RandyA Posted January 15, 2016 Report Share Posted January 15, 2016 A couple in the same CG as we are came in today with a 1998 MH with a Cummins 8.3. The entire rig is cherry with only 60K. His problem is the engine will occasionally suddenly rev to max RPM even if he is not pressing on the accelerator. It can be idling or driving down the road. Obviously a dangerous situation. He asked if I could look at it since I had a HDT. Unfortunately my knowledge of this engine is minimal. Charlie jumped in with me and we could not find a problem or make the engine repeat the problem. As expected, the accelerator is wired. The pot on the pedal feels smooth with no flat spots. The injection pump is the square one (vs. round) and of course the injection system is mechanical. The owner is hesitant to drive the rig with the problem and he is not familiar with any service facility in the Melbourne, FL area. Anyone have a clue what might be going on with this engine? Randy, Nancy and Oscar "The Great White" - 2004 Volvo VNL670, D12, 10-speed, converted to single axle pulling a Keystone Cambridge 5th wheel, 40', 4 slides and about 19,000# with empty tanks. ARS - WB4BZX, Electrical Engineer, Master Electrician, D.Ed., Professor Emeritus - Happily Retired! Link to comment Share on other sites More sharing options...
NoDirectionHome Posted January 15, 2016 Report Share Posted January 15, 2016 I would "guess" that you are experiencing a crank position/speed sensor signal dropout that makes the engine think it is stalling. That would in turn, kick up the fuel to maintain idle speed. Just my guess "There are No Experts, Do the Math!" 2014 Freightliner Cascadia DD16 600hp 1850ft-lb 18spd 3.31 260"wb SpaceCraft S-470 SKP #131740 Link to comment Share on other sites More sharing options...
shorts Posted January 16, 2016 Report Share Posted January 16, 2016 I'd be looking real close at the fly by wire side of the system, it doesn't take much corrosion or work/age hardened 18 year old electronics to make them suspect, the inline P series Bosch injection pumps have a very solid reputation Link to comment Share on other sites More sharing options...
NoDirectionHome Posted January 16, 2016 Report Share Posted January 16, 2016 I'd be looking real close at the fly by wire side of the system That was my 1st thought as well Shorts, but as the throttle is jumping while just idling, I kind of ruled that out. They are also (for safety reasons) designed to fail low as opposed to high. "There are No Experts, Do the Math!" 2014 Freightliner Cascadia DD16 600hp 1850ft-lb 18spd 3.31 260"wb SpaceCraft S-470 SKP #131740 Link to comment Share on other sites More sharing options...
shorts Posted January 16, 2016 Report Share Posted January 16, 2016 Stekay, If I read the original post correctly, the only electronic stuff is the accelerator linkage, mechanical injection doesn't use any of the sensors and microprocessor feedback inputs to run the engine like the newer electronic emission control engines do. Historically the mechanical pumps either do or don't work, nothing inside to be an intermittent problem. Link to comment Share on other sites More sharing options...
RoosterBooster Posted January 16, 2016 Report Share Posted January 16, 2016 no expert on this , but may check if engine is feeding off a intermediate engine oil leak somewhere ?!? (like turbo bearing that only leaks when hot/cold or something like that) any unusual oil consumption? " Diamonds R 4 ever " "class of`95" Pete 379 "Toterhome": Cummins N14, Super10, single axle, 278" WB, 162" sleeper ... sold current project; 1952 Diamond T, Cummins 8.3l @ 375hp/ 800ft lbs, single axle, 239" WB, 1954 Spartan 137" air ride sleeper .... full timing in a 39 foot "sticks & staples POS" Toyhauler (planing to build an all aluminum 42-45 foot replacement soon) ... Link to comment Share on other sites More sharing options...
jkoenig24 Posted January 16, 2016 Report Share Posted January 16, 2016 Has he contacted Cummins directly? I sure would. Link to comment Share on other sites More sharing options...
NoDirectionHome Posted January 16, 2016 Report Share Posted January 16, 2016 Has he contacted Cummins directly? I sure would. I agree completely! Shorts, researching online it appears electronics were introduced in '96 as the C8.3E "There are No Experts, Do the Math!" 2014 Freightliner Cascadia DD16 600hp 1850ft-lb 18spd 3.31 260"wb SpaceCraft S-470 SKP #131740 Link to comment Share on other sites More sharing options...
