Weak Ignition?

ok, one last thing before i turn my bronco over to the experts. i noticed when setting the timing, i dont get a steady flash from my timing light. it's a snap-on with all the bells and whistles. the problem is i do have a random missfire that i've been fighting, and blaming on carburetion, and vac leaks. i've been able to elimate all but the carb, and possible intake leak below the manifold. i highly doubt any leaks from the manifold, but i can't rule it out. so now i'm starting to suspect the ignition. my question is can a weak spark cause my timing light to not detect the plug wire firing? i used a spark testor, you know the cheap ones that look like a spark plug wire with a light bulb in it. i plug into both sides of the plug wire and i'm gettig a steady spark, but the timing light is not reading steady. i have replaced the ignition module, cap, spacer, rotor, rebuilt distributor, coil (ford style), salvaged an engine harness that wasn't all hacked up, battery, and the starter solonoid. that was before i suspected a problem. is there any way to test for weak ignition without pulling plug wires with the vehicle running? i have real bad luck with electricity, and it's a long ways down from my egine compartment.

Does your engine run?

you mentioned missfire, how do the wires look? are they in a position so they dont crossfire?

yea it runs. it idles better since i bought it. i drove it home about 30 miles, it ran so rough that the brake booster didn't have enough vac to operate. the plugs and wires are new. as far as crossfiring i'm not sure, i never got far enough to realy rout the wires neatly. i was more into getting it running. what would cause the wires to crossfire?

when two wires are routed close to each other and follow the firing order of engine, and the spark from one wire could jump into the other wire causing the cylinder to ignite in advance. (i think that it can cause detonation) the chilton manual has a diagram that you can check.

Crossfiring can sometimes be hard to explain so I hope you'll bear with me. It generally occurs when two adjacent cylinders fire at the same time, throwing the engine out of synch. For example, the 351M firing order is 1-3-7-2-6-5-4-8, with me so far ? If you look at the photo You'll see that cylinders 5 & 6 are not only right next to each other but they also follow one another in the firing order. When this happens you have to be careful to keep the wires for those two cylinders as far apart as you can because current leakage thru the insulation of one wire can fire the spark plug in the adjacent cylinder out of turn. In this case what would happen is when cylinder 6 fires the current leakage would cause #5 to also fire at the same time. This will ***** up your engine. Everything needs to happen in an exact order & when it doesn't you have problems. Problems like you're describing. Now crossfiring might not be the cause but it's certainly worth a few minutes of straightening out your plug wires to be sure it isn't an issue.

Now don't confuse this with the whole Chrysler Crossfire thing which is an intake/carb deal and not really a part of what we're discussing at all. Brand-X issues belong on someone else's board.

thanks for the tip. i'll check if that could be an issue. my wires are a mess, and i doubt my distributer is set up like the diagram. actuly i just checked and #1 is were #5 is. i'll pull the distributor back out and see if i can set it up like the diagram. also #5 & #6 are routed next to each other, they might as well be coiled togather. i rebuilt my carb again last night, couldn't find anything wrong other than the choke plate, and pull off not adjusted properly. i'll try agai tonight. wish me luck. thanks again guys!

no good still runs like ***** it's got to be a vac leak. the egine runs like ***** but smooths out a little when i close the choke plate. well guess i'll be pulling the manifold again. is it possible for the manifold to be cracked internaly?this time i'm gettin a new one. edelbrock makes a replacement one that is legal here in ca. just as long as i use the egr spacer and the orig. carb. it will make it easy to swap to a four barrel after smog. i might even try another carb. anybody know of a good source for rebuilt carbs?

new wires or anything built now days is not a guarantee its good. Look under the hood at night while the engine is running and ,yes sometimes the new wires-will look like a super highway. Or in the daylight---lay your hand on them and ground yourself good(I like this feeling) Also if you take a screwdriver and put it up into your plug boot ,then have someone start the truck. If you have a good ground----your muscles will jump good---------BUT THIS IS DANGEREOUS TOP YOUR HEALTH---I ,M A ADDIST OF IT-the va doctor chewded me out and told me to quit-**** maybe it shortened out my brain.Of course I have been doing this for years. I was even inhight voltage onetime-dureing a light rain -----and slept like a baby for about 10 hours after.and the power company had to file a report on me.

electricity and i don't mix. i've been blasted many times, and consider myself lucky to be alive. in a sick way i did at one time enjoy a little zap. i used to static time my vw's with the wires in my mouth (i was to cheap, and lazy to make my own static timing light). i can't tell you how many times as a kid i blew the circuit brakers in our house. the last time i was shocked was at work and it scared the **** out of me. i was moving a huge fan, and when i touched the back of the motor it shocked me so bad people heard it in the next stall. my palm looked like it was burned under the skin. now i'm scared to death of electricity. besides like i said before it's a long ways down from my engine compartment. thanks for the info Johnny, once this old girl is back to runing i'll check those wires at night. no way i'm touching them b-(