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View Full Version : Wrong Spark Plugs...


sflrainmaker01
03-12-2014, 08:14 AM
Hey, I have been spending my normal MM.net time on Corral.net lately. Still trying to sort out some tuning issues with my 86 Mustang. Anyway, it was brought to my attention that the shop that installed my motor put the wrong plugs in it. So, I was just wondering (since I really couldn't get an answer on Corral about this) what affect would a longer plug have on the combustion process? The plugs that were used have a 0.708 reach whereas the ones that should have been used have a 0.406 reach! :eek: Luckily, there wasn't any piston to spark plug interference. :rolleyes: Of course, I hadn't run it that hard either (been under 4000 RPM) for the entire 375 miles I have logged since the new motor was put in.
fastblackmerc
03-12-2014, 09:54 AM
If they aren't the correct plug why leave them in? :dunno:

For the price of 8 correct plugs I'd change them.

If not you'll be kicking yourself after you damage the motor over less than $50.00 in parts.......
sflrainmaker01
03-12-2014, 10:02 AM
If they aren't the correct plug why leave them in? :dunno:

For the price of 8 correct plugs I'd change them.

Sorry, I should have stated that I already have the new plugs ready to put in. But, out of curiousity, I was wondering what the affect would be (or what would expect the affect to be.
fastblackmerc
03-12-2014, 10:10 AM
Sorry, I should have stated that I already have the new plugs ready to put in. But, out of curiousity, I was wondering what the affect would be (or what would expect the affect to be.

Punching a hole in the top of your pistons....................
sflrainmaker01
03-12-2014, 10:25 AM
Punching a hole in the top of your pistons....................

Luckily, that didn't happen....:P
whitey
03-12-2014, 10:29 AM
The autolite ap104's are longer i believe from the factory motorcraft plugs. If the existing plugs would have hurt the motor, you wouldve knew it from the first start up. Its not like the compression ratio/ piston travel changes as it warms up, however there could be some evidence of spark placement in the cylinder, such as a spark closer to the top of the combustion chamber might yield better performance. All in all, i dont see a issue.
RF Overlord
03-12-2014, 12:08 PM
The autolite ap104's are longer i believe from the factory motorcraft plugs. Where did you get that idea?
whitey
03-12-2014, 12:15 PM
Rf, i couldve sworn when i replaced the plugs when i got the car, the threads were longer on the ap104's. I could be wrong...
RF Overlord
03-12-2014, 12:19 PM
While the factory plugs were half-thread and all service plugs are full-thread, that has nothing to do with reach or being "longer". Reach is measured from the plug's seat to the tip of the electrodes, nothing to do with amount of threading.
whitey
03-12-2014, 12:27 PM
I did not know that, thank you.
sflrainmaker01
03-15-2014, 06:37 AM
Well, FWIW, the "wrong spark plugs" sat in the hole approx. 3/16" further in the hole. I only know this because I have a spare set of E7 heads and tried both in the plug holes to see the difference. Anyway, after gapping and installing the correct plugs, I noticed virtually NO difference. :mad: AND, all the idle surge issues etc are still there. Back to the drawing board....:shake: :depress:
whitey
03-15-2014, 06:47 AM
Idle surge screams vacuum leak to me.
sflrainmaker01
03-15-2014, 07:13 AM
Idle surge screams vacuum leak to me.

It's complicated. BUT, oddly enough, when were re-installed the powder coated valve covers, intake, AFPR, FP gauge and new BBK 70mm TB and EGR spacer, I must have knocked off the vacuum line to the fuel vapor canister solenoid. So, I started it, it fired right up and idled at like 1000 RPM. No surging, no stalling. Boy, was I happy. I drove it to work for 2 days after and while showing off the new motor to one of our service technicians (fellow gear head), he noticed the vacuum line dangling there (at this point the car is running). I plug it with my finger and the car stalls. I reconnect it and restart, within a couple minutes, the stalling and surging is there. Disconnect and it ran at 1000 RPM idle again, no stalling or surging. I wonder.....would it hurt the car to run it like that until I can figure this out?
Point is, it ran better with the vacuum leak...:confused: :o :mad2: