4788 Cummins 6BTA 5.9 Starboard Preheater Inconsistent/Not Working

[MalNSF]

Hi All,

I am super frustrated with our starboard engine preheater. I turn the key on and the green preheater light flashes on for a split second and then goes out. The preheater light/preheater doesn't stay on for the 30 seconds or so needed. It's super cold here lately so we need the preheater. Starting without it smokes out the whole marina. I spoke with Seaboard and they said replace the solenoids. I did that today and it worked fine the first time and then after that I turned the key on and the same symptoms started again.

What's weird is that it won't come on when it's cold. Sometimes when we are using the boat for the weekend, it will come on when it is time to start up to come home. That's the intermittent part.

Does anyone know what other things I could check. What really sucks is it's the starboard engine, so super hard to trouble shoot.

I want it to work as it should and when I turn the key, the green light comes on while the engine preheats and then goes off when it is time start the engine.

Has anyone else experienced this and have thoughts?

Thanks
Jeff

[Northwester]

The intake air heater is controlled by a module that takes input from a temperature sensor , magnetic pickup for engine speed, and voltage. The most common failure point is the 2 relays mounted on the starboard side of the engine next to the starter, they will melt and fail, it is visually obvious, usually. The second thing is low voltage at the air heater control module. If voltage is under 10.5 volts the module will shut off the system. This voltage should be checked with a multimeter at the module since there may be voltage drop in the vessel harness and the volt meters on the dash may not represent the actual voltage at the module, based on your symptoms that is what I suspect may be the issue. Verify connections at all the components, including the actual grid heater which is mounted on the outlet of the after cooler assuming your engine is 315/330/370 HP. Finally, the magnetic pickup which monitors engine speed may have a bad connection, may be dirty or simply failing. It is located on the bell housing at the aft end of the engine. Occasionally the modules are the issue, which will be really annoying since Cummins now wants something north of $1,500 for them.

[MalNSF]

Hi Jim. These are some great steps for me to start figuring this system out. Thank you for breaking it down so well for me. We know the relays are good because I replaced them today. I look at all of the wiring harnesses and get overwhelmed because I know enough about the engines to be somewhat effective, but when it comes to the electrical part of the engines, I'm at a loss. All of the harnesses are overwhelming. One question, Could a bad battery be a cause not sending enough voltage to the system? I think the new ECM's are well north of $2K now, maybe pushing $3K so I hope the ECM isn't the issue.

[Northwester]

I'm thinking highly unlikely its a bad battery. A lot would depend on how your battery/electrical/charging system is configured. If your vessel has had more than one or 2 owners over the years its hard to say what others may have modified. Usually if it's voltage related its connections. We have replaced a few modules over the years, while easier said than done I would swap between engines before buying one. It is usually the last component to fail. The tips below about the thermistors and loose wires on the circuit breaker are spot on as well.

[Renilyab]

I spent days troubleshooting the pre-heater on my port engine a few years ago. My problem was low voltage to the pre-heat module which I traced to loose and corroded connection at the engine mounted circuit breaker, located on top and aft of the valve covers.

The Cummins service manual has a good troubleshooting chart for the pre-heat system. It is complicated and you have to go through things carefully with a voltmeter until you find the issue.

[SuperiorDiver]

When I had an issue with the preheaters, I contacted a cummins field technician. His advised to look for loose connections, then a weak battery. He said in his 25 years of servicing, he only replaced one module.

Just like Renilyab stated, one of mine was a loose wire on the breaker on the top_rear of the engine, the other was a loose ground wire from the module. I only ran into an issue years later when the battery voltage dropped too low as Northwester stated.

[Woodsea]

I also had an issue with loose connection on the breaker located near the heater. On ours it is a red push button. The connections are underneath.

[CBAB]

In addition to the above I have had 3 temperature sensors fail. The temp sensor is on the forward side of the aftercooler. You can test for this by interchanging with the other engine and see if the symptoms move to the other engine.
If you have to get a new temp sensor be sure to get the correct part number: 3613547. There is another sensor that is available and looks the same but has a different resistance, the correct room temp resistance is 10,000 ohms. The incorrect one has a room temp of 3,000 ohms which incorrectly tells the ECU that the engine temp is hot so the engine doesn't need preheat.

