Author Topic: What is an auxiliary ground and where does it go?  (Read 120 times)

Offline kryptek49

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What is an auxiliary ground and where does it go?
« on: November 10, 2017, 03:13:40 PM »
Hi, I own a 1992 GS which is currently only firing on one cylinder.

Every thread related to one cylinder misfiring seems to have the Buddha suggest the problem is either the crank trigger or the auxiliary ground.

I've got a new crank trigger turning up tomorrow, but can't get my head round checking the ground.

The cable going off the negative battery terminal has 2 wires branching off which go into the wiring loom and reappear attached to the brake lights, and the actual negative cable connects too the side stand bit.

Am I missing something or is one of these connections the auxiliary ground?

Thanks for the help :D

Offline kryptek49

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Re: What is an auxiliary ground and where does it go?
« Reply #1 on: November 13, 2017, 06:05:49 AM »
Bump - can anyone help?

Offline mr72

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Re: What is an auxiliary ground and where does it go?
« Reply #2 on: November 13, 2017, 07:46:32 AM »
You should take a look at the wiring diagram.

http://www.bbburma.net/Scans/Haynes_WiringDiagram_US_90-96.jpg

I don't know what you mean by "auxiliary ground", that could mean a lot of things. But in the GS500 ground is kind of distributed in a rag tag manner that works mostly because nothing really demands a low impedance ground to work properly.

Sounds like your bike has ordinary stock ground at least from the negative battery terminal as far as you mentioned.

I've not read about an auxiliary ground related to misfire. Ground as it applies to firing the spark and the igniter etc. is common to both cylinders so whatever your problem is, it's not likely ground related. The cylinder head is at ground potential and provides ground for the spark plugs.

I think you are chasing a ghost here.

Offline The Buddha

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Re: What is an auxiliary ground and where does it go?
« Reply #3 on: November 13, 2017, 08:51:17 AM »
Aux ground is that extra black wire coming off the negative battery terminal and has a one way click style connector right behind the battery.
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Offline kryptek49

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Re: What is an auxiliary ground and where does it go?
« Reply #4 on: November 13, 2017, 09:24:08 AM »
Thanks mr72, I have no idea what an auxiliary ground is, but every thread related to one cylinder seems to have the Buddha comment to check the auxiliary ground - hence why I'm trying to rule it off my list!


Offline mr72

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Re: What is an auxiliary ground and where does it go?
« Reply #5 on: November 13, 2017, 10:14:51 AM »
Who knows. There may be a ground wire connected somewhere. Maybe he will respond.

If you have a new signal generator on the way, just replace that and hope for the best. Wait to debug until you know there's still something wrong. You know, if it ain't broke, don't fix it.

Offline kryptek49

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Re: What is an auxiliary ground and where does it go?
« Reply #6 on: November 13, 2017, 10:41:30 AM »
I replaced the signal generator on the weekend and no change, so I've ruled that out now.

Although my right cylinder has now died too. I pulled the carbs out and gave them a full clean beforehand so i don't know where I messed up.

Tbh I really don't understand what is going wrong, I've tried everything I can think of, and am close to just scrapping the bike and buying a different GS instead.

Offline mr72

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Re: What is an auxiliary ground and where does it go?
« Reply #7 on: November 13, 2017, 12:37:24 PM »
Yeah that's not a ground problem and I seem to recall I didn't think it was an ignition problem at all before. But it could be the igniter if you still really think it's the ignition. You just have to go over the entire wiring with a fine toothed comb. I think a lot of folks think misfire == ignition and don't bother to check anything else.

What were your compression numbers? I seem to recall you had low and very low compression. I would be willing to bet that's the problem. And it's probably not a valve adjustment issue, even though we always hope that's all it is. Probably needs a top end rebuild and you'll be in business.

Offline kryptek49

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Re: What is an auxiliary ground and where does it go?
« Reply #8 on: November 14, 2017, 03:54:58 AM »
So the left side (that misfires) is at 130 PSI, right side is at 125.  Is that considered low & very low?

The left valve shim is tight and I can't fit a 0.04 feeler gauge in there, however I cannot for the life of me get the shim out using the correct tool.

Low compression can be caused by a tight valve though, and if the PSI on the left increases to 150 after reshimming (is that possible) then I believe compression would be in spec.

Trying to avoid a top end rebuild as I think that is past my mechanical knowledge and I would probably have to sell the bike and buy a new one.

Any thoughts?

Offline mr72

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Re: What is an auxiliary ground and where does it go?
« Reply #9 on: November 14, 2017, 08:36:02 AM »
125 and 130 psi are both low enough to cause misfire when hot, depending on the cause.

You'll have to fix the valve clearance issue to know for sure if that helps but running a long time with zero valve lash can lead to a burnt valve. And you have to consider what common cause leads to both cylinders being 50-60 psi low when you know it can't be valve clearance on both sides. To me that says very worn valve seats or rings or both. Otherwise like my bike, bent valves due to long running on carbon build up. BTW I think with bent intake valves on both cylinders my bike had 115 psi on the low cylinder and maybe 140 on the other. It died dead after 15 minutes running in that state. I did all the same stuff you are doing to no avail. The bike would run beautifully for 15 minutes from a cold start.

BTW you can always loosen the cam caps and get the shim out the old fashioned way. I used to do this all the time on my Miata by zip tying the timing belt to the pulley. As long as you take care not to let the timing chain go slack and absolutely don't turn anything then this can work.

Then you will still be left with low compression on the other cylinder even if valve clearance fixes one. Or you may replace the shim and not improve the compression. With that low compression on both cylinders I'd be planning a top end rebuild if I were you.

