Webasto Intermittent Operation

Holiday season greeting all,

I have a 2003 Marathon H3-45 with intermittent Webasto operation. On a typical Las Vegas cold morning (30s), while testing the unit, I turn on 12 V Heat switch and call for heat from thermostats (double push on heat buttons). The unit comes on as it should and the coach starts heating. After about 1-2 hours, I check the coach and Webasto turns off with cold air blowing into the coach. When I try to turn the Webasto back on right away, it starts (motor whirring and cold air from exhaust pipe) but never ignites the diesel heat. After a few minutes the unit turns off as it should with no ignition. If I wait long enough to cool off, the unit starts over just fine, and sometimes stays on cycling on and off as needed for heating.

Same issue when turning on Webasto through 12 V Water Heater. It is a hit and miss.

I had it checked from Marathon in Coburg earlier this year in July, and they saw similar issues. They services the unit and changed out the igniters and it worked fine when they tested it. Next time I tried it after leaving the shop, same intermittent operation started again.

Sounds very much like a control box or sensor type problem. Just checking to see if any of you have thoughts on how to troubleshoot this.

Appreciate the responses.

Regards,

Shahzad Lateef
2003 Marathon H3-45, DS

What model Webasto do you have? Check the high temp sensor.

Thanks Mike.

Should have thought to add the model number. The label is a bit warn out in the picture. I believe it is DBW 2010.74, 24V/60W, 132kW.

High temperature sensor is a good start. I just need to locate it. I don’t have schematics of the unit but I am sure can find it online somewhere. I know of the flame sensor. High temperature sensor makes sense as it runs well when it is cold outside.

Will try that out.

Regards, Shahzad Lateef
2003 Marathon H3-45, DS

http://forum.prevostownersgroup.com/...id=18502&stc=1

There are many manuals online, The sensors are easy to get to, i just replaced all 3 of mine.
http://forum.prevostownersgroup.com/...id=18503&stc=1
http://forum.prevostownersgroup.com/...id=18504&stc=1

MINE was coil. had been replaced once before.

We have run into that before as well. Make sure the fuel pressure is right and if there was anything left in the fuel line or pump, etc. then it likely clogged the new nozzel as well. After we got the fuel pressure right and put in a new nozzle and temp sensors we were good to go. Also double check that they are using the right nozzle. When we picked up the Parliament, the previous serving firm put in the wrong nozzle and had the fuel pressure way to low.

If you keep the bus for awhile, you can buy the pressure gauge and the testing box for about the same money as an annual pm.

There are other threads on POG where folks have had bad bearings that heated up and slowed down the speed of the unit but fortunately that was not our problem.

Here is an ebay link to a Louisville Engineering tester for $279.00 that will work. If you scroll down this page a little bit you will see the pressure gauge for $115.00. I have seen others in the past in a similar price range but I know this one works.

https://www.ebay.com/itm/26576719274...3ABFBMtuyR3Khh

Thanks all. I will get sensors changed out and see if that resolves it before buying the test apparatus. I figure that the test apparatus may not catch sensor issues as it completely bypassed the Webasto controller.

Pulled out three sensors and ordered new ones. I know it is not the overheat fuse because it had been shorted. I have included pictures below. There is no inspection detailed enough that will catch something like this. The sensor is $30, so I don’t know why someone will bypass this important feature.

Will let everyone know of the outcome.

Regards, Shahzad Lateef
2003 Marathon H3-45, DShttp://forum.prevostownersgroup.com/...id=18518&stc=1

Quote:

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Originally Posted by shahzadlateef

Thanks all. I will get sensors changed out and see if that resolves it before buying the test apparatus. I figure that the test apparatus may not catch sensor issues as it completely bypassed the Webasto controller.

Pulled out three sensors and ordered new ones. I know it is not the overheat fuse because it had been shorted. I have included pictures below. There is no inspection detailed enough that will catch something like this. The sensor is $30, so I don’t know why someone will bypass this important feature.

Will let everyone know of the outcome.

Regards, Shahzad Lateef
2003 Marathon H3-45, DShttp://forum.prevostownersgroup.com/...id=18518&stc=1

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This is the test box I use. It doesn't bypass the Webasto controller it goes in it's place and allows you to control the system right there at the unit. There is a light that will tell you if your thermostats are bad.

https://www.suremarineservice.com/He.../5011070A.html

Thanks Mike. I will replace the sensors any way as they are fairly cheap and easy to replace. If that doesn’t solve the issue, I will get the test box and troubleshoot further. Just felt like the test box for end user is a fairly limited application tool.

Regards, Shahzad Lateef
2003 Marathon H3-45, DS

Limited tool? not really, having the test box allows me to fully test every function of the Webasto independently while i am standing right there in front of it. Think of it as having a multi meter at your disposal when diagnosing an electrical problem.

http://forum.prevostownersgroup.com/...id=18519&stc=1

Thanks Mike. This is really helpful. May bite the bullet ($500) and get tester and pressure gauge.

My thought on limited use was that this is the first issue I have had with Webasto in over 3 years, so a specialized tool may be just sitting. You are correct that it is a good tool to have in the toolbox so I am not looking around when I need it.

Happy Holidays

Regards, Shahzad Lateef
2003 Marathon H3-45, DS

Replaced all three sensors and the heater still did not kick on (same issue as before). Will test in the morning to see if it still kicks on when it’s cold outside. On to next phase of troubleshooting. Will purchase the test box to see if i can isolate the problem.

