OT-360 V8 running on 6 cylinders?? - Page 2

Chicane · #16 03-10-2003, 02:10 PM

Quote:

Originally posted by Ron Mummert
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.

As opposed to those overhead cam v8s of the 70s? ;P

heh.

Yeah, pull the valve covers. It doesn't take long, and it's worth a shot. You could have a busted valve spring or whatnot.... or a rocker arm... but ...hrm... never heard of that happening in a mopar small block unless it was making a lot of power. >shrug<

Beav · #17 03-10-2003, 03:47 PM

Big Cheros and Wagoneers are known for their vacuum hose appetites. Especially if you can hear hissing.

Engines need three things to run - air, fuel and spark. If you have 110# (close enough) you should notice little difference when you pull the plug wire. If you have a new cap and rotor, the wires are good or at least swapping them around makes no change, you can probably assume they're o.k. also.

Here comes the tricky part - the fuel. Apparently you have fuel to some of the cylinders or it wouldn't run at all. However if you have a vacuum leak or two your fuel (mixture) is too lean to make enough power in your dead cylinders. Some vacuum lines originate in/on individual intake manifold runners, thereby causing individual cylinder misfires. Usually on V8s the two center cylinders on one bank and the two end cylinders on the opposite bank are tied together in the manifold. A vacuum leak at a hose or the front or back of the carburetor could cause two of the four cylinders on that one particular manifold plane to run lean and misfire - this is what I would suspect has occured as 5 & 8 would either be the two end cylinders on one bank or one end and one center on opposite sides of the engine. Pretty fart smeller, ain't I?

I would go look at all the vacuum hoses, move them around a bit. I'm pretty sure that most of them are brittle and will break very easily when disturbed. The V8 Jeeps run extremely high underhood temps. If you still can't find the leak get a can of flammable carb cleaner and carefully spray around the carb base and where the intake manifold joins the cylinder heads while the engine is running. Any increase in idle speed will indicate a leak. Just please be careful and not spray anything that might ignite the carb spray, like plug wires, exhaust manifolds, etc. And you don't need to spray excessive amounts that would pool up on the manifold - that could be dangerous also. If you have an extinguisher keep it handy next to you.

Good Luck!

huck369 · #18 03-10-2003, 04:40 PM

I've also seen cam lobes wear down and cause individual cylinders to lose power.

But I'd bet on Beav's thoughts, ....if I was a betting man

Chicane · #19 03-10-2003, 06:28 PM

I had an intake manifold leak on my charger when I got it. Didn't have these symptoms though.

>shrug<

Ron Mummert · #20 03-10-2003, 07:22 PM

[QUOTE]Originally posted by mattski
[B]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.

D'oh!!! Good point, although I didn't check it. I yield to Beav, as always. I'd really like to help, but I'm rather busy rebuilding my DOHC Olds engine. BTW Rob, GM did make a SOHC production engine in the '60s. Do you remember which division did it?

Ron.

Chicane · #21 03-10-2003, 07:39 PM

I don't pay attention to anything GM much. Enlighten me.

mattski · #22 03-10-2003, 07:43 PM

Beav, thanks a bunch. What you are saying makes the most sense so far. #8 is closest to the passenger and #5 is second closest to driver. I will check vacuum hoses next.

The guys at Full Size Jeep Association think that it may be more catastrophic. I hope that you are right.

Thanks to all for providing their thoughts and I will keep you post ed.

Matt

Bobb · #23 03-10-2003, 07:52 PM

Lets try the pontiac straight six. With a four barrel carb. It was also the first use of the toothed belt for the over head cam, BOBB

huck369 · #24 03-10-2003, 08:07 PM

Quote:

Originally posted by Bobb
Lets try the pontiac straight six. With a four barrel carb.

Also availiable with a single barrel carb.

Ron Mummert · #25 03-10-2003, 08:21 PM

Quote:

Originally posted by Bobb
Lets try the pontiac straight six. With a four barrel carb.

Good try. In fact, it's the right answer. The correct carb count eludes me.

Ron.

huck369 · #26 03-11-2003, 05:31 AM

Quote:

Originally posted by Ron Mummert

Good try. In fact, it's the right answer. The correct carb count eludes me.

Ron.

Yep,
Availiable with a single barrell
a four barrell
and, Yes I've even seen a factory 3 duece set-up for them (that'd be one barrel per cylinder!

)

(I used to be a Pontiac nut

)

mattski · #27 03-11-2003, 07:12 AM

Here is a comment from someone on the International Full Size Jeep Association:

"What intake manifold are you using? I know on the performer the #5 & # 8 intake runners share a common section that has a vacuum fitting. There is also a vacuum accessory fitting on the #8 runner. A leak in either of those intake runner vacuum ports WILL affect the closest cylinders more than others. Take a look at the vacuum lines in the rear of the intake. You might just plug those fittings and see if that fixes the problem. If there is a large leak in either of those vacuum circuits it could lean the mixture to those cylinders to the point that they won't fire. I think the power brake booster connects to one of those runner ports and the cruise control to another."

Looks like Beav hit the nail on the head again. I will try to confirm tonight by replacing the vacuum lines.

Matt