DX 3 Cummins Diagnosis

[bkballard3]

Looking for some helps here. I have 2014 DX3 with 2012 Freightliner M2 Chassis. Cummins engine I believe it is an 8.7 L. The issue is while climbing grades, full throttle, towing a full size pickup, as the vehicle slows and RPM gets into the 1100-1300 area the engine feels like it is missing, as it is doing so, I hear a cough in the exhaust (lighter version of a backfire). It has been to a freightliner x3 after extensive work replacing the turbo the first time. The second and now 3rd time, they report they can't replicate it or that there are any codes. By the way I have a 2 minute video that shows the symptoms. I am hoping someone may have had similar and was diagnosed correctly solving the issue. I have a longer story, but I think this is at least a start. Sorry for the long read!

Brian

[rskeans]

It seems to me that pulling grades at 1100 rpm is very low. Why now just kick it down a gear or two and get the rev's up where they belong. Something like 1800 rpm.

[bkballard3]

Thanks for the comment. I agree, from what I am told regardless of the load or lugging of the engine the engine should not react that way. The Freightliner dealer is are blaming the transmission. Of course they said that after they told me on the first call it was normal according to Cummins! next stop is Allison on Tuesday to check parameters. I just worry if this condition is somehow harmful to the engine.

Forgot to add this symptom occurs just prior to the downshift by the transmission.

[Thebackpacker]

Brian,

When I first acquired my DX3 last December 2015, I also observed the lugging and delayed downshifting at low engine rpm, especially when climbing hills. I have not noticed "coughing." I read in one of the Cummins' manuals that when operating the engine at wide open throttle, the engine should be operated between the rpm for maximum torque and maximum horsepower.

I brought my DX3 to Freightliner for evaluation. For the price of an hour of labor, they told me the transmission was performing normally. They would make whatever changes I wanted, as long as Allison agreed to them. I made no changes.

Subsequently, if I feel the need for improved performance I manually down shift to get the engine to 1,900 rpm and maximum torque. The improvement in performance is very noticeable upon mannually downshifting to bring the rpm up to maximum torque.

Just last night, I was talking to a Force owner. He told me he took his Force to Cummins. For $1,000, they made a few changes to the engine to get more torque and horsepower out of it. He next took his Force to Allison. For approximately $200, they changed the transmission’s shift points from economy mode to performance mode. He has noticed improved performance, especially from the changes made by Allison. He has not noticed a change in economy, i.e., miles per gallon.

Gerard

[bkballard3]

Thank you Gerard,
I talked to the Allison guy today, I will see him on Tuesday to learn about my configuration. That will go a long way, although may not solve what I consider an engine issue. Thanks again for the information!

Brian

[mikew968]

Somewhere I read there is a selectable mode from normal to economy. Not sure what year

[mikew968]

Allison says there is a secondary shift schedule

[HappyGuy]

Sounds like a transmission that is holding gears. The "performance" tune would likely adjust downshift points for the trans. It doesn't sound like an engine issue but if the turbo engine is at WOT and lugging that can cause damage.

https://www.youtube.com/watch?v=soJea7xEt-8

Adjusting the shift points will help matters and the fact that you're driving a HD diesel and not a turbo 4 banger will limit damage thanks to parts durability but I would still be manually downshifting until the transmission shift points can be adjusted to your preferred driving style. For me personally I have always manually downshifted before hitting a grade so I would never have even picked up on this issue.

[bkballard3]

Thank you very much, for the info. I will be heading to Allison on Tuesday to learn more about how this transmission is programmed. You would have thought the Freightliner folks might have figured this out. Especially with a 2 minute video of the activity occurring while driving.

Thanks again

Brian

[bkballard3]

Thanks, in phone discussions with the Allison guy the more button on the shift selector can be programmed and may not be programmed at all. Will learn all about this on Tuesday.

Thanks for the info!

[AWF1945]

I will be following this topic. Looking forward to your findings. Thanks for sharing.

Slim

[ard58]

On this engine your peak torque is at 1400rpms. I wouldn't let them drop below 1200 before forcing down shift. Cant say about the noise, but Allison should be able to help you.

[bclemens]

Also make sure the carpeted mats are not under the gas pedal. I've seen that happen.

[Hogq]

Just thinking out loud... at low rpm, under a heavy load, the rack may be opened, and a fuel rich condition present in the exhaust stream. An air leak anywhere in the exhaust system especially near the down pipe, would result in the potential for explosions, like mini-backfires. I would look for a loose clamp, corrosion, or any source for an air leak in the exhaust pipe or near the turbo housing.

[bkballard3]

Thank you, I will check this out. I appreciate the help!

[bkballard3]

Yes sir I have seen this too. Mine is clear full pedal is available.
Thank you!

[Farmboy55]

I believe the issue you have is a condition known as turbocharger surge. You can google it to see the technical description of the problem. Not a problem easily resolved from an engine perspective as the engine calibration or turbocharger need to be revised. Changing the shift points with the transmission to keep the engine above the engine speed range where it occurs will likely be the best way to resolve this issue.

[JRM63]

I believe I have the same issue, a backfire popping noise at lower RPM. I would like to watch and listen to your video. The Freightliner dealer here has been of no help.

[bkballard3]

Just a quick update. I visited Mello Transmission Company (Modesto, CA) this morning met with Correy Mello, very helpful and knowledgeable. So my transmission has a primary programming mode for economy, if I were to use the "mode" button on the selector it would have been Performance mode. Not that anyone could tell me that except to tale to an Allison Tech to plug it in! It is now programmed the opposite, it will now have the primary mode as performance and secondary program (via the mode button) will now be Economy. I will take it out on a trip next week, hopefully there will be a hill or two to test this out and see if it solved the "feels like a miss, and sounds like a cough" under full throttle with towed vehicle. I was also supplied a Shift Selector Manual that discusses all the features of these shift selectors. You can check oil level, oil life, error codes etc. I am going to try and make this available on the forum, under manuals? I will try and figure it out!

Thanks all, I will post more as I get it.

[bkballard3]

Great Videos on Allison Automatics:

https://www.youtube.com/watch?v=p9gmW6MVSpk