[rodell]

On one of my boats I had to power the preheater with heavier wire more directly to the solenoid. There was too much loss in the aging wiring and connections. Solved my problem.

[MalNSF]

Hi Guys. Thank you so much. It sounds like it's likely it is wiring from your descriptions. Does anyone have a good picture of the areas to check? I unplugged the wrong fuse the other day and shut off the engine. I think it was the fuel pump fuse. I get a little intimidated by all of the wiring bundles not knowing which each one does. I am looking forward to starting to troubleshoot this weekend.

[Cool Change 4788]

My starboard side would intermittently not work and/or sometimes while running I would notice it flickering on and off, I also would see the volt meter fluctuation while running above 1100 rpm which should turn the pre heat off. I checked all the harness connections and cleaned them best I could with no joy. I decided to install pre heat on/off switches since I am in so cal and don’t fight the cold temps much. During install of the switches wiring I found the main (large) alternator wire loose at the back of the starter (on the starter power stud). I was not able to contort around the heat exchanger to effectively hold the stud while tightening the nut so I removed the heat exchanger for access. This allowed me to thoroughly clean the stud and wires and properly tighten them while holding the stater stud from rotating while torquing the nut. This solved my problems. Pre heater works perfectly, no flickering, no voltage fluctuations and the bonus is I have on/off switches for the pre heaters that were easily routed to the main electric panel and mounted. I found this loose wire by wiggling it and using a mirror and flashlight.

[Bacon]

The heaters will cycle depending on temperatures, not RPM. On my boat when its like 50 out the heaters will stop cycling if I run about 1300rpm or higher and then start cycling again if I back off to less. Its about the heat though, not RPM.

[Renilyab]

Hi Guys. Thank you so much. It sounds like it's likely it is wiring from your descriptions. Does anyone have a good picture of the areas to check? I unplugged the wrong fuse the other day and shut off the engine. I think it was the fuel pump fuse. I get a little intimidated by all of the wiring bundles not knowing which each one does. I am looking forward to starting to troubleshoot this weekend.

The SBMAR website has a lot of good pictures. There is a wealth of information under Tony's Tips. Also I highly recommend the Cummins factory service manual (available from SBMAR) it has color diagrams identifying major components.

[WILDER TIMES]

I had my port engine heater inoperative. I troubleshot it to a blown 10-amp fuse. The fuse holder location was buried in the wiring harness below and near the heater. This was not the 10-amp circuit breaker on top of the engine. It is an automotive blade type fuse inside of a plastic holder. You should be able to find it in the wiring diagrams. Hope this helps.

[Northwester]

When checking for system voltage to determine if the module is seeing actually battery voltage and not affected by voltage drop, this fuse holder is the place to do so.

[Woodsea]

Cool change,
I also wired on/off switches into my preheater circuit. I used the two extra switches on the bottom right of the helm switch panel. It is wired in line with the 10 amp automotive fuse. How did you wire yours?

I also wired in led indicating lights by each switch. In theory these are to indicate when the preheaters are energized. These have never quite worked right. There is a stray current (not sure what to call it) that causes the indicating lights to dimly glow all the time. I disconnected them.

[Cool Change 4788]

Woodsea, I wired mine to the ground side of the preheat relays and put guarded switches on the electrical panel right above the hour meters.

[MalNSF]

Well, we did some troubleshooting and can't find an answer. When we first turned the key on it, worked. Then we turned the key off and it stopped working. They are getting power to relay's for a millisecond when you turn the key on and then it drops out. We cold started later that afternoon and it smoked us out. Now here's the weird thing. We went about 20 miles away for the weekend. I tried it on arrival and it didn't work. Then on Sunday when it was time to come home, it worked. It's like once the engine is warmed up, it works, but if it's cold and been sitting, it won't work. So strange.

[Woodsea]

Just a guess but I bet there is is a loose connection somewhere.

[rogerkarenorth]

I also think it is a voltage problem. You might try something simple - just turn on the battery charger to be sure that engine battery is high; then try to start with the battery charger still running.

[Bacon]

Just a note, the starter draws significantly more current than the air heaters. The air heater power wire goes to the starter. If your engine cranks normally its likely not a low voltage issue. Since the light comes on briefly and then things shut off that suggests the ECM quickly decides the heaters are not needed. See Chucks post #6
above where he talks about sensors he had trouble with, maybe that fits this case?