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1997 U320 ECM and harness trouble

April 24, 2018, 03:31:52 pm

My coach started showing and intermittent stop engine light. Sometimes simply stopping the engine and restarting would clear it. Checked fuel filters, coolant, oil, pressure and temp gauges and all good. Coach runs fine and never went into a limp mode. Then the stop engine light would not go away. Took it in to a repair facility after a couple months running like this. Scan showed a lot of communication errors with the ECM. cleared them and they would come back. He found a few frayed wires and fixed them. Still got comm errors. Re-flashed the ECM...still got comm errors. Still more frayed wires. I instructed him to buy a new harness. I hope this is the fix. Anyone have any experience with this? I feel like I'm going down the rabbit hole with this...

Jody

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Re: 1997 U320 ECM and harness trouble

Reply #1 – April 24, 2018, 03:49:18 pm

Would start shopping Ebay now for a deal on the ECM.

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Re: 1997 U320 ECM and harness trouble

Reply #2 – April 24, 2018, 05:18:16 pm

Dont panic yet! 
My 96' U320 did this and the solution was simple.  If i turned on the "boost" switch before starting, the stop engine light would not come on.  I had exactly the same symtims you do.  It may be as simple as your starting battery is getting weak, and the voltage with starter engaged goes low enough to cause com errors with the ecu.  It's what was wrong with mine.  My coach is equipped with the M11 Cummins 400 hp engine.  Check the battery terminals first.

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Re: 1997 U320 ECM and harness trouble

Reply #3 – April 25, 2018, 06:16:12 am

Yeah that was the first thing they did. Went through and cleaned up the battery terminals again. ECM is about $950 online with lifetime warranty. If the harness doesn't fix it then that will be the next step.

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Re: 1997 U320 ECM and harness trouble

Reply #4 – April 25, 2018, 08:58:50 am

Following Kemahjohn's comment, I would sure put a voltmeter on the ECM 12 VDC positive feed to harness ground to see how low voltage goes while cranking.  Lots of connections between batteries and ECM.

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Re: 1997 U320 ECM and harness trouble

Reply #5 – April 25, 2018, 09:01:35 am

Since you're getting an intermittent loss of signal you might want to pull off the connectors at the ECM and clean them with something like Deoxit then use dielectric grease.  Also check any ground connection.  Quite a few problems are caused by oxidized connectors and bad grounds.  Worth trying before you buy a new ECM.

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Re: 1997 U320 ECM and harness trouble

Reply #6 – April 25, 2018, 10:09:11 am

What would be the minimum voltage allowed at the ECM?

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Re: 1997 U320 ECM and harness trouble

Reply #7 – April 25, 2018, 04:57:43 pm

Try Heavydutypowertrain.com these are Cummins Ecm guys. They have techline # talk to Terry Chorn. It definitely sounds like low voltage.

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Re: 1997 U320 ECM and harness trouble

Reply #8 – April 25, 2018, 09:23:37 pm

My 1995 U320 #4707 Cummins 400 HP ECM died last year outside of Waco, TX on our maiden voyage after purchasing it last year. I purchased a replacement through Heavy Duty Powertrain. My check engine and stop engine light would come on erratically. I replaced the Ecm, Complete Wiring Engine Harness, Shut down Solenoid and Camshaft Sensor in the parking lot of Stewart Stevenson in Waco on a Saturday after waiting on various mechanics for six weeks. Budget 4 coachbucks doing the work yourself. I have traveled several thousand miles since then and it runs great. The Harness was shorted out behind the front engine lifting eye. (Which I found while replacing the harness)The roadside mechanic put in a 30 amp fuse in place of the 20 and a puff of white smoke quickly arose from inside the ecm.

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Re: 1997 U320 ECM and harness trouble

Reply #9 – April 26, 2018, 10:07:20 am

My friend's cousin from a big diesel shop in Albuquerque flew in for a vacation late last year. We were trading engine stories in the hanger when the subject of Cummins ECUs came up. The ECUs are not protected well and the stock wiring harness is substandard so any chaffing, etc. can cause a short and ECU failure. A shorted injector can also cause ECU failure. So, good to replace harness when ECU is worked on and take a glance at it on a regular basis for wear/damage. Cheap insurance.

He also advised checking for exhaust manifold leaks, especially down toward #6 cylinder. The stock manifolds are prone to shrinking and can be a time consuming to replace because of broken studs. 24 valve engines also more prone to valve seat problems so good to adjust valves as Cummins recommends.

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