generator 2003 Windsor 7500 Onan not starting

[danwegand]

Generator 2003 Windsor 7500 Onan not starting in cold weather.  turning over fine, started with a little ether.  20ys old built in 2002, is it just glow plugs?

 

Dan wegand 2003 windsor

[CAT Stephen]

Never use ether with a diesel engine to avoid piston damage and piston melting due to the high compression ration of diesel engines.

Onan fuel filters are small and clog easily.  Replace the Onan fuel filter first then prime the fuel filter by turning over the starter in 15 second increments with a 1-2 minute starter rest time between increments for a total time of ~120 seconds

Edited November 17, 2022 by CAT Stephen

[MyronTruex]

I would bet the glow plugs are not working. In cold weather I will let mine pre-heat before turning over as it does normally but will stop short of letting it turn over after the first pre-heat. I then push the start button again and it seems the additional heat works well.

There is likely a fuse that supplies power to the glow plugs and needs to be checked of course. 

[jacwjames]

How cold is it where you are at??

Agree with both of the above, especially the ether. 

X2 on the doing the preheat several times before tying to start. 

If that doesn't work you may have check your glow plugs, my manual shows a 25 amp fuse for the glow plug circuit under the access panel at the start button area.  The fuse would be the first thing I'd check!!!!

[JetAburner]

Mine was a clogged fuel filter. Very hard to start.  Also, noticed it would stall under heavy load. Figured it was fuel starvation. New filter solved the problem. Now in addition to Amzoil additive,  I'm using a fuel biocide as well.  Pops right off every time hot or cold now.

[GeneHe]

I had to replace the relay behind the front panel. Starts great now.

[Bruce S]

We have a 12.5kw Onan Quiet Diesel that with the recent cold weather will not start reliably.  I have torn the unit apart, checked relays, wiring diagrams, glow plug resistance, ground connections, etc.  The unit will turn over at various rates but only occasionally would fire up making me think I had a bad ground.  The service manual stated to check the direct wiring connection from the control module to the glow plug terminal for continuity and if good then you needed to replace the control module.  Our unit is an older Spec B unit which did not have a separate glow plug relay but was fed directly from the module.  Starting with Spec C they wired a separate 87a relay for this purpose with only the control power to the relay coming from the module.

I was thinking of rewiring our unit to integrate this new relay with control power tied into the start circuit at the local control switch.  My concern is that the local switch does not have a run position but the remote wiring does.  I don't want to miswire the glow plugs to stay powered up after the unit successfully starts nor do I want to purchase another board if this is the only problem.  This would be the second board to be replaced.  I had to change the original when we bought this coach 9 years ago and it really hasn't seen that much use but you definitely want the generator available when travelling especially in the winter.  Present temps here has generally been slightly above to below freezing. 

I have attached both wiring diagrams versions.

I look forward to any suggestions or confirmation of my ideas.

Thanks,

Bruce

I forgot to add that I also replaced the chassis batteries with new Interstate ones.

[Ivan K]

1 hour ago, Bruce S said:

We have a 12.5kw Onan Quiet Diesel that with the recent cold weather will not start reliably.  I have torn the unit apart, checked relays, wiring diagrams, glow plug resistance, ground connections, etc.  The unit will turn over at various rates but only occasionally would fire up making me think I had a bad ground.  The service manual stated to check the direct wiring connection from the control module to the glow plug terminal for continuity and if good then you needed to replace the control module.  Our unit is an older Spec B unit which did not have a separate glow plug relay but was fed directly from the module.  Starting with Spec C they wired a separate 87a relay for this purpose with only the control power to the relay coming from the module.

I was thinking of rewiring our unit to integrate this new relay with control power tied into the start circuit at the local control switch.  My concern is that the local switch does not have a run position but the remote wiring does.  I don't want to miswire the glow plugs to stay powered up after the unit successfully starts nor do I want to purchase another board if this is the only problem.  This would be the second board to be replaced.  I had to change the original when we bought this coach 9 years ago and it really hasn't seen that much use but you definitely want the generator available when travelling especially in the winter.  Present temps here has generally been slightly above to below freezing. 

I have attached both wiring diagrams versions.

I look forward to any suggestions or confirmation of my ideas.

Thanks,

Bruce

I forgot to add that I also replaced the chassis batteries with new Interstate ones.

If I was in that situation (I have Spec A), I would have a relay activated by the momentary ground signal from start position of the switch. It does prime and heats the plugs for few seconds before it starts and then, once the momentarily switch is off, it would turn off. I never heard of this happening but good to know, maybe the relay would be a good preventative measure for me too when I open the case again one day. 

[Bruce S]

I should have pointed out that the glow plugs are presently not getting power 90% of the time and that when I run this new power supply I am also going to need to install an inline fuse, probably in the same location as the current fuses which are located behind a small panel by the start switch.  I don't know why Onan configured their generators in this fashion which might explain their later modification.

[Boyd B.]

There are 3 fuses under the access panel at the front of the generator. You may have to reach in and search for them. They are inline fuses. I missed them the 1st time I went looking for them. once you find them there should be enough wire to pull them out to check  or replace them.

[Bruce S]

Our coach only has 2 fuses, neither of which are bad or feed the glow plugs which is what I am trying to remedy.  I had checked these earlier as well as everything else I could think of.  The rewiring task was a last resort if no other issues like dirty contacts solved the problem.  The last time I replaced a control card it was getting hard to find and cost me $1200 CAD and I'm sure it would be more now and harder to find.  I did find a mouse nest in the control box resonator housing as well as hickory nuts in the air hose restricting cooling airflow which may have led to the partial failure I'm seeing now.

Regardless, I've started the wiring job and will post the results if I'm successful.

[Ivan K]

Looking forward to see how you have done it and what is the actual current to glow plugs. Just an idea I had few years ago when my stator burned out due to air blockage. A simple fan grill held on by magnets, held fine for many thousands of miles.

[Bruce S]

I mounted the new relay beside the existing ones at the top right corner of the cubicle.  I wired my 87a relay with the 30 contact connected through a 15A fuse directly to the main input terminal block.  The 87 contact was then routed to the glow plugs.  86 relay was routed to the chassis ground block.  The 85 contact was temporarily jumpered to the local start switch terminal connector.  Generator was then attempted to start from the remote switch inside the coach.  No power was received by the glow plugs.  I figure that the reason for this is that the relay coil has a resistance of about 80 ohms so the ground current takes the easier route to ground through the regular wiring.  My next intended move was to cut the original ground wire to the control module and tie in the 85 contact this way however I found out that Cummins currently has a clearance sale on my control module at half price so I have now ordered a replacement.  Lastly, I may have had to reroute the 86 contact back to the control module ground wire downstream of the 85 splice so that you completed a loop in the existing ground wire in case there was some issue with the control module needing to see this ground signal.

I will leave my new wiring intact in case I need to further this modification down the road.  I did not include any pics since my experiment wasn't successful.

[Ivan K]

Thanks for the update. I'll still keep the relay in mind to eventually make it like the later revisions. I don't see any relays on the controller board  so the glow plug current must be going through a FET. I could see how it might fail if strained or shorted.