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Possible beginning of runaway engine???
Started my coach today to air up a tire. Left it at normal (low) idle. Over a 10-15 minute time frame the engine RPMs started creeping up 50 to 100 RPMs at a time. When the RPMs reached 1100 I turned the high idle switch on and off, still stayed at 1100 RPMs. Tried holding the brake pedal, releasing the parking brake and putting trans in Fwd & Rev. Trans would not shift because idle was to high. Turned bus air on and idle returned to 700 RPMs, turned bus air off, idle went back to 1100 RPMs. If I stepped on the accelerator pedal RPMs would increase above 1100 then fall back to the 1100 (now creeping to 1200). Turned bus air back on to lower RPMs back to 700. Then shutdown the engine, tried turning power switch on dash off then back on. Restarted engine and still had high idle.
Shut everything down AC and DC at breakers then disconnected chassis battery for about 5 minutes. Reconnected battery and everything seams to be back to normal.
Was this just a gremlin or is this the beginning of a bigger issue?
Chuck
2000 Featherlite H3-45
2024 Jeep Grand Cherokee
Leesburg, FL -
10 Replies
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More likely a sensor issue since rebooting the ECM seems to have fixed it.
Check your electronic accelerator pedal (just a rheostat) and make sure it is not caught on anything. Lift it off the rollers and reset it. Turning the engine off and on will re-establish the digital throttle range.
I had a similar problem a long time ago. The jake brake would not engage going down a mountain. The cause was my accelerator pedal not returning to full idle. The ECM reads the digital idle value from your pedal upon start.
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Three greens:
Did your reset fix the issue or did you end up replacing any parts?
Chuck
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We have experienced very similar symptoms on occasion over the last 2-3 years. The first time it happened I immediately hooked up a code reader, but there were no active codes. Suspecting a possible fuel issue, I changed both fuel filters and the problem went away, only to return a few days later. Since then it comes and goes intermittently with no obvious pattern. After much online research, discussions with experienced DD 2 cycle mechanics, etc, we still see it from time to time. However, a while ago I learned that when it occurs if I quickly and strongly “punch” the accelerator pedal, the symptoms go away.
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I just cleaned the guides/rollers and made sure it would travel back to the idle position. No problems in the last 5 or so years.
Replacement would be easy if the actual rheostat (potentiometer) is the problem, i.e. not giving smooth continuous read-outs or developing dead spots. The pedal assembly is just plug and play.
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John & ThreeGreens: Thanks for the input:
I will clean the roller etc on the back of the throttle pedal. I watched a marine diesel engine runaway once, it was scary and costly.
Sounds like this is just a glitch, can’t imagine having one of these beast running away while heading down the road
Chuck
Jeff and Lindsay
91 Marathon XL -
A runaway with DDEC is almost unheard of. It was much more common on mechanical 2 strokes.
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Even 2 stroke runaways are not an issue since about 1968. This is the approximate Detroit came out with the “broken back” rack. This rack was developed to prevent run aways which were caused by a sticking injector.
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Called Prevost PASS and told them I had code 22 (EFPA -Electronic fuel pedal assembly) show up on the DDEC flashing display. PASS said it could be two things, a bad potentiometer on the back of the throttle pedal or a bad wiring harness. As Jon would say “go for the low hanging fruit”. I ordered a new potentiometer $120 and will install this weekend. PASS tells me its a simple plug and play, hope it’s that simple…
Chuck
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Many moons ago I had a gas pedal fail. At least I thought that is what it was.
As it turned out when I started to pull it out to get a part number from it I found the connector had been pushed together with one of the pins skewed sideways, not in the hole but touching the metal around the hole.
I think it came from the factory that way. The coach was about 10 years old at the time. The fix was to straighten the pin and make sure it went into the connector.
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Just received part and installed. Was pretty simple,except they have changed the wiring harness plug on the new part to a 4 pin configuration instead of the old 3 pin configuration. They provide a new harness with the new 4 pin on one side and the original 3 pin on the other side. It is just a matter of swapping out the harness. Not as easy as it sounds, but jobs finished and all is well.
Is there a way to clear out the old fault codes without the DDC reader (I.E. through the dash buttons)?
Chuck
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