1999 mag mpi 454 horizon manifold temp

[370Dancer]

Where is that sensor? On the water so can’t look it up. Port eng -38 degrees f on startup
Stand 85 degrees. Port wouldn’t start, acting like it was vapor locked. Once started all good at idle. First time it’s done that, but has been acting up by dying when coming down off throttle. Starts right back up.

 

[scoflaw]

Screws into the plenum, bottom. Probably gonna have to take it off to get to it.

 

[techmitch]

Where is that sensor? On the water so can’t look it up. Port eng -38 degrees f on startup
Stand 85 degrees. Port wouldn’t start, acting like it was vapor locked. Once started all good at idle. First time it’s done that, but has been acting up by dying when coming down off throttle. Starts right back up.

#13 here https://www.marineengine.com/parts/...200-thru-0l086049/senders-and-harness-bracket

#47 here https://www.perfprotech.com/mercury...y/2356/150?search=805223T&sortpartnbr=805223T

Not 100% sure these are your engines, but maybe it will at least get you close.
You can mouse over the pic in the second link to zoom in.
That reading of -38 make me think it is unplugged or the sensor is open.
Is this the engine that you were having fuel pressure problems with before?

 

[techmitch]

Screws into the plenum, bottom. Probably gonna have to take it off to get to it.

That's what I was seeing and why I asked about the fuel press. problem because I thought he had that apart before.

 

[scoflaw]

It's on the stbd. side not too far in, maybe able to get it out without removing the plenum. That's the correct pic.

 

[370Dancer]

Thank you gents. We are docked at Mar Vista off jewfish so after lunch, I’ll throw the crew below and see if this is just a fumble finger of not seating the plug. Lord knows it’s been off 50 times over the past year.

It's on the stbd. side not too far in, maybe able to get it out without removing the plenum. That's the correct pic.

 

[370Dancer]

On order, arrives Friday. Harness plug was seated, but still throwing bad temp reading (-38 degrees F)
I think I can get it out without raising the plenum. Ironically, it started right up hot.