Weak spark and wont turn over

T

Tommy D.

New member
Weak spark and won't start

I have a 79 Scout II 345 v8 4x4 that I bought as is. I am having trouble getting it to fire. It turns with no trouble, has a new battery, new mechanical fuel pump, rebuilt carb, new wiring and spark plugs, and a new distributor cap and guts. It seems to have a weak spark. Could it be a problem with the distributor parts, maybe they are the wrong parts? Or could my wiring be wrong? The distributor info is 496004c91
prestolite
idn 4002r 7s9
thanks for the help
 
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Welcome to the forum. How did you determine that the spark is weak? Were you careful to change out only one plug and wire at a time so that the firing order would not be mixed up? Was the distributor removed from the engine during this process? Have you verified that the carb is able to deliver sufficient fresh fuel into the combustion chamber?
 
I determined my spark is weak by pulling the spark plug out and grounding it, changed out one plug and wire at a time, the dizzy was not removed from the engine, and after I put in a new mechanical fuel pump the fuel was being pumped into combustion chamber. If I have an electronic ignition, should I even have a point gap? When I get a multimeter that actually works in the next day or so, I will check continuity to all necessary areas. Unfortunately work seems to get in the way of fun more so then not! Thanks for the help!!!
 
Grounding the spark plug is not the only or even best way to test for spark, especially in the day time. That you saw spark at all in this fashion is encouraging. Try this. Remove the plug wire of your choice and push the boot back to expose the brass contact. Have it held roughly 1/4 of an inch away from a metal surface while the starter is cranked briefly. It takes a good, strong spark to jump the air gap. Another method if you have an inductive timing light is to clamp the pickup on any/all plug wires whilst starter cranking. No flash means no sparkie, sparky.
There's no point gap with a breakerless ignition since there are no breaker points to gap. What you do have is an air gap between the reluctor (8-pointed miniature throwing star) and the electric module. Sorry, I don't know what the gap is. I hear ya loud and clear on the work thing. I just wish I could land a job. Thanks messiah!:prrr:

edit...after a little sleuthing (I have the free time), I discovered the following...prestolite airgap is .008 thousandths of an inch to be set with a non-magnetic, ie brass or plastic feeler gauge. There ya go. Oh, one other thing. What are you using for a coil?
 
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Without running out to the shop through all the fresh snow and checking the manual, iirc the air gap should be .008".

Hth, ken
 
I think he means as is and no warranted.

It is not the air gap. The solid state switch that is triggered by the reluctor/mag pickup is not an analogue device. If it triggers it is on not half on or any place in between...

Take scoutboy's advice and test large spark gap ability. Typically 1000v/.04" or 1kv/mm of gap. Without going through paschen's law. This value goes up with air pressure so we are testing only a gap exposed to one atmosphere (14.7 psi).

A 1/4" gap would be 6250v. A min for a healthy battery ignition system. One also remember that the large gap will test the systems insulation quality. You have new stuff so that should be ok. Look for a blue-white arc.
Let us know how things go and we'll move on to other items to check.
 
Hey gang thanks for the help we, tried everything that was suggested, still wasnt starting, so found a wiring diagram for the plug wires, all the plug wires were in the wrong place.
Also the dizzy was about 60-90 degrees out of wack. Fixed it all and fired it right up!!! Got some small leaks to take care of but more or less ready to wheel!


Thanks!

Tommy d.
 
Fairly typical. You can send the previous owner a nice Christmas card:prrr:. This is the reason for all the questions about the maintenance history. Of course you didn't have all the answers and that's often the case. That's where starting at the beginning and verifying everything becomes so necessary. Glad you got it going.
 
I've heard of this syndrome before. The one where an IH is picked up as a bargain because the previous owners threw in the towel on getting it to run. Usually stemming from the lack of basic IH knowlege. Time it off of number 8....really...yes really
 
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