I have a 998 motor in my mini. I have felt for a while that it runs a little rough, almost like it has a miss. So, this spring I decided to do a little looking into it. As I pull my spark plug wires off 1 at a time the motor begins to miss real bad and almost die. However, when I get to the third plug wire and pull it off the Motor doesn't even miss a beat. I know that there is spark getting to the plug because I can see it spark from the plug wire to the plug.
Question is this - is my cylinder bad/dead or could it be some other issue?
Thanks,
Devin
Hmmm. Some questions: What is the condition of the plugs? Does #3 look any different from the others? How old are the plug wires? Does the inside of the distributor cap look okay? Have you tried swapping the wires out between 3 and 4? (i.e. Swapping out on both ends at the same time)
Do you have a compression tester?
I do not have a compression tester. I have switched the plug wires on the plug end only and nothing seems to change. I have not switched them on the distributor end. I have not taken the distributor cap off. The last time I took the plugs out - last summer they didn't look any different from each other.
A compression tester from HF is under $30, far cheaper if you can find one at a garage sale. But I bet you know someone who will loan you theirs.
A miss like this could be down to a tight valve too, but best to run a compression test to see what's what.
You have to start with the basics - if you have no or low compression nothing you do to carbs or ignition will make a lick of difference. Likewise, if the compression is good then you move on to the next thing, which is ignition.....but I'm betting it's compression....a burned valve won't generally make the plugs look different....my bet is a burned exhaust valve.
Also, check the valve clearance settings.
A Mini I had for a very brief time turned out to have two cylinders miss firing.
One I solved - it had a/c and the reposition of the alternator kept pushing the #1 cable off the plug. A little relief grinding of the offending ridge on the alternator gave the clearance needed for the plug wire to stay in place.
The other turned out to be the lock nut for the valve adjuster on one of the valves for #3 had back completely off allowing the adjuster to back off as well and that valve was not opening properly.
There could be something wrong with the plug. Remove the plug and ground it and then check that the electrode has spark.
Can also rent tools from Autozone / Advance auto for free.
New set of plugs are 9-12$ = NGK - BPR6ES NGK Number 7131