520H ignition issue

[Bryan K 0]

I have an '88 520H with an Onan P220G.  Over several weeks, it became harder and harder to start.  It would cough and spit and act like it was flooded.  It would eventually start, but I would have to let it run for a while to warm up before I could throttle up.  Eventually, it would not start at all.  Taking the air cleaner off, when turning it over, there is gas mist and droplets spitting up out of the carb.  Maybe a carb issue?  Long story short, I pulled the plugs, and they were pretty black and fouled.  Replaced them.  Still no go.  Pulled a plug and put it on the block with wire attached and turned it over.  I did not see or hear any visible spark.  Checked coil and secondary was open.  Replaced coil (and condenser which came with coil).  No go.  Replaced wires.  No go.  Checked voltage on coil + and have 12.5V with key on so interlocks seem okay.  Checked voltage on - of coil while turning motor by hand.  Voltage cycles between 12.5V and around 1V, so ignition control seems okay.  Put sprak tester on and turned over.  Tester is flashing, but it is pretty dim and orange.  Weak spark??  Still won't start.  Wondering if contacts in ignition control can get worn or fouled and cause weak spark like points in an older car??

 

Help!

 

Thanks

 

Bryan

 

 

[gwest_ca-(File Mod) 11,483]

Check the voltage at the coil (+) with the key in the start position and motor turning.

It was not an Onan but just had this problem. The coil is a step up transformer but low voltage in = low voltage out to the plugs. Bad ignition switch in my case. You likely have a relay that powers the coil.

Garry

 

No relay in 1988. Ignition switch, to pto switch, to seat switch, to 9-pin connector, to coil.

[Bryan K 0]

I checked the voltage at the coil with the ignition on, but not turning over.  It was about 12.5.  When I turn the key to start and turn over the engine, it drops to about 10.5.  I installed a jumper directly from the battery + to the coil to bypass the interlocks and the ignition switch.  Now it is constant 12.5 at the coil.  Now, when I turn it over, it still drops, but a little less, now 11.0V.  Still doesn't start, and spark detector, although flashing, is still dim (at least it seems dim to me) with or without the jumper.

 

Thanks for sharing the demystification guide.  I have been reading that also.  That is where I read to turn the motor while watching coil voltage to see if ignition control is working.

[Bryan K 0]

Anyone...

 

Is it normal to see a voltage drop like this at the coil when turning over?

 

Could it be as simple as the battery is shot?

 

Could the contacts in the ignition control be dirty or shot causing weak spark?

 

Is it normal to see a fairly dim orange flash on a spark tester, or is that indeed a weak spark?

 

Ideas?

 

Thanks

 

Bryan

 

 

[953 nut 60,013]

5 minutes ago, Bryan K said:

Could it be as simple as the battery is shot?

 

Could the contacts in the ignition control be dirty or shot causing weak spark?

[lynnmor 7,817]

The engine has no mechanical contacts for the ignition, only the solid state ignition module.  It can be tested using the Onan service manual.  You replaced the coil, are you sure that you got the one for the solid state ignition?  Since a condenser came with it, I suspect you bought a cheap eBay one made for the points type ignition.

[gwest_ca-(File Mod) 11,483]

The inline spark tester I have has an orange looking light I suspect because of a neon bulb.

Test spark with a grounded spark plug and see what the spark looks like.

 

Garry

[Bryan K 0]

953 nut, I had the battery checked, and it is good.  We also looked at the voltage drop under load of my battery and a brand new battery.  Mine is at least as good if not better than the new one.

 

Lynnmor, the original coil that was already in the engine had a condenser also.  It is part number 166-0761 from the original parts list.  From what I find, that has been replaced by 166-0820.  That coil needs the mounting clamp which is included on part 541-0522, and that also includes a replacement condenser.  If that is not the right part, please point me in the right direction.

 

Garry, I started by grounding the plug to the block while turning over the engine, and I could see little if any spark.  I tried the spark tester thinking maybe my eyes were failing me.  With the tester, I can see the spark is firing, but it seems like maybe it is weak.  I expected to see (and hear) a strong spark when grounded on the block, and did not see that.  I am unsure if it is weak or not.

[Bryan K 0]

Another thought - I have the air cleaner off, and when I try to start it, there is raw gas spraying up out of the carb - mist and drops the size of #8 shot or more.  That seems odd to me.  Is that normal?  I thought maybe the carb was the issue and is flooding.  Maybe I only got sidetracked on the spark because I burned up the coil trying to start it when it was flooding, replaced the coil and got distracted by the spark.  I took the top off the carb.  Everything looked really clean.  Where the floats are located, there is gas about 1/4" deep or so in the chambers.  Is that normal?  The floats looked fine to my untrained eye.  To see if ti was maybe flooding by the carb, I got that gas out of the chambers under the floats and removed and plugged the fuel line so there is no gas in or getting to the carb.  I turned it over, and sure enough, no gas spraying out.  I gave it a quick shot of starting fluid.  It coughed a little, but would not really start, however briefly.  I reconnected the fuel line, and still the same - won't start.  But I can't get my mind off that spray of gas coming out of the carb.  Is that normal?

 

Back to the ignition control - is it possible that the ignition control is making contact to make the spark fire, but it is too weak?  When that fails, does it get weak?  Or does it go from great to dead?  It seems it must be functioning since the voltage cycles at the coil when turning the motor manually with the ignition in RUN and because I get the flashing light ojnt he spark tester, but could it be bad even if it is "making contact?"

 

Does anyone know the proper resistances for the primary and secondary side of the coil ont eh '88 520H?  In the demystification guide, it gives resistances for other coils 71-6000, KH10321 and NN10530, but not for the '88 520H P220G which is WH part NN10745.  I think I have the right coil per the part number, but maybe not.  I would like to be able to verify.

[cleat 7,257]

I had a 416 with the Onan that I sold.

It was harder to start than my 520's which I thought was odd at the time.

Anyways a couple weeks later the buyer calls me and it will not start at all.

 

Just on a whim I installed a good used coil I had and it fired right up.

Talked to the owner almost a year after that and it has been starting up just fine every time.

 

Coil was the problem all along.

 

[Bryan K 0]

Thanks for the input, cleat.  I have replaced the coil.  Any other thoughts?

[lynnmor 7,817]

Since you have spitting out of the carb, check the compression to see if you have a valve issue.  Since you have only 1/4" of fuel in the float bowl, check the fuel pump by directing a fuel hose from it into a can while cranking the engine. I still wonder about that condenser, you should have one mounted to the air filter support, if it is bad that could short out the ignition.  The part number for the coil is correct, did you perhaps get a cheap eBay coil that is bad?

 

The Demystification Guide will only help with the tractor wiring, download the Onan Service Manual for information about your engine.  The ignition tests and carburetor information is all in there.

[Bryan K 0]

lynmoor, thanks for the additional input.

 

I will check compression.

 

How much fuel is normal in the bowls?

 

There is a condenser attached to the air filter support. It is the new one that came with the coil. I assume it is good since it is new, but I will check it.

 

The coil was $50 on Amazon. I don't know if that is "cheap" or not. I assume if the coil resistances are good, it is good. Hopefully I can find what those are supposed to be.

 

Thanks a million for the service guide link.

 

BK

 

[lynnmor 7,817]

The carburetor float settings and the test procedures for the coil and ignition module are in the Onan manual.  You bought just another Chinese coil and it might be OK, the prices are all over the place on those and higher doesn't mean better.