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Jess

518H 18HP Onan

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This is my first time trying to upload picture , I'm not sure if they'll come out. I also included pic of some of the parts I've changed SR# 1873262205  Model P218G-1710539B a pop up keeps coming up reading I am only allowed 1.4 mb ? 

  Didn't have time to look at the machine today . 

Edited by Jess
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There is no pos or Neg on the coil , Just make them as you want . This is the coil the other member recommended and I purchased it from the same supplier at the time .

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Here is Martins solution using the Harley coil -

I followed his advice and used the same coil on my 520h about a year ago. Has been and still runs great. My original coil was only firing from one side. It appears that your coil is the correct ohms for you also. Googled Ultima 53-317 http://www.catalystcycles.com/ultima-dual-fire-coil/

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  Thank you , This is the one Martin recommended when I first was having trouble . Some members think I might have fried my new ignition module by using this instead of an Onan coil. 

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Jess, I'm not saying the aftermarket/Harley coil fried your ignition module, but possibly the missing " insulator" as your picture shows all metal unlike my original unit I believe earlier Onans did not have the the insulator as some have posted about this before but obviously if the newer versions do it must be from an apparent issue without, also follow up with Boomer seems like he may have cheaper alternatives for you and what he said the BLACK trigger rings are known to have weak magnets vs the GRAY ones my old trigger ring may be good I was adivesed to change it all out new when doing the module, and I feel for you not wanting to buy things twice three times over, FYI when GM first came out with the HEI distributor and the ignition module would bad most people replacing them at the time did not know about or would not use dielectric grease under it when installing new unit shortly after it would fail again repeat this 2-3 times and those modules weren't cheap so my point is you really need to replace once more with a new insulator trigger ring since you'll have to pull flywheel anyways change/replace one component another, again just my experiences and opinion,Jeff.

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Jess, I'm not saying the aftermarket/Harley coil fried your ignition module, but possibly the missing " insulator" as your picture shows all metal unlike my original unit I believe earlier Onans did not have the the insulator as some have posted about this before but obviously if the newer versions do it must be from an apparent issue without, also follow up with Boomer seems like he may have cheaper alternatives for you and what he said the BLACK trigger rings are known to have weak magnets vs the GRAY ones my old trigger ring may be good I was adivesed to change it all out new when doing the module, and I feel for you not wanting to buy things twice three times over, FYI when GM first came out with the HEI distributor and the ignition module would bad most people replacing them at the time did not know about or would not use dielectric grease under it when installing new unit shortly after it would fail again repeat this 2-3 times and those modules weren't cheap so my point is you really need to replace once more with a new insulator trigger ring since you'll have to pull flywheel anyways change/replace one component another, again just my experiences and opinion,Jeff.

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Hey Jesse, good to see you're back at the 518 issue. You are getting like me, everything takes two years anymore.

 

Some random thoughts for you on the twenty minute run issue. I'm sure your head is swimming in all the help and opinions being offered on "what to replace next". You know from working with me before I do not suggest random replacement of parts on a "guess" and I treat other peoples' money as if it were my own. So, a few comments and then my suggestion for moving forward in the correct fashion on this fix.

 

Harley Coil

there are at least 3 different types of coils out on the market. For our purpose we will call them the 5 ohm coil, the 3 ohm coil and the 0.5 or "half ohm" coil.

We can immediately take the "half-ohm" coil off the list of usable coils. These sub 1 ohm coils are STRICTLY for use in high energy electronically controlled automotive environments. Yes, the ignition module on the Onans are electronically controlled, but the ignition module in the Onan does not come close to the same level of design refinement seen in the automotive world. Measure the primary resistance of your Harley and Onan coils. They should be in the 3 to 5 ohm range.

 

 

onancoilprimarymeasohms_zps1f4e2d7f.gif

 

 

Stator / Regulator

Do not pursue any further troubleshooting or parts replacement in the charging system. These parts only serve to keep the battery charged. A properly functioning battery should keep the 520 running for at least 1 hour even if the charge system were disconnected.

