rpm gauge not working after new engine is installed?

[boating maniac]

The shop said I need a new gauge because it was getting a signal and nothing was happening. They also said the engine wouldn't be running if the tach wasn't getting a signal. My boat has VDO gauges. I find it a coincidence that all the other gauges work, but not the tach. what gives? It worked before with the old engine.

 

[boating maniac]

What is it that powers the gauge and gives it a reading?

 

[Bondo]

What is it that powers the gauge and gives it a reading?

Ayuh,.... The tiny (-) terminal on the coil,..... usually a grey wire,....

 

[alldodge]

What motor are we discussing

 

[boating maniac]

A 350 Chevy mpi marine engine the shop just installed.

 

[alldodge]

A 350 Chevy mpi marine engine the shop just installed.

That helps, but now it could be a MEFI 1 thru 4 or 555 ECM/PCM, I should have said serial number

Its true if a working tach does not move when engine is cranked, then it will not start no matter which engine. If the tach is shorted it will keep the distributor from firing.

If the tach is not shorted then with a MEFI it could be the distributor and/or module or something like a connection.

If its a ECM/PCM then in most cases its the crank position sensor but could also be something else such as a connection.

The motor does not need a tach to start, the tach is just an indication if its working that something else is not. Disconnect the wire at the tach and if it still will not start, then its something else

 

[Scott Danforth]

and what vintage boat is it going into? it is not uncommon for the older VP powered boats to have the terminal push out of the trapezoidal shaped plug when plugging back into the harness.

 

[boating maniac]

It's a mefi 5 mefi engine and a 1989 boat. Also I noticed that the oil pressure guage starts all the way high, then then goes lower with more rpm.

 

[Scott Danforth]

in the 1989 boat there is a trapezoidal plug under the black rubber cover in the harness (standard AQ series wiring harness). there most likely is an adapter harness at the engine unless the mechanics spliced the wire. trace the grey wire from your engine to the dash.

if its an adapter harness, make sure the pins in the boat side of the harness connector are seated in the connector.

if they used a splice, make sure they did a good job. crimp style butt connectors are not a good job.