Ok i need to pick some brains because this is making mine mushy .......i have a 1966 dodge 383 with electronic ignition and i have a miss.......things i have done so far......replaced distributor out of a 400 replaced ballast replaced cap rotor and wires cleaned and gapped plugs checked and rechecked firing order and yet still have a miss.....help
Let me tell you a story, propbably has nothing to do with your miss but let me tell you anyway. Once I had a hemi car come into the shop a long time ago, uh a 426. It has a miss that could not be cured. Looked at everything in the ignition circuite, tuned until I was blue in the face and finally decided that I was going to pull the heads and take a look at the valves. Thought that maybe there was a bent valve or at the very least that they may have needed lapping. So I have all the pushrods layed out on the bench and I am just getting ready to start breaking intake bolts and etc when someone bumps into the bench really hard and several of the pushrods roll off the bench, all but about 3 of them to be exact. Hmmmmmn. So I took the push rods and started rolling them turns out that the 3 that didn't roll off the bench were mildly bent. replaced them and threw it back together really quick to see if that cured it. Yep cured that bitch. No more miss.
He says it runs but just has a dead hole. A vacuum gauge can tell you a lot on the way an engine is running especially with a miss and a compression test is the first thing I would have done.
I have a '67 440 HP motor in my '65 coronet....when i got it, it had a really bad miss just like you are discribing....i couldn't get rid of it so I pulled the heads and found the right rear (when looking at the motor from the front) exhaust valve was badly burnt due to a blow exhaust gasket that was ignored for way to long. Had the heads redone and the miss went away. I probably could have found it with a compression test, but I was planning on pulling the heads anyway to verify the valve size in the 915 heads(not all have big valves installed...just FYI for you mopar guys)
The offending cylinder should be within 20% of the others. Generally ya check all of 'em at the same time. the lowest is usually the problem. After that, add oil to the cylinder and re-check compression. if it goes up, the ring seal is bad. if it doesn't change, time to put air in the cylinder with the valves closed. air outta the crankcase, piston issue. out of either exhaust or intake, its valves. hthy
Is it only missing on one cylinder? I'm asking because I once had a small block mopar that was missing on two cylinders, turned out the distributer shaft was bent. It's a long shot but took me lots of head scratching to find it. Posted using the Full Custom H.A.M.B. App!
sometimes it misses and pops and sometimes it runs smooth.......will check compression hopefully tomorrow......once again thanks everyone
I'd pull the plug wires off the distributor cap one at a time while the engine is running. On a BB Mopar, it is easy since the distributor is up front - right where it belongs If removing any one or more wires has little to no effect on the idle speed, thats your misfiring cylinder(s). If the engine clears up just as you start to reinstall the plug wire (the spark is arcing to barely reach the plug wire) - you may have a bad or fouled plug on that cylinder.
One more thing: if it has a Chrysler electronic ignition system, make sure the ignition box has a good ground. You said you cleaned and gapped the plugs - how did you clean them? When does the engine have the miss - idling, under load, all of the time, in humid/rainy weather?
cleaned them with carb cleaner and a wire brush to knock the big stuff off then used some 220 sand paper blew them off regapped them and stuck them back in......misses at idle and under a load.....driving me crazy
compression test time as placed above, do a dry test then add a few shots of motor oil into each cylinder one at a time. if it comes up with oil you have bad rings, if not a valve problem, issues found in the past are bad intake gaskets at the ports making it run lean, broken springs, burnt valves .with your miss I would lay personal odds on a burnt valve and seat since these motors were not meant to run on lead free gas which causes the valves and seats to burn
did not get time to do test yet.....when I get home it is 3am and don't think my neighbors would like it to much....lol
Don't do that, the wire bristles leave metallic scratches on the porcelain which lets the spark travel down the insulator instead of across the gap which leads to misfires. Sandblasting is the best way to clean a spark plug but new plugs are cheap enough, just replace them and be done. I'll bet a fresh set of plugs cures your misfire problem.
If the cylnider balance test shows one or 2 cylinders consistently "bad" it makes troubleshooting lots easier. Would be useful before the compression test. As a trial I'd close the choke a little while idling. Carbon tracks on the distributor cap would also be on my list of things to check, along with the other excellent suggestions so far.
When I saw this thread, it reminded me of 40 years ago when I was a teenager out in the driveway working on my first car ('66 Chevy with 396). I came into the house and poured a glass of lemonade as I told my mom, in my most expert mechanic voice, "My engine is missing." Without missing a beat, she replied, "Well, where do you think it went?"
I would first replace the old plugs as you could have a carbon trace on one of them causing it to short out , silica blasting ( glass bead) is the only way to clean them , if a plug has any heavy carbon on it and the tip is rounded , pitch it .plugs on older cars were only meant to have a life of 25-30K , 1960-70's was 50 K only the later years with EFI have we been seeing 75-100k miles , and simpler the plugs the better .
guess i'm a real old fart here and will admit to being one, since I remember when I started working in dealer ships plugs on the old 36 and 40 hp vw bettles their owners manual saying they had a service life of only 6.000 miles they came out and got cleaned at 3.000 and my first brand new chevy "a 1964 impala 409/425" it's owners manual saying to replace them at 10.000 miles. ( sure a plug street racing back then lasted maybe a week )then we got the copper core plugs and saw 30.000 service times then platinum plugs and omg they went 60 then 100.000. now cars come with iradium plugs and are supposed to last 120.000. sad part is we still have to deal with them seizing in the alloy heads
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