ok so I've been having an issue with this engine 350 chevy mild cam , it was running good but it Had a slight miss fire once in awhile it seemed, I took it out for a ride and it seemed to be running pretty good. I put my foot in it and when I backed off, just a short spurt, it was running rough,missing. So I've been trying to figure out what is going on. This evening I took an infrared gun to the headers and found #5 not firing.a lot cooler then the rest of the headers. I also did a water test and all cylinders sizzled but that one. I changed plug wires , new rotor and cap and it still is not firing # 5. I pulled the wire and put a spare plug in and no fire coming from the distributor only on # 5. I swapped wires to see if anything Changed, no luck. So now I'm stumped, what could it be?
You need to do a compression check. I'm thinking burnt or bent valve-or maybe a bad lifter or cam lobe. alex
Make sure there is not a crack in the cap close to that terminal. Carbon built up on a crack will make the spark take another path. #5 and #7 fire one after another too, make sure they are seperated and not loomed right next to one another.
I just put a new cap and rotor on it, plugs are new as well as the plug wire I've attached a photo of the wires I'm pointing at #5 with a screw driver
Not a lot of room by that firewall is there? Try running it in the dark and see if you can see any spark jump.
I took a spark plug and plugged it to the wire. Then took the plug to ground looking for spark I'm not getting any spark there
This is where a scope would come in handy to see if the distributor is firing the coil on number 5. It almost has to be that the Pertronix isn't working on that position. Maybe the magnet in that part of the ring is bad or the gap is off.
Have to go with FORDORS. See if the plug wire at the cap is arching to the firewall. In the dark you should be able to see it, and possibly even be able to hear it. (Shouldn't have to be dark for the hearing side of this.)
This is the best test to ferret out an arcing condition. I had a miss in my SBC and I found the wire arcing to the heat shielding around the wire. New wires have been purchased. Non-conductive heat boots as well.
If it is not arcing somewhere, Probably the Pertronix unit has a issue. I had a similar problem years back, turned out to be the pertronix unit.
Well I called pertronics today and it turns out they have a magnetic pick up there are 8 little magnets that fire each cylinder. They tech guy walked me through the check and once I pulled it, it was obvious that one of the magnets was missing this the one cylinder not firing. I think replacing t his will. Solve my delema! Thank you all for the help!
The Jalopy Journal
