I know this forum mainly covers dodge pickups, but I'm hoping someone can help me out. I have a 99 Ford F800. It has a 5.9 24 Valve Cummins mated to a Allison auto transmission.

Here is what I have going on. The motor starts up perfect, idles smooth and at normal rpm's, the throttle responds perfect and I can run the rpm's up smoothly when its in neutral. As soon as I drop it into any gear, its like the motor is trying to take off. I have to hold it back with the brakes to keep it from going, but the tach is still reading normal idle rpm's. Its basically like I'm power braking it, but I'm not touching the throttle. When I pop it back into neutral, its pretty harsh, and you can tell the engine was trying to go and running at high rpm's. What I did one time when it was in gear was depress the throttle until it moved the tach and I could hear the rpm's increase a little, and then held that position and popped it into neutral and the rpm's were around 1700. The weird thing also is that once you take off and start driving, the trans shifts fine, and it runs like normal down the road. Its just at idle with the trans in gear, something is telling the motor to GO.

It just started doing this the other day out of the blue. Its not throwing any codes. It has a new VP44, coolant temp sensor, air intake sensor, oil pressure sensor, and transmission. I also tried a back up ECM that I have, and it does the same thing, so its not the ECM itself. I've cleaned all the sensor connectors (well, all but the crank sensor by the starter) and the ECM connections and coated everything with dielectric grease. I've tried unplugging a bunch of different sensors but no change.

I'm thinking it has to be some sensor that is telling the VP to increase timing and fuel for some reason when its dropped into gear, I just don't know which sensor would do that. Any thoughts or suggestions on what to check would be greatly appreciated. Is it going to do any good to take it to a shop and hook it to a computer if it isnt lighting up my check engine light? I hate taking it to the shop. Last time I had them install the oil sensor and recalibrate the ECM it ended up costing me $800. My butt still hurts from that one!

 

Kinda weird but sounds like your TC is locked up when put in gear (not fluid coupled and trying to stall the TC)???

 

Thats what I was thinking at first, but the Allison AT545 does not have a lock up torque converter.

 

I doubt it has anything to do with the engine. By your words [ but the tach is still reading normal idle rpm's.] tells me its nothing to do with the engine. I have a 98 f-800 and its an inline p-pump with a 6 speed. My idle is 800 rpms. You need to get some diagnostics on your transmission it sounds like one clutch is hanging up like they will with a burnt warped clutch pack.

 

Are you sure about that? I've driven a number of Allisons in fire trucks over the the years and they all had a lock up converter. That's as far back as '74. In fact, I had one of them do exactly as you describe and it was a locked converter. If you can find the lockup wire you can clip it and then it won't lock until you get it fixed. That's what the fire mechanic did when mine locked. I'm betting that's what it is.

 

I'm positive. Its non-lockup.

 

It has a allison reman trans in it with only 5000 miles. If a clutch pack was burnt or warped, wouldn't I be able to smell it in the fluid and wouldn't it affect the driveability of it? Fluid looks and smells fine, and it shifts good when I drive it down the road.