Gentlemen I have a question concerning what seems like misfiring on my 73 challenger 340 four bbl. A little history, I totally rebuilt back stock but had to bore .030 over other wise totally stock. On initial start up she seemed to run best at 10 degrees before with vacuum advance plugged and around 900 rpm then hooked vacuum back getting around 34-37 degrees. She would start good, quick throttle response with no preignition shutting off. Due to having to do a lot of other things was not able to go very far just down the street and back and seemed to do well but unable to do a good run till last week took a 40 mile run. Turns out it wouldn’t go into 3rd so keep rpm around 25-2800 rpm and after about 10 minutes starting misfiring off and on , made it back home and removed fuel filter hoping it was clogging but was clean. I realize it could be many things mainly electronic. Has new standard coil, wires, plugs, blue ICM , regulator, rebuilt thermo-quad, and engine wire harness. Hoping someone can lead me closer to that needle in a haystack possible problem. Thanks in advance for any imput.
Misfiring issues
- Thread starter HYDRO
- Start date
Challenger RTA
Well-Known Member
How long and what engine speed was the break in? Does it go back to good character? Rocker arms loose after heating up. I would put a vacuum gauge on it. Check the cap and rotor for corrosion. Been there done that new cap the summer before, go figure.
Xcudame
Well-Known Member
I'm assuming it's an automatic. Not going into third (direct drive) is certainly an issue that needs to be addressed.
Ricks72Chlgr440
Well-Known Member
Did you initially run the rebuilt engine at ~2000 rpm for at least 20 minutes?
Ricks72Chlgr440
Well-Known Member
If you are using a flat tappet cam & lifters then you may have wiped your cam out.
Xcudame
Well-Known Member
Yes @Ricks72Chlgr440 might be correct, flat tappet cams need to be broken in on initial startup for 15-20 minutes at 2500 to 3500 rpms. And it's helps to have breaking lube installed on the camshaft lobes prior to installing the lifters. And priming the engine using an oil with lots of zinc phosphate prior to startup.
Years ago in the engine rebuilding shop I worked, all the reground camshafts were parkerized after grinding which also helps during the break in period. I believe Howard Cams are still parkerized. Not sure of other brands these days except a Mopar 440 camshaft kit I bought from Summit earlier this year was parkerized.
Years ago in the engine rebuilding shop I worked, all the reground camshafts were parkerized after grinding which also helps during the break in period. I believe Howard Cams are still parkerized. Not sure of other brands these days except a Mopar 440 camshaft kit I bought from Summit earlier this year was parkerized.
Ricks72Chlgr440
Well-Known Member
Not sure what manufacturer the cam came from, but there have been quite a few problems with some. He will need to pull the intake and look at the lobes. If questionable he will need to pull the rocker shafts & pushrods to have a look at the lifters. That will tell the story.
540HemiCuda
Active Member
A small tip that will help with cam installs; Before you drop the intake on, put a mark on each lifter. Spin the engine over at cranking speed and watch to make sure ALL of the lifters spin. They don't have to move much or fast, just some rotation as the lifter comes up on the lobe. If any do not rotate, just swap them with the fastest ones. They will not all spin at the same speed, but they ALL must spin some. Otherwise.................
Cam lube is an absolute MUST for initial start up and if you have to crank the thing too much checking the lifters for spin, then apply some more. Oil with plenty of ZDDP, like Valvoline Racing is also a must for flat tappet cams. Oils with enough ZDDP and such for our old flat tappet cams will not certify for modern engines that have catalytic converters. And additives are a no-no.
Cam lube is an absolute MUST for initial start up and if you have to crank the thing too much checking the lifters for spin, then apply some more. Oil with plenty of ZDDP, like Valvoline Racing is also a must for flat tappet cams. Oils with enough ZDDP and such for our old flat tappet cams will not certify for modern engines that have catalytic converters. And additives are a no-no.
All being said is food for thought and trust this isn’t the case. When I rebuilt the engine the original factory cam was used with the machine shop blessing after inspection with assembly lubricant and using high zinc Lucas 10w30 for classic cars. I did check the vacuum holding steady 14-15 “ at 850 rpm I also found the power brake vacuum gauge vacuum tap rubber cap with small holes and replaced after checking the vacuum hope to make a run and will let you know how it went and thanks for your suggestion's
Challenger RTA
Well-Known Member
I found what I’m hoping is the issue yesterday,I was double checking the timing, vacuum and idle and ran her appropriately 20 minutes when the problem appeared showing the timing light starting to intermittently loose fire and trying again today with the same results after about 20 minutes shutting down and restarting is when it got worse. I’ll let it cool down, starts right up sounds good for about 20 minutes , thinking coil what say you thanks for your input
mrmopar340
Well-Known Member
MSD Blaster coil.
Xcudame
Well-Known Member
Or this one on eBay. Rick isn't going to sale crap.
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