OT-360 V8 running on 6 cylinders??

[mattski]

My 87 Jeep Grnd Wag driveway plow lost a lot of engine power. I traced it to two cylinders misfiring. Disconnecting #8 and #5 at the cap does not alter performance. Disconnecting all others does. Replaced cap, rotors and all plugs, switched wires and the problem persists.

The two cylinders in question are on opposite sides of the cap. Coincidence? But there is spark at the plug.

Fuel is present and fresh.

I am stumped.

Matt

[Chicane]

>scratches head<

If there's spark at the plug, what exactly do you mean by misfiring?

When you switched wires, did you put the wires real close to anything? It could be arcing. >shrug<

I'm stumped as well. If you have fuel, you have spark, what could be the problem?

zero compression on those two cylinders?

[huck369]

Maybe bad injectors or connections to the injectors.

[Subafreak]

87 Grand wagoneers were fuel injected?

[Subafreak]

But really throw a compression gage on it.

[huck369]

Originally posted by Subafreak
87 Grand wagoneers were fuel injected?

Doh!?...I was thinking 97

[mattski]

First, thank you all for trying to help me.

By misfiring, I mean that they are not firing at all, I think. When I disconnect cylinders 8 and 5 at the cap, there is no effect on the engine. When I do the same for the other 6 cylinnders, there is a definite drop in rpms.

I replaced all the plugs, cap and rotor. No improvement.

When I re-connect the wires at the cap, I can see an arc between the cap and wire as I insert the wire. I also get spark at the plug when I ground it to a bracket. So I seem to have spark unless it magically disappears when I put the plug back in the engine.

I switched wires with no improvement or change to which cylinders are misbehaving. I ran it in the dark and did not see any arcing.

The engine is carburated and the choke opens up as intended once the engine warms up.

Cylinders 8 and 5 are exactly opposed on the cap. Coincidence?

I checked compression on 5 and it is ~115psi. #8 is a PITA to get to so I have not checked it.

The engine does produce a hissing sound. Could some kind of intake or exhaust leak cause this?

The engine also taps somewhat. Could this be valve related?

Thanks again.

Matt

[huck369]

Could be a vacume leak in the intake (but that would probably cause all cylinders to act up.
More likely something directly linked to the spec. cylinders, maybe a burnt valve in each of the cylinders in question.

I'm not sure if 118 lbs is in spec on that engine or not (though it sounds a little low to me), I'll let somebody with access to the specs field that part.

[Chicane]

Keep us updated.

[mattski]

I still have not replaced the coil and condensor. Could a weak coil, combined with low compression in two cylinders cause them not to fire?

Matt

[Chicane]

Well considering coils are only like 30 bucks for a BLASTER or something, I say go for it. Even IF that isn't hte cause of the problem, once you DO fix the problem you'll have a better ignition system. I had an MSD Blaster in my charger, worked great.

[mattski]

I may have to do that even though I already spent $16 on plugs and $30 on cap and rotor with no solution in sight. But if that last $30 solves the problem, it will have been the best $30 investment ever.

My last plow was a 77 Scout which had an intermittent starting problem. I wound up replacing everything until the ignition "black box" solved the problem. I may actually try a left over coil from it to see if it helps.

At least parts are not as expensive as for our favorite car. A starter with a 3 year warranty set me back only $30 last month.

Thanks for the advice.

Matt

[Ron Mummert]

Originally posted by mattski
I still have not replaced the coil and condensor. Could a weak coil, combined with low compression in two cylinders cause them not to fire?

Matt

As you know, I'm no mechanic, nor do I play one on TV, but I had a similar problem on a '77 Olds pushrod V-8 engine. I had lost a lot of power & had some "funny" tapping on one side. I pulled the valve cover & found the (oops, can't think of the part name) uh...the "connector" uh..rocker arm? had come loose, thus there was no connection between the push rod & one of the valves. Consequently the valve (intake, exhaust, dunno) just floated. It would be unusual for TWO to screw up at the same time, but we do love surprises, don't we?
Good luck. Ron

[mattski]

Ron, did you have compression? I would think that if the valves were floating, you would not get any. I get ~115 psi on cylinder #5 and #8 is a PITA to get to.

Thanks for the help,

Matt