Volvo Penta 4.3

[choppz]

After any sort of help from other boat owners/mechanics.
Recently fitted new 4.3 v6 into our Mariah. Had it running on the new 4 barrel Edelbrock carb for about 1 hour while we sorted dynamic timing and adjusted carb mixture screws. Couple days later it doesn’t want to run fires up on the key every time but soon as we leave key it cuts out. Very annoying issue but hoping it’s something simple or somebody has had this issue previously.
Thanks in advance for any replies

 

[alldodge]

Need more info on the old motor
Was it a GL- something?

It might be the key switch, see if 12V is at the coil with key ON

 

[choppz]

Yeah 4.3 GL. Changed the key switch incase that was at fault. Had 10.5v there this week when testing things but think that was only when cranking engine

 

[alldodge]

GL what? A, B, C etc

 

[choppz]

4.3 GL PEFS if that’s what you mean

 

[Lou C]

Electric fuel pump? If so how is power being sent to the pump after the engine starts? Volvo's way is different than the Merc way. Mine still has a mechanical pump, but all the newer ones need to have a safe way of powering the fuel pump after the engine starts.

 

[alldodge]

Thanks, EST ignition
My wiring diagrams don't show the man overboard kill switch, but also don't think that's the problem

The purple comes straight from the key to the coil and Alt.

There is a possibility the Red/Yel start circuit could back feed the ignition if the Alt diode was shorted. But this would also mean there would be no 12V at the coil with the key ON "if" the purple wire connection was broken or kill switch was tripped.

Re-check the voltage at the coil with key ON and while cranking

 

[ScottinAZ]

I posted some screenshots of the electric fuel pump schematic in another 4.3 fuel issues thread here about a week ago (it’s further down in this page). Check for power according to that, or if that isnt the issue, it may be ignition. Sometimes there is a separate power feed for “run” vs “crank”. I would have to check my manuals

 

[choppz]

@alldodge I have been there today and found both diodes seem faulty. Will get new ones ordered and fitted. Is there possibly a reason behind them popping?

 

[alldodge]

@alldodge I have been there today and found both diodes seem faulty. Will get new ones ordered and fitted. Is there possibly a reason behind them popping?

In most cases a diode blows or shorts due to to much current. Something in line with it started drawing more, like the fuel pump or relay. The diode can be replaced with a higher wattage one with no ill effects

Note: you do know how to test a diode?
Using a ohm scale you can get close by reading back to front (swap leads) to get low ohms in one direction and high in the other. If meter has a diode test scale it's best to use it

 

[choppz]

Have fitted these diodes and same issue still measured voltage across the coil feed but only get 10.5v if earth to engine across the plug we have nothing. Is there any other things to check or test. Could we run a 12v + and - to feed to coil direct to test it. Alternator is pushing out voltage to coil fuel pump and choke.

 

[alldodge]

Sounding like corrosion
Yes, you can jump 12V direct to the coil
Don't have diagram for pefs only A thru E so here is the E