Actually for an over 220,000 mile engine they're pretty damn amazing. It's a hell of a PITA to do a test with the headers in the way though. The old Snap-On tester I had had too big fittings to get into more than a couple of the plug holes. I went to sears and picked up a new one that fit better. The readings were noticably higher on the new one, but it's the difference between the cylinders I'm concerned with anyway. Here's what I got:

#1 - 200 psi

#2 - 195 psi

#3 - 195 psi

#4 - 195 psi

#5 - 200 psi

#6 - 195 psi

#7 - 200 psi

#8 - 195 psi

I replaced the #8 plug wire with an old one I had lying around, but it still ran rough. I guess the next step would be to replace the cap and rotor.

 

the main thing is to have the readings within 10% or so, if they aren't you have a problem. the actuall number isn't that important.

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ICON Motorsports

1st & 3rd

 

Andy,

That's pretty impressive for a relatively high-mileage engine. Whatever you're doing for maintenance, don't stop.

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Later,
Vader
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"I'm'a do Things My Way - It's My way or the Highway."
Adobe Acrobat Reader

 

I agree, good readings. The small cam in those motors will make the readings high, plus if the engine was even a little bit warm, they'll be high. They're consistent which is the most important thing.

Is the engine doing something wrong?

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"So many Mustangs, so little time..."
ICON Motorsports

 

Yeah, it's not running right on #8. Last week it started running slightly rough. It's not a random misfire, but consistent, like only one cylinder isn't firing right. What I did was after the engine was cold, I fired it up, and squirted water on the header primaries. After just a minute, the water would immediately flash of the hot primaries, except on #8, where it would only slowly evaporate. This led me to believe #8 was midfiring. Pulling the #8 plug wire while running didn't change the way the engine ran at all. A check of the plugs (even swapping the plug with another) and of spark at the plug revealed no problems. That's why I did a compression test, in case something was wrong there. After the compression test I replaced the plug wire incase it was not allowing full power to get to the plug, but it still misfires on 8...