1994 random mis and spark waveform

Mustang sa11y13

New Member
Nov 18, 2010
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Hello again. Got my 1994 Mustang with a 3.8L again. as far as the random misfire, there is no code set, but you can tell there is an intermittent mis fire when you stick a piece of paper to the tail pipe and it is an uneven pulse. I have check for everything else. Fuel pressure is normal, there are no vacuum leaks, and the battery and charging systems are all good as well. I have also hooked up all of my spark wires to a PICO scope. When I did this, the secondary waveform looked very odd. So i was wondering if anybody had pictures of what the waveform is suppose to look like and if you know if it is a wast sparking and multi-stick system. I have also found when testing the wires that i had an intermittent spark on cylinder 5, replaced the wire with a different one and the idle got a little smoother. I also check all of the coil pack with a spark checker and found that it works so that is ruled out. Just thought if any of you had any thoughts and if you had any problems like this. Thanks.
Mustang Sally
 
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Waste spark system... yes. An example of this is... when the main spark fires for a specific cylinder, a smaller spark is fired on the other cylinder connected to that coil. There are 3 coils in the coil pack, from left to right standing at the front. Top to bottom is one coil. They are in pairs. And the adjacent one always fires at the same time the timed cylinder does. Its just to burn off excess gases and also helps with economy. This may explain your secondary system measurements looking a bit "odd" as you put it.

Idle got better after replacing wire on cylinder 5, then you should look into replacing the entire set of wires, not just one. If one is faulty, then chances are the others are also or getting NEAR to. The internal conductor may have a partial break in one or more of the wires. Happens with age. The hi-Voltage stresses those wires over time. Also I'd look into replacing all of the plugs as well if you have no idea if they have ever been replaced. It wont hurt it.

How many miles on this one? Also, has the car been sitting for awhile? Just wondering if the gas is fresh or old.