Slow/dead pedal at startup

[ewo1]

What is a BAP (Barometric pressure sensor) and how does it relate to your codes that indicate problems with the APS/IVS? unknow as of this moment...still figuring it out.

Googling for 10 seconds showed me that a BAP was the baro pressure sensor. I'm going to SPECULATE based on the t444e/7.3 engines that I've worked on, that the BAP has nothing to do with those sensors, UNLESS they share a power or ground wire. YES THEY SHARE VCC AND GROUND The BAP will only change "with the weather". CORRECT

Your codes indicate a mismatch between the APS and IVS. CORRECT The computer is going to "expect" a certain APS when the IVS indicates idle position. CORRECT Isn't the IVS an on/off switch at idle? YES Doesn't the APS produce a couple of comparable voltages.... YES IT DOES ON A LINEAR SCALE, 0 - 5 VOLTS DEPENDING ON THE POSITION OF THE REOSTAT (VARIABLE RESISTOR)

CAUTION: Car info follows: some cars have one sensor that ranges from 0 to 5 volts while the other ranges from 5 to 0, they will always "mirror" each other with a voltage that totals 5 volts. If the computer ever sees a total that is NOT 5 volts, it has no idea where your foot is and gives you idle speed.

So how does your bus APS work? I speculate you will have two variable voltages from idle to WOT, CORRECT and one IVS that switches as the pedal moves from the rest position. CORRECT, ACTS AS AN ON/OFF SWITCH, IF YOU WILL...

those are some good questions, my response in red, above...

So basically the IVS, used as an on off switch, is nothing but a hall effect sensor, tells the computer you are intentionally stepping on the gas pedal and it is ok now for the TCM to respond, spin the wheels....

the AVS is nothing but a simple adjustable resistor, the more you step on the peddle, the more voltage to the computer, computer responds by adjusting the fuel to get you going.

So how can the BAP or MAP interfere with the APS/IVS circuit. They both share power and ground on the same circuit...at least on my bus.

 

[Mr P]

So your diagram is for a t444e. Your info says your bus is a dt466e. ?

Have you seen this: https://static.nhtsa.gov/odi/tsbs/2014/SB-10044293-1044.pdf

 

[ewo1]

So your diagram is for a t444e. Your info says your bus is a dt466e. ?

Have you seen this: https://static.nhtsa.gov/odi/tsbs/2014/SB-10044293-1044.pdf

Yes, that diagram is actually for my '99 Amtran. I got the bus up in Louisville and went I went to pick it up, the manager at the bus yard gifted me the paper service manual to Amtran RE busses. many, if not most, of the Chassis diagrams are for the T444E. Body wiring and the rest of the chassis wiring is the same, only the engine wiring changes. The wiring on my bus matches the diagram.

And YES, I have a copy of that doc.

 

[ewo1]

Pic of Amtran manual
post #22

AMTRAN RE Electrical Diagrams

Thanks for the info, I will do that test for you today and post the results. By the way, is there any way you can email me a copy of that manual for future reference? Much appreciated. Talk soon.

www.skoolie.net

 

[ewo1]

Fault Detection / Management
When the key is on, the ECM continuously monitors the APS/IVS circuits for expected voltages. It also compares the APS and IVS signals for conflict. If the signals are not what the ECM expects to see, Diagnostic Trouble Codes (DTCs) will be set.
.
Any detected malfunction of the APS/IVS sensor circuit will illuminate the amber ENGINE lamp.
If the ECM detects an APS signal Out of Range HIGH or LOW, the engine will ignore the APS signal and operate at low idle.
If a disagreement in the state of IVS and APS is detected by the ECM and the ECM determines that it is an IVS fault, the ECM will only allow a maximum of 50% APS to be commanded.
If the ECM cannot discern if it is an APS or IVS fault, the engine will be allowed to operate at low idle only.


My issue...
DTC 134 -APS signal and IVS disagree•
If neither the APS or IVS is changing, or both are changing, or the ECM cannot determine the DTC in specified time, DTC 134 is set and engine rpm is restricted to idle.

 

[Mr P]

I have enough experience working on faults like that on various cars that when I selected a bus....I got a dt466 MECHANICAL so that I won't ever be faced with your problem, yet, here I am concerned with yours..

My car repair experience would lead me to graph data from those two sensors when the problem occurs, and see which one was incorrect. If you can graph "normal" data, and compare that to a failure, you'll know a lot. Regarding the BAP, also the MAP shares power and ground. It is POSSIBLE for a sensor to fail and short the power supply to the rest of the sensors. Graphing/scoping data frame rates (whatever computer term for speed) needs to be sensitive enough to catch things that might "confuse" the ECM.

Once I caught erroneous data being cause by a bad alternator putting some AC voltage into the battery. Putting a meter on the batter to measure AC is cheap/easy.

 

[nikitis]

My car repair experience would lead me to graph data from those two sensors when the problem occurs, and see which one was incorrect. If you can graph "normal" data, and compare that to a failure, you'll know a lot. Regarding the BAP, also the MAP shares power and ground. It is POSSIBLE for a sensor to fail and short the power supply to the rest of the sensors. Graphing/scoping data frame rates (whatever computer term for speed) needs to be sensitive enough to catch things that might "confuse" the ECM.

I'm no mechanic, but this is why I suggested putting it up on blocks and "graphing" the values and comparing prior