Compression check - hot or cold

[illru]

Having the engine die on idle after a few hours running. Starts up again without problem but will die randomly. Was going to start testing and taking the fuel system apart for cleaning and replacing parts but did a compression test to start.
Cold motor, sparks out, WOT - 125, 125, 127, 125, 125, 127.

The manual dose not say hot or cold. Anyone know if the Merc compression spec a hot or cold one?

 

[Dr Honda]

do it on a cold engine. those numbers are ok for a 240efi.

I would say you have a port side temp sender going bad... or.... a fuel regulator going bad... OR.... fuel injectors that are leaking, and are spraying too much fuel. (Most noticeable at idle)

 

[illru]

Going to fog the cylinders to see if those numbers pump up.

Would not have looked at the temp sensor, its only a couple years old. I still have the old one laying around here somewhere, going to throw that back in and see what happens. Thanks for the idea.

Was going to pull the power head at the end of the season to get at the injectors for cleaning. Maybe this is the motor telling me to hurry it up.

 

[Tim75]

Going to fog the cylinders to see if those numbers pump up.

Would not have looked at the temp sensor, its only a couple years old. I still have the old one laying around here somewhere, going to throw that back in and see what happens. Thanks for the idea.

Was going to pull the power head at the end of the season to get at the injectors for cleaning. Maybe this is the motor telling me to hurry it up.

I pulled throttle body on my Challenger without pulling the whole engine. Are you that constrained on access space?

 

[Dr Honda]

Going to fog the cylinders to see if those numbers pump up.

DON'T !!!!!!!!!!!!

If you spray oil into the cyl's.... the numbers will absolutely go up. It would be giving you a false reading. I can take a crap engine that won't start... wet the rings and see acceptable numbers. Merc standards are 125 to 135 cold. So.... like I said... those #'s are OK.

When I did my rebuild, I took 0.010" off the deck, and only saw 145 psi.

 

[poolshark28]

DON'T !!!!!!!!!!!!

If you spray oil into the cyl's.... the numbers will absolutely go up. It would be giving you a false reading. I can take a crap engine that won't start... wet the rings and see acceptable numbers. Merc standards are 125 to 135 cold. So.... like I said... those #'s are OK.

When I did my rebuild, I took 0.010" off the deck, and only saw 145 psi.

MR. Honda, a little off topic but are you still making the MC Numbers? Need some for my 96 xp and I started a conversation with you but never received a response. Thank you

 

[illru]

Ink e

DON'T !!!!!!!!!!!!

If you spray oil into the cyl's.... the numbers will absolutely go up. It would be giving you a false reading. I can take a crap engine that won't start... wet the rings and see acceptable numbers. Merc standards are 125 to 135 cold. So.... like I said... those #'s are OK.

When I did my rebuild, I took 0.010" off the deck, and only saw 145 psi.

Ack! Won't do that then. I was always under the impression that wetting the rings in a two-stroke gave a more accurate reading.

Update: Put my old sensor back in, ran around all day today and it's back to normal. As proud as Mercury is with thier part prices I would expect more than 2 years of life out of that new sensor.

 

[illru]

I pulled throttle body on my Challenger without pulling the whole engine. Are you that constrained on access space?

Plenty of room to work in there. But it's easy enough to pull and drop it in my garage where I can leisurely work on it over the winter. I have a laundry list of things I'd like to do the motor.