Why is my accelerator pedal sometimes non-responsive? (Series 60 with B500)

[belfert]

I have a Series 60 engine (DDEC III) with B500 transmission.  I had some issues on my recent trip with my accelerator pedal not responding all the time.  I would push the pedal to the floor and the engine would not accelerate from where it was at.  I have a Silverleaf that shows engine load from 0% to 100%.  The engine load might be at 80% and it would not move to 100% when the pedal was pushed to the floor.

This mostly happened with cruise engaged.  Maybe I wanted to accelerate to pass a truck on interstate a little faster, but mashing the pedal sometimes did nothing.  We also saw times going up a grade where the cruise didn't increase the engine power so the bus started to slow dramatically.  The bus sometimes seemed to want to stay in 6th gear too long which also didn't help.  I would at times downshift to 5th which helped somewhat.

No codes set.  This happened only maybe 25% of the time.  It seems more like a electronics issue and not a problem with the accelerator pedal.  Any ideas on what to check?

[Jon]

My first thought was the TPS, but a bad turbo boost sensor can do the same thing. This presumes all connections are clean, tight and free of corrosion.

[luvrbus]

Is this the 1st outing since having the 6th gear unlocked ? I am thinking you have a communication problem between the B500 and the 11.1 series 60 did Allison do your programming ? 

[Hard Headed Ken]

Brian, I have another question. Has your Silver Leaf ever displayed 100% load?

Ken

[belfert]

Brian, I have another question. Has your Silver Leaf ever displayed 100% load?

It shows 100% engine load quite often.

6th gear has been unlocked for several years and I don't recall this issue before this year.

[luvrbus]

Does it ever idle rough ?

[Hard Headed Ken]

Considering the way percentage of load is calculated in the ECM program (it's much more than just throttle position) I'm surprised you ever see 100%. I don't think I ever see 100% load on mine.


If the throttle position sensor is faulty it should set a code but it's possible that it might not.  Most of the time I use the diagnostic software to guide me to the problem then prove that out with a voltmeter or scopemeter. Because the diagnostic software and check engine light only knows the component has a voltage/resistance that is above or below a set amount. The low or high voltage could be caused by a corroded connection or damage to the wires between the component and the ECM. The component, TPS sensor in this case could be good and the fault code or problem maybe caused by a bad connection or damaged wiring anywhere between the TPS and ECM. 

Here's a method you could use to determine if the TPS is faulty. I would probably do this even if the diagnostic software told me the TPS was at fault.  Especially on an intermittent problem.

Back probe the Sensor Supply wire at the ECM, connect a wire, run it all way to front of the bus, connect a volt meter to that wire, ground the other lead and watch the volt meter as you drive. It should always remain steady at about 5 volts. That test verifies your sensor supply voltage is good. Now move your back probe to the Throttle Pedal Sensor return wire. Now your volt meter should read between 0 and 5 volts depending on throttle position. If you don't see any unusual readings when you lose power then you have some other problem. If you do see unusual readings it would be best to check the 5 supply at the TPS and the output at the TPS this would help eliminate wiring problems between the ECM and TPS.

I tend to over complicate things because it's never the simple thing for me. I hope your luck is better.

[Oonrahnjay]

... Here's a method you could use to determine if the TPS is faulty. I would probably do this even if the diagnostic software told me the TPS was at fault.  Especially on an intermittent problem.

Back probe the Sensor Supply wire at the ECM, connect a wire, run it all way to front of the bus, connect a volt meter to that wire, ground the other lead and watch the volt meter as you drive. It should always remain steady at about 5 volts. That test verifies your sensor supply voltage is good. Now move your back probe to the Throttle Pedal Sensor return wire. Now your volt meter should read between 0 and 5 volts depending on throttle position. If you don't see any unusual readings when you lose power then you have some other problem. If you do see unusual readings it would be best to check the 5 supply at the TPS and the output at the TPS this would help eliminate wiring problems between the ECM and TPS. 