 

I have read about your volt gauge reading being maxed out. Going forward, replacement of the voltmeter is a good idea. We need to keep an eye on the function of the regulator to assure the charge voltage doesn't skyrocket to over 16 volts. Excessive charge voltage not only will damage the battery, but can easily contribute to over stressing the ignition module. Higher voltage to the ignition module means more heat generated by the ignition module. And speaking oh heat ...

 

 

Ignition Module Insulator

 

Get one !! 

The last one I bought was less than $5.

The addition of the insulator could very well resolve -or at least help - your problem.

As a simple test, if you have access to hi temp gasket material sold at automotive stores, a homemade insulator one or two layers thick may give us some insight if heat is the root cause of your issue. Use the asbestos style compressed material for exhaust systems, not paper, rubber or Silicone. The gasket material must be rigid so it does not compress under tightening of the mounting bolts on the ignition module.

 

 

9 PIN Connector/ Jumper wires / Safety Switches.

 

I never saw anyone mention to run a separate GROUND wire directly from the engine block back to the battery negative terminal. Bypassing the 12 volt pin in the connector by jumping the coil + to the battery + was mentioned several times but never the ground wire also located in the 9 pin connector. The ignition module needs both. Hopefully the block is grounded thru the negative battery cable, but you have to ask yourself why the Onan also has a ground wire thru the 9 pin also. Definitely worth a try. Any additional effort to bypass safety switches is just leading you in circles. The jumper from the battery to the ignition coil positive post eliminated all the wiring, ign switch. and safety switch concerns.

 

Regulator black pigtail wire

many engines that use this style of regulator mount the regulator into a plastic (un-grounded) engine shroud. The pigtail allows the metal regulator case to be grounded to the engine block by connecting this pigtail to a metal area of the engine block. It is not a bad idea to use this pigtail even on a metal shrouded engine. The ground to the regulator then does not depend on good contact between several metal shrouds to establish a good charging system ground to the regulator case.

 

 

Trigger Ring Magnets

Magnets tend not to lose and then regain their magnetism in 20 minutes. Think hard, when have your magnetized screwdrivers ever lost then regained their power. Weak or marginal magnets installed in black trigger rings  during manufacturing - fine - that is believable. Losing and gaining magnetism - not sure anyone has seen that happen.

 

 

My thoughts on how to proceed

Place one jumper wire from the engine block to the battery NEGATIVE post.

Grab your INCANDESCENT bulb test light. LED based testers will not work for this  test.

Start the tractor, run at idle.

Connect the alligator clip of the test light to the POSITIVE - repeat POSITIVE battery terminal .

Touch the test light to the coil NEGATIVE post and watch the lamp flash. The lamp will only flash ON briefly when the ignition coil grounds out the ignition coil. Run the engine throttle up and down and get very comfortable with the "look" of the flashing test light. This will set your visual baseline for a properly operating ignition module.

While the engine is still running well, switch the alligator lead on the test light to the NEGATIVE battery lead. With the test lead wire going to the negative terminal, THE TEST LAMP WILL FLICKER OFF BRIEFLY on the ignition module grounding the coil.

 

Choose which configuration you are more comfortable with. Hopefully you will be good with the testor wire lead connected to the POSITIVE battery lead, Some testers are quicker to respond than others due to various brands of bulbs used, so chose which method allows you to detect the flickering most clearing.

 

Again, become very comfortable with the "look" of a properly running engine on the flickering tester.

 

When the engine dies, hookup the tester to in the same configuration you feel most comfortable with and crank overt he engine while monitoring the coil negative post. Do not worry about the ignition coil POSITIVE terminal as any change in brightness there while cranking only shows how much your battery voltage is varying as the battery strains against the starter current - not a helpful observation.

 

NO FLICKERING = bad ignition module

FLICKERING just like when the engine was running OK = ignition module is still functioning.

 

I would say I'm betting you will find the ignition module will be the cause of your issue., but let's check it out first and leave guessing for those with fatter wallets!

