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+--- Thread: Small hesitation at frwy speed on ISX CM871 (/showthread.php?tid=9363)
Small hesitation at frwy speed on ISX CM871 - Dieselboy - 01-25-2024
So I have a 2008 ISX CM871 in my motorhome with a slight hesitation (like sub 1 second) today while driving at about 65mph on the freeway. Was fine for the first 4 hours of the drive then on a very slight uphill it hesitated about 5 times within about 45 min. No CEL. No Allison transmission error either. Everything else is fine like temps and pressures.
Cruise control was on while this took place. I proceed to drive for another 35 min without cruise control, it does it one more time but less pronounced. Motor pulls fine from a stop and runs through gears just fine as well.
I might add that I've replaced fuel filters about 7k miles ago.
Very odd to me. Any thoughts?
And thanks!
RE: Small hesitation at frwy speed on ISX CM871 - Rawze - 01-26-2024
When is the last time a proper EGR tune-up was done to it?.
ref:
RE: Small hesitation at frwy speed on ISX CM871 - Dieselboy - 01-26-2024
It has a brand new EGR valve on it about 7k miles ago. As well as pipe.
RE: Small hesitation at frwy speed on ISX CM871 - Rawze - 01-26-2024
(01-26-2024 )Dieselboy Wrote: It has a brand new EGR valve on it about 7k miles ago. As well as pipe.
and the delta-P sensor.. and its cross-pipes?.. IMAP and all the other sensors that are old?.
Delta-p alone can cause the accel. to hesitate like your describing.. nonetheless several other sensors if they are reading incorrectly.
I remember when mine acted up, It refused to accel. for several seconds at a time, like your foot was not on the pedal, .. then took off like a rocket once it caught up to itself. - It was the delta-p sensor cross tubes dirty that caused it on mine.
of course, there are many reasons that one can act up like that aside from just sensor reading incorrectly.
worse case scenario, someone can monitor all the important engine data and see what is triggering it too. Fuel control state, and what it switches into/out of in particular...
ref: http://rawze.com/forums/showthread.php?tid=6641&pid=58693#pid58693
RE: Small hesitation at frwy speed on ISX CM871 - Dieselboy - 01-26-2024
(01-26-2024 )Rawze Wrote:(01-26-2024 )Dieselboy Wrote: It has a brand new EGR valve on it about 7k miles ago. As well as pipe.
and the delta-P sensor.. and its cross-pipes?.. IMAP and all the other sensors that are old?.
Delta-p alone can cause the accel. to hesitate like your describing.. nonetheless several other sensors if they are reading incorrectly.
I remember when mine acted up, It refused to accel. for several seconds at a time, like your foot was not on the pedal, .. then took off like a rocket once it caught up to itself. - It was the delta-p sensor cross tubes dirty that caused it on mine.
of course, there are many reasons that one can act up like that aside from just sensor reading incorrectly.
worse case scenario, someone can monitor all the important engine data and see what is triggering it too. Fuel control state, and what it switches into/out of in particular...
ref: http://rawze.com/forums/showthread.php?tid=6641&pid=58693#pid58693
Upon some research it seems that if could likely be the pedal assembly/throttle position sensor. It is made by Kongsberg and there is a magnet that rotates with the pedal movement that the sensor reads. Quite a few other RV'ers have reported having to replace theirs and it cleared up the problem. I need to bust out the multimeter to see if it gives me any insight. Process of elimination I suppose.
RE: Small hesitation at frwy speed on ISX CM871 - hhow55 - 01-26-2024
Once had the problem like you describe and turned out to be the Vehicle speed sensor..........The one located on rear of tranny.
RE: Small hesitation at frwy speed on ISX CM871 - Dieselboy - 01-27-2024
Thank you. I will have to look at that as well.