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Old 07-11-2020, 06:57 PM   #1
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ISL 400 Surging Throttle

When driving under no load just maintaining speed my engine gets a surge going like you are driving with a toggle switch turning on/off quickly which causes the drivetrain to backlash. If you do not back off the throttle it continues getting worse and you can hear the driveline/rear end banging around. If you back off it stops and then you can accelerate again. Having it on cruise control makes it better as I assume the computer can react quicker to what ever is causing this?

In searching for a cause I have replaced the throttle position sensor at the throttle pedal. After installing the new sensor I calibrated it by turning the key on and slowly depressing the pedal then slowly releasing it 3 times per Cummins. That made no difference.

I looked closely at the throttle pedal itself and found a plastic shaft used in the pivot point. It was not solid so I installed a 7/16 bolt which stopped the flex in the pedal. That made no difference.

I recently made a 1200 mile trip and the surging was really annoying to deal with. Running cruise control as much as possible minimized the condition. The surge will occur at any speed while under no load or just maintaining speed.

When I returned home I searched again this time looking at the turbo thinking boost was fluctuating?? I found the pneumatic actuator for the variable geometry broken allowing the variable geometry lever to float. See pic. I ordered a new actuator and after 3 hours got the old one off the shaft of the variable geometry shaft. It had seized on the shaft. The variable lever itself was not seized. I tested the variable action with the engine running, in the down position it develops boost at idle and in the up position it does not.

The new actuator arrived and I checked it to ensure it was identical to the one removed and had the same stroke see pic. When I installed it I had to blow air into it to extend it to make it long enough to align mounting bolts. This severely limits the stroke of the actuator therefore the variable geometry function it is connected to. The variable geometry lever itself has a movement of about 3/4" up/down. With the actuator connected and air pumped into it, it now has a movement of about 1/4". I'd estimate the variable function extended is 90% and retracted it is 75%?? I don't know if this is how it is supposed to be or if somehow the lever is not properly timed/connected to the variable geometry mechanism inside the turbo?

I went to the local Cummins dealer who had never heard of a pneumatic operator for the variable geometry function. They thought it was for a wastegate. I looked up my engine number on Cummins Quickserve and they list it as a variable geometry turbo model HE431VTi which matches the tag on the turbo. I got the dreaded motorhome treatment but not a lot of guidance of what to do. I have a video of the new actuator stroke but cannot figure out how to upload it. Have to YouTube it and put a link in here?

I installed a boost gauge so I can see what is going on with boost and did a short test drive with the new actuator in place. Boost is slow to build as the VG function is limited but it did run up 25 psi of boost under full acceleration. Performance appears to be better on the short test drive. However, my hopes of finding the cause of my surge was not successful, it still surges under no load.

I had the Cummins shop update the calibration of the engine ECM and they found no error codes. That made no difference to the surge.

The 2004 pre emissions engine has 65,000 miles on it and otherwise runs great.

Any ideas of what is causing this surge?? I'm running out of places to look.
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Old 07-11-2020, 09:20 PM   #2
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If this is what I think it is, that being a sliding nozzle type turbo the fact that you had to apply air to the actuator to get it to bolt up would lead me to believe there may be a problem with the nozzle/guide plate in the turbo. The ISX engine would wear theses items and the sliding nozzle would stick causing all kinds of weird poop to happen. Turbo disassembly is required to inspect these parts. Just my worthless 02 cents though. Any check engine lights at all?
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Old 07-11-2020, 11:03 PM   #3
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No lights up front or error codes in the ECM. I agree, something must be wrong with the variable portion of the turbo and the lever the actuator connects to. That being said boost is happening and it would be normal for it to drop to near zero under a no load condition. It surges when it is at or near zero boost. Once it accelerates and generates boost all is well. It is as if the boost sensor is sending false values to the ECM at low pressures causing a surge in fuel delivered?? Not sure how to test that theory though.
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Old 07-23-2020, 11:26 PM   #4
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Update

Took rig into the local Cummins shop to see if they could figure out what is causing my problem. 3 hours later 3 master mechanics were stumped, could not figure it out. What they did accomplish was to confirm what is working ie; turbo, correct boost, boost controller, all sensors, ECM, throttle, fuel pressures etc.

They have had some issues with some alternators producing wild spikes that affect the fuel pump. Cummins has a service bulletin on it and a grounding kit to stop the spikes from bouncing the fuel pump. The quick test is to remove the power wire off the alternator and see if it stops the surge. I did that and it did not change anything on my coach. Another find was the power wire was not tight so that was snugged up when it was bolted back on.

What they are wondering about is the lock up torque converter in the MH3000 Allison cycling in and out. I guess there has been some history of that. That requires an Allison shop which is 140 miles away from home.

I addition there has been some problems with the fuel delivery tables between the throttle and cruise control input. Cummins has a different program for the ECM that fixes that problem. Waiting for them to get back to me about compatibility with my ECM.

In looking for anything drive train related, I pulled the driveline off to examine u-joints and found both of them damaged by lack of grease. The Spicer part number was still good and local shop had new ones in stock. This is not the cause of my pulsing throttle but good to get fixed now.

