Hello everyone. I have a misfire that started last week, and I cannot seem to determine what is causing it. I have no real loss of power, my engine does not overheat at all, and I’m not burning oil. I changed out my intake manifold two weeks ago and found on Saturday that three of the bolts were pulling. I tightened them down. I also found that plug 2 had white buildup on the node and tang. The misfire seemed to get worse after I cleaned it, go figure. I thought it may have been a blown head gasket, but the block test came back negative. I feel the miss most when the motor is warmed up and when I accelerate. The fuel air mix was rich before Saturday and I have since leaned that out. I’ve not done a compression test yet. Any ideas?!
Wires are pretty cheap if you're interested in just swapping parts! Good starting place is.......get the engine good and warm. Then take a spray bottle and squirt a stream of water on each primary header pipe (or mani) and note which one does NOT SIZZLE. That's you missing cylinder. Now you have a starting place. 6sally6
Is it possible something is wrong inside the plug after only 2 months? I didn’t see any cracks when I checked everything. I traced all the wires and taped every spot I found even the smallest crack.
I was trying to prevent arcing to the block. I know, replace is better, but I was on a roll and in the moment.
I agree with what others are saying about starting with new wires but did you happen to drop a plug while cleaning it or side load it with a socket? A crack won't always show in the plug. When I was younger I dropped a plug while setting the gap and my Dad said remember what cylinder you put that plug in because if you have a miss it's going to be that plug. Sure enough, even though the plug looked fine it had a miss. Changed just that plug and it was fine.
The more I think about it, the more I’m inclined to replace that plug. I didn’t drop it, but you never know. I have to tighten mine with a combo wrench because I have no room, so that may have done it.
Even over tightening at a tight angle with a spark plug socket can crack the porcelain... you can check resistance of plug wires with ohm meter. Fought a misfire under load in OT work van pulling trailer, wires cured it.
So, replacing the plug did not work. Boo. I’m going to have a leak down test run on the problem cylinder next week to see if we can’t pinpoint the issue.
Start with the obvious stuff!!!! For example plug wires With small cracks that need tape. SOB if you can see a crack in the insulation it’s done. Eye eye eye
I found a misfire on my truck after swapping out plugs, wires and distributor cap by running her in the dark. Turns out I cracked two plugs during the install. I sprayed water on the hot header tubes of the offending cylinders to isolate the miss. Pulled her into the garage and turned out the lights. I was able to see the arcing spark. Ernesto
I know I’m going to have to. This car is a daily driver and I need it to run well. The buildup on cylinder 2 still bothers me though. I am interested to see why that is happening.
I'd say you damn well answered your own questions. Quit being cheap and buy a new set of wires and a new set of plugs.
I agree. Just went through a similar scenario on my flathead, and it turned out to be plug wires. An easy way to check is to start the engine in a dark garage and look at the plugs and wires. If you see arcing, especially between the plug base and the cylinder head, the wires should be replaced.
It’s amazing when you don’t know something. An older mechanic friend of mine told me the “why” behind some off what I am hearing hear and it’s clicking. If the #2 cylinder wire is bad, not o it does that contribute, but it’s also burning my coil out. Doesn’t help that the coil is older. It feels good to have some understanding and not freak out about a major problem inside of the motor. I know that’s still possible, but knowing this other information makes t easier to believe the problem is not as bad as I thought.
The coolest "new" tool I have is a Heathkit ignition oscilloscope. I had a real problem with arcing at coil and distributor cap in high humidity and replacing parts with new just made it worse. Just because parts are new or NOS doesn't mean they are any good. I've heard that tale about dropped spark plugs before, and it's true. It's rare, though sometimes a plug is defective right out of the box. Mistakes happen. The 'scope lets you look at each cylinder firing voltage trace individually, both primary ignition and secondary (high tension) and, altogether as a whole. An ignition coil will only supply as much voltage as required to fire the plug and no more, when parts or tolerances are defective than the voltage can start to spike very high. The scope will show this, high resistance in the wiring, defective condenser, worn distributor bushings etc.
Did a compression test this weekend. All cylinders were within 2lbs of each other, so that’s a relief. In fact, I got a consistent 122 on all but 2 cylinders. No cylinder leaks! Everything points at the wires(like you all said), so a new set goes on this weekend after I get paid. Ha!
I will definitely have to look into those. Just got a find me a good set of crimps and I would be good to go.
Ok, I bought the wire set listed above and installed them. On the distributor, the boots are 90 degrees instead of the stock style straight boots. I wonder if this is making the connection there difficult as the wire has to bend to get into the distributor cap. I drive the car and it still has a miss, actually t feels like more than one now.
Have you ran it at night or in dark garage to check for arcing? High voltage is weird stuff. If it's arcing to ground somewhere, or inside the cap or at the coil, etc., and you replace parts, it may well get worse, till the actual cause is remedied.
No, not yet. Guess that’s what I’m doing tonight. I can’t imagine what it would be now that I have good wires with no cracks. The distributor was new. Only thing that has real “miles” on it is the coil. Maybe that’s it.
What's this new distributor you've installed and why were intake bolts loose? Did it run OK before you tore into this thing? What engine exactly by the way?
Buy a new cap, rotor, wires and plugs. Why? Because they are cheap and easy to install! Make sure you feel and hear a nice little click when you push the wires on the cap and spark plugs - putting a little dielectric grease inside the boots helps them slide on and helps conductivity. Take your time route the wires nicely.
On those 90 degree terminals, slide the boot back a little, and make sure the terminal goes all the way in. Then push the boot into place.
Since you have replaced all the plugs this won't help now but may others.....i don;t know how you cleaned that plug but NEVER use a wire brush as this leaves a metallic coating on the insulator and can't really be fixed short of replacing the plug/plugs. JW
Just changed the wire ends back to the stock style straight connectors at the distributor. I then ran it in the dark to heck for arcing. Nothing. And it is still running rough. Ugh.
The Jalopy Journal
