Firing consistency

azfordman · #1 (**permalink**) 09-17-2010, 08:24 PM

So....I have narrowed one of my problems down to a defective timing light (timing marks was jumping around 30 to 180 degrees.....!). Replaced it today and am working on resetting my timing, the problem is I am not getting consistent firing of the spark plugs.... If "F" is the timing light flashing when it is supposed to and "M" is the light not flashing when it is supposed to....plug #1 is FFMMMMMMMMFMFFMM plug #2 is FFFMFFMMFMMFM but plug #4 is FFFFFFFFFFF.......does that make sense? Cap and rotor are clean, worn, but look good. Wires, don't know, haven't been able to do a ohm test (can't find my tester) swapped out the coil and the ignition module from my Bronco and it didn't help the situation. So without randomly buying new parts have any ideas??? I thought I had read somewhere on the forum that if a tach goes out (which mine has) it can affect the ignition. Any thoughts on that aspect?

Gaz64 · #2 (**permalink**) 09-19-2010, 02:24 AM

A faulty tacho can take the low tension side of the ignition system out intermittently.
I would take it of the circuit altogether, I'd also replace your ignition leads if they are over two years old.
You could also see how much "crossfiring" you may have in complete darkness, you maybe surprised.

sllib · #3 (**permalink**) 09-19-2010, 07:07 AM

Some timing lights don't get along with MSD ignition boxes. Something to consider.
Bill Stradtner

Caprimaniac · #4 (**permalink**) 09-19-2010, 08:10 AM

Never had this problem, but doubt the tach has something to do with this.

Can you hear/ feel (when driving) any misfire? If not, put the tomig correct & drive.
(Had a problem like this in a friends car, left it alone and it worked 100% correct. That was a wasted spark DIS setup).

RS

azfordman · #5 (**permalink**) 09-19-2010, 03:41 PM

FWIW, went through everything, tried swapping the good firing #4 plug wire for the misfiring #1 plug wire...no difference. My final step was swapping spark plugs....voila! #1 started firing consistently, but the motor picked up a pretty bad backfire.. Replaced the spark plugs (had previously checked, cleaned and gaped them), put on a new stock coil, cap and rotor, and it is running fine now. I seem to need to retard the timing advance a bit now...getting closer to 10BTDC...but at least she is on the road again... At some point I still want to find a dependable local shop to fine tune this engine....As always I appreciate all of the input! Mark

Caprimaniac · #6 (**permalink**) 09-25-2010, 04:25 AM

Hope i'll last, then!

RS