Briggs 16 hp vanguard engine troubles

Hi All,

I'm working on a Briggs vanguard 16 hp v twin engine. The problem I have is it is only running on one cylinder. It runs great on #1 cylinder, no problems. #2 cylinder is another story. I have put new plugs in it. Set the valve lash to .005 on each valve. Cylinder has 120 # of compression. Has strong spark. Previous owner had put on new magnetos. The air gap is .010 on both.
When I take the plug wire off of #2 cylinder, the engine runs great on the #1 cylinder. Once I put the #2 plug wire on, it starts bogging down and smoking. If I only have the #2 plug wire on and try to start it, it pops and backfires out of the carb. I have gotten it running on the #2 cylinder a couple of times. It smokes and runs rough when I did. I double checked the valve lash agian and both are at .005. Ready to pull my hair out. Need pushed in the right direction.

303777
1147-E1
98081911

Thank you,
Cory

 

Sounds like a problem with the head or head gasket, possibly even the piston. What color smoke is it?

 

It looks white. Smells like oil burning when you spill some on the muffler. It fills the garage with smoke pretty quick.

 

Yep, I'm sticking with my original reply.

 

Forgot some important details. When I got this tractor, it had the same problem that it does now. First thing I did was new plugs, filters and set the valve lash. For a couple of days, it ran like a top. Although I didn't pull the number two plug wire off, there wasn't any smoke at all. It was running rough at all, even with both plug wires on it. So I am wondering if there is something intermittent causing this. Thanks for any advice.

Cory

 

like said , probably the head gasket. Is there oil in the air filter housing?

 

Is the oil overfull or thin and smell like gas? Is the exhaust pipe on that side covered with oil?

 

No oil in the air filter. Oil in engine is clean and at the right level. No gas smell either. There isn't any oil on the muffler or the exhaust pipes. No external oil leaks at all. The smoke comes out of the muffler itself. Should I just pull the head and check out the gasket?

 

Yep, sounds like you'll find the problem there.

 

Pulled the cylinder head off. Piston, cylinder wall, both valves and gasket looked good. Everything is clean inside. I will get a new gasket and put it back together. Anything else I need to check while it is apart?

 

Get a bright light and look down the sides of the piston. You should be able to see the top ring barely. Put your thumb on the piston and wiggle it from side to side. Does it move, and does the ring stay in contact with the cylinder regardless of what the piston does? Might be stuck rings.

 

Piston does have normal side to side movement. Ring does stay in contact with cylinder wall as it should. Top ring is not stuck or broken.

Could this be ignition related? Wondering why someone replaced both magnetos to begin with. I am getting good spark from the bad cylinder. Could I be losing some spark when plug is in the block?

I did notice when I unhooked the coil ground wires from the ground lug, I could still shut it off with the key. I thought I would have to choke it to get it to stop running.
Just throwing that out there.

 

It really sounds like you have oil coming into the cylinder and the difference with the number 2 plug wire is that you're either igniting it or not. Since the number two is acting up you would have a somewhat smoother running engine on just the one good #1 cylinder. Are you getting the 120# of compression on both cylinders?

 

Just reading the rest of your post. I imagine the coils were replaced as a shotgun approach to fixing the problem you're working on now.

Are you saying with the kill wires disconnected you can still shut off the engine with the key. That would really be odd and for the most part not possible if the kill wires were disconnected at the coils.

 

if you can move piston side to side , doesn't that indicate rings need replaced?

 

No, the piston should be able to move side to side. If it can't that means the rings are stuck.

 

Got everything back together. Nothing has changed. Checked the other cylinder, it has 140# of compression. I double checked on the magneto ground. I started the engine with the magneto ground unhooked. Started up and ran, as good as it can right now. Turned the key off and engine shuts off. I thought I would have to choke it to get it to turn off. Wondering if the problem is related to that. Ground wire is new and no bad spots on it.

 

Is the ground wire you're referring to running directly from the coil to ground or does it juncture into a common wire and run to the ignition switch eventually? The only way the ignition switch can kill the engine is by the wire running to juncture and on to the switch. A grounding wire solely for the purpose of grounding the ignition module is just to provide ground in addition to the ground provided by mounting the module base.

Given the valves are set and the cam working properly, with the 120/140 # of compression, I believe I would look to the wiring of the modules going to the ignition switch. Go to the ignition coils/modules and locate the kill wire. That is the one that runs back to the switch. There should be a juncture with the opposing coil. Disconnect that wire at the first juncture with the other coil and disconnect the remaining wire at the first connection you find running back to the switch.

With that done the only way you can kill the engine is with the choke. See how it runs then.

