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Mercruiser 5.7 efi electrical fault

A

Acrook

New member
Hi guys,

Banging my head against the wall atm. Went to start my engine today for the first time this year, and since taking manifolds off for a coat of paint and inspection.

Engine turns over perfectly, there's power at ignition switch.

However, no start alarm which normally sounds on mine until engines running. No spark. No fuel pumps running.

Is there anything more likely than anything else because I'm fed up with wiggling wires and cleaning connectors!

Thanks a lot.
 
Hi everyone thanks for your thoughts! In the UK here so will be back on the boat when I get home from work this evening.

Kill switch is definitely on, however that's exactly what the problem seems like. If it was switched off I'd have the exact same symptoms. Do they go faulty very often?

Will have a good look at the rear of the port head - what does the wire go to?

My question is, I've read that the ecm and alarm are all controlled by 3 inputs - gear lube level (float switch in reservoir), water temperature at thermostat, and oil pressure. However am I right in thinking that a problem at any of these would cause the alarm to sound, not silence and deaden everything like I'm suffering at the moment?

Many thanks,
Alex
 
Check all your earth connections. If you took off the manifolds, you may have missed one.
If it was running OK before you did your "repair" then it would make sense that you missed a simple but critical thing upon reassembly.
 
Get a good schematic and a volt ohm meter and follow the path from key on hot to the computer could be a bad fuse or it has dirty connections. For giggles get a can of electrical cleaner and some dielectric grease and one by one pull a connector and clean it and put back together with dielectric. One at a time and test the ignition. That way you know where the problem was. Keep going until all the connectors are clean. Then go through and pull all the grounds and sand them metal to metal. It should be done regularly as preventive maintenance anyways. Once you know all the wiring is good then you can test individual components. Just take your time now and your less likely to be having those issues out there on the water.
 
If I am not mistaken and I could be, don't the EFI models have a few relays where this issue could be coming from?

No EFI expert but ............The fact that the engines turns over says he has power........
 
Might have power to starter but the earth (ground) wire to the EFI ECU may not be attached which means...yup, you guessed it.
Oh and see if all your fuses are good, and if there are any circuit breakers