I'm baffled with this one. who can help with this one.

[66hemi]

Hey all, I am having some trouble with a missfire at lower RPM say around 1400 to 2300 or so. Its a 69 Charger rt 440 4 spd. Here is what I have done so far. I checked the timing and vac. both are good. I purchased new cap, rotor, plug wires, 3 sets of spark plugs. Same problem, I changed the carb from a holly 800 to a 750 AFB edelbrock. Same missing issue. I checked the compression. Low on #2 120psi. I took off the heads found two bent push rods on #2 and sent the heads out to be cleaned and have the hardened seats in them. Put it all back together with new pushrods ran it and the same issue. Today I swapped the orange ignition. boxes and distributors with my 66 hemi (that runs fine) and have the same issue still. The symptoms are when you hit it, it has no trouble breaking them loose. Under full load you would think nothing is wrong at all. Runs strong and hard but the lower rpm you give it a little gas and it almost seems to slow then takes off. Acts the same with both carbs. What am I not seeing?

The car is:

30 over
6 pack rods
edelbrock torker 2
holley 800 dbbl pump. (put back on)
electronic ign.
direct connection purple shaft 509

timing set to 18 btc
vac was about 16

[Patronus]

fuel pump?

[Just 6T9 CHGR]

What caused the pushrods to bend?   After replacing them did the compression rise?   Possible worn cam lobe?

Moving this to the engine section....

[66hemi]

The cam looked good and the lifters seem to be in great shape. too. I don't know what caused them to bend. Over rev perhaps. I'll do another comp test. It seems electrical because when you nail it it will break them loose and fishtail from already ready rolling about 15 mph. I'm just stumped

[66hemi]

I would like to add that it isn't actually misfiring or backfiring just cutting in and out. Not poping but jerkey while driving. I tried the coil out of the other car today and same thing. Any imput would be great. I think I have tried everything but not something. Electrical stinks.

[skip68]

Ballast ?      

[FLG]

Slacked/Worn timing chain 

[oldkimmer]

............may not b electrical..........r u running vac advance.......if so disconnect it..........kim.........

[firefighter3931]

Check all of you electrical connecters, especially the harness that connects the box to the distributor. We had one that would cut out intermittently and break-up at high rpm. The wiring to that plug was intact but loose and slightly corroded.



Ron

[66hemi]

I'll check the harness. I am running vac advance also. I just pulled the plugs and they all look good. I had it idling in the drive and pulled each plug from the cap and they all made a difference in the idle.

[firefighter3931]

I'll check the harness. I am running vac advance also. I just pulled the plugs and they all look good. I had it idling in the drive and pulled each plug from the cap and they all made a difference in the idle.

The idle balance test indicates that there is nothing wrong mechanically. Block off the vac advance....it's worthless on a performance application. The cannisters are designed for stock engine builds that make waaaay more vacuum than the 509.   

Your engine may want well over 20* advance at idle with that cam. What is your idle speed and how does it idle ? You might have to play around with the idle circuit to clean it up. The 509 is a "dirty" cam down low and is a Pain in the azz to tune. 



Ron