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ElizabethMeyer

2500 Allison and no full throttle downshift - at times

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I'm having a VERY strange problem with my 2015 Tiffin with a 2500 Allison coupled to a 340 ISB Cummins. The problem is related to a full throttle downshift issue or lack thereof. The weirdness is that the transmission seems to have a "working" mode and a "not working" mode. When it is working I can do a full throttle request at 50 MPH on a flat road and it will downshift. Every time. When it is in "not working" mode, at the same speed on the same road, it will not downshift. Every time. The really weird part is that what triggers the flip from "working" to "not working" is stopping and turning the ignition key off and back on. Once it is in "working" or "not working" mode it will stay in that mode until you cycle the ignition again. I have driven hundreds of miles in both modes and I know for a fact it will stay in either mode.  I know none of this  makes sense but I was down at Red Bay for 2 days last week with this issue and I demonstrated it to a Cummins tech and an Allision tech who were down there just for this issue. They agreed cycling the key was causing the problem but they had never seen it before and everything they tried to do failed. To date the ECM, TCM and TPS have been replaced. The techs are going to regroup with Gary Harris from Tiffin for next steps but everyone is completely puzzled. Gary Harris does not think it is a wiring issue either which leaves Freightliner out of the dance.

If it is in "not working" mode it will still manually downshift via the key pad and  pulls strong. Cruse control also downshifts in "working" and "not working" mode. 

One other oddity is that while cycling the ignition is the only thing that will flip it from one mode to the other, cycling will not always flip it. Sometimes it will flip modes with a single cycle and other times it can take dozens of ignition cycling to get it to flip.

Cummins says they are reading and sending 100% throttle even in "not working" mode while Allison sees 100% throttle only in "working" mode and a partial throttle request in "not working" mode

Gary Harris and the two techs were non-believers until I demonstrated this repeatedly to them.  The problem occurs for all full throttle downshift requests at any speed. I've tested this often enough that I know the exact downshift ranges for each gear so I know when it should execute a downshift. 

Yesterday was a great example of the problem. We left our camp site and the coach wouldn't do a full throttle downshift. Pulled over, cycled the key off and on and it full throttle downshifted fine until we stopped to refuel. Left the gas station and it wouldn't downshift. Pulled over, cycled the key and the full throttle downshift worked fine until we stopped for lunch and we had to repeat the process. Today it worked right out of the gate when I took it from my house to storage. These are typical experiences for me. 

12,000 miles on coach and I've put on 8,000 of those.  Any thoughts that I can share with Tiffin and the 2 techs? 

 

Mark (using my wife's account)

 

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Mark.  You have the best at hand.  I'm as lost as your Tech's are! Only thing I see, is a loss of communication, between your engine & transmission.  Sorry. 

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Mark, Excellent explanation of the issue !  The primary Modules have bee replaced - if I'm reading your information correctly. 

There are 2 items that could cause this issue that have come up over time, that I know of. One is the intake manifold pressure sensors and the other is poor ground point. 

The ground(s) are supplied by direct connections or through relays during the start cycle. Should the Logic circuit not get a ground - some times a circuit will not toggle. No error codes would tend to make one wounder if the issue is in a throttle subsystem or intake manifold pressure sensor system. 

Please post what they find on this one.

Rich

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Mark, One more Question ?

Does the problem happen when you first start the engine ? or after things warm up any you have driven for a length of time?

Think I know from you OP but just want a conformation from you !

Rich.

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Rich,

It doesn't matter whether it is cold or warm and it also doesn't seem to matter if you stop and cycle immediately or wait for 5-15 minutes to cycle. I've tested this many times. I'm sort of feeling that it cycles more readily from "not working" to "working" but I don't have any hard evidence to support that. 

 

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Has the Cummings Tech, plugged into the engine or transmission with their portable program yet?  Has anybody, done anything yet and what have they found?  