Will continue to update as I progress............
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Old 07-24-2020, 05:11 AM   #5
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I feel your pain. My only help is to offer a story of my own experience with what sounds like a similar occurence.
This year, we made several trips of about 1000 miles round trip. I was getting a surge, jerking type sensation while driving mostly at highway speeds. It felt like a jerking coming from my toad. I checked everything on the tow hook up. Nothing was apparent.
On the last leg of the trip, the surging got so annoying, I stopped and changed the fuel filter. That helped a little bit, but the surge was still there.
When we got home, I spoke with several friends that are knowledgable diesel mechanics. Both responded, without hesitation, it is in the lift pump.
I changed the lift pump, and it now runs as smooth as ever.
Good luck and I hope you have the same results, if you decide to go the lift pump route.
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Old 07-24-2020, 05:48 AM   #6
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I had a 2004 American tradition with a 370hp cummins engine that did the same thing. The cause of my problem was a partially clogged screen in my lift pump. The material was black with the consistency of chewing gum. Cummins said it was a result of algae. The New biodiesel acts as a detergent cleaning all the gunk accumulated over the years. I still try to find good old # 2 diesel if I can.
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Old 07-24-2020, 07:05 AM   #7
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I had a similar issue with mine several years ago on a quick trip to Yellowstone NP. It felt to me like fuel filter restriction so I replaced both primary and secondary fuel filters while at the campground and on the drive home noticed no change.

Upon arriving home I commenced diagnosing by disconnecting line by line and testing for air leaks and/or restrictions. Ultimately it turned out to be a restriction in the lift pump. I replaced the lift pump and it's been perfect ever since. The lift pump replacement was not an easy component to get access to but the replacement solved my problem.
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Old 07-24-2020, 07:35 AM   #8
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Lift pump restrictions huh. Well that is a new thing to check out.

This engine is a common rail high pressure system, not the CAPS version. It has an electric primer pump which runs for a few seconds to prime the gear drive fuel pump and then the electric pump shuts off. Some earlier versions had an inline lift pump that was known for issues.

I'm not aware of a filter or screen beyond the two large filters, one of which is a water separator. I changed both filters this winter but might be a good idea to do it again in case there is some algae present. The prior owner had spent some winters in Florida so that is a potential problem. I had not considered filters as wide open throttle has no restrictions or lack of power.

I will have to do some digging now to confirm the lift pump situation.

Thanks for the tips!!
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Old 07-24-2020, 08:21 AM   #9
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Quote:
Originally Posted by Windward View Post
Lift pump restrictions huh. Well that is a new thing to check out.

This engine is a common rail high pressure system, not the CAPS version. It has an electric primer pump which runs for a few seconds to prime the gear drive fuel pump and then the electric pump shuts off. Some earlier versions had an inline lift pump that was known for issues.

I'm not aware of a filter or screen beyond the two large filters, one of which is a water separator. I changed both filters this winter but might be a good idea to do it again in case there is some algae present. The prior owner had spent some winters in Florida so that is a potential problem. I had not considered filters as wide open throttle has no restrictions or lack of power.

I will have to do some digging now to confirm the lift pump situation.

Thanks for the tips!!
The lift pump on the CAPS system operates similar to the HPCR system in the fact that it doesn't run constant. Just enough to prime the system then shuts off. However, the fuel is drawn through it and mine had a restriction causing a surging issue.

I documented my repair over on my coach mod/repairs thread several years ago as I went through the diagnosis and the repair, however, I don't think the pictures are available any longer due to the tinypic debacle. The description and process should still be there though.
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Old 07-28-2020, 10:49 PM   #10
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Mike I've enjoyed your posts and YouTube videos. It says a lot to share your knowledge and make the effort to create videos for others to benefit from! I did find your post about the lift pump among the 84 pages of your repairs and upgrade thread. Too bad the pics are gone.

Not sure if the ISL common rail lift pump (#10 lower pic) has a screen or pre filter on it?? Where I do not have a lack of full power or difficulty starting not sure if fuel flow is my issue.

I followed fuel lines off the pre filter/water separator back to the fuel plumbing manifold located just above the starter. Not made to reach or get to. #2 on the upper pic is the fuel inlet fitting to that manifold. Not very big if it does have a screen? I did not see the lift pump and will need a second person to turn the key on so I can listen for it to find it. If it is behind the fuel manifold block it would take hours just to access it.

I have both fuel filters coming to replace again as I did see some flecks out of the water drain and I did check that the rectangular O-ring is in place on the filter/water separator threaded stud. If filters don't make any difference I'm running out of things to check.

Still waiting for Cummins to get back to me about the different ECM program.
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Old 08-11-2020, 04:23 PM   #11
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Got it Fixed

After much work and chasing down the wrong rabbit holes my surging throttle problem has been solved.

I replaced fuel filters again, installed a vacuum gauge on the final filter to confirm no restrictions, replaced u-joints, new tires checked and had a complete check of the ECM and its functions done only to still have the surge.

The Cummins shop was questioning the transmission as they did not find anything wrong with the engine.

Getting two different Allison diagnostic logs recorded for analysis was next. The Allison shop referred me to Pacific Power Group to see how to proceed. Their 30 year service representative from Lodi, CA called me back wanting to see the Cummins Insite image from when Cummins worked on the engine. After looking at that file he noticed the engine governor was set to "Variable" not "Automotive". He recalled some fire trucks with my engine/transmission having a surge problem caused by the wrong governor setting. Further he noted the wrong gear ratio for 6th gear which would affect the speedometer. He suggested I have Cummins go back into the ECM and change the governor to "Automotive" as well as putting the correct gear ratio on 6th gear.

Per Cummins "Variable" holds the RPM and "Automotive" holds the speed. Some trucks prefer to hold the RPM with changing loads vs: holding a speed. Country Coach typically specs this setting and I don't know how long it has been wrong in the ECM? Don't know if prior owner changed this or not? With this engine/transmission combination it did not like the "Variable" governor setting.

Once the change was made the foot pedal is as smooth as silk. The surge is gone and all is well.

Thanks for all the suggestions.
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Old 08-11-2020, 10:06 PM   #12
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Wow,
Thanks for all the info.
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Old 08-12-2020, 06:13 AM   #13
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Good info.

I have not run across a governor setting issue before.

Thanks for sharing the information.

Mike
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