Spark plug wires on correctly?? - Mercruiser 470 3.7 L

Blueghost924

Petty Officer 1st Class
Joined
Sep 19, 2013
Messages
250
Re: Spark plug wires on correctly?? - Mercruiser 470 3.7 L

Thanks for the help. I did some quick checks this morning, including a compression test, and came up with this:
#1 - 121 psi
#2 - 127 psi
#3 - 120 psi
#4 - 132 psi

I also grounded the spark plug for #2 and #3 against the engine block, turned it over, and saw a faint blue spark on each (which may not be enough). After I run a purple bypass wire, I'm going back to the original thread subject and make sure I wire the dizzy cap in line with the rotor and #1 TDC compression. I think B-Doctor was onto something in that making sure I'm at the "compression" point of #1 TDC, and not the exhaust stroke. On each spark plug, I do smell gas traces.

The way I see it, having decent compression on the cylinders gives hope for troubleshooting the rest of the engine systems!
 

Blueghost924

Petty Officer 1st Class
Joined
Sep 19, 2013
Messages
250
Re: Spark plug wires on correctly?? - Mercruiser 470 3.7 L

One additional question: When cold starting, what position should the throttle plate and choke be in (i.e. throttle plate all the way open, etc...) ?
 

nola mike

Vice Admiral
Joined
Apr 22, 2009
Messages
5,023
Re: Spark plug wires on correctly?? - Mercruiser 470 3.7 L

Choke should be closed, throttle plate usually 1/4-1/2 open for me.
 
Joined
Mar 27, 2010
Messages
3,008
Re: Spark plug wires on correctly?? - Mercruiser 470 3.7 L

Picture someone choking... their airway is close off. Same thing with the engine. As the engine warms up it should open.

Putting you finger over the spark plug hole while the engine is being turned over. When your on the compression stroke you will feel air pushing your finger off the hole. Then look at the mark and continue turning slowly until the mark lines up. That will be TDC on the compression stroke.
 

Blueghost924

Petty Officer 1st Class
Joined
Sep 19, 2013
Messages
250
Re: Spark plug wires on correctly?? - Mercruiser 470 3.7 L

Thanks for the help all! This is really a great website, with excellent stickies and guides and very knowledgeable folks. I followed the above advice (including with finger over #1 cylinder hole) and yes, I was 180 degrees out with the spark plug wires on the dizzy. Now I have to start examining all the other engine systems until I find what is out of whack...I would love to get this beast up and running.

One thing that bothers me is that in reading through articles on the compression test (I found the Mercruiser service bulletin on this), I didn't perform the test exactly per manual. I didn't remove all the other spark plugs from the holes when checking compression on each cylinder. In other words, I had my compression gauge threaded into #1 cylinder, while the spark plugs were installed in #2, #3 and #4 cylinders (and on down the line). I am really thinking about re-performing the compression check this weekend per the manual (which states to remove all spark plugs).
 
Top