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Manholt,

 

Both the Cummins tech and the Allison tech have plugged in. Multiple times.  Cummins shows 100% response to TPS full throttle request in "working" and "not working" modes. Allison shows 100% in "working mode but only a partial throttle request in "not working" mode. What the Allison computers shows in "not working" mode is what I term a rolling throttle response. Meaning, that when I have the pedal to the floor, instead of seeing 100%, Allison sees a request for 40% that then rolls up to 90% or even 100%. It doesn't always hit 100% often pegging around 94% throttle request. 

 

Mark

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Has anyone checked to see if the rear end has the correct gear ratio? I have over the years known of instances that the gear ratio was to high for the auto transmission which caused very similar problem with the downshift at WOT. As a matter of fact, the jeep wrangler that I use as a toad had the very same symptoms when I bought it used. It had slightly oversized tires and absolutely would not downshift at WOT, I replaced the tires with the correct size tires and the problem was immediately fixed. Not saying that is your problem, but just a possibility, manufacturers have been known to put the wrong differentials into the right case, meaning that the marking on the outside is different than what is on the inside. An easy check for you is to check the speedometer reading with a very good GPS set to the lowest update setting most can be programmed to as little as ten feet.

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Good point, Kay!  Mind is set on 2 components, forgetting other's!  If that is not the problem, then I would suggest to Allison, drop and replace my transmission!  Time is expensive and irreplaceable!

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3 hours ago, ElizabethMeyer said:

Manholt,

 

Both the Cummins tech and the Allison tech have plugged in. Multiple times.  Cummins shows 100% response to TPS full throttle request in "working" and "not working" modes. Allison shows 100% in "working mode but only a partial throttle request in "not working" mode. What the Allison computers shows in "not working" mode is what I term a rolling throttle response. Meaning, that when I have the pedal to the floor, instead of seeing 100%, Allison sees a request for 40% that then rolls up to 90% or even 100%. It doesn't always hit 100% often pegging around 94% throttle request. 

 

Mark

Mark, My question regarding the percentages the Cummings  ECM see's and the Allison TCM see's. Do they both receive the TPS (Throttle Position Sensor)information from the same circuit? or is the transmission receiving information from the Intake Manifold pressure sensor?  The amount of fuel available and the intake manifold pressure readings are used by the ECM to determine the proper mixture over time. 

       The Turbo Boost increases over time as the RPM's increase and this will cause a delayed increase in the percentages displayed. Have they measured the turbo boost levels over time and the fuel lift pump pressure / and flow rate over time,relative to horsepower / torque?

Is the issue caused by changing or low fuel flow - even if the TPS is reading at 100%  and  

          The 2 control modules are talking to each other over a CAN network. These networks are well know to have data dropout due to cabling and connection issues.  

The ECM should be supplying engine status to the TCM - so is knows how much power is being requested to reach the proper gear.

       These 2 piece's of information need to be all-way's exchanged - if the engine or transmission is sending the wrong information - it is still being exchanged and no Error Codes will appear or display IMHO.

       The devil is always in the details.

Rich.

Just a personal note regarding the Cummings lift pump's. I have replaced a number of them for low fuel flow and low fuel pressure issues.

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8 hours ago, kaypsmith said:

Has anyone checked to see if the rear end has the correct gear ratio? I have over the years known of instances that the gear ratio was to high for the auto transmission which caused very similar problem with the downshift at WOT. As a matter of fact, the jeep wrangler that I use as a toad had the very same symptoms when I bought it used. It had slightly oversized tires and absolutely would not downshift at WOT, I replaced the tires with the correct size tires and the problem was immediately fixed. Not saying that is your problem, but just a possibility, manufacturers have been known to put the wrong differentials into the right case, meaning that the marking on the outside is different than what is on the inside. An easy check for you is to check the speedometer reading with a very good GPS set to the lowest update setting most can be programmed to as little as ten feet.