 

I don't get much time anymore to do much online troubleshooting but I will stick with you on this one Jesse.

 

 

BTW

 

below is a slide showing the internal function of the ignition module. It is over simplified but shows the "guts" of the module are really nothing more than a magnetically controlled on and off switch that grounds the negative lead of the ignition coil. When one magnet in the trigger ring passes the nose of the module, the switch is turned on , whe the OPPOSITE pole magnet passes the nose, the internal switch is turned off and the coil fires a spark.

Very simple - just like the mechanical points on the K series engines. Instead of a mechanical cam lobe, this circuit uses opposite polarity magnets to alternately turn on and then off a switch to power the ignition coil.

 

 

igm%20mod%20function_zpsj4ulb5ay.gif

 

 

 

 

For those of you playing at home and are more electronically inclined, the autopsy I performed years back on one of these modules reveled a Darlington pair BJT switch driver fed by a latched hall effect sensor mounted in the "nose" - about $2 worth of components just begging for someone to home-brew a replacement.

 

 

 

 

 

 

 

 

 

 

 

 

 

Edited by Save Old Iron
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Well Good morning,  Glad to see your still around !  yep 2 years (HA)   not that I'm lazy but as you know I can and have spent days and weeks on this project .I  kind of shelved it after we replaced the last new ing module , coil, act .among other many things . About the only thing I didn't replace last time was the stator and rectifier which I did this week .  I was going to pull the shroud and flywheel off again and test the module like you showed me last time but if I can test it like this without doing all the tare down , I will try.

I did not replace the trigger ring as I wasn't aware of this when I di the module . It is a black one which am being told are not very reliable . Could this be the cause of what's still going on ?   I will try and spend another day on it today and report back where I'm at .

    Good to hear from you and the as always thank you and the other members  for your help and time

          Jesse

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Follow the squirrels advice! He has this troubleshooting down pat. Thanks again for the education.

Edited by 312Hydro
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I Ran ground to neg post from block .  I have 3.5 OHMS on the Harley coil and 3.8 OHMS on the original Onan coil .  I took my test light and hooked 1 of the alligator clips to the positive side of the battery and the other to the negative post of the coil . The light stayed on ?  The tractor would not start with the test light hooked up so I removed it and it started right up but as soon as I try and connect the test lead to the coil the tractor would die .  I took my meter and read the OHMS on the 2 ignition module Red & Blk leads and got around 18.69 OHMS  just for the heck of it . Is this something I should be getting ? I read OHMS to ground on each of the same 2 wires I get 3.5 on the Red and nothing on the Blk .  Does this mean my new ing module is shot or is this the way the position of rotor  might be at the time .
           Should I just order another new ing module and rotor and start there again ?  I'm going to go out and pull it apart and get the flywheel off and see if I can see anything in there again?
    Thank you
   Jess

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I  pulled the flywheel off and removed the ignition module , there was no insulator behind it . There must not have been one on the original or I would have replaced it. Doesn’t the Bakelite on the module isolate it from the block ?  I read ohms on the old module and it had none I took a reading on the new one I had replaced last year and it reads 24 ohms . When I read to the metal backing plate on the module I get 3.5 ohms to the red wire on each of the modules . I tried to bench test them like SOI had showed me but got no light nothing , the bulb doesn’t light .’'

Where you touch the ground jumper from the battery to the back of the module , the small round spot I have 4 of them but they are all covered with Bakelite  . Is this how it suppose to be ?  If I were to get and insulator for the ignition module do you think it would work , or is it worth the try ?
  Maybe they added an insulator to later models ? But since there was non I mine , that is the way it must have come .
                Thanks again for your help
    Jess
Edited by Jess
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I tried a test light once too on the negative side and the engine had no spark.

 

Test light must add too much load. Meter worked so maybe an LED light would work there ?

