Set Fast Idle on 2005 Thomas Cat c7

[Peterjk]

Hey everyone,
Need some help setting the fast idle on my 2005 Thomas cat c7. I took it for a oil change and now it fast idles at 2300. It was about 1600. Shop says they didnt change it. I somehow dont believe them.

Peter

[Peterjk]

I found out myself. This is done via the Ecm. So will require a trip to a Cat certified dealer.

[Peterjk]

A little more background on why I think this happened . I took my bus for a oil change. The truck shop said they discovered a slight air hiss noise coming from the drivers side electrical panel which is excessable from outside the bus. Theres a part which controls the pressure to the brake air reservoirs. They flipped the part but it wasn't a Cat part. They never tested the fast idle. Soon as i picked up the bus i hit the fast idle and it shot up to 2300 rpm . It used to be around 1600. So i need this fixed.

[Peterjk]

Im wondering if i can get ahold of the software they use and set this myself to spec.? How hard can it be? Laptop, software, cable? Unless Cat controls this bit of software and wont release it for anyone to download.

[PorchDog]

I think you have to use CAT proprietary software to do anything to a late model CAT engine.

Other folks here can probably shine some additional light.

Hard to see how changing a brake pressure related solenoid/relay could change the fast idle.

[Marceps]

Why in tarnation did you entrust your bus to a shop for a mere oil change, instead of doing it yourself? Do you not love her?

The closest I have for you is 15-2 (page 298) of Thomas MVP-ER Service Manual TBB 85410204 (1998). Good luck.

[Peterjk]

I had forgotten this thread, as the problem fixed itself after the first "shake out" drive. But yes, I dont know why I took it to a shop to change oil, prob because I live in a apartment, so there's no place to work on my bus, im doing it myself next time once i find a place to work on it. I do want to see if I can buy a old laptop and find cat software so i can monitor the ECM while driving. Ive heard of other folks doing that. Thanks you both for replying, thank you for that schematic Marceps. Cheers! Peter

[Booyah45828]

Fast idle speed is adjustable on some buses/engines, typically the ones that use the cruise buttons for engaging/setting high idle. Hold the accel/decel button up or down in order to set idle speed at a certain rpm. I believe that feature is for adjusting PTO speeds on certain models. Other buses just have a high idle toggle switch. I have no idea what yours uses.

The part air is hissing from doesn't do anything with brakes, it's likely the pressure regulator for the stop arm or air door. If it's the stop arm, and seeing how this isn't in school bus service, I'd follow the hose to wherever it goes near the tank and plug that port, eliminating the hose/switch/regulator and any future leaking.

If your bus has an adjustable high idle speed, the mechanic did likely "change" it in order to speed up air pressure build up after they dumped the tanks. Nothing malicious there. Service writer probably had no idea, as it's such a minor thing not worth mentioning in a work order. Not a big deal IMO.

[Peterjk]

re: Other buses just have a high idle toggle switch...
Mine has that.


The part replace by the shop I took it too, which caused the hissing is the ""Air Regulator 1/4NPT FML 1-60 psi PN:41735K11"
It was/is located below the drivers side window, behind the electrical fuse panel door.


It was a straight up replacement, no ECM work was required.