Which pins in diagnostic port spin starter?

#1

I think it’s pins 11 + 14 but can someone confirm which pins spin the starter and does this only spin the starter and nothing else (no fuel, spark)? I’m trying to do a compression test by myself and I could use any tips. Thanks,

Kevin

#2

Pull all the spark plugs

Pull the coil wire

Screw compression gauge into Cyl 1, reach in cockpit and use key to spin motor over. Repeat for #2-6

Al

#3

no problems with fuel being delivered into cylinder with plug out and no spark?

#4

kmsnsx wrote:

[quote]no problems with fuel being delivered into cylinder with plug out and no spark?[/quote]you can pull the fuel pump relay too…

Remember you need to hold open the throttle when doing a comp. test.

#5

Yes, 11 & 14 to spin starter only. Do it all the time.

Michael
#36
Great Lakes Region

#6

Sean - did not know that. Why?
Thanks,
Ed

#7

edavidson wrote:

[quote]Sean - did not know that. Why?
Thanks,
Ed[/quote]Representative of actual operation. Throttle plate closed, air going in is restricted…

#8

I think you’d get the same result either way. Since the engine really isn’t running, you’ll get air in the cylinder from the exhaust valves and air can come through other cylinders into the intake manifold. Doesn’t take much time at all for pressure to equalize. As long as the cylinder you’re testing reaches atmospheric before the valves close, I’d think you’d get accurate numbers.

Would be interested to test now that I’m curious, but too lazy to do it just for that.

#9

mskeen wrote:

[quote]I think you’d get the same result either way. Since the engine really isn’t running, you’ll get air in the cylinder from the exhaust valves and air can come through other cylinders into the intake manifold. Doesn’t take much time at all for pressure to equalize. As long as the cylinder you’re testing reaches atmospheric before the valves close, I’d think you’d get accurate numbers.

Would be interested to test now that I’m curious, but too lazy to do it just for that.[/quote]

I suppose it would be ok…

Everything I ever heard, or read says to open the throttle all the way and make sure you use the same number of revolutions to make your measurement a good comparison so that is how I always have done it.

#10

Thanks Sean. I learned 2 things. I have never counted revolutions either; just cranked until it reached a peak value/stabilized. I guess these procedures are more critical for determining between cylinder differences (8-10%) than a truly low compression engine or bad cylinder. However, I will do it in the future. Thanks for the info.
Ed