Ignition breaking up off idle to 1600 RPM
 

Another day, another mystery.

My right engine has a problem with the ignition just off idle and up to about 1600 RPM where the advance kicks in. The idle is perfect but as the power is advanced off of idle after about 1000 rpm I get a nasty stumble and roughness in running kind of like a chug chug chug.....After 1600 RPM under load or not the engine smooths out and runs fine as soon as the advance takes over. This problem has existed since day one on this rebuilt engine now with 28 hours.

I put my timing light on the marks and at full idle they are steady at 12 degrees. As I touch the power open the mark jumps sometimes retarded, and sometimes advanced from the idle of 12 degrees, each by about 2-3 degrees. With slightly more power (around 1000 RPM) the mark will jump from 14 degrees advance to 8 degrees and jump back and fourth between the two. After the advance module (v8-HP) kicks in the mark steady's throught the entire advance curve and thereafter.

I clipped my timing light lead onto each plug wire and all were showing a intermintent light pattern in the troubble zone on power. Nice smooth steady flashing at idle and into advance.

I switched modules, wire harnesses to the modules, new caps and rotors, new sensor, new coil, new coil lead wire, checked all grounds, etc without change. I'm thinking the gear to the distributor worn or a problem with the camshaft. (supposedly new). I'm not sure if the mechanic replaced plug wires or not but they don't really look new, and they seem fine at higher and lower power than the trouble spot.

454's (basically stock MCM 420's) thunderbolt IV ignition, 8mm wires etc etc)

Any ideas on this one? I am hoping this is the last problem for a while. (especially since I will be putting it away in a week or two.)

Re: Ignition breaking up off idle to 1600 RPM
 

Swap coil and iginition modules (one at a time) from one engine to the other.

Since you've been having ignition problems previously I would start there to be sure.

Re: Ignition breaking up off idle to 1600 RPM
 

Accelerator pump?

Re: Ignition breaking up off idle to 1600 RPM
 

Already swoped coils, modules, harnesses, everything....

Problem seems to definitely be ignition related, not carburation. Timing is all over the place from about 1000 RPM through 1600 RPM where the advance module stabalizes it and the engine runs normally.

Re: Ignition breaking up off idle to 1600 RPM
 

Yea, I gotta think that at this point too. Look at squirt quantity and quality, dont burn your eyebrows off (having done that myself too many times)

Re: Ignition breaking up off idle to 1600 RPM
 

Hmmm, could the cam be walking? Flat tappet I assume. They usually are stable to the block due to load from the oil pump. Hmmm, oil pump harmonic causing the cam to dist gear to load and unload? Just thinking wildly now.

Re: Ignition breaking up off idle to 1600 RPM
 

:)

Re: Ignition breaking up off idle to 1600 RPM
 

check your wires on the dist, grn wht red wht are switched ?

Re: Ignition breaking up off idle to 1600 RPM
 

swap the whole distributor into the good known engine,dont bother with bits and pieces,if the dis shaft is worn in the housing,the rotor will wobble and timming and ignition will not be accurate!

Re: Ignition breaking up off idle to 1600 RPM
 

depending on the cam, the gear may be the wrong gear and she may be lashing on you. also if the distributor is of the adjustable height type like an msd , that same prob diff reason. more t han likely th pickup is on its way out. have seen it a couple times with an msd distributor.


good luck.