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EngineerMike · 02-13-2015, 06:11 PM

2005 Contessa 40ft., Cat engine, Roadmaster chassis (posting for a friend)
Engine intermittently keeps running when key is shut off. Ignition switch checks OK (run voltage goes off when key is Off). Starts & runs fine otherwise.

I'm assuming there is a Run relay that feeds power to ECM that is sticking so engine still thinks it should run.
Good assumption?
Any idea where to find relay?
Any other ideas on how to diagnose?
I posted in Roadmaster forum but not much action there.
Thanks, Mike

gatorcq · 02-14-2015, 07:03 AM

you are going to have to call or post on the roadmaster forum. diagram i needed.
Check the chassis fuse box and look for a fuse, if it has a fuse then possible goes to a relay

NeilV · 02-14-2015, 07:14 PM

How many miles on it? Diesels will run on if you get a buildup of purged crankcase oil in the intake. They will run pretty good on ATF also.

Deny · 02-14-2015, 07:34 PM

look for a bad ground
switch/solenoid-connections-ground- double ground to be sure

phays · 02-15-2015, 04:26 PM

Check your ignition solenoid. When mine refused to shut down I first used the kill switch in the engine bay, turned off chassis batteries and then pounded on the ignition solenoid with a wrench (didn't have a hammer). Turned on the engine batteries, restarted coach and shut ignition switch off and back to normal. If that doesn't solve the problem, start the engine and try disconnecting one side of the 'big' wires on the solenoid and see if the engine shuts down.

I've since replaced the ignition solenoid with a heavier duty solenoid from Cole-Hersee, their 24213 model.

DIYRVGuy · 02-15-2015, 04:46 PM

You didn't mention any error codes or check engine lights and so suspect voltage is still being sent to fuel supply system (pump).

Suspect switch first but could be a poor connection elsewhere.

Did you check the owners manual for troubleshooting steps?

gatorcq · 02-20-2015, 01:22 PM

By the way, for a C7 or 3126E, once the ECU looses power the engine should stop. The loss of power will shut down the Injector actuator Pressure Valve

paul6050 · 02-27-2015, 10:26 AM

Diesel engines are compression ignition engines, so they have no spark plugs and they don't need electricity to run. When troubleshooting an engine problem, I like to start at the effect of the issue and work my way back. Whenever the engine won't stop running, find the fuel valve solenoid and disconnect the positive wire going to it and the engine should stop. If it doesn't, then it is getting a source of fuel other than diesel, like the crankcase oil or ATF. If it does stop, then you need to figure out why the voltage isn't getting turned off, when you turn off the key. And that would be a relay somewhere that probably needs replacing. Just follow the path of electricity/wires back to the ignition switch. Good hunting! Paul

gatorcq · 02-28-2015, 03:46 PM

Except for CAT, the fuel flow is controlled by High Oil Pressure. The IAP sensor and the IAP valve is controlled by the ECU. The ECU regulates (open/close) the pressure of the oil. The Valve is electronically controlled. Meaning once you loose ECU power, the valve will close, thereby shutting off oil flow to regulate fuel flow.

caseydc57 · 03-02-2015, 08:42 PM

Keep in mind that the ECM is what sends the signal to the injectors to run the engine. No mater if the IAP sensor or the HEUI pump is active the ECM cancels the injectors to operate. It sounds like you may have a short to the OEM 70 pin connector or ignition switch problem. Pin 70 on the P1 connector should be checked for 12 volts with ign switch off. Note: This connection does not need a relay switch to run this engine. Some manufactures may have a relay. Many do. If it has power. Checked the ign switch. If the ign switch is off but power shows up at the P1 connector pin 70. Check for a relay switch. If no power from the relay for pin 70 power but still it will continue to run with power showing up at the 70 pin, it would tell me that there is a short from some other power source. Before any of this is checked above, it is best to have a monitor check ECM status. You may have something showing up that would help locate the problem. I have yet to see an ECM keep things running with the ign switch power off at pin 70. Note: There is 3 or 4 other constant power suppies to the ECM P1 connector that are powered on all the time. ECMs do some funny things at times too.