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Old 09-05-2022, 08:02 AM   #1
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Cummins 5.9 12 valve towing issues

Having issues when going up long hills after driving for over 2 to 3 hours with the RV and trailer. The RPM's drop from 2200 to 2000 to 1700 . Stay there for a short time ,then go back up. Some times have to drop into 3d gear to get the RPM;s back up to 2000 and craw up the hill at 35 MPH. When entering the Hill , try to increase the RPM,s and the engine will not respond, just start to go down. The 5.9 is inter cooled and turbo charged. Anyone having the some issues. Thanks.
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Old 09-05-2022, 10:49 AM   #2
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Crawling uphill at 35mph is pretty normal; use whatever gear it takes to keep rpms near the peak of the torque curve and if the speed is 35mph so be it.
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Old 09-05-2022, 11:38 AM   #3
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The issue is that I never had that problem before. RPM's would go down a little before , but I just used a little more throttle and the rpm,s would still stay at one spot. Now , even on little grades the rpm goes way down and when I apply more throttle , the engine does not rpm up.
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Old 09-05-2022, 11:40 AM   #4
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transmission? Is it downshifting?
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Old 09-05-2022, 02:08 PM   #5
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when is last time fuel filters were changed?
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Old 09-05-2022, 02:16 PM   #6
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Quote:
Originally Posted by windsorbill View Post
when is last time fuel filters were changed?
BINGO!!!! We have a winner!!!
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Old 09-05-2022, 03:41 PM   #7
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Arrow

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Originally Posted by lllkrob View Post
BINGO!!!! We have a winner!!!
Not a winner.

The ISB will go into limp mode if there is not enough fuel to the injection pump.

Before heading north this I had both filters changed before heading north this year.

I go over White Pass on US-12 and take the road to Ocean Shores several times a year plus some other mountain with 10 MPH curves.

The trick is to keep RPM above 2500. This year I hit once section of road just right. I crawled up at 20 mph instead of my usual 10 mph. For the record, I crawl down an 10 mph. Heat is not an issue.

However, the last time I went east over White Pass, I was not paying attention to my RPM. Ended up going 10 mph in 1st. It was a hot day but onnce the grade became less steep I was able to back up to a normal speed.

I had to slow for a farm truck but with the RPM up I was able to acclerate and pass him.

Here is the basic issue. I shift at 2000. Sometimes RPM will increase to the max. When I shift up, I will slow back down to 2000 RPM. I try to pick a speed that I can maintain without shifting.

As a point of refernce, hit the scales on my last trip. MH and TOAD came in at 16,800 #. My ISB with a BanksPower pack is rated at 300 hp.

My ISB will go into limp mode if it overheats. Happy New Year in west Texas when the water pump replaced. I have cleaned or had steam cleaned the after cooler and radiator. Does not seem to make a differnce. Going up a grade, the check engine light will come on but it does not go into limp mode.
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Old 09-05-2022, 04:43 PM   #8
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4 years on both fuel filters. Yes, no issues with downshifting . I did try down shifting and the rpm,s came up for a short time then went back down. I have the 1994 5.9 12 valve . Do I have limp mode in that year? Only happens after driving for 2 to 3 hours and does not happen on a level road or going down hill.
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Old 09-05-2022, 05:51 PM   #9
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Originally Posted by rseibenick View Post
4 years on both fuel filters. Yes, no issues with downshifting . I did try down shifting and the rpm,s came up for a short time then went back down. I have the 1994 5.9 12 valve . Do I have limp mode in that year? Only happens after driving for 2 to 3 hours and does not happen on a level road or going down hill.
4 years on diesel fuel filters is a long time. I have a different engine, but my manual says every 12 months. You can have brand new filters and still have an issue with them getting clogged or restricted.

The pump pulls more fuel than the engine requires and returns it to the tank, at least on the ISL's. All that fuel is being filtered as it circulates.
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Old 09-05-2022, 07:52 PM   #10
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You don't have modes; it's all mechanical.

Change those fuel filters and definitely change the air filter. Be very suspicious of the exhaust manifold, turbo and air system downstream from the turbo. You may be losing boost pressure.

Get thee to a Cummins shop. It could turn into a huge deal.
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Old 09-06-2022, 12:12 AM   #11
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Quote:
Originally Posted by followingsea View Post
...The ISB will go into...
...limping...
My ISB with...
...limp...
My ISB will go into...
.
Different engine.
Nothing you wrote is applicable to the Cummins 12-valve mechanical.
Nothing.
.
Our ExpeditionVehicle has the size up from the 359ci/5.9-liters 12-valve, a Cummins 505ci/8.3-liters 12-valve mechanical.
About four years ago, a batch of funky Sacramento fuel clogged both of my parallel-mount Racor filters.
This fuel system circulates excess fuel through the tank to cool the fuel and reduce aeration.
If my massive after-market filters are clogging, we get the issue you describe.
.
Just as we got to the 20mph stage, we coasted into a NAPA parts-house in the farming community of Corning, California.
They carried a smaller -- 'saner' -- version of our components, we did the swap -- filling the new elements with ATF for style points -- and continued our merry way.
.
.
An aside:
2003, in anticipation of a trip around South America, we foraged the Racor manifold at a heavy-truck dismantler.
In this case, the filter unit was the only thing left on the stripped frame... no cab, no fuel tanks, no engine nor trans.
It was ready to go to the smelters.
I vaguely recall we offered them a couple fedbux, they countered with five, done and done.
.
New, in 2003, the manifold ran a couple hundred fedbux.
2022, would you believe that same system is nearly two grand!
http://www.amazon.com/Diesel-Filtrat.../dp/B002MBSHDC
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Old 09-06-2022, 07:29 AM   #12
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followingsea,
"As a point of refernce, hit the scales on my last trip. MH and TOAD came in at 16,800 #. My ISB with a BanksPower pack is rated at 300 hp."



Under 17k including toad seems light for a DP, unless there is helium in the tires.

Maybe a typo?
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Old 09-06-2022, 09:45 PM   #13
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Filters would be first on my list as well. What year 12V? If not filters (I’d be shocked), there are other options if a P-pump. If the filters don’t fix it, I can get you a few other options that might be causing you problems.
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Old 09-07-2022, 06:45 AM   #14
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1994 Diesel pusher. P7100 pump.
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