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Engine won't stop! (Post DUVAC replacement, 28SI)


Go to solution Solved by Bjohnsonmn,

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Funny that this post is following an post called "Engine won't start".

2000 Windsor 32PB, House and Chassis 12v systems fully isolated (LiFePO4 house swap)

As is the case for many of us, my DUVAC Lacee alternator generated its final amp and died in rather remarkable fashion. When I pulled it from the engine, the positive post pulled out of the alternator. It had somehow been acting like a foundry and was melting the various metals surrounding the stud in the alternator into some kind of new metal that surrounded the threads. The cause: the stud had cracked and separated about a half inch into the alternator and had been welding and unwelding itself to the point it had every color of the rainbow burned into the stud.
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I went the Remy Delco 28SI route as other have had great luck with them here and on that other RV owners forum. Easy install, direct fit, and my local heavy truck shop had one at a very good price on the shelf with a new pully. Now, I have an alternator generating voltage in the low 14's at high idle reliably. As I state in the title of this post, I have removed the connection between the house and chassis 12v systems and will be placing a DC-DC device between them in the future.

The problem is, I fixed it too well. Now, the engine does not stop until I turn the disconnect switch off. My assumption is that by removing power to the ECM, it is signaling the fuel shutoff solenoid to fire.

I have all three terminal connections reconnected on the new alternator. There's the ground and positive lugs + 3 connections: Relay, Ignition, and DUVAC/Remote Sense.
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The Remote Sense is a 20amp fused connection to the battery distribution stud. Now harm in leaving that connected. I did remove that fuse to see if that was the source of a back feed to the ign line, but it kept running. I'm ruling that out.

The Relay is a possibility, but I am not sure that would do it. Plus, that is the terminal signaling the tach. It is listed as half voltage (6ish v). I suppose that could be it if the HAMSAR 6v Alt Fail relay is stuck, but it was fine before the alternator swap.

My hunch is that it is the Ignition connection. Others have had this issue and have left the IGN terminal disconnected from the alternator. I've been reviewing the chassis schematics for my rig, and it doesn't appear that it is a critical connection for the system. Any unintended consequences for leaving the 28si disconnected? The 28si is self-exciting. The installation manual explicitly states that the alternator works fine with only the positive and ground connections made. (Though the RV does need/use the relay connection).

My next step in troubleshooting is to remove and tape the ignition connection that goes to the alternator.

Any other thoughts on this subject? I searched "Engine won't shut off" on the forum and didn't find any posts about this topic.

Cheers!
Brad

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Edited by Bjohnsonmn
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I cannot give you technical details surround the why but I can tell you I spent alot of time and money trying to first get my Leece Neville rebuilt with cheap internals " I did not know any better at the time "  That failed instantly. I then used the same Delco 28si and I had the same exact outcome. The engine would not shut down. I then started to diagnose the ignition switch. I swapped the switch and still had the same issue. I finally took the advice of this forum and many others. Took my Leece Neville to a very reputable shop in my area. Spent $1000 for a all original leece neville internals. Completely rebuilt and upgraded with heavy duty. Installed and never had an issue again.  From my understanding the 28si can only be used when the Duvac system is eliminated. Hope this helps!

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1 minute ago, Tillman111 said:

I cannot give you technical details surround the why but I can tell you I spent alot of time and money trying to first get my Leece Neville rebuilt with cheap internals " I did not know any better at the time "  That failed instantly. I then used the same Delco 28si and I had the same exact outcome. The engine would not shut down. I then started to diagnose the ignition switch. I swapped the switch and still had the same issue. I finally took the advice of this forum and many others. Took my Leece Neville to a very reputable shop in my area. Spent $1000 for a all original leece neville internals. Completely rebuilt and upgraded with heavy duty. Installed and never had an issue again.  From my understanding the 28si can only be used when the Duvac system is eliminated. Hope this helps!

I had considered going that route, but did end up completely removing the DUVAC system. In the case of the 2000 32PB, it didn't have the full diode isolated big blue block. It had something closer to a trickle charger that kept things topped off and used a high-capacity solenoid to bridge the two 12v systems. Plus, I wanted to be setup such that if I had a failure on the road, I wasn't left high and dry looking for a part that can have weeks of lead time.

I'm wondering if the Leece ignition post behaves differently than the Remy does. There should be some way forward with a diode, a relay replacement, or something else. The challenge is figuring out the difference between the IGN post on the old and new alternators.

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Guest Ray Davis

If I'm not mistaken electronic engines ( ECM ) do not use the alternator for the tackometer.  Earlier mechanical engines used the pulses of the alternator so the pulley size is important for accuracy.

Pretty sure your engine is electronic.

Edited by Ray Davis
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1 minute ago, Ray Davis said:

If I'm not mistaken electronic engines ( ECM ) do not use the alternator for the tackometer.  Earlier mechanical engines used the pulses of the alternator so the pulley size is important for accuracy.

That makes total sense to me. I'm going to assume (dangerous I know) that the ign connection to the tach is therefor  for the backlight or something?image.thumb.png.b0fd2611eac9b1e60b02a575094dbc53.png

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3 minutes ago, Frank Bergamo said:

Had this same problem after replacing a LN with a Delco alternator. I installed a diode in the ignition circuit at the alternator. It was back feeding through the ignition circuit preventing shutdown of engine. Hope this helps.

That does help! SO, voltage is allowed from the IGN circuit TO the IGN terminal on the 28si? (Confirming). Which diode did you use? I am guessing something that supports 12-15v up to a few amps?

Thanks!

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1 hour ago, Bjohnsonmn said:

Happy I could share what's happening with you! This forum has been quite helpful in our efforts to renovate and reinvigorate our rig.   
 

I’ve have managed to keep my Rig in pristine condition and mostly due to this site and it’s experts and experienced advisors. 

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  • Solution

Solved!

I got on the phone with a technical representative from Remy Delco. Nice guy. We talked about the Leece alternator (he was familiar). He shared that there is a compatibility chart that states which of their alternators work and don't work as a drop in. Because I had removed the DUVAC requiring components (moving to DC-DC controlled charging), I was a free agent and that the 28si is a solid choice.

Here's the key difference.

The 28si IGN stud IS bi-directional. It can take 1amp in and it pushes 1amp out. As he put it, it is for running indicator lights in most applications.

Solution: Remove the IGN wire and tape the connector at the end of the IGN wire. Boom. Worked perfectly, no alt warning light, and everything ran smoothly.

I'm not sure this is the fix for everyone, but the 6v relay seems to still get that 12v IGN power via the rest of the circuit.

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It's good to see accurate info on this topic rather than the superstition around the original DUVAC alternators.

I installed a 28si when I replaced the old failing isolator with the BlueSea ML-ACR and since the 28si was self-exciting I only connected the +/-/tach connections and it works just fine. I do wish I'd have done a DC-DC charger and Amp-l-charger instead of the ML-ACR because I don't see a good use-case for joining the battery banks since switching the generator to start from chassis batteries.

 

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