I appreciate the thought, and no, they haven't. That said, it full throttle downshifts fine in "working" mode which it wouldn't do if it was geared incorrectly. It would have the lack of full throttle downshift all the time, right?

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6 hours ago, DickandLois said:

Mark, My question regarding the percentages the Cummings  ECM see's and the Allison TCM see's. Do they both receive the TPS (Throttle Position Sensor)information from the same circuit? or is the transmission receiving information from the Intake Manifold pressure sensor?  The amount of fuel available and the intake manifold pressure readings are used by the ECM to determine the proper mixture over time. 

       The Turbo Boost increases over time as the RPM's increase and this will cause a delayed increase in the percentages displayed. Have they measured the turbo boost levels over time and the fuel lift pump pressure / and flow rate over time,relative to horsepower / torque?

Is the issue caused by changing or low fuel flow - even if the TPS is reading at 100%  and  

          The 2 control modules are talking to each other over a CAN network. These networks are well know to have data dropout due to cabling and connection issues.  

The ECM should be supplying engine status to the TCM - so is knows how much power is being requested to reach the proper gear.

       These 2 piece's of information need to be all-way's exchanged - if the engine or transmission is sending the wrong information - it is still being exchanged and no Error Codes will appear or display IMHO.

       The devil is always in the details.

Rich.

Just a personal note regarding the Cummings lift pump's. I have replaced a number of them for low fuel flow and low fuel pressure issues.

Rich,

I don't have a clue. I forwarded your earlier response to Gary Harris at Tiffin and he noted that he had been thinking along those lines too.  I'm forwarding him this email too. I spoke with Cummins today (trying to get warranty information) and ended up talking to a guy who seemed very interested in the problem and mentioned a Level 3 group that works on odd issues like this when the field tech and second level support get stymied. He is going to contact the field rep to see if he pulled data from the system when I was down in Red Bay. He wants to ship that data to the mysterious Level 3 group. My note of caution to him was that I was interested but I need somebody to own the problem and coordinate with the other vendors because it doesn't do me any good to have them go "no problem on our side. Been there, done that, cut the large check. Coordinating with the vendors was why I ended up in Red Bay. Gary Harris made that happen. 

Mark

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Mark

i have the same year chassis as you on my Forza. Haven’t had any issues at all with the transmission. Back in May of last year I received a letter from Allison about an issue with upshifting, Did you receive one as well and was the Allison tech aware of it or mention it. The letter mentions an upshifting problem, I know it’s the opposite of what you are experiencing but maybe all related. When I went to freightliner for engine related issues I showed them the letter, they said they would have to send the TCM to Allison to be reflashed as they didnt have the means to do it there. I figured if ain’t broke don’t fix it so I ignored the issue. 

I am attaching a copy of the letter for everyone to read 

Good luck with your issue I’m sure they will resolve it for you.

Phil9F3E9C3C-86CE-4DF8-936C-32011569AB40.thumb.jpeg.f8b2dd42a5a31869f24db7654f33368f.jpeg

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Well, the PITA process continues but with some hope too. First the whining. Tiffin has basically, and in a very nice way, opted out of the diagnostic process. Their advice is to take it to Cummins or Freightliner. The problem with that is I know what the responses will be because I''ve been there done that. Everybody points to everybody else and the financial bleeding goes on with no progress. My hope was that Tiffin would own the problem because of their influence with their vendors. I was looking for leverage not necessarily financial assistance. They did to a degree but when the initial effort failed that was pretty much it.

Then, I got excited with Level 2 at Cummins because they seemed very interested and told me that they often solved others problems. Great. Got an appointment scheduled at Cummins in Hodgkins Illinois and contacted Level 2 to make sure Hodgkins had any and all background data from the two techs who worked on it down in Red Bay. Crickets. Get down to Hodgkins and, surprise, surprise, "nothing wrong on our end you need to take it to a great Allison shop in Grand Rapids, Mi." NOOOOOOOOOOOOOOOOOO! 