 

 

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I have it pulled apart right now and am picking up a piece of exhaust gasket material to add behind the ing module . I will put it back together and see if it helps. Taking the flywheel off is no big deal but the metal shroud to get to the wheel is a pain !
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I picked up a sheet heat shield from Napa It is like a perforated metal on one side and a heat gasket on the other . It is about 1/16” thick . So I cut 2 pieces the same size and mounted them between the wall and the ignition module . It looked like it might have thrown the module a bit further out from the rotor but there was still clearance between the module and the stator.  Put it all back together and now it wont start at all. No spark .Maybe the module is made to be right against the block ? 
  That’s where I'm at right now ! Like I had mentioned the original ignition module had no insulator between the module and the block .
Done for tonight . 
    Thanks for the help
 
   Jess

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I believe the module needs a good ground. Maybe your gasket material in combination with old screws made it lose electrical grounding.

 

I installed the thin insulator and also used star washers on the screws to ensure a good ground connection from the metal tab to the engine block.

 

Your insulator may be too thick keeping the magnets from doing their job.

 

For a test at least, just try a piece of thin gasket material or even a piece of cardboard like a cereal box.

 

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My understanding was I needed and insulator to protect the module from heat build up? I used the original screws and star washers . I also pulled the air breather hose off and checked the mesh wire screen )Like Billow )  and it was as cleaned as the day the tractor was built . As another member had mentioned to check it .  I will pull it apart again tomorrow and try just using one piece of insulator material. Would the rotor magnets be to week to make the new module I put in last year not work properly ? I changed the ing module but not the rotor a year ago or more but I still cant get this thing to run for more then 20 minutes .  SOI had told me not to use paper or cardboard .

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I realize that you are concentrating on the ignition system ,but just for the heck of it, take a look at the fuel shutoff valve mounted in your tank. Could you have dirt in the tank which collects on the screen or a screen that is collapsing? Just something little that you might want to look at. Cheap to replace too. If you do get a new grommet with it. 

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I Ran ground to neg post from block
:handgestures-thumbupright:  good , one less connection to question.
 
 
 
I have 3.5 OHMS on the Harley coil and 3.8 OHMS on the original Onan coil
:handgestures-thumbupright: both are electrically similar and within published Onan primary resistance spec's. I would guess the Harley coil did not fry the ignition module.
 
 
 
I took my test light and hooked 1 of the alligator clips to the positive side of the battery and the other to the negative post of the coil . The light stayed on ?
:handgestures-thumbupright: yes, with the engine off and the ignition switch on, the off tractor testing I did indicated the ignition module powers up with current flowing thru the ignition coil. The coil being charged up when the ignition key powers up the module is probably intentional so the engine doesn't have to crank over too many times to get the first spark from the coil. No real issues so far.
Question - you mentioned "one of the alligator clips" - does your test light have more than one clip ? 
I'm going to post another image later this morning on how to check how much current your test light draws. This may be a factor in why it causes a running engine to die.
 
 
 
The tractor would not start with the test light hooked up so I removed it and it started right up but as soon as I try and connect the test lead to the coil the tractor would die
 
Interesting and unexpected. When I used this procedure to test my ignition modules, it was on an engine that already had a dead coil, It never ran to begin with so obviously I never experienced an issue with the test light causing the engine to "die" when the light was connected. Interesting.
 
Question - did the test light flash while the engine was cranking? All said and done, that was the visual indication we need to check the module. Flashing during cranking is all we really need to check the module when it dies after 20 minutes of running.
 
 
 
I took my meter and read the OHMS on the 2 ignition module Red & Blk leads and got around 18.69 OHMS  just for the heck of it . Is this something I should be getting ? I read OHMS to ground on each of the same 2 wires I get 3.5 on the Red and nothing on the Blk .  Does this mean my new ing module is shot or is this the way the position of rotor  might be at the time .
 
