Curing a miss

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Curing a miss

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Curing a miss

Postby Bucolic » December 16th, 2017, 11:49 pm

What will cause a miss? My jeep starts every time with some choke and as soon as it's running I push the choke back in. I do, however, have a miss. It is there regardless of my speed or what gear I'm in.
I cleaned my plugs and checked or regaped them. I had my carb rebuilt by Billy in Florida. I checked and/or cleaned everything inside the distributor, which is brand new. I am running points and not an electronic ignition. The plug wires metered at or very close to zero on my ohmeter.
How do I cure the miss? Could I have yet another coil going bad?
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Re: Curing a miss

Postby rickf » December 17th, 2017, 7:28 am

Would not be a coil, that would involve all cylinders. When was the last time you adjusted the valves? Have you done a compression test? What does the plug look like on the missing cylinder? Have you checked the intake manifold for a vacuum leak? There are many things that can cause a miss but need some more information on what the plugs are telling you before I could say what may be the cause.
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Re: Curing a miss

Postby Bucolic » December 17th, 2017, 11:36 pm

The valves were adjusted about a year ago. As far as the compression, I'll check it. However, I should first check for a vacuum leak.
How can I tell which cylinder is the one missing? It's not a steady miss. I mean it has a miss all of the time but at 3600rpm, each plug should be firing about 450 times a minute. I'm not getting 450 "stumbles" per minute. (3600/2=1800, 1800/4=450). Did I calculate that correctly?
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Re: Curing a miss

Postby Mark » December 18th, 2017, 1:52 am

How about have it running, then pull off each spark plug wire.Seems to me, the cylinder that is missing, would have no effect on engine performance when you pull that plug wire
mark


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Re: Curing a miss

Postby rickf » December 18th, 2017, 9:15 am

What Mark said. Your calculations are off a little bit. At 3600 rpm each cylinder is firing 1800 times a minute. Do you have a dead miss in one cylinder or is it sputtering around on different cylinders at idle? Can you hear/feel the miss while driving?

Here is your statement that is very confusing to me. "It's not a steady miss. I mean it has a miss all of the time "
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Re: Curing a miss

Postby Horst » December 18th, 2017, 9:25 am

on my jeep engine (Go Devil motor), when it idles, it misses one cylinder every 30 seconds or so. I have never understood why that is the case.
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Re: Curing a miss

Postby rickf » December 18th, 2017, 9:31 am

I had an old 1960 Jeep pickup with a flat head 6 and it did the same thing, it idled on five cylinders. Everything checked out fine but that was how it liked to run and as soon as it came off idle it ran great. These should not do that though so check it out.
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Re: Curing a miss

Postby m3a1 » December 20th, 2017, 5:01 pm

I don't know if you have a mechanical or electronic ignition but I once had an experience with a rotor that was loose - just a little sloppy on the shaft. I tore my hair out on that one until I found it. Because there are an infinite number of degrees of looseness, such a problem could produce the minor symptoms you are describing to the other end of the scale; an engine that will not start or run just awful. It might also be right one moment, and wrong the next which is a lot like what you are describing. This also brings us to the possibility that your whole distributor assembly might be the culprit. If not properly tightened down, or if terribly worn it would have the same effect as a bum rotor, regardless of what type of ignition is in there. Just something to think about.

Cheers,
TJ
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Re: Curing a miss

Postby muttguru » December 20th, 2017, 6:46 pm

Bucolic wrote:What will cause a miss? My jeep starts every time with some choke and as soon as it's running I push the choke back in. I do, however, have a miss. It is there regardless of my speed or what gear I'm in.


Does the water level in your radiator drop? Even slightly?
Ken
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Re: Curing a miss

Postby Bucolic » December 20th, 2017, 10:45 pm

No, the water level is right up where it belongs. Found a lot of rust on the underside of the radiator cap, so I probably should flush the block and radiator. The distributor is about a year old, it was a NOS points type when I bought it. I will check the rotor though.
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Re: Curing a miss

Postby rickf » December 21st, 2017, 9:05 am

Look at the inside of the cap real close for anything like a pencil line from one of the contacts down the side of the cap, that is a carbon track and would be the cause of the miss. You will need a new cap. You can try to clean it off with carb cleaner but it is most likely etched into the cap. That would be a best case scenario if that was your problem. Since you have points be sure to check the point gap while you are in there and then check the timing again since changing gap will change timing. If it is one cylinder with a dead miss then it is not timing, it is either something in the ignition like a bad plug, wire or cap or it is mechanical like a burnt valve. If it were missing on two adjacent cylinders I would say a head gasket. That will happen with no inclusion into the water jacket. It can also blow a head gasket out the back and not get into the water, mine did that and I found that the rear head bolt holes were not properly tapped all the way down. I found that on three motors so far.
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1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone
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