Briggs 23 hp Vanguard

[Bret4207]

I have a Briggs 23hp Vanguard in a repowered skid steer. Unit has 150-ish hours on it. I had a problem with it killing plugs (NGK's) and then a no spark situation. Pulled engine and traced that to simple rust on coils and flywheel. This is a farm machine and not always out of the weather. Out of concern about having to pull engine again, I replaced the original factory coils with new aftermarket. Re-installed and got several hours of run time. Ended up back to a no spark scenario. Pulled engine again and found no rust, no apparent cause for no spark situation. Tried engine while half out of machine and had a nice blue spark!!! Figured I must have done something to fix issue and put engine 90% of the way back in, left a hydraulic pump unhooked. Tried to move machine and it's popping and backfiring. My gut (been in the small engine/chainsaw biz 40 years) says ignition problems. I have no way to test coils. The wiring on this is pretty simple and this doesn't appear to have an instant "kill" type set up where the spark is grounded out. I'm probably having a mental block, but I'm wondering if I should put the original coils back in and check what wiring there is. I can't see where it can be anything else.

Am I over or under thinking this? Am I missing something obvious? Wouldn't be the first time I overlooked the obvious, but this is a much larger and newer engine than I'm used to playing with.

[KE4AVB]

First rust on the flywheel and the matching coil legs does not affect the ignition although rust around the coils mounting screws can affect the ignition. Magnetism is not affected by rust. Rust usually only cause clearance issues.

As for it killing coils, there a good possibility that a positive voltage is monetarily being applied to the coils kill terminal shorting the electronics in the coils. This is usually caused by induced voltage as you turn off the ignition switch where instead of being break before make contacts a monetarily contact is between the magneto terminal and the run terminal that supplies 12v to the rest of the equipment. Also the kill wire harness does have two or more diodes that can short out cause one coil to affect the other coil. As simply diode check can pinpoint if it is an issue of shorted or leaky diodes. Another good possibility is the kill wire has a bare spot that is grounding out randomly and as move the wiring harness you are removing the shorting area which vibrates back to randomly grounding out again.

To test the coils they are either working or not. No electrical checks with an OHM meter is possible due to the electronics configuration. IF no fire at the plugs about the only test possible if the disconnection of the kill wiring harness at each coil which isolate the coils from the rest of the wiring harness.

Now to the NGKs plugs. You say it killings the plugs, how do you determined the plugs are bad? NGKs are fairly robust plugs and very seldom fail due normal use.

[bgsengine]

First rust on the flywheel and the matching coil legs does not affect the ignition although rust around the coils mounting screws can affect the ignition. Magnetism is not affected by rust. Rust usually only cause clearance issues.

AND ground contact issues - rusty or corroded aluminum mounting surface affects magneto grounding to engine block.

Although much older (antique these days) point ignition engines could be *slightly* affected by rusty magnets and legs, but only very little - a very marginal running point ignition system could sometimes be "revitalized" to run a few extra hours by sanding off the magnets, (Used to do that as a field repair sometimes when I worked in the gas fields up here long long ago, so from experience, it actually did work maybe 10% of the time... ) but often more of it was when they would unbolt the coil to sand the coil legs, thereby ending up improving ground contact on the magneto armature to engine block.. hence the ancedotal evidence for rust causing a problem.. (merely coincidence - would have gotten same results just unbolting and re-setting air gap, changing and improving the ground resistance) That went away with the magnetron ignition system, it would either work or it didn't - there was no "marginal" to them any more.

[bluemower]

in my experience, the newer style ignition coils have not been as reliable as the previous style. My guess is the new style is from a Chinese manufacturer. Spark was leaking through the rubber lead at the spot where the lead passed through the blower housing. This was on a new horizontal 23 hp vanguard.

agree with Ke4 concerning the voltage feedback. One idea is to disconnect the kill wire where it connects to the switch. Test the engine to see if problem continues. Does not cost anything for this test and it may save another engine removal.

[KE4AVB]

in my experience, the newer style ignition coils have not been as reliable as the previous style. My guess is the new style is from a Chinese manufacturer. Spark was leaking through the rubber lead at the spot where the lead passed through the blower housing.

Yes many of the Chinese made products are of inferior quality. And it seems every manufacture are using the Chinese stuff too because it is so cheap.

IF this is the case then an upgraded lead should installed but depending the OP experience level a new coil might be easier to do. Just because I know how to replace them don't everyone know how. It just that I hate throwing good coil just because of a bad high tension lead.

[hanz63]

You mentioned "The wiring on this is pretty simple and this doesn't appear to have an instant "kill" type set up where the spark is grounded out." Does that mean it has no coil harness with diode and kills via the carb solenoid? It would have the harness from the factory. Ditto on what's covered already. I've found that the new OEM coils are more prone to stray voltage as noted by Bluemower. I won't even buy the Briggs Optwin coils anymore as most of the machines they're on are long in the tooth. It's probably best to replace the ignition switch along with new coils. If you can safely use a toggle- if only for test purposes that would take the switch out of the loop as mentioned. What aftermarket coils did you use BTW? Were they the smaller bodied as the new OEM?

[bgsengine]

What aftermarket coils did you use BTW? Were they the smaller bodied as the new OEM?

Actually the new OEM coils look like Briggs has been re-packaging those same aftermarket knockoff coils .. which wouldn't surprise me at all, they probably do have their own QC checks and tests before the re-packaging, and at least they come with Briggs new parts warranty (which they have made harder to claim for new defectives, especially on over-the-counter sales, to the point that it's hardly even worth the time spent to file a claim)

[Bret4207]

Thanks for the quick replies guys. Yes, the new coils were the same size as the Briggs but were white box Chinese. I also used a new keyed switch when I fixed it last time. The comments on rust not being a killer surprise me, but I see the point. That fly wheel was badly rusted and after cleaning things up I had a nice spark. The stray voltage idea might well be the problem after mulling it over a bit. I'll admit I'm a chainsaw guy, not so much of a 4 stroke guy. My memory, what there is left of it, is that this engine always had a lag between shutting the switch off and the engine dying, 3-4 seconds, and I put that down to a fuel shut off system rather than a kill switch. This was a make do repower of an engine that "might fit" (SEW) and the wiring diagram was limited to labeling the starter, oil pressure (not used) and ignition switch. I'm going to check everything I can after reading through your posts again. Thank you all, you've given a direction to go in.


Oh, the dead NGKs- what would happen is they would appear to die after the engine started giving me issues and they'd foul some. Cleaning didn't seem to help much. New plugs would often give a good spark. Honestly some of the intermittent spark issues may well be the machine and not bad plugs.

[Bret4207]

Ok, just so I understand this correctly, if I have power backfeeding through the key switch, it will fry the coils? That sure makes sense to me. I am also unsure about the tab on the coils which I always was told was a grounding/kill connection. Is that correct? I can't find anything saying one way of the other in my manuals, but again, this is a much, much newer and more complex engine than I'm used to dealing with.

[KE4AVB]

Ok, just so I understand this correctly, if I have power backfeeding through the key switch, it will fry the coils? That sure makes sense to me. I am also unsure about the tab on the coils which I always was told was a grounding/kill connection. Is that correct? I can't find anything saying one way of the other in my manuals, but again, this is a much, much newer and more complex engine than I'm used to dealing with.

Yes the tabs on the Briggs coils are to grounded only; otherwise, they are left floating until the main NPN transistor is triggered grounding this terminal to collapse the coil's primary winding magnetic field which induces a resulting voltage in the secondary winding firing the plug. Applying a positive voltage the kill terminal just shorts out the associated transistors (currently 5 surface transistors and one D13003 transistor in lastest Magnetron coils config) in the trigger circuit; permanently grounding the coil primary winding. Now there are coils out have multiple terminal such the Kohler versions where 12v is applied to one tab but those have a external control modules. This also why when two coils are used the wiring harness contains steering diodes so one coil don't trigger the other at the same time.

Last year I had a replacement ignition switch that was applying only 1V to Briggs opposed coil's kill terminal that destroyed two coils before I found this voltage feedback. The customer complained that he just had the new switch installed and was questioning why I had replaced it again as I was the second tech to replace it.