Ohms testing on an transistorized electronic circuit is typically meaningless. Ohms measurement may be useful if the module is completely shorted and you get a 0 ohms reading, but in a transistorized module, even swapping the meter leads on the same two wires of the module can give completely different readings. As evidence of this, consider how we check a diode for proper function.
 
diodetesting_zpsfb82f8c3.gif
 
 
Same diode device, ohmmeter reads completely opposite readings when the leads are swapped - and that's normal and anticipated to happen. Add to this a meter to meter difference in the voltage applied to the device used on the ohm meter function range and you will easily see different brands of ohmmeters will show different ohm readings. The same meter will also show different readings on the same transistorized device as you switch the meter between different resistance ranges on the meter!
 
I have no data on how an ignition module should read with an ohmeter. I have one used spare module and another in a "one of these days years I'll get to it 520H.
 
 
Should I just order another new ing module and rotor and start there again ?  I'm going to go out and pull it apart and get the flywheel off and see if I can see anything in there again?
 
If you can wait until this weekend, I know I have a spare (used) trigger ring (white color). If you want to try it with my spare ignition module, I can ship those out to you next week. I know I won't be needing them for some time. The 520H is low on my list of things to do before retirement.

 

 

Edited by Save Old Iron
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9 hours ago, Jess said:

I  pulled the flywheel off and removed the ignition module , there was no insulator behind it . There must not have been one on the original or I would have replaced it. Doesn’t the Bakelite on the module isolate it from the block ?  I read ohms on the old module and it had none I took a reading on the new one I had replaced last year and it reads 24 ohms . When I read to the metal backing plate on the module I get 3.5 ohms to the red wire on each of the modules . I tried to bench test them like SOI had showed me but got no light nothing , the bulb doesn’t light .’'

Where you touch the ground jumper from the battery to the back of the module , the small round spot I have 4 of them but they are all covered with Bakelite  . Is this how it suppose to be ?  If I were to get and insulator for the ignition module do you think it would work , or is it worth the try ?
  Maybe they added an insulator to later models ? But since there was non I mine , that is the way it must have come .
                Thanks again for your help
    Jess

 

Jess, bench testing the modules is probably not valuable to you as your issue has never been a no start condition. We know the modules work , but only for 20 minutes. Unless you pulled out a hair dryer and heated the modules up, bench testing is not going to help us here.

I'll put together a quick movie in the next few days to show the off tractor test setup and how the module and trigger ring interact.

 

 

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3 hours ago, cleat said:

I believe the module needs a good ground. Maybe your gasket material in combination with old screws made it lose electrical grounding.

 

I installed the thin insulator and also used star washers on the screws to ensure a good ground connection from the metal tab to the engine block.

 

Your insulator may be too thick keeping the magnets from doing their job.

 

For a test at least, just try a piece of thin gasket material or even a piece of cardboard like a cereal box.

 

 

The module absolutely needs a good ground. The BLACK wire from the module IS NOT A GROUND WIRE, The black wire from the ignition module performs the same function as the wire coming from the points to the coil negative post on a K series ignition - the wire BECOMES GROUNDED when the points close or the ignition module is triggered by the magnets in the trigger ring. When the second magnet in the trigger ring passes the ignition module, the black wire becomes an open circuit - just as in the points based K series ignition.

 

The metal tab on the ignition module is the module GROUND. The heat insulator does isolate the metal tab from the engine block but the metal bolts thru the tab to the engine block establish the ground to the ignition module. As long as the module metal tab is grounded with the mounting screws, the insulator not an issue.

 

Yes, the insulator can be too thick and displaced the ignition module nose too far away from the trigger ring. Try one thickness of the gasket material. The reason I steered you away from paper or rubber is to prevent paper from becoming wet and disintegrating when you hosed the tractor down and possibly sucked water into the module area. Paper would compress / disintegrate, loosen the module on the block and cause future issues. Same with Silicone or rubber, eventually they would compress and loosen the mounting bolts and result in an intermittent ground. Compressed asbestos-like material would be best and mimics the OEM material.

 

 

 

 

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3 hours ago, Jess said:
My understanding was I needed and insulator to protect the module from heat build up?

