2 dead cylinders - Please help

[Kelly Thomas]

First post here, glad to find another vette site. I have an engine problem and was hoping to get some advice. #2 & #8 cylinders are dead. I've replaced the plugs, checked wire routing, tried different wires, pulled the valve cover and checked the valve movement, checked the pushrods, did a compression ck (all cylinders are right around 165 psi). When I pull the wire for # 2 off the distr cap it has no effect on engine rpm - same with #8. This developed during driving the car. Oh, I also replaced the module and dist cap yesterday and sanded the contact on the rotor. The engine is 2 yrs old with maybe 1500 miles on it. All new parts, block was machined to 20 over, flat tops, performer intake, 600 cfm carb, headers, HEI, new timing gears and chain.
Sorry to be so long but I wanted to give as much pertinent info as possible. I'm at a loss with this problem. Any help is appreciated.

[Terry F.]

Re: 2 dead cylinders - Please help

I would pull the ignition wire from that cylinder and put it on a good used plug and visually see if it is not firing or intermittantly firing. Then I would work backwards from there. After you do that, let us know what you find out.

[Mike M.]

Re: 2 dead cylinders - Please help

Have you determined if the plugs for these cylinders are firing or not. To really help I would need to first determine if the problem was ignition or fuel delivery. What is interesting is these two cylinders (along with #'s 3 & 5) are on the same "plane" of the intake manifold (All Performers are two plane, correct?). If you determine that spark is present on #'s 2 & 8, double check the response of #'s 3 & 5 vs. #'s 1, 7, 4, 6 which are on the other manifold plane. That would isolate the problem to fuel delivery. Then on to further diagnostics!
Mike

[Chuck R.]

Re: 2 dead cylinders - Please help

If the valve train is operable I would look at the distributor cap, rotor button and the plug wires.

Just because the cap button & wires are fairly new doesn't mean a thing, they can still fail.

Look at the studs on the underside of the cap, you may find them either burn't or corroded. If scraping resolves the issue replace both the cap and button, don't trust them.

Thanks for stopping by, and hey, why not join? You won't find a more knowing group regarding Corvettes (present company excluded ).

Regards,

Chuck 32205

[Mike M.]

Re: 2 dead cylinders - Please help

if you're running a delco or generic rotor, replace it with an Accel rotor.mike

[Kelly Thomas]

Re: 2 dead cylinders - Please help

I tried two different plug wires that were good and no change. I replaced the cap yesterday, no change.
Would the rotor cause just the same two cylinders to be dead? I figured it would affect them all.

Great forum! I plan on joining.

[Chuck R.]

Re: Beat me to it Mike!

Go for the rotor.

Chuck 32205

[Kelly Thomas]

Re: 2 dead cylinders - Please help

I sent the wife to grab some new plugs to stick on the wire and ground to the block to verify good spark. I tried that a couple of days ago and just saw an orange spark and cut the engine off quickly due to having an open cylinder (no plug in 2). I'll try watching for good, consistent spark and let you know.

Yes, the performer intake is dual plane. I'll do the check on 3 & 5. I do recall that when pulling the plug off the distr the 3 & 5 dropped the rpm's though.

I sincerely appreciate these responses.

[Kelly Thomas]

Re: 2 dead cylinders - Please help

Hey Mike,
I'm thinking of replacing the entire distributor with an accel if I can't get this figured out.

I'm wondering if fuel is the culprit? I have a edlebrock 600 cfm. Do carbs deliver fuel in a way that could be causing the two cylinders to miss?

I should have mentioned this before...When I try to hold the accelerator at say 1500 rpm for instance, I get a surging condition. Drop of rpm's then back to 1500 rpm.

[Kelly Thomas]

Re: Beat me to it Mike!

Made a call - rotor on it's way here now.

Thanks!

[Michael H.]

Re: 2 dead cylinders - Please help

Kelly,

I have a question. Is the problem of two dead cylinders just at idle or does it continue up into a higher RPM/load range? When you drive the car, is it missing on these cylinders or does it hit on all eight under load. If the car has an automatic transmission, you could probably duplicaye the load condition right in your garage. If the cylinders seem to fire under load or part throttle operation, you would then know all is well with the engine internals and you would probably then be looking for a/some vacuum leaks or plugged idle circuit in the carburetor.

What did the spark plugs that you removed look like? Were the carbon fouled or dripping raw gas? Or were they white like a very lean condition?

Hanson

[Mike M.]

Re: 2 dead cylinders - Please help

Kelly,
I forget if the Performer has a divided plenum or not. If so, that is where I was headed to concerning cylinders #2,8,3,& 5. These are all on the same plane that is fed fuel from ONE SIDE of the carb. If all of these cylinders are affected then you likely have a problem with the fuel feed coming from the primary carburetor barrel that feeds these cylinders. The key here is the actual RPM drop you have on cylinders 3 & 5. This is a shorter run from the carb as compared to the cylinders at the opposite ends of the head (i.e., 2 & . If the fuel flow is reduced to that manifold plane for whatever reasons, the end cylinders starve first. The same problem could occur in a manifold without a divided plenum, but be less pronounced since both sides of the carb can feed either plane.

Mike McCormick

[Kelly Thomas]

Re: 2 dead cylinders - Please help

It seems to have a constant miss at idle. When I put load on the engine in neutral or when driving I get a surging condition. So I believe it does intermittently hit on all eight.
The plugs are wet, not dripping though. They appear to have had some fire. No carbon or white coloring.

Can you give me some idea of how to check for a plugged idle circuit on the carb? Carbs on one area that are a total mystery to me.

Thanks in advance.

[Kelly Thomas]

Re: 2 dead cylinders - Please help

Makes sense to me Mike.

What's the fix for a condition like this? other than a new carb? Like I mentioned in my earlier post - I'm a carb idiot. So any details you can provide about what to ck or look for would be most appreciated.

Thank you.

[Mike M.]

Re: 2 dead cylinders - Please help

Kelly
I just looked up the Edelbrock web site and the Performer does have a divided Plenum.
MMM