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Air Throttle without Air

Yahoo Message Number: 15821
Hello

I have been troubleshooting my hard to start 8.3l Cummins mechanical engine.

Aside from the hard to start after sitting for 24 hours the symptom is that the air throttle has no air pressure until about 50 seconds after the engine begins to run. During that period, I can control the RPM with the electric cruise control but not the air operated accelerator pedal. My air tanks will have 120 PSI in each but the Throttle does not have air pressure.

Once the throttle is air pressurized, it works fine for about 24 hours and the engine fires promptly each time. So the leakdown is slow.

I assume the problem lies between the secondary air tank and the throttle valves. Perhaps a line leak or a check valve failed?

Does anyone have a similar experience to help me fix this thing?

Thanks

Dean

95 Magna #5280

Re: Air Throttle without Air

Reply #1 –
Yahoo Message Number: 15822
Dean,

Your auxillary tank will be feeding the air throttle, so you won't have any gauge indication. After sitting, the aux tank could be completely empty if the leak is bad enough, the brake guages could still be at 120 each. The guages are for the brakes only, front and rear. I would start the soapy water test from the throttle controller all the way to it's source. Build up air until the dryer pops off, then you know the aux is full.
Good luck...
Tom

04 Allure 30979

Re: Air Throttle without Air

Reply #2 –
Yahoo Message Number: 15837
Dean I'm not sure what kind of throttle control you have but I'll relate my story with my 8.3 in my 98 allure. It has a King throttle and one morning I started up and the engine refused to gain rpm when the acc. pedal was depressed. To make a long story short I had to have it towed in and they diagnosed it as a bad electronic King control unit. Replaced this and it has been fine since.
Regards
Ron #30185

Dean wrote:

Re: Air Throttle without Air

Reply #3 –
Yahoo Message Number: 15839
Mine is air pressure vs your King Control electric. I do have the King Control cruise control set up and that works to vary the throttle until I have air at the accelerator pedal(throttle). I am guessing that part of my "hard to start" is that lack of air pressure at the throttle even though the tanks are at 120 lbs.
 

Re: Air Throttle without Air

Reply #4 –
Yahoo Message Number: 15840
Tom,

Aha!!! Here I thought the aux tank was full because the bottom indicator was at 120. Thanks for the clarification. I'll check it this weekend

Dean

95 Magna 5280