Car only runs when I let the spark jump 10mm
Thread Starter
Joined: Jan 2010
Posts: 1,360
Likes: 10
From: Woodbridge, Ontario
Car only runs when I let the spark jump 10mm
Hey everyone, so I got this odd issue that still boggles me.
i had a misfire issue which only would go away if I let the spark physically jump to the plug on my 94 fd with a 13b Bridgeport in stock ignition.
So I replaced it with aem coils and it seemly went away.
A few months later, I had the same issue come back and in order for it to run, I have to again... let the spark jump around 10mm. Till it gets warm and then it’s ok. At first I had a thought it was my fuel, but on a really close investigation, the spark dies the closer I bring it to the plug.
What could possibly cause this as it’s very bizarre
i had a misfire issue which only would go away if I let the spark physically jump to the plug on my 94 fd with a 13b Bridgeport in stock ignition.
So I replaced it with aem coils and it seemly went away.
A few months later, I had the same issue come back and in order for it to run, I have to again... let the spark jump around 10mm. Till it gets warm and then it’s ok. At first I had a thought it was my fuel, but on a really close investigation, the spark dies the closer I bring it to the plug.
What could possibly cause this as it’s very bizarre
Racecar - Formula 2000
Joined: Sep 2002
Posts: 4,034
Likes: 370
From: Bath, OH
Back in the old days, that was a common trick to make fouled plugs fire. When the voltage across a fouled plug rises normally (it ramps up quickly, but is not instantaneous) the voltage can leak down the fouled center insulator and the plug won't fire. When you jump a gap first, the plug sees the full voltage instantaneously and fires before the voltage leaks away. There were even spark plugs made with internal gaps to help cars that quickly fouled their plugs start normally.
Depending on the voltage needed to fire, a larger gap might be necessary to get the extremely high instantaneous voltage needed.
Depending on the voltage needed to fire, a larger gap might be necessary to get the extremely high instantaneous voltage needed.
Last edited by DaveW; Jun 1, 2018 at 09:05 AM.
Thread Starter
Joined: Jan 2010
Posts: 1,360
Likes: 10
From: Woodbridge, Ontario
Ohhh I see, so changing the plugs should help then correct? My old man actually uses this trick to fire our circuit car but never could scientifically explain it.
What if putting new plugs didn’t solve this.
What if putting new plugs didn’t solve this.
Racecar - Formula 2000
Joined: Sep 2002
Posts: 4,034
Likes: 370
From: Bath, OH
New plugs will likely solve this, but it may not last long, depending on what is causing the plugs to foul. Do you drive very conservatively, almost never using full throttle? Are you premixing in addition to what the oil metering pump provides? Are you using colder plugs than recommended? If so the plugs may foul again quickly. If they foul quickly you should attempt to find out why.
Thread Starter
Joined: Jan 2010
Posts: 1,360
Likes: 10
From: Woodbridge, Ontario
It’s a full bridge and I drive pretty conservative. I do have a 1” silencer for whenever I drive around the neighbourhoods. Does this mean I shouldn’t use it?
Racecar - Formula 2000
Joined: Sep 2002
Posts: 4,034
Likes: 370
From: Bath, OH
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Thread Starter
Joined: Jan 2010
Posts: 1,360
Likes: 10
From: Woodbridge, Ontario
Update: Put new leading plugs back in and it fired up first key.It also idle's much much better! I will continue to monitor it for the weekend and hope that it stays ok! Should it stay this way, I will probably have to run my race plugs only when the car has fully warmed up.
Thanks a ton for all the info.
Thanks a ton for all the info.
Racecar - Formula 2000
Joined: Sep 2002
Posts: 4,034
Likes: 370
From: Bath, OH
Update: Put new leading plugs back in and it fired up first key.It also idle's much much better! I will continue to monitor it for the weekend and hope that it stays ok! Should it stay this way, I will probably have to run my race plugs only when the car has fully warmed up.
Thanks a ton for all the info.
Thanks a ton for all the info.
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