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| Re: [GMCnet] Onan No Spark [message #280809 is a reply to message #280776] |
Fri, 26 June 2015 18:59   |
Jim Miller
Messages: 501
Registered: March 2008
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On Jun 26, 2015, at 12:35 PM, Justin Brady wrote:
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> The thing that's getting me is that the points are opening and closing with power to the coil and I'm still getting no spark.
> Perhaps this points to the condensor?
Just because the points are actuating does not mean they are functioning properly - Oxidation and corrosion on the contact surfaces of the points can easily prevent the coil from firing. As for the condenser you can disconnect it during your testing with no harm - it is there only to quench the spark generated at the points contacts and thus prevent damage to the points. If the engine runs with it disconnected and then acts up when you connect it back up then you’ve confirmed a bad condenser.
I read through most Onan threads on the mailing list and continue to marvel at the troubleshooting technique that people use. Perhaps I’m just an oddball but I try to decompose a system to its constituent parts and test them individually - rather than take an assembled complex system and flail around in the hopes that I’ll be lucky enough to stumble across the source of the problem. In many cases there are more than one problem with these units and the flail-around approach is unlikely to ever be successful.
For Onan engine problems here’s what I suggest:
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First: Jumper battery+ to coil+ and confirm that 1) the fuel solenoid opens, 2) the fuel pump runs, 3) fuel is delivered to the bowl. If all three do not occur
then FIND OUT WHY AND FIX IT BEFORE MOVING ON.
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Second: Make sure there’s the proper level of oil in the sump. With the coil+ jumper from step 1 still in place: try to start the engine either with the control board’s rocker switch OR by applying battery+ to the starter’s solenoid coil terminal.
If the starter cranks the engine slowly or sluggishly and you KNOW you have a strong battery and good battery connections then fix the starter. Common starter problems in decreasing order of probability: worn-out nose bushing, defective starter solenoid switch contacts, defective starter brushes / damaged commutator / damaged armature.
If the engine cranks at a reasonable speed but does NOT start AND run smoothly THEN FIND OUT WHY - there are only three possible causes: 1) carbureation, 2) ignition, 3) compression (with lack of compression being an unlikely cause). Absolutely do NOT move on to other troubleshooting steps until the engine runs SMOOTHLY with the coil+ jumper in place. Confirm the engine runs smoothly under both no-load conditions and with maximum electrical load applied.
If the engine DOES start and run smoothly you can be quite reasonably assured that you have a controls problem. Move on to the third step.
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Third:
Check all wires and connections including the multi-pin control board connector. Clean up ALL corroded connections - Check the fuse on the control board - then bypass the LOP sensor and try to run the engine.
If it RUNS with the LOP bypassed then you either have: 1) bad LOP sensor, 2) damaged LOP wiring, 3) no oil pressure!
If it does NOT run with the LOP bypassed AND you have an OEM board then you should SERIOUSLY CONSIDER getting a Dino board from one of the GMC vendors - you won’t regret it. If you are going to keep the OEM board and try to fix it… then hopefully you are a patient person or an electronics expert or both.
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I’m sure someone will find fault with my procedure but it works for me and it has fixed many Onans that have come through the Miller compound over the past 8 years. Your mileage may vary.
--Jim "saving the lives of Onans...one unit at a time" Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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