Not grounding plug wires??

[nathanhooper]

Well, I am buying a 1968 merc 500 from a guy at work. I took it home last night and wanted to check compression. Would have done it at his house, but he is a pretty nice guy and told me to just take it home. Anyways, when I checked the compression I just left the wires hanging. Now I have always heard that you should ground them, but I was not thinking I guess. I think that my thoughts were if I did not have the key turned then they would not get any fire. Well I was wrong.

So I did get spark from them, well three out of the four, battery died before I could test the last one. So my question is did I damage anything by doing that? Or if I had damaged it then I wouldn't have been able to get spark afterwards? After i tested them, I made sure to keep them grounded.

Also, when I checked compression they all came to 80 on my gauge. It was a brand new gauge, just opened that day, so I was wondering if it was just stiff? Anyone have this happen before? I have heard it said that as long as they are all pretty close to the same pressure then you are alright, true even if its a low pressure?

 

[Chris1956]

Re: Not grounding plug wires??

It is best to jumper the solenoid (ign key off) to do the compression test. That way the ign is off.

It is likely that you did not damage anything. if your comprssion is all even, the motor is fine, and your gauges accuracy is suspect.

I suppose there is a finite possibility that all cylinders would wear exactly the same amount, and all show the same low compression, however, that possibility is extremely, extremely remote. it is much more likely that your gauge is inaccurate.