Over the years the RV manufacturers kept hanging more and more accessories off the accessory switch connection on the ignition switch that they started to run into problem with over heating switches, and subsequent premature failures.
 

jubileee

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Dec 17, 2013
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In the mid nineties when our big block GM engines acted up like that it was nearly always the fuel pump relay/wiring. If not the relay, then it was the oil pressure sensor acting up. Newer models maybe different.
 

YaddaYadda

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Sep 17, 2011
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Our 2003 National Dolphin with the 8.1L and Allison 1000 acted up a little like yours, a couple of months ago, going up hills.  Showed a knock sensor when scanned.  Air filter, fuel filter replaced and MAF cleaned.  New Allison filter.  O2 sensor not checked.  Filled with premium in lieu of regular gas.....took a trip to CA up to 4000 ft and down/back.  Ran fine.
 

Bill and Debbie

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Jun 7, 2014
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Poulsbo, WA
I'm not sure if an 8.1 has an ignition control module, but your symptoms are exactly what I experienced in a 454 at one time. And also going up grades, the engine light would come on and go away if I restarted. Replaced the ignition control module and problem went away totally.
 

R JONES

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Oct 14, 2018
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CLEANED THE MASS AIR FLOW TODAY AND DROVE IT 50 MILES WITH NO PROBLEMS AT ALL.  NOT SURE ITS FIXED OR NOT
 
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