Now some good news. I call Cummins Level 2 and BEG him to help get this solved. Told him my experience with Hodgkins was exactly what I expected and without his involvement I was going to get exactly nowhere. So he calls Hodgkins and calls me back. I'm to go back to Hodgkins the next day (yesterday) and they have been told what data to capture for Level 3. I also provided some additional information that when the trans wouldn't downshift at full throttle, the turbo boost was also low - never above 20 - psi. (Didn't even know I had a turbo boost gauge. Why didn't the Cummins tech at Red Bay notice that?????)

So I get down there, we do the test trips, they gather the data and the tech starts acknowledging that Cummins has problems with turbos, turbo actuators, etc. that could cause low boost and yet throw no codes but causing the transmission to see no power and therefore no downshift request. FINALLY SOME CRITICAL THINKING TAKING PLACE.

So now I am going back next Tuesday to do some more trips with an interactive CAN bus tool so that Level 3 can see what is happening in real time from wherever  they are located. 

No idea what the costs are going to be but it sounds like the parts are under warranty. Don't know about the labor. It would be helpful if anybody who knows the warranty with certainty wouldn't mind chiming in.  

Keeping my fingers crossed.

Mark

 

 

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Mark, for what it is worth. I think there in the right area.

What Allison transmission do you have in the coach? There are throttle position wires required in some harnesses running between the ECM and TCM. Electrical engineers some times shot themselves in the foot trying to solve one issue - while creating another.  Software programs get tested, but in the real world. The time needed to get real time data is limited and high level test equipment is expensive. In meetings with all the personal, The system tech's are the key drivers of a solution. The devil is in the details an engineers are smart, tech's are the ones that pickup the crumbs.  

    It is allot like the Medical field. The best results are often driven by good nurses . They spend more time with the sick.

Rich.

Mark, setting at the computer and got to thinking. The wiring Harnesses are made by a supplier and tested before shipping. Considering  the number of connections, there are thousands of them. There is a strong possibility of one being intermittent - like looking for a needle in a haystack. The issue you are having, one might just see it the harness wiring section connecting the circuit that is most likely to be the culprit could be replaced. There are to many systems that use the same setup working - that fact, should for the most part eliminate a number of items.  We often refereed to it as the point of heights probability.

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Rich.

Thanks for the continued responses. I have a 2500 Allison. I''l share your thoughts with the tech when I am down there on Tuesday. 

The only thing that will cause my issue to cycle from "working" to "not working" is turning the key off/on and shifting from Drive to Neutral and back to Drive after starting. However, cycling the key won't always flip it from one mode to the other. Taking it down last Thursday I had to cycle the key 30 times (cycle, drive, cycle, drive, etc.) before it switched from "working" to "Not working". Once I got down to Cummins, and we finished the "not working" data gathering, it took me just a couple of times to cycle it back to "working". Does that seem more likely to be a wire issue or a sticking electrical device (whatever that might be)? They were talking about some sensor or device that "sweeps" when you turn the ignition on and were speculating if that might be the issue. Above my technical pay grade.

Mark

 

 

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I did a little research. I called a friend of mine also and confirmed that most of the time when you get no downshift, its because the program written in the trans controller will not allow a downshift if it will cause a over-rev condition for the engine. As far as the working mode/not working mode, he is not familiar with that term. Sorry for not being able to answer your concern any better.

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Mark, The Lack of DCT's ( Diagnostic Trouble Codes) Will drive tech's nuts. No issues at all when the coach was new and then(if I'm reading you correctly) The mode problem has gotten progressively worse, but when the system is in the correct mode everything works fine. Has anyone measured the transmission shift point pressures. A number of the tests are run with the coach park brake set and the wheels chocked,transmission in neutral. While changing the engine RPM's from idle to 1500 RPM's

Basically, the drive train,  engine and transmission communicate Via a CAN network to monitor RPM relative to  transmission Turbine speed an internal system pressures.       