     All good advice.  I'd expect the "unusual readings" that Ken mentions to be a voltmeter needle that starts to move smoothly, then stops for a moment, and jumps up, then goes on smoothly to the full 5 volts (as you move the accel pedal, of course).  You could also have a VM needle that begins to move, drops to 0 again, and then jumps up; or you could have the needle go up smoothly and then stops even though you keep pushing the pedal further.  All of these things will tell you about the actual failure mode inside the TPS, but the bottom line on all of them is that the sensor is bad and has to be replaced.  Don't expect your driving glithch to correlate exactly with the volt meter anomaly; sometimes, they do but often they don't.
     Having said all this, it just seems to me that your issue may not be in the actual TPS sensor itself.  They're usually pretty straightforward and you have an intermittent problem that just doesn't seem to act like a failure I've ever seen (note that my experience has been pass. cars and buses may be different).  But, as Ken has said, all you can do is track the problem down with fault codes, your software reader, and your voltmeter.

     (Oh, and one other thing (WAIG here) ... when this occurs, does it just occur once or twice and then go away (as opposed to happening and then continuing to happen every time you push the pedal for a few minutes)?  What I'm wondering here if the fact that you have SilverLeaf connected might be triggering an issue.  If it happens and then seems to continue to happen for a few minutes, I'd disconnect the SilverLeaf and try it again.  Of course, if it's totally random, that won't prove much.  I'm thinking that this is very unlikely to be your problem, but when you have a totally weird-@ss problem, you have to consider everything.)

     Good luck (I hate intermittent electrical problems ..)

[luvrbus]

I would have someone check the calibration on the cruise,it was calibrated for 0.74 in 5th with his rear gearing from the factory now he has 0.64 with 6th gear and he saying it stays in 6th too long and down shifting to 5th helps.
The B500 has 2 speed sensors that sends the data back to the engines ECM.I don't know who enabled his 6th gear. I tried to get Williams to enable 6th in the Dina here and they refused same bus as Brian's with a 11.1 series 60 and that said it may not be his problem he may have a different problem 

[belfert]

I checked the TPS earlier this summer when I was helping someone in Alaska who had TPS issues.  I'll have to check it again.

It looks like I might have to break open my wallet and take the bus to Interstate Power to have them check out the settings for cruise in the DDEC.  I sent the WTEC to Reliable Transmission down in Florida and they enabled 6th gear.  I can see the gallons of fuel used per hour go up if I downshift to 5th gear so 6th gear does seem to save fuel.

[robertglines1]

outside ch>>>  the plug connector to wiring harness from pedal. Mine is in front bumper compartment. ? minor corrosion. easy ck.

[blue_goose]

The change to 6 speed wouldn't make any change in the cruse speed.  You should have two modes in the transmission.  Try the mode and see if it down shifts faster. 
Jack

[belfert]

The change to 6 speed wouldn't make any change in the cruse speed.  You should have two modes in the transmission.  Try the mode and see if it down shifts faster. 

My understanding is the default on a typical B500 is to use normal mode when the mode light is not lit.  When the mode light is lit the transmission will be in economy mode.  I understand this can be reversed in the WTEC so economy is the default, but I have no idea how to check if this is reversed.  I did try hitting the mode switch at one point, but it wasn't clear if it helped.

Even in 6th gear shouldn't pushing down the throttle to the floor increase engine power?  If cruise is enabled sometimes the throttle just seems dead and the engine doesn't increase power or barely increases power.  It isn't all the time.  I use cruise most of the time, but sometimes I want to speed up and should be able to do so.  Sometimes cruise will allow the speed to fall dramatically instead of increasing engine power.  I think Clifford is onto something about needing some tweaks made to DDEC settings for cruise.

[blue_goose]

The program in my B500 gives economy as normal and more aggressive in mode.  The only setting in the ecm for cruise is where it drops out and max speed that you can set. 
The most important thing you can look at for power is your boost pressure.  When you push on the throttle you should see a change in your boost. 
Jack

[luvrbus]

 The only setting in the ecm for cruise is where it drops out and max speed that you can set.  

That's not right Jack there are a lot more than 2 functions.I guess it could depend on the version on the software but mine will let you set the min and max speeds for the cruise,enable the VSS,set the number of teeth on the VSS,tire revolutions,drive line ratio,transmission final ratio,pulses per mile and top end speed limit,then when you are done you go into the Allison to finalize the process.The VSS is a Oem sensor (vehicle speed limiting) that most used like Eagle and Dina when 6th gear was locked out fwiw