861 Misfires: plug wires?

After 6 months of working on my 861 I finally got it running, problem is... it isn't running very smooth, but only when I push the plug wires all the way on until the connection click is felt.

I converted it to 12 volt. It's got new wiring harness, distributor cap, rotor, rotor clip, spark plugs, spark plug wires, points, condenser, and a new 12 volt coil with internal resistor.

Initial timing: 4 degrees B.T.D.C. at 450 rpm
Idle speed: 450 rpm
Distributor points: .024 to .026
Spark plug gap: .025 to .028

The wires are Motorcraft SIPCON, part number CPN 12259 B, from NH/CNH. Pushing the plug wire all the way onto the spark plug so that the connection click is felt seems to cause little or no spark delivered to the plug as if the plug can't pick up the spark - result, engine runs poorly, misfires. If I pull the plug wire off so that the metal in the plug wire is close to the spark plug end, (the boot is long enough to do this, see pic) the engine runs very smooth with no misfiring, this is the technique I used to set the timing and carburetor adjustments, but I can't leave the wires like that as they will come off when the tractor is moving.

I've tested the plug wires resistance and they test good. I even bought another identical set of wires, they test the same, no improvement between sets when installed. The number 1 cylinder is the most problematic, however, the 2, 3, and 4 cylinder all seem to fire better when I pull the plug wire and let it just touch the tip of the spark plug. At times they will all fire when fully seated and I can drive the tractor all day, but something happens, I don't know what and it starts misfiring again.

Engine Compression Test Results:

#1 cylinder: 155 psi
#2 cylinder: 140 psi
#3 cylinder: 145 psi
#4 cylinder: 155 psi

Results after oil was added to cylinders:

#1 cylinder: 165 psi
#2 cylinder: 150 psi
#3 cylinder: 150 psi
#4 cylinder: 165 psi

Any thoughts/suggestions?

Thanks,

Matt

The plugs fire when you remove the leads or loosen the leads at the plug because you are increasing the resistance to the plug by making another gap at the lead terminal. This gap is just another form of resistance.

Make sure you are using resistor plugs. This could be your problem.

Plugs and leads must have enough resistance to delay the current flow for a short time to build up the voltage to make a strong spark. Low resistance lets the plug fire too soon with a low voltage weak spark. Works kind of like a condenser but different.

If you get leads with higher resistance the plugs will fire better. Increasing the plug gap will probably have the same effect but the exact gap will have to be found by experimenting.

Your point gap has nothing to do with this problem if you are setting it by the book nor will reversing the coil primary leads have that much effect.

Make sure you aren't using an external ballast resistor in the coil primary circuit, this would make the coil primary voltage too low. Use one or the other.

Mark

Jerry,

Here is a copy of the wiring diagram I used to rewire my 861. I'm not done with the lighting circuit and the fuel gauge is not hooked up yet as I need to change the sending unit and gauge to 12 volt parts or figure out a way to use the old 6 volt components.

So, I think the answer to your question is yes, but I included the picture just in case.

Thanks,

Matt

First off I am going to assume that all parts are new. Your point and plug settings are correct per the book.

While It could be bad wires or bad plugs it is unlikely since these are not common with all cylinders. You need to look at things that are common to all cylinders.

Things I would check even know I do not think these are problems you are having.

Play in dist. shaft causing points not to open the same amount all the time.
A good ground on the plate that points and condenser sit on.
No breaks or bare spots on the wire where it goes through the side of the dist.

What I think you are going to find is a bad condenser. I have had them bad out the box many times. I have even had to buy 4 of them before getting a good one. Go to page 94 of your Ford service manual and read section D. This should help you.

When I picked up the second set of plug wires I also bought a second tune up kit... points, plugs, condenser, etc., so I"ll try all that brand - brand new stuff and double check everything and try some of the others suggestions and post back.

It was a real pain tuning it up. It just did not want to idle at 450 rpm, so I adjusted the linkage to be able to get the idle screw to adjust down that far.

When I got it the idle was up around 750 to 800 rpm"s. The timing was so far advanced it wasn"t even close to 4 degrees BTDC. When I set the timing it would run-on after turning the key off.

My biggest worry is that the engine is beat, and that the guy I got it from had it patched up just enough to run, i.e. high idle, advanced timing.

But now that I"ve got the settings per the book it runs great, that is when it"s not misfiring.

Thanks,

Matt

The gap may not be a gap at all. The plugs may be loading down the coil by breaking down internally ( outside possibility). The gap seems small. Haven't looked, but try setting the gap out to .035. That will do much the same thing.

The point gap seems large. I'm thinking more like .018. This is a smaller gap which allows the coil more time to fill with energy which means more energy to develop the spark you need.

Don't have my books handy, but try what I said. It is definitely in the right direction.

Prior to doing that, with wires properly seated on plugs (where it misses), crank engine and pull wires off one at a time AT THE DISTRIBUTOR CAP. You should get a nice smart crackling blue flame out to at least 1/4 inch gap (metal of the wire to metal of the cap). Check each plug. Would like to know the answer to this question. Engine should run better when doing this to insure we are on the right track.

Mark

"...with wires properly seated on plugs (where it misses), crank engine and pull wires off one at a time AT THE DISTRIBUTOR CAP. You should get a nice smart crackling blue flame out to at least 1/4 inch gap (metal of the wire to metal of the cap). Check each plug. Would like to know the answer to this question. Engine should run better when doing this to insure we are on the right track."

I'll post back with the answer.

Thanks,

Matt

This past summer my 860 started running like crap. It happened all at once, not gradually. After changing this, doing that, adjusting this, checking that, etc, there still was no improvement. I finally determined that the points were bad. So, I went to the local NH dealer and bought a new set, along with the rotor button, dust cover, and distributor cap. It still ran like a turd. So I thought, "Will, perhaps I was unlucky enough to have actually bought defective points." So, I went back to the NH dealer and bought another set. When I installed the second set I noticed that the wire that attaches to the pionts had some of the conductor exposed right at the ring terminal. I also noticed that there was some white discoloration there too.

Eureka! I'd found it! The first set of replacement points were indeed operating properly. However, the exposed conductor was arcing to the distributor housing, thus causing at terrible misfire!

I hope that this helps you with your problem.

Gil