 

Sorry. The wire that I was calling the ground wire is the kill wire. With the kill wire unhooked, it starts and runs. Then I can turn it off with the key. Didn't think that was right. Thought I would have to choke it to stop the engine running.

 

If you can turn it off with the key even though the kill wires are unplugged from the coil, then you have an electric fuel shutoff solenoid on the carburetor and this is a battery start unit and it's killing the fuel.

 

Well that rules out that for the problem. No matter what I have tried, I end up with the same result. Running on one cylinder. Ugh!

 

Did you try swapping the coils?

 

Just swapped the coils and no difference.

 

What'x the compression on that cylinder? Does it still smoke?

 

120# on the bad cylinder. It still smokes. About ready to pull this engine and replace it.

 

This is an excellent engine, top of the line performance and durability wise, so it just makes me wonder what could be wrong.

We need a little background on the engine, what it's on, how this problem began, history of the engine, etc... The lowest cylinder is the smoking one, right? And there is no chance the oil is too thin or too full?

 

When it was suggested to swap the coils, I only swapped one of them. Not realizing that the bad cylinder now started up even though it did smoke alot. So I put the non running side coil on the other cylinder and of course it would no longer start. Big duh on my part. So I picked up a coil yesterday and now both cylinders are running good. I let each cylinder run on its own and no problems. With both cylinders hooked up, it is running good also. I also changed the oil before putting new coil on.
When engine first started on the previous non running cylinder, it smoked for probably five minutes. Then cleared up and doesn't smoke at all now. The bad cylinder did run a few times. It had spark. I guess the coil was going out.

One problem that have now is that I hooked up the kill wire to each coil and to the lug just as it was before. Whenever the kill wire is hooked up to the new coil, it won't fire. If I unhook it, it runs just fine. I used a coil that was a direct replacement for my engine even though it is a different part number than original. I double checked both numbers before I installed it and they interchange.

 

The kill wire only grounds for kill through the switch normally (and through safety switches). If you only get a kill on one cylinder all the time you must have a direct ground on that cylinder coil without going through the switch/s.

As far as the kill function about all modules work the same on the post 1986 coil configuration. So if it runs without the kill wire hooked up, you have a direct ground when you hook it up. If the good cylinder is running ok, just merge the two kill wires, then back to the switch.

Sounds like you're making progress though. You'll get it. It's probably something simple now.

 

Wanted to make sure that I explained it right. I am starting it with the opposite cylinder plug wire off for my testing. The number 1 cylinder is the one that ran good from the start. Number 1 has the original coil. I can hook the kill wire to that coil and the kill wire lug. It starts up and it shuts off with the key. I know it also shuts off because of the fuel supply being cut off with the key turned off. The kill wire kills it instantly, unlike the fuel being shut off. So the number 1 is working good. Once I hook the two coils together just as they were before, number 2 cylinder won't fire.

I can just have the number 2 cylinder plug wire on (no kill wire) and it starts right up and runs good. But if I try just the number 2 plug wire and the kill wire, it won't fire.
So close to solving this, ready to be done with it.

 

I see what you have now.

It's not the coil you have that's doing it. It's something farther up the circuit that splits the two module circuitries. That could very easily have a resistor or something similar to keep the two apart. In a multi cylinder engine with a distributor or battery fed coils you would simply cut the power to the coils, but with the self contained modules you have a different animal. If they were firing simultaneously the problem wouldn't surface, but with the alternate firing one serves to ground the other when it's firing. I'm not sure why both wouldn't be killed off, but apparently not.

What is the engine model # and the serial number on that engine?

 

There is a diode in the kill wire that is bad.

 

303777
1147-E1
98081911

I will see if I can get a new harness with diodes today or I will order one on partstree. I will let you know how it turns out.

 

I got the new coil to coil wiring with the diodes. It is the right wire, I looked up the part number. Put it on and still have the original problem. Engine runs fine as long as I don't hook up the coil to coil wire. I can hook the wire up to each individual coil and the ground lug and it runs good. When I connect the coil to coil wire, it will only run on one cylinder.

Just for kicks, I put the original coil back on and it runs good as long as I don't connect the coil to coil wire. So the coil wasn't bad after all.

I was thinking it might have something to do with the ignition switch. But with the kill wire unhooked from the ground lug, it still only runs on one cylinder when the coil to coil wire is on.

 

Try turning the wire around so that the diode is reversed. You're feeding through the wire and that can't happen if the diode is good.

 

Turned the wire around. That was it!! Running great now on both cylinders. After all that, it was the coil wire. Always good learning something new.

Thank you!