How to check which spark plug I need to replace?

mark0101

mark0101

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My 97 Mark started to shake when you accelerate, and it's missing when idling. I am pretty sure it's either the COP or plugs but no codes are being thrown so I don't know how to check which one it is. How would I go about checking which COP or plug I need to replace?

FYI: Changed boots and plugs (copper 764) at 110K, it now has 150K.
 
If you go somewhere with a real-time scanner, they should be able to tell you which one is acting funny...

....or you could just wait til it throws a code.....


...or you could just buy one new one, and try it in different spots until it goes away....


....or you could take them out and hook up an ohm-meter to them, and see which one(s) is different....
 
mark0101 said:
My 97 Mark started to shake when you accelerate, and it's missing when idling. I am pretty sure it's either the COP or plugs but no codes are being thrown so I don't know how to check which one it is. How would I go about checking which COP or plug I need to replace?

FYI: Changed boots and plugs (copper 764) at 110K, it now has 150K.
Click to expand...

764's should be changed every 10K, at least 20K. Might just wanna go get you another set and change all 8 since they're cheap. See how it runs after that.
 
Well I changed all of them and... it's still missing. It's weird though, it runs fine when I am driving at say 30 MPH, (can't feel it missing) but starts missing on idle or lower RPM. Looks like I am going to take it to a mechanic and let him figure it out.
 
Update: So I went to a mechanic and was told it was the MAF sensor. He replace that and two vacuum lines for $153. The mechanic was also charging me for a service called "induction cleaning" which I passed on (it was $90). From what he said about the service, it was basically running seafoam through the intake. Since it had been running rich, he said it would clean it out. Hell, I'll just do it myself for $5 bucks. Got the car from him and drove it home running smooth. Took a nap and remembered I had changed the SCT tune to factory (at the time I was thinking it was a computer problem). Put the tune back on the car and started it up. Same old problem, started to miss and vibrate again. I then proceeded to do seafoam and changed the IAC which fixed the problem. Just gotta see if it gives me trouble now.
 
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