I went through the invoice notes from Marathon from October 2022, and it stated the following,

”Ran unit, it fired but smoked heavily. Performed complete service. New fuel nozzle and filter, cleaned photo eye, repaired fuel leak on supply line. Ran unit on 12V heat and 12V water heater until unit cycled. Unit now working as it should. Next morning unit failed on third firing. Tested with no signal from ignitor. Bled system of air so it would not overheat. Fired and ran for 2 hours on water heater.”

Two things stick out. One heave smoke. I had noticed it as well when it works. It is white smoke only on initial cold startup. Second was no signal from ignitor.

Will clean the electrodes ignition sensor tomorrow and see if that replicates what Marathon found. Something to do while I wait on the test equipment.

Regards, Shahzad

Two things

1) it is not unusual for them to smoke on start up when they have not run properly the prior time. There is a lot of fuel and stuff in the exhaust pipe and it takes some time to burn it all out. After it has run properly for awhile there will be limited if any smoke on start up and no smoke while running.

2) Marathon says that they bled the air out so it would not overheat and then it fired. So did it overheat and if so why? Was the cause of shut down on 3rd firing?

Update 2/21/2023 - Finally received the Webasto testing equipment. Once the outside temperature was high enough, I ran the heater and it did not ignite. I connected the test equipment. Battery, flame sensor, motor and circulator pump all tested fine. Solenoid also clicks when engaged through test equipment. The ignitor did not respond to the test equipment. I removed the ignition coil and electrodes, cleaned connectors and re-gapped the electrodes. Once again it failed to run. Leads me to believe that it is the ignition coil that is not functioning properly when outside temperature is above 50 degrees. I don’t think there are any serviceable parts within the ignition coil unit, so I will order a new unit and replace it.

Thanks for the links to test equipment.

If the igniter will not fire on the tester then I agree that it is likely bad. However, I dont know what the outside temperature would have to do with it.

Any electronic component can be temperature sensitive. However it usually indicates an underlying structural failure in some internal component. Cold (or heat) can cause existing cracks in circuit boards to expand/contract leading to intermittent failures that are observed as temperature dependent.

Continuing to chase the Webasto gremlins. With the outside temperature below 50, I was able to get the ignition coil to fire. I also checked the fuel pressure and it registered 150psi. With both fuel and ignition working, I closed the unit and it will not fire using test equipment.

With the unit open, I can see the arc across the electrodes. I can also see the fuel spraying out of 0.35 nozzle. Again when I close it up, it wont fire up.

First thought is to change the nozzle to see if it is not properly vaporizing the fuel? Any other thoughts?

Regards, Shahzad Lateef

Call Rudy in Texas and he'll steer you in the right direction. Got his contact information?

Found Rudy’s information from a previous post (For reference his phone number is 713-818-3234). Will call him tomorrow.

Thanks. Shahzad

It is not hard to change the nozzle, I would do that just to be sure. There can be some minor stuff in the lines that will foul the nozzle. You still need to figure out why it has to be below 50 deg as well right?

I already know that I need to change out the ignition module. It only works when the outside temperature is about 50 or below. I was started to have problems with ignition when spark and fuel was there, so solving one issue at a time.

Talked to Rudy. He recommended two things that could be wrong. First is nozzle. He said the same thing that it can be spraying but if it is not the proper mist, it will not ignite.

Second thing he mentioned was that sometimes if the electrode gap is not properly set, it starts arcing to the casing when the unit is closed. That leads the arc away from the fuel spray. He recommended that I change the nozzle first to see if that works. If that doesn’t work, I will need to check if it is arcing to the enclosure. I have set the electrode gap using the tool that is mounted on the motor casing, so I should not be that far off from proper gap. Hope nozzle works. It should be here in a couple of days.

Regards, Shahzad Lateef

Shahzad:

FYI I purchased my nozzle from Walmart online. That’s right Walmart, exact same nozzle you would get from Webasco and a lot less. Couldn’t believe it until I received it and installed it.

Chuck

Continue to chase the gremlins in my Webasto.

Cold weather operation was restored. It was the electrode gap that was not on the right spot in the fuel stream. So even though I could see arcing and I could see the fuel spray, the arc needs to be in the perfect spot within the fuel spray for ignition to take place. It was rookie mistake on my part as I set the electrode gap tool on the nozzle and it needed to be on the nozzle holder. That put the electrodes a little further from the fuel nozzle than they needed to be. I adjusted that and Webasto started working just fine - in cold ambient temperatures.

Now into the second part. I know the problem is with the ignition module. Using the tester, I can see that the ignition module doesn’t fire when the ambient temperature is above about 50 degrees. I removed the ignition module from the top of the motor housing to check if there was 24 volt to the ignition module. Interestingly, when I removed the 4 screws to the ignition module, the ignition started working and Webasto worked in 60 plus degrees ambient temperature. I put the ignition module back on with all 4 screws, and it stopped working again. So as of today, the ignition works when the module is not screwed on and stops working as soon as I tighten all 4 screws. I know I need to change ignition module. The electrical engineer in me wants to make sense out of it so I am going to play some more with different iterations of screws and ignition module install. It is not pinching the two wires when tightened, so that’s not the cause. It can’t be motor vibration as vibrations are same at all temperatures.

Will keep posting results for reference.

Regards, Shahzad