When having my car tunned a few weeks back the mechanic showed me a interesting thing with the ignition. He hooked up a timing light and while revving the motor past about 3k the light flickering started to be rough and every few secs there would be a very noticeable change in the rythm of the light. He reckons its definitly something to do with the distributor. He said that it could be some as simple as the air gap, or maybe i need new ignition modules. I recently installed new coils, dizzy cap and rotor, leads and spark plugs. Do ignition modules play up like this sometimes?

cheers,
heb.

 

His clip-on inductive timing light could have been getting its signal from an adjacent wire. I've had that happen before. I thought my ignition was all screwed up at first. Heh, silly me.

 

Well, that is something to keep in the back of the head when timing my car.

 

so like the as the rpm's increase so does teh power and hence why its interupting the light? It revs really smooth which is a sign that is not knocking/pinging right?

cheers,
heb.

 

My old timing light could keep up with increasing revs. My friend's can't. It gets all choppy at higher RPM. It's a problem with the light's xenon strobe tube flash circuitry.

 

whats else could it be?

 

Not sure. If it runs smooth, it's ok.

 

Thing is when you rev it about 3-4k and hold it there you can hear what sounds like miss firing or something from the exhaust but as soon as you give it a bit of gas its fine.

heb.

 

I could probably get a sounds sample for you.

 

Vacuum advance? Trailing vacuum retard? Could be either of these things.

Steady state throttle at 3k-4k rpm should not cause any 'missing' of the ignition system unless your plugs are fouling at this rpm range, or your ignition system isn't keeping up - ignitors/coils. If this were the case, upper rpm ranges would exhibit similar symptoms.

The fact that it clears up when you give it gas in this range suggests that it may be a problem with vacuum on the advance side. Vac advance on the leading system causes the spark plug to fire sooner, building more power and accelerating the engine faster than just adding more air/fuel. This helps to get fast throttle response, but could be a vacuum leak leading to your leading system. The vacuum line comes from the rats nest and on acceleration, pulls vacuum against a diaphragm on the outside of the dizzy. This diaphragm is attached to an arm that turns a cam on the dizzy, changing the angle of the pickups to the ignition rotor. This effectively accelerates the 'timing' of the engine to speed up ignition. On deceleration, the opposite happens, and trailing ignition is retarded to help burn fuel efficiently even though the engine isn't making power - helps prevent backfiring and poor fuel economy.

Ignition timing at idle should be set WITHOUT vac systems (leading or trailing) attached - this helps to get clean values during idle conditions to help get the best possible idle.

What someone above said about the timing light could be a problem with the light itself - the xenon tube needs time to recharge, and if it's circuitry can't keep up, you'll get off-time flashes that will look like bad engine timing. HTH,

 

every damn first gen Ive heard or ridden in, except maybe a small few (and I couldnt name any owners off the top of my head) all have what sounds like a miss while cruising/idling at like 3K+, my car does it I know... It sounds like a miss, very well could be, but when you jump on it, it revs quick and smooth, so I know its not anything to worry about....


Its his light or his signal is jumping wirres.. if it was your ignition it would rev like **** and idle like **** and do everything..... like ****!.... so, if it revs nice, pulls good, and idles smooth..... its not your ignition..... be sure your reading from the L1 (lower front rotor) plug......


Laters, Andrew

 

great feedback thx. There is no vaccum advance hooked up for a reason that I do not know. Aparantly it used to be hooked up but isnt no more. I have no rats nest, its all very clean and tidy. I run a holley 465 and 12a bridgy so if timing was out or ignition was playing up it would probably be a nightmare to drive right? I'm going to order some new ignition modules (like $100 each over here) and hope that fixes it.

cheers,
heb.

 

whats wrong with it?


IT would be a freakin night mare to drive.... I dont think you have a problem....

 

that. I just don't want to drive it if theres a chance I'm hurting the motor.

heb.

 

that is good to hear cuz i asked the same ? and got no feedback bubt this explains exactly what my car does ecespecially in cold starts when car is choked.

 

Mine has always done that too, don't know why, but it's not hurting anything.