 

That is correct. I'm not sure what the airflow is behind the flywheel and if the module enjoys any level of forced air cooling during engine operation. The module will be exposed to elevated temperatures from the block - probably 10's of degrees higher than the oil temperature in the block. The module is also likely to be exposed to "heat soak" issues when the tractor is shut down while the engine is hot and all air cooling is lost from the flywheel. The heat insulator would delay radiant heat transfer to the module while the engine was cooling down. Conductive heating would be present thru the module mounting bolts - no practical way to eliminate that.

 

Best case scenario is if you mount the insulator, you issue may be cured - or at least you may start to see 30 - 40 - 50 minute runs before shutdown. This will confirm we have made a change to the predictable 20 minute shutdown cycle. IF the ignition module is compromised and still shuts off after 40 -50 minutes, you may be forced to try to put the old module back in and give it a try before buying another module.

 

Hopefully the insulator makes a noticeable change or even cures your issue.

 

I was rolling around the thought of "misting" the air screen area with water while the tractor was nearing its 20 minute shutdown - to see if the shutdown time was extended or disappeared. Just tossing out ideas. I have no idea what the airflow looks like behind the flywheel.

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Jesse, Cleat

 

here is the best method to check the current drawn by your test lights. Mine checks out at about 120 milliamps or 0.120 amps. This amperage will certainly not strain the ignition module even when used in conjunction with the ignition coil. I have seen some test lights where the user had replaced out a defective bulb with a much higher powered car dome light that draws significantly more amperage.

 

Note, the meter is set to read in amps with the positive lead in the designated AMPS socket.

Don't forget to switch the positive lead back to the VOLTS socket  and function switch back to OFF when you are finished with this test.

 

 

test%20lite%20current_zpsdt9xu4at.gif

Edited by Save Old Iron
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Good Morning, 

 (Recap)   When this all started my tractor died and would not restart at all ( First time ever)  Then I started !  cleaned and checked all switches,  replaced the coil (Harley)  new Onan condenser , new key switch , new starter solenoid new spark plugs and wires . I then bought and installed the new ignition module .  Until I installed the new module the tractor would not start .  After we installed the new module it started  an ran . I though we had it licked. Then after running it for a short time it shut off and had no spark and would not restart until I let it sit for 40 min . that was where I left it  .  Now this Spring I installed a new rectifier , stator and came back to my old friends here to see if we could finally get this thing figured out.  I removed the Harley coil and went back to my original Onan coil as changing the coils made no difference .

     I have used a home made test light. Car bulb single element socket wires and 2 alligator clips. When I hooked the one to the positive side of the battery and the other to the negative post of the coil the light would stay on with out having the key in the on position and the tractor would not start. I had to take the bulb off for it to start. and when it started if I hooked the bulb up again it would die. Question ?  If the Harley coil did  not fry my then newly bought ignition module  that I bought from Cummings at the time. Could the coil just have bee defective from the get go ? That is why I never could get this thing to run right and the old ignition coil was the initial problem ?  
 
   This is not a pressing issue and I appreciate the offer of you spare coil and ring , but do not want to put you out . I can order a new rotor for around $30 bucks , Should I try that or am I better off ordering a new set together ?  I'm almost tempted to take my other set out of my 520H but if you remember last time I got myself in trouble swapping parts from one working machine to another (HA)   Don’t think I want to get into that again. I will pull it apart this morning and remove 1 of the insulators I made and check to make sure my module mounting plate is getting a good ground before putting the flywheel back on .   After today I will leave it alone for a few days , have some mowing and other things to catch up on !  If changing from 1 insulator helps I will let you know .
  Thank you for your time and help !
 
   Jesse

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I took it apart again and just put 1 of the insulators between the module and the block . Checked for good ground to modular tab and bolts/star washers !   Have goo ground .  Put back together , still no start . I don’t think the module is bad ?  I will order the new plastic rotor and see if it does anything for me .  Meanwhile I will go out and take it apart again and take the insulator out from the module and put it back the way it was originally with no insulator and see if I can at least get the 20min run back ?
   Thank you
    Jesse

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