Cat 312BL: cant get full revs

[digger_hunter]

Hi guys,

We have just got a Cat 312BL (Perkins engine) serial 9FS00746. Found a problem with it that when I try to increase the throttle from 1-10 it doesnt rev fully. I disconnected the stepper motor cable (only 1 cable on this type of Cat compared to the 2 cable models i am used to) and revved the engine full by pushing the arm on the injector pump. So engine seems to be OK.

So i went it to the diagnostics on the display and the engine speed knob works fine and the target RPMS in the computer are ok as well. Engine speed sensor checks out as well. So i tried to calibrate the stepper motor and it starts off the calibration but immediatley halts the calibration and comes up with an error of H 04 (engine high idle speed too high). I tried a stepper motor from another one of our Cats and same behaviour so the problem is not the stepper i guess.

I checked the computer for any error codes but cant find any and the computer shows green LED as well.

Any help is appreciated from anyone who can tell me what to try next.
Thanks

 

[digger_hunter]

oh by the way i tried increasing the engine speed from the backup switches and still the engine speed will not increase beyond what i can set using the engine speed knob which is weird as well. I chekced the RPMS i was getting and it maxes out at about 1400-1600. Should be able to get 2100 at full speed.

 

[kbeen]

Hello digger_hunter. sounds like you got a good one alright. have you put you volt meter on the acuator motor and see if you are still getting voltage to it when you are asking it to continue to throttle up the engine. i have hooked some of the cat spoons in the wires to check them before. 1) If you are still getting the 24volts to have the motor pull on the cable then possible is the throttle to stiff for the motor to pull it against the governor springs or something causing binding. 2) but if you are not getting any more voltage when it stops throttling up then it is a different issue. i do not see how you can be losing voltage when you use the manual switch though. as long as you are holding the toggle switch you should have voltage to the governor motor. so i would thing possible the other is going on.try putting a helper spring on the governor lever that will assist in pulling it to high idle just to maybe see what it does. good luck and keep me informed.

 

[digger_hunter]

Hi Kbeen

Thanks for the reply
will try your suggestion tomorrow. Whats really weird is that i have swapped a computer and a stepper from one of our other Cat 312Bl's and the problem is still there! its weird! To just cover all teh bases i am gonna try this stepper on the good machine just to eliminate any issues with the stepper as well as check voltage. But do you know of the fault code i mentioned? "Engine high idle speed too high"
or 70 HF 09 when you run the calibration?

 

[kbeen]

Do you mean 70 HF 04. my book does not have a 70 HF 09 ??

 

[digger_hunter]

Sorry 70HF04. You are right

 

[digger_hunter]

Actually just checked my notes and what happens is when I start the calibration I get PSP and then I pres button 8 and immediately I get 70 H 04. And when I press button 8 again I get 70HF09

 

[kbeen]

My book only says it is " Faster Than the high Idle Speed " it does not go into any detail as to what will cause this error. i assume it would be exactly what it is saying. the engine rpm is to high, possible the engine computer is seeing to high of engine speed, possible the speed sensor, might swap it with the other machine to see what happens.

 

[digger_hunter]

Hi Kbeen. I will swap the rpm sensor and check as well. But when I rev the engine manually using te injector pump arm, I see the correct revs on the display. Very weird!

 

[freedom digger]

Maybe it is something as simple as an adjustment on the actuator rod. If you can manually bring the motor up to speed will adjusting the rod length allow the actuator to bring the motor up and still have enough throw to return to idle?

 

[digger_hunter]

hi fredom digger,

tried this as well but doesnt help.have adjusted the actuator to max length and still get the same issue. I am gonna try kbeen suggestion of checking voltage at the stepper and also check out the rpm sensor just in case. I am also gonna try the stepper in our good machine see if it carries the problem across

 

[digger_hunter]

Ok guys thanks for all your help and suggestions. The problem was that the injector pump arm that's held to the stepper arm by some sort of clamp had come off. So when the stepper is pulling the cable the lever just moves and moved the injector pump arm only a tiny bit. I clamped the two together and recalibrated and all is well.