Here is my situation: I was putting on a new set of wires on my Fairlane today, afterwards I fired it up. It ran like it always does when cold. Then I got to thinking about it, and it occurred to me that it sounded like the left bank (driver's side) had a steady misfire. It sounded no where near as smooth as the right bank. So, in my infinite wisdom, I grabbed the #7 wire and pulled it from the distributor, OUCH! Well, needless to say, that cylinder was getting fire, however idle didn't change (lucky guess on the cylinder) I certainly would not have wanted to repeat that step three more times. I pulled the valve cover and bumped the engine around a few rounds to make sure I didn't have a collapsed lifter, and everything was working as it should, any clues? This just doesn't add up to me. I'll recheck my crimps on the #7 plug wire, just because I got a jolt, doesn't mean I didn't make a bad crimp, but I would be surprised if that was the case. I guess my next step would be to run a compression test?
if you got zapped problem is plug or internal....make sure you didnt drop the plug or close the gap when installing it
yea, I pulled the plug and it looked fine, and they are screw in rocker studs, I watched the valves open and close. I'll try swapping the plugs with another cylinder, and I'll try an old wire and see what happens, like I said though, it had been running like this for a little while prior to changing the wires. of course, thinking about it, the plug looked a little too good. maybe it is a faulty plug.....
May have bent a push rod, cracked the ceramic of the plug. What did you end up gapping your plugs at? Mine ran better for a while with a 45 gap but they fouled faster.
Tip on checking for an electrical miss. Buy a plasic or make a set of wooden plug wire pliers. Loosen up all the wires at the cap or plug wire end and pul the wires off one at a time. Verify the cylinder on the other end of the plenum runner isnt dead or weak to verify intake manifold leak. If it wasnt missing before your repair recheck all your work. Like the guys said try known good wire and plug. To verify your wire is OK take a spare plug and install the wire on the plug and lay the plug on a known good ground and watch the plug to verify it is firing. Open up the gap in the plug to about .050. It should be able to jump that gap with a crisp clean spark. With the wooden or plastic you can grasp the wires at either end without getting that nasty and painfull shock.... unless your into that sort of thing. Look inside the cap for traces of carbon tracking. It will look like someone used a pencil to draw lines inside the cap.
pull the wire off at the plug with the engine running and hold the wire 1/2" from the spark plug. if you don't see a fat blue spark, the fire isn't making it through your wire. just because the spark is traveling out of the distributer to the wire, doesn't mean that your wire is delivering the fire to the plug. If there is a fat blue spark when you pull the wire at the plug, you could have broken the porcelan on the plug while in there. also, an ignition miss will be is worst with the car in gear, foot on brake and rpm about 2000. internal engine problems such as valves or rings will be worse at idle, but seem to smooth out during the torque brake test i just mentioned.
Thanks for all of the insights guys, I have an in-line spark light I'll hook up at the plug, I can't believe that I didn't relate how good and clean the plug looked when I pulled it and put together that there is a good possibility that the plug was bad, given that this is the second set of wires! Good point on the cap, too. It, and the distributor, are almost brand new (> 5 months), but I will check it as well. Frank, I've left them at 45, I guess I can't be so sure how well it's doing only running on 7 cylinders! I'm going to try to back it down to about 42 all around (with a new plug!) and see how she does. Once I get all 8 lit up again, of course.
What did the plug look like? Brand new? Is it carbed or FI? I just ask cause when I hear 302 I think 80's-90's 5.0, and if the plug looks new it could be a fuel system issue (bad injector = no gas = no carbon = new plug). JMO If not I'd try swapping the plug and wire with a cylinder on the other bank, if the miss moves you found the problem...
check the plug wire with an ohm meter,just because its new don't mean its good,even if you got a good jolt dosnt make it a good wire it might have enough resistance it won't fire under a load..then check the compesion you need at least 75 lbs...good luck
Haha. I love it when people say that. Reminds me of the person that asked me today if I could tell them if their alignment was OK. Well......the only way to tell is for me to do an alignment
If the vacuum connector is screwed into the # 7 cylinder intake runner, check the vacuum lines. I had this very thing occur with a '70 Bronco with a 302. The # 7 cylinder was almost lifeless. The plug looked like the fuel/air was way, way, way too lean. (It was, because that cylinder was ****ing additional air.) I stopped the vacuum leak, the truck ran like a top.
My reading should show an open correct? So long as it's removed from the distributor and the plug. No - it should read a direct short, or 0 resistance<!-- / message --><!-- sig -->
IIRC stock Ford wires are around 7000 ohms (per foot?). Have you pulled a compression test on that cylinder? After checking for good spark, that's the next step. Also, try a new spark plug. You can't tell by looking if it's any good. Now this is way out there but one time I had a carbed 302 come into my shop with a dead hole, everything was fine with the ignition and the cranking compression test showed good, BUT if I left the compression gauge in that hole and started it up, the dead cylinder made hardly no compression while the engine was running. The customer bailed out at that point so I never got any deeper into it.
Never pull a plug wire off a running engine to check for misfire...Use a jumper wire,firmy grounded to the engine block,and with a pointy tool on the other end to "ground " out the wire at the distributor or plug by slipping it under the wire boot.You can loosen the plug boots first to make it easier.
Three things required for an internal combustion engine to run; fuel/air, spark, and compression. Did you check the compression on the dead cylinder? You know you have spark and if there was so large a vacuum leak the cylinder couldn't draw in a fuel/air mixture it would run like ****. I've had many V8's that pulling the wire on one cylinder barely changed the idling rpm but if you pull off two more wires and then touch the wire to the "dead" cylinder there will be a definite change in rpm. Even my straight 8 Buick with what is known as one of the smoothest running engines ever will have an intermittent burble in the exhaust.
that is where I would start also check the dist cap sometimes if there is a hairline crack it will jump to the other side of cap causing a misfire on the cylinder it should be firing on.
If it ran okay before the wire changes, take some of the advice and swap a wire around or slap an old one back in. Do the cheap and easy stuff first. Look at the distributor cap tower, inside and out. I always use a new one when I change a wire set anyway. And of course plugs. Bob
It ran the same before and after the new wire set, the only reason I replaced them is because my old ones were too short to route neatly and looked like garbage. When I get a chance to get back to it, I'll check compression, swap wires and plugs and check the cap and rotor, I'll fill you all in on my findings. Thanks again everyone for your suggestions! Sent from my iPhone 4 using TJJ
The Jalopy Journal