The 2500 transmission is not the newest model, but you have a newer Cummings engine. That fact means a different ECM setup(programming). but it sounds like you have run a data string monitor while driving and no issues regarding data errors. Also, They should have run a transmission software evaluation on the TCU and the ECM.

If my interpretation of the information to date. It is looking like a simple issue(always the hardest to find). When the ignition key is cycled, a reset process is run. In most cases the reset is pulling required circuits to ground. 

Grounds' Corrosion an intermittent connections have always been the biggest PITA. There are internal connections to sensors, out of sight out of mind.

    Not having the entire wiring diagrams for Harness and internal wiring of the TCM and transmission.  So the thoughts are only from years of loosing over many hrs of work.

Rich.   

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10 hours ago, f442485 said:

I did a little research. I called a friend of mine also and confirmed that most of the time when you get no downshift, its because the program written in the trans controller will not allow a downshift if it will cause a over-rev condition for the engine. As far as the working mode/not working mode, he is not familiar with that term. Sorry for not being able to answer your concern any better.

The "working" mode and "not working" mode are my terms. I use them simply because they are easy to understand. Everything works or it doesn't. I think the tech used the terms "power" mode and "derated" mode. Those may be more accurate but what the **** do they mean to the average guy? Also, not in an over rev mode. Actually it is under revving. This has been one of the points of contention between Cummins and Allsion. Allison is saying they are dong what the engine is telling them to do - partial throttle so no downshift required.  Cummins is saying they are responding to a call to derate the engine. This is where I get so frustrated because they each wash their hands of it rather than trying to find out exactly what is causing this miscommunication. in the systems. 

The good news is that during this last go around Cummins is starting to acknowledge, or at least consider, that they may not be making power. It helped immensely that the Cummins shop manager worked with the Allison tech in the near past and stated that if Darren (the Allison tech) said it wasn't an Allison problem then it wasn't an Allison problem. 

3 hours ago, hermanmullins said:

Elizabeth,

I know this is a strange question, but by some chance have you by installed a chip to boost your Horsepower? If so that can present several problems.

Herman

Herman, unit is 100% stock.

 

2 hours ago, DickandLois said:

 Has anyone measured the transmission shift point pressures. A number of the tests are run with the coach park brake set and the wheels chocked,transmission in neutral. While changing the engine RPM's from idle to 1500 RPM's

Rich.   

Rich, nobody has run that test.

 

Mark (aka Elizabeth - my wife and the actual FMCA member)

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Mark, we won't hold that against you! :lol:  My Fiance Linda has her F# and a DP...I have mine.  We are both members of the Forum, but now, since she has me she feels that there is no need for her to get on Forum!  Ironically, she is a better trouble shooter than me. 

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Start with the lowest cost items to replace, I would replace the ignition switch before diving into expensive diagnostic tests.  I know I need to replace mine(I can remove the key in any position), once a year the gauges will swing from operational to pegged to the max., and the engine stops for perhaps 1 second the resumes running. I pull over, turn of the key and wait a minute, restart the engine and everything is normal again for many months.

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Mark, Just keep looking for possible simple fixes for the issue you are experiencing. 

Personally a strong believer in the KISS factor (Keep is simple stupid)

      Armed with only a strong curiosity and no wiring info. found 2 items to check.

 Note-there is an inline fuse (10 amp mini) between the transmission harness and engine ECM . I would check this out first before anything else if you can find out your coach is wired with an inline fuse. Take the fuse out and look at the fuse holder for corrosion. This will also reset the transmission TCU.

Also found a post that mentioned unplugging both speed sensors and reconnecting them cleared the problem.

I do get Tack speed errors on my older Allison - The transmission fluid weeps out past the sensor connections at the sensor, clean the sensor connections male - in the sensor and the harness connection female. With some CRC reconnect and problems gone for 2 or 3 years. Think it is related to how many miles one drives.

That it for this post. Please let the group know when a solution is found !

Rich.

     

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