OU812 Posted January 16, 2016 Report Share Posted January 16, 2016 Randy A This internet site might help with the Cummins 8.2 RPM problems. Give them details....year, make, ect. I"ve used it and they got right to the problem. Go to " Justanswers.com/medium-and-heavy-truck " Sounds like, to me, a air leak or a injector pump shaft seal problem to me....??? good luck OU812 Link to comment Share on other sites More sharing options...
Scrap Posted January 16, 2016 Report Share Posted January 16, 2016 The King ETS was a kinda common control in the 90s when you couldn't use rods. So follow the throttle cable from pump to the box on the frame......errr, well, wherever a motorhome puts it...... and if you land at a King 2500 or 2600 here is your diagram and a troubleshooting tree: http://www.cruisecontrolking.com/throttlediagnostics.html And this tells you what and where to meter on the pedal : http://www.alpinecoachassociation.com/chassis/Throttle%20&%20Cruise%20Manual%20&%20Troubleshooting%201998.pdf Of course your problem isn't in the book but it gives you something to start with. I know you brought your meter on vacation with you Randy...... Link to comment Share on other sites More sharing options...
Broncohauler Posted January 16, 2016 Report Share Posted January 16, 2016 Had that happen on one of my past freightliner work trucks while hauling a 80k lb hazmat load. I pulled out of a brake check area onto a 6% grade with a 35 mph speed limit and the truck took off up to 55 mph. I had no idea what was happening and started trying to figure out a course of action before I got to the runaway truck ramp a mile ahead. If I put the truck in neutral, I might be able to stop and hopefully the rev limiter would work? Or I could just shut the truck down and have no power steering,and hope enough air to stop the truck? As I made a decision to go for neutral just before the run away ramp the throttle started working again? So I kept going on past the ramp. I thought about it and decided if it happened again that I would be able to safely stop by putting the truck in neutral. It did happen again as I past the ramp and 3 more times on the way down the grade. After I got to the bottom everything was ok so I continue to my stop in El Centro California,where I turn around and return to San Diego California. It was the middle the night and wanted to try and get the truck as far back as I could before I had to call a tow truck . Not exactly the smartest idea or company policy but that's what I did. Everything was fine until I got to our warehouse and while trying to back into the dock, The truck again want to full throttle no matter what I did I could not get it to idle down. So I shut it down and left it till morning it once again seemed fine and we are able to drive it to the dealership down the street from my work.. The truck also was a flyby wire and it was the sensor on the pedal that was bad. Link to comment Share on other sites More sharing options...
Scrap Posted January 17, 2016 Report Share Posted January 17, 2016 That would not be fun! Early '90s? Link to comment Share on other sites More sharing options...
Broncohauler Posted January 17, 2016 Report Share Posted January 17, 2016 If you're asking me Scrap? Late 90s century class. My truck was in for service, it was only the 2nd time I drove the truck. It had a lot of electrical problems after being repaired from a rollover ( not me) when it was 4 weeks old. Link to comment Share on other sites More sharing options...
RandyA Posted January 18, 2016 Author Report Share Posted January 18, 2016 Thanks for all the feedback and suggestions. I realize some required time and research. The owner of the MH wanted me to share he is very appreciative. Using the info and links Scrap provided led us to some trouble shooting that keeps pointing back to the actuator module. I should have picked up on this early on and noted here that his cruise control was not working but at the time I just assumed it was probably an issue with the micro switch on the brake pedal (never assume anything). Not sure at all what is going on inside the actuator and felt it was best to encourage the owner to visit a facility qualified to service the actuator vs. a generic diesel engine mechanic down the road from us. Everything I could get to for checking appeared OK but you know how it is trying to nail down an intermittent - if it ain't really broke it is often an Easter Egg hunt (using application logic, of course). Anyway, I think we have the guy headed in the right direction and at the same time afraid to drive the MH "as is". Personally, I'm glad he is not following behind me going down the highway until he gets the thing fixed . Randy, Nancy and Oscar "The Great White" - 2004 Volvo VNL670, D12, 10-speed, converted to single axle pulling a Keystone Cambridge 5th wheel, 40', 4 slides and about 19,000# with empty tanks. ARS - WB4BZX, Electrical Engineer, Master Electrician, D.Ed., Professor Emeritus - Happily Retired! Link to comment Share on other sites More sharing options...
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