350 MAG MPI ONLY TRIES TO START WHEN KEY IS RELEASED

Mujibot

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Nov 24, 2014
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Hi Everyone glad I found this site. Hope someone can help me out. 350 MAG MPI ONLY TRIES TO START WHEN KEY IS RELEASED serial# OM369894 has all vitals 40# fuel pressure, great spark, dist bearings good, cap and rotor new. Only obvious thing is tach not working at all. very puzzling.
 
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Fun Times

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Hi there, welcome to iboats!:)

Do you see 12 volts on the volt gauge at key up?

Sounds like you have a bad ignition key switch or a problem with the ignition system (purple wire).

Might want to try jumping the wires at key switch to see if it will start.

Let us know, good luck.:)
 

thumpar

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Jun 21, 2007
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What do you mean by "only tries to start when key is released"? If you have a lanyard switch check it. You can remove the tach wire to see if that is the problem also.
 

Bondo

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Hi Everyone glad I found this site. Hope someone can help me out. 350 MAG MPI ONLY TRIES TO START WHEN KEY IS RELEASED serial# OM369894 has all vitals 40# fuel pressure, great spark, dist bearings good, cap and rotor new. Only obvious thing is tach not working at all. very puzzling.

Ayuh,.... Welcome Aboard,..... Disconnect the tach wire from the coil,.... It could be shortin' the ignition out,....
 

muskyfins

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Jun 7, 2012
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578
I had the same problem on my last boat. Problem went something like this: not enough voltage when cranking to power the coil. When key released from "start" to "run", engine would start. Problem remedied by replacing the coil. (I am paraphrasing the root cause; would have to really think about EXACT cause. but solution was replace coil)
 

Mujibot

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Nov 24, 2014
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Thanks for the responses and the welcomes. Have 12 volts at the coil spark looks strong and blue in the spark tester. Fun Times yes it shows 12 or same as at the batterys. Thumpar that switch appears to be working properly. Going to try jumping the switch out and Bondo's suggestion, disconnect tach. Be back later
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
MPI... I'd also be asking questions about the relays. And as they are cheap (unless you buy them from Merc :facepalm:, it's a Hella H41410051 or Omron G8W-1C6T-R-DC12) I'd just throw new ones in... Also check connection points, like the main harness connector, the cable lugs on the starter motor. Look for anything that can cause a voltage loss.

Chris.........
 
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Mujibot

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Nov 24, 2014
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Sorry I didn't get back to everyone sooner. Pulled out dash and disconnected tach whamo started right up. Hooked up an Autometer tach and it is all good. Going to order a new tach and it should be good to go. Thanks again for the help!
 

thumpar

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Jun 21, 2007
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If you have a Faria tach you might call them and see what they can do for you. They have some warranty and service options that may be cheaper than new.
 
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