Cylinder not firing

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Mike_Schrank

Mike_Schrank

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Looking for some advice... Engine started running bad. Found that I have a cylinder not firing. Checked for spark...which it has. Everyother plug was clean except one. It idles ok...just sounds a bit off...and down on power. No smoke out of the exhaust or anything. Did it go out of timing? I am pretty new to this...just a shade tree mechanic of sorts. Thanks for any help!
 
Can't see it going out of time. Might want to first do a compression check then pop the valve cover off to see if there's an issue in the valve train. Could be distributor, there are a lot of variables so start with the basics then keep us informed. Need a little more info on the motor.
 
What does that one plug look like? Can you describe it? Is it sooty looking? Is it black and grimy with oil? What does the center electrode and the grounding electrode look like? What engine is it? Have you tried switching out or changing that plug with a new one?
 
One cylinder, and one plug fouled is not timing

You SAY you have spark but that may or may not be true. You might, example, have a damaged plug wire, which will 'arc past' when checking an open gap, but fail when under load

Very first thing is to suspect the plug and or plug wire. Easiest thing, is to replace both

Then look for miss. Get a clip lead and something for a probe. You can even use a 12v test lamp with the clip grounded. Loosen the distributor boots and wires so you can slide them out.

Use your grounded clip, and some insulated pliers (fuse pullers) to pull the wires out of the cap one at a time, slide your grounded probe in behind. At idle, you'll hear the difference.

If it really is a "dead" cylinder, run a compression and or leak down test and pull the cover and look for spring/ rocker/ valve damage.

You can "rig" most compression testers -- with the schrader valve removed -- to inject air at piston TDC and listen for air leaks at exhaust, intake, or look for bubbles in radiator, etc.
 
Thanks guys. Sorry for being kind of vague. The engine is 360, it is a 87 truck motor in my 73 Dart Sport.
The plug was black and kind of grimy with oil. I did put in a new one and started the engine with the plug out and did have spark.
I didn't think it was timing really...just spitballing. It was just so weird that I went to a car show and the thing was running great. Went to leave and it started running bad... I am going to take the valve over off and see if there is anything out of the ordinary. I am also planning on doing a compression and leak down test. I just figured I would throw it out there and see if there was an easy answer.
Thanks again!
 
If you were doin any burnouts, or missed a shift, over-revved it at all, it's not uncommon to pop a pushrod thru a rocker arm.. ( I used to carry a spare left and right rocker in my trunk, with the tools to change it.)

hope it helps..
 
The spark seemed strong to me?! I did go and buy plugs, wires, and a rotor just in case I needed it. The spark seemed as strong as others that I checked.
There might of been a chance of over-revving. On the way out to the show the road was wet from rain the went through. I did have some spinning issues as a result. I don't do any excessive burnouts as I don't really want to break anything! Lol!
Thanks Inertia...anything helps!
 
I have had same problem before and found pushrod shoved thru the rocker. Was just cruising along about 40-45 mph. Easy to see when you pull cover off, Joe
 
Well I took the valve cover off and everything looked normal. Except that one of the (adjustable) pushrods on that cylinder was a bit loose compared to the others. Would that be enough to cause my problem?
 
a bit loose could mean bent valve! with the rocker assemble off, are all the valves the same height. if one is lower then the rest, you have a bent valve and compression check will show no or vary low compression on that cyl.


does the motor clatter? could be a bad hyd lifter.
 
"Bit loose." You need to determine if that is on the dead cylinder, and in any case WHY

In addition to above, you might have a (cough, gag) cam lobe goin' away
 
Yes hydraulic lifters. The engine doesn't have any odd noise other than the sort of rough idle and small stumble off idle. I will have to check the valve height. Thanks!
 
Turns out is was one of my pushrods that was out of adjustment. Got that right and now she runs great. Thanks everyone for your help!
 
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