Fwiw I hired my top end rebuild and it cost about $800. Was too much to spend on the bike but I figured at least I would buy some peace of mind. Another cheap used bike may have had that and other issues. Better the devil you know. I could have done it myself easily but I would have been busy for a few weekends with the bike in pieces in my garage, so I thought the shop could do it quickly and be done with it correctly for only a few hundred dollars more than it'd cost me. I was wrong, but c'est la vie.
« Last Edit: November 14, 2017, 08:42:41 AM by mr72 »

Offline kryptek49

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Re: What is an auxiliary ground and where does it go?
« Reply #10 on: November 14, 2017, 09:02:55 AM »
Wow I didn't realise it would be so expensive. At that cost I may as well buy a new GS that works, or even buy a new engine.

142 PSI appears to be the minimum compression per the Haynes manual, meaning I'd have to hope reshimming would bring the compression up by about 15 PSI. Even then the right side would still be out of spec so I don't see a way to avoid a top end rebuild at this rate seeing as the right side valve clearance is in spec.

At this point would you agree it would be best to give up?

Offline ajensen

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Re: What is an auxiliary ground and where does it go?
« Reply #11 on: November 14, 2017, 10:23:11 AM »
Don't give up! Even if you do need a valve job, you can do it yourself. It just takes a few tools, a service manual, a place to work, and patience. The purists often disagree with me, but I like to get things running with the minimum of expense. You can fix it my way with a little lapping compound or maybe a couple of exhaust valves and a gasket set. You may have to have a machinist recut the valve seats. I do not recommend grinding exhaust valves. Others can chime in. I am not touchy about people disagreeing with me.

Offline The Buddha

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Re: What is an auxiliary ground and where does it go?
« Reply #12 on: November 14, 2017, 11:14:59 AM »
The not firing switching sides is also sometimes aux ground. I've seen those plugged in and connected nice, and still not make good electrical connection.
I pull em apart and sand and clean the metal spade tounge and even sometimes give it a bit of a twist and plug back in.

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Offline gsJack

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Re: What is an auxiliary ground and where does it go?
« Reply #13 on: November 14, 2017, 11:30:54 AM »
Your 125 and 130 psi compression figures are about what you get when you don't hold the throttle wide open while cranking to check compression.  Are you holding it wide open?

Only time I ever had misfiring in 180k GS miles was when I had a loose coil wire on my 02 when it was almost new.  Did you check this, GS plug wires are screwed into the coils and bonded tight in place.  Can't budge them with considerable effort.

My 02 had  140 psi in both cylinders at 100k miles:

http://gstwins.com/gsboard/index.php?topic=67148.0
407,400 miles in 30 years for 13,580 miles/year average.  Started riding 7/21/84 and hung up helmet 8/31/14.

Offline mr72

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Re: What is an auxiliary ground and where does it go?
« Reply #14 on: November 14, 2017, 12:18:56 PM »
All depends on why the compression is low. If it's a combination of bad valve seat condition (burned/bent/carbon/worn/you name it) AND rings then you will need to hone it and fit new rings in addition to doing the valve job to get it back to right. Plus it's so cheap to do rings once you have the head off then there's really no good reason not to.

I agree replacing the valves is absolutely the way to go rather than trying to grind the original valves. I'd send the head to a machine shop and have the valve seats done. Be sure and replace the valve stem seals in addition to the head gasket.

You will then need to deal with getting the right shims when it all goes back together. It's totally doable by a home mechanic and probably cost a couple hundred bucks including the machine shop work, which would include rings and buying a ball hone and new valves all around plus machine shop. Say $200-300 depending on local market prices. Then you'd have most of a rebuilt engine. As long as the bottom end is in good shape then you will be golden. Totally worth it.

Now you might run into other issues while you are in there, decide you want to do the intake boot o-rings, maybe replace the intake boots too, maybe rebuild the carbs before you put them back, etc. That all causes the cost to creep up but again well worth it.

About the only big mistakes you can make doing this job is getting the valve timing off and not torquing the head correctly. Just be extra attentive on those things and you'll be in business.

125/130 psi real compression is cause for a top end rebuild. Bike will probably run ok and burn a lot of oil with 130psi on both sides as long as the valves are good and the cause of bad compression is rings. But if it's valves then bad things happen when it gets hot and it'll never run right until you fix it.

Offline kryptek49

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Re: What is an auxiliary ground and where does it go?
« Reply #15 on: November 14, 2017, 03:01:03 PM »
Are you holding it wide open?

Yes, throttle wide open while the bike was warm.

Did you check this, GS plug wires are screwed into the coils and bonded tight in place.  Can't budge them with considerable effort.

I've tried 3 different ignition coils and none of them have worked any differently, so I believe they are fine (also all in spec)

I've decided to pull the trigger and buy an 08 GS500f with 18,000 miles on the clock for 1300, seems like a good deal to me!


Offline mr72

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Re: What is an auxiliary ground and where does it go?
« Reply #16 on: November 14, 2017, 03:46:54 PM »
My bike had 20,800 miles on it when it required a top-end rebuild.

Good luck but I still think fixing the bike you already have may be the more economical solution.

Wish you were local, I'd sell you my GS500!

Offline kryptek49

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Re: What is an auxiliary ground and where does it go?
« Reply #17 on: November 14, 2017, 04:17:41 PM »
Good luck but I still think fixing the bike you already have may be the more economical solution.

Thanks, don't tell my girlfriend that though  ;)

I will still do my best to fix the bike as it will still be sat in my garage anyway