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Old 06-03-2023, 10:24 PM   #1
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8.1L stuttering going uphill?

I am having a problem with my 2002 8.1L P32 coach with 4L80E, intermittently when climbing a hill on the our last few trips the engine will stutter or surge as it is climbing the hill, it is as if it is kicking out for a tiny fraction of a second 2 to 3 times per second until I get to the top of the hill, and I don't know why. LF1 and LF2 look good on Scangauge II, I have added a fuel pressure gauge and it looks good with a constant circa 60 psi while going up hill.


The catch is it does not do this all the time, or to the same intensity, we just got home from a circa 3,000 mile trip from Louisiana to the badlands in South Dakota (so not too many mountains this trip, but a few significant hills), and it only did this stutter / surge thing four or five times for less than a minute at a time on the entire trip, and only twice was it strong enough that my wife could notice it from the passenger seat.


I was having a knocking problem while climbing hills after the engine was hot some of the time on our previous trip, and I seem to have solved that by installing new coil packs, as well as replacing the EGR valve (which was leaking externally). Yet this stutter issue still persists.


Any thoughts? Spark plugs were replaced about 25,000 miles ago, plug wires are Ultra RV Magnum Extremes installed circa 20,000 miles ago.


I am thinking about getting a data logging OBD-II monitor, but which one, and what are my chances of catching the problem with as rare as it is.
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Old 06-04-2023, 04:37 AM   #2
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I used a FoxWell 301 to record data for our ‘02 coach - it recorded well enough that Jon from Brazel’s could help me diagnose LTFT and STFT issues with our engine.

I had bought a ScanGage but the FoxWell does everything the ScanGage does except give transmission temp - so I sold my ScanGage and bought 12 volt temperature alarm and strapped and insulated the sensor onto the cooler line as it feeds into the cooler.

While it doesn’t sound like your problem, you might check the fuel dampener on the fuel rail - roughly located above #7 on the fuel rail and has a vacuum line going to it. When I pulled that vacuum line off, raw fuel squirted out at me (engine off of course). Shouldn’t be any fuel there, or even the smell of gas, at all.
They quit installing that dampener sometime in ‘04.
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Old 06-04-2023, 05:53 AM   #3
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Water in the fuel tank will do this. BTDT
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Old 06-04-2023, 06:03 AM   #4
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It's actually a fuel pressure regulator on the 2002 model, they did not start installing dampener until they moved to an in tank regulator in either 03 or 04, and mine has been checked and replaced even though it tested good due to being 20+ years old and containing rubber parts which are prone to age related failure.
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Old 06-04-2023, 08:07 AM   #5
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Hello, check your plugs and spark plug wires. When the engine is under a load is when you will notice this issue. Not familiar with yourt particular model but if it has a distributor check the timing as well. Plugs and wires are your cheapest option to check first. Good Luck
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Old 06-04-2023, 09:10 AM   #6
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It's actually a fuel pressure regulator on the 2002 model, they did not start installing dampener until they moved to an in tank regulator in either 03 or 04, and mine has been checked and replaced even though it tested good due to being 20+ years old and containing rubber parts which are prone to age related failure.
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Old 06-04-2023, 09:53 AM   #7
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My immediate thought was this was a plug and/or plug wire issue but it looks like you've already considered that. Still, it might be worth a shot to at least visually inspect them to make sure.

This may be way off base and I'm sure you've probably already checked, but I had an eerily similar problem with my 2004 Itasca a couple of years ago. We were headed from our home in northwest Alabama to visit family in South Carolina south of Charlotte. Just east of Knoxville, the coach stumbled and lost power. I was able to limp to the next exit but just looking at it, couldn't really find anything out of the ordinary. It started right up and seemed to run fine for 50 miles or so when it stumbled again for a minute then seemed to run okay again. We made it to our destination without another hitch.

I initially thought it was either a fuel or ignition problem but it turned out to be an intermittently blocked air filter. It looked to me like there may have been some type of foam material used in the air intake ductwork, perhaps as some sort of a pre-filter placed there by one of the previous owners, that had eventually degraded, became dislodged, and partially blocked the air filter when under a load.

Grasping at straws, I know, but it wouldn't hurt to check.......
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Old 06-04-2023, 10:15 AM   #8
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What kind of trans temp when this happens ?
Good luck and keep us posted
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Old 06-04-2023, 10:43 AM   #9
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OP,
It almost sounds like a vapor lock situation, where the engine is hot and pulling a hill.
We have that as a way of life out here in central Colorado. I live @8500' and nothing is level out here.
On my coach, I rewired the 2 pancake fans up front to a toggle switch and they go on at the base of any long pull.

Mike in Colorado
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Old 06-04-2023, 11:37 AM   #10
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I concur water in the gas tank, have 32’ class A with the 8.1 workhorse from 2002. Was on I-70 in Colorado and 2 cans of dry gas saved the day.
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Old 06-04-2023, 12:02 PM   #11
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Thanks for the replies, you have given me a few things to consider, like checking the air filter.


To answer the questions, transmission temperature has been in the normal range, at least on our recent trip these have not been long uphill grades, just individual semi-steep hills. It is also likely not altitude related, as I just googled the elevation of a couple of memorable places where it occurred on our last trip, and they were in the circa 2,000 ft range. As to water in the gas tank it is a remote possibility, however we did burn through a lot of gas on this last 2,800 mile trip, sometimes getting down below 1/4 tank before filling up, with the problem happening at all fuel levels.



Here is a bit more information, I can't say for sure that there is a pattern to this, it may be my imagination, but it does seem to be more likely to occur if the engine had been at idle for a few seconds shortly before the stuttering happens. I am not talking long enough for significant overheating to happen while stopped, but just a momentary slow down or stop. One memorable hill where this happened was right after a making a turn at a 4 way intersection with a 4 way stop, and the road we turned onto had an immediate uphill climb within a few hundred feet of the intersection after we had been driving on flat land for a number of miles (just outside Smith Center, Kansas which is the geographic center of the US, or so the marker sign we passed in the middle of nowhere said).
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Old 06-04-2023, 12:27 PM   #12
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Just to throw something else in the mix. Dirty injectors.
When we take out coach out on a long trip, I always throw in 2 cans of Seafoam. They say 1 can treats 20 gallons so that is the full treatment.
2 cans in 80 gallons is a half treatment, but it lasts about 400 miles at that strength. Enough, I believe to do its job cleaning the injectors.
Might be worth a try.

Mike in Colorado
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Old 06-04-2023, 02:09 PM   #13
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OP,
...
On my coach, I rewired the 2 pancake fans up front to a toggle switch and they go on at the base of any long pull.

Mike in Colorado

Good idea, I think mine are set to come on at 210 or so now, so did you keep the temp sensor also right?


I see you have the Ultra RV ECM / TCM's I was thinking of buying the set as soon as I get to a free state (we have been in CA for two months.) were they an easy install and do you like them? I also have the factory Banks kit (intake and headers) installed.
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Old 06-04-2023, 02:20 PM   #14
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