Two Dead Cylinders

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mchandford

Well-known member
Joined
May 23, 2012
Messages
170
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Location
Marysville, WA
My Car
'71 Mustang Mach 1 "M" Code. 351C and 4 speed toploader.
So I need to start a list of things to check when I get to visit my car. It just got shipped finally and my best friends neighbor came to check it out. said he thought it was missing. So they pulled each spark plug wire one at a time, and sure enough, two cylinders were not firing. I did not catch which ones.

So now I need to start thinking of things to check when I get there. Someone mentioned putting a timing light on each wire to check that they all seem in sync. I think I will probably get a new coil to take that out of the equation as well. I am not so sure about tackling the distributor. It is electronic, but I didn't pay much attention to what type. I think i should be able to check the 'gap' if its magnetic pickup. What are some other things to look for on the distributor?

Oh and I will replace wires, just replaced plugs.

 
Depends on which 2 are missing. side by side could be head gasket. if firing order is lined up it could be collapsed lifter, or broken valve spring. could just be 2 bad plugs. I would find them and run compression check before I bought anything

 
could be simple stuff as well. 2 bad ignition wires that fell off the plug or came out of the distributor.

could be a bad ignition module depending if you have electronic ignition. Could be a damaged lobe on the distributor cam. Cracked plug isolator.

you can use the timing light, just swap the pickup between all 8 cylinders and it will tell you which are not getting a spark. if you have a ignitor 1,or 2 ignition it usually means the magnetic disc that the sensor uses is no good. basically you can check the obvious first. loose wire, bad plugs. after that you can open the distributor and look for damage. if it still will not fire, then your looking at bad wires or plugs. if all 8 are firing and the engine it missing, then you start getting into some kind of engine damage and you will want to start with a compression test.

and start getting into things like caspianwendell said.

many times it is simple and the ignition wire got loose and came out half way from the distributor or the boot is not fully seated on the plugs. with the stock ignition wires you can damage the carbon filament pulling the boot off the plug, in that case you just swap in fresh wires.

 
Don't replace the coil to take it out of the equation. The coil is working fine. Replacing parts while trouble shooting other problems often leads to additional issues.

The timing light trick is a good indicator that you 'do' have a problem but might also give you a false positive that a cyl is firing. It's worth a try.

When you replaced the plugs how careful were you with the gap? What plugs did you get? How hard was it to remove the wires from the plugs? Were you careful with the firing order?

 
So another piece of info I got last night: The wires were all sparking as they took each one off the plugs. but this doesn't mean it couldn't be the magnetic pickup in the dizzy messed up right?

Also, the reason I suspect the coil is because I read somewhere that the coil going bad would cause two cylinders to fail. Because the cylinders share one portion of the coil. They didn't explain very well, just figured I would put it on the list.

The plugs are Autolite 25s. I have just recently regapped the plugs to .035. That actually helped the car run much better. Or at least it sounded and felt much better.

The plug wires are very difficult to get off of each one. And I know I need to replace the wires because one of the wire clips (?) on the plug end came off and stayed on the plug. But I am not sure if this was one of the cylinders they tested that was not firing.

I was pretty careful about the firing order. I only took one wire and plug out at a time and made sure to put each one back on before moving to the next. But that doesn't mean it wasn't already wrong, or I did screw something up. I will have to double check when I get new wires anyway.

 
That is what I am hoping. I will have to let you all know when I get to see my car again in person.

 
Check the simple stuff first...before you start replacing things.

I am thinking .035 is not enough gap for electronic ignition, one of the young guys will know.

and I would do the compression test to start with.

 
Ya. i was just looking for things to put on the list to check when I get there.

1) I know I need new plug wires.

2) check firing order and wire location.

3)Timing light to each wire to check for erratic spark.

4) check distributor for damage, and check the gap on the magnetic pickup

5) Compression test.

That is what I have so far. I think I may need to take the intake off and re-seat it. If nothing more than just to confirm it is on correctly. The Ford dealer had it off during a repair and I have heard it is a commonly mis-installed part. but that will be lower on the list.

The base in Everett has a hobby shop and I think I could borrow a compression test kit. What all do I need to perform that? Is it just a fitting to take the place of the plug and a gauge?

 
Check all of the above...A easy way to check for spark "old school way" Just take the plug that is not sparking out..And stick it against the block or bolt on the motor and have some one crank it over and see if its getting spark on that dead plug...Or if you have a brave enough freind to grab the end of the wire while you turn it over...lol..Ouch...But i know some people who really do that..lol...I would not thou..specialy if you got a weak heart...Make sure you unhook gas and run out what is in the carb before you try that thou..lol

 
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The guy that was looking over the car took each plug off one at a time and the ones that didn't change the idle were sparking. So i think that means either the two wires are crossed or the spark is not working with the plugs actually in place. Maybe because of a bad wire. I will be at the car for a little bit this next week end.

 
Check for bent or missing pushrods. If they were sparking there may be another reason. Look at the spark plugs on the "dead" cylinders after running, see if they smell like gas. If not it may be a bent intake pushrod.

 
Check for bent or missing pushrods. If they were sparking there may be another reason. Look at the spark plugs on the "dead" cylinders after running, see if they smell like gas. If not it may be a bent intake pushrod.
So that seems like something a mechanic would know how to do real easily. The car is going to be sitting for a while so I guess if I try to take something apart and mess it up I can take some time to get it back together again.

Can you walk me through the basics of how to check push rods? Is that under the valve covers?

 
Pull the spark plug out and connect it to the wire and verify it was firing first. If you had a bent or missing push rod I would think you would have heard it. Pulling the valve cover is no big deal to verify the push rods though. Would definetly give you piece of mind before you damage something.

 
A compression test is 'easy' and will either point you to the specific cyl or remove a lot of possibilities. Most checker/krager/autozone/etc parts stores will 'loan' you a tester.

Remove all spark plugs.

Get the throttle wide open.

Attach to each cyl. Crank until the needle stops increasing. Usually takes about 5 or 6 cranks.

Record each value.

You mentioned you swapped out the lifters, did you replace the cam too? Did you do a break in?

 
I have not replaced anything mechanical. I have been too scared to because I am moving soon. I will be able to tackle a few of these other things once we get settled into the new place.

Compression test sounds easy, I think i could manage that.

Taking the valve cover off doesn't seem that tough either. But I might not know what I am looking for under there. But that is what pictures are for. i would just post them here and let the pros tell me whats wrong.

I am not sure if a true 'break-in' was done. I got the car with about 400 miles on the new engine and trans. since then I have put what I have been calling break in oil in the car. It was just the ZDDP additive but the name is escaping me at the moment. Lucas oil I think. Since putting that in I probably have another 400-500 miles on the engine. That is all.

Pull the spark plug out and connect it to the wire and verify it was firing first. If you had a bent or missing push rod I would think you would have heard it. Pulling the valve cover is no big deal to verify the push rods though. Would definetly give you piece of mind before you damage something.

I think you are referring to a spark test here and that was done by the guy who looked over the car. He said they all sparked. But I still need confirm the spark is correct and not erratic.

Anyone have any other thoughts?

 
until it is in your hands and you start with the basics its all speculation.

again confirm spark on all 8 and check plug gaping as well.

 
If you dont know how to check if you plug wires are on the right plugs maybe you should close the hood. And stop fiddling with the carb! You adjust it and leave it.

 
If you dont know how to check if you plug wires are on the right plugs maybe you should close the hood. And stop fiddling with the carb! You adjust it and leave it.
See earlier post concerning respect and dignity.

 
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