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2n Ociliscope

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John43 2n

04-03-2003 08:32:16




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I have been trying in vain to find the source of a nagging misfire on my 2n. A friend has a osciliscope that we can hook up to check the ignition system. This is a older Hitachi brand scope not a true engine analyzer Has anyone done this before?
What aprroximate voltage does a 6 volt front mount coil to the spark plugs?




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BOB

04-03-2003 21:10:21




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 Re: 2n Ociliscope in reply to John43 2n, 04-03-2003 08:32:16  
John43 did you drain gas out of bottom of carb? this could have water in there and making your miss. water and gas aint good. BOB



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raytasch

04-03-2003 15:00:01




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 Re: 2n Ociliscope in reply to John43 2n, 04-03-2003 08:32:16  
I did this more years ago than I care to admit when I was trying to perfect my O-scope skills. Only thing I remember is that you CAN detect a problem with a plain ol' O-scope. I did my playing with a 12v system and yes, I used an inductive pickup on the plug wires. You can spread the signal out and figure out pretty much which cylinder is causing a problem. ray



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Don H

04-03-2003 14:18:34




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 Re: 2n Ociliscope in reply to John43 2n, 04-03-2003 08:32:16  
If the scope has an input for a triger, wrap a piece of wire around one of the plug wires and that should give you a view with the proper firing order.

Don



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Hobo,NC

04-03-2003 12:40:25




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 Re: 2n Ociliscope in reply to John43 2n, 04-03-2003 08:32:16  
How do the plugs look. Rich or lean. Does the choke help out when it misfires. Have you tryed to inrich the mixture when this happens with propane. Can you Get hold of a timming light that will tell you the total advance of the ignition timming.



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Larry

04-03-2003 09:43:15




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 Re: 2n Ociliscope in reply to John43 2n, 04-03-2003 08:32:16  
Attempted to contact you however your server wouldn't accept the message.

I doubt if a scope would give you much information and rather doubt that it could be connected effectively.

Remove the distributor cap and rotor and check for any side-to-side "slop" in the distributor shaft. Check in every direction (all around the clock). There shouldn't be any. If there is this denotes wear in the distributor bushings which are easily replaced at little cost. This "slop" changes the point gap and usually begins by cauing one plug not to fire and as wear continues the problem will migrate to other plugs.

Hope this is of some help.

Regards,
L and C Ranch

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John43 2n

04-03-2003 10:17:31




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 Re: Re: 2n Ociliscope in reply to Larry, 04-03-2003 09:43:15  
Larry,
The missfire I hear is at idle and quite frequent and also sounds to miss at higher rpms.
I already have replaced my dist. bushings and I get even point gap at all lobes (.015"). No slop in dist. shaft. I have cleaned and lubed the advance mechanism. Compression is 95 to 98 psi engine hot.New plugs,solid core wires,coil,points,condenser,cap rotor,manifold. Timed the dist. per the manual
I have good strong spark. Had the head off and lapped the valves, blued the contact area which showed good contact.Leak tested the valves with gasoline and found no leaks. Valves appeared to be closing properly ( not sticking). Valve timing is correct( #4 valves rock when #1 is at tdc). Valves adjusted to the wide side of spec.Checked for vacume leaks around the carb flange and manifold gasket did not find any thing.Carb adjustment doesn't effect missfire.Float level 1/4" and float is good. I have not been able to isolate the miss to a particular cylinder by removing plug wires one at a time while running.I took off the muffler and can hear miss.All this recent testing has been done after a rebuild last year. Anybody have any other ideas? I have reviewed all the archives pertaining to missfire or stumble or sputter and have not hit on the answer yet. I know this tractor should run better and I will not give up!

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Don C

04-03-2003 15:46:17




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 Re: Re: Re: 2n Ociliscope in reply to John43 2n, 04-03-2003 10:17:31  
Get rid of the points and go electronic.



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Joe Ferguson

04-03-2003 12:01:26




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 Re: Re: Re: 2n Ociliscope in reply to John43 2n, 04-03-2003 10:17:31  
Hi John

You must use an HV probe with the oscilloscope when connecting to plug wires which carry 12 to 20KV...anyway its useless. But... On a regular coil connecting the point side terminal of the coil with an high impedance probe and scope input voltage set to 300-400 volts you will see a pip parade by adjusting the horizontal scan to have 4 pips which are the HV for the 4 cylinders representation (not nessessarily in the right order I mean 1234.)

Adjust vertical gain to obtain a trace 1/4 of
the total screen and observe carefully when the
miss occurs if one of the pips is higher than the
others sometimes out of scale range. That means that there is an intermittent lack of compression
because higher is the compression higher is current demand and voltage drop. If there is low
compression there is no load and the HV will be
higher. Sudden intermittent loss of compression means sticky valve which stays open sometimes caused by weak return spring...bent valve stem or sticky stem or guide. You can simulate that state
by disconnecting a plug wire from one plug then you will see the effect on scope screen and you can find which cylinder is defective by removing and replacing wires one by one.

Unfortunately I don't know how to hook the scope
probe on the point side winding of a front mount.

Sorry for the long post

Good luck


Joe Ferguson

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Joe Ferguson

04-03-2003 16:51:25




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 Re: Re: Re: Re: 2n Ociliscope in reply to Joe Ferguson, 04-03-2003 12:01:26  
As Don mentionned..
If the scope has an external trigger or external
sync input wrap 1 or 2 turns of this wire over a plug cable then the display will stay sychronized
and stable even if engine RPM changes.


Good luck

Joe Ferguson



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Joe Ferguson

04-03-2003 12:24:35




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 Re: Re: Re: Re: 2n Ociliscope in reply to Joe Ferguson, 04-03-2003 12:01:26  
Forgot to mention...

Misses may be due to old gas, water in gas
bad gas batch at gas station. You may remove the gas and put fresh gas from a gas station which
has fast gas turnover.

Good luck

joe ferguson



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John43 2n

04-03-2003 12:30:02




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 Re: Re: Re: Re: Re: 2n Ociliscope in reply to Joe Ferguson, 04-03-2003 12:24:35  
Joe,
Thanks for the reply. I think I can get to the point side of the coil. I will try your scope test. My gasoline is fresh from a Costco station and they appear to move alot of fuel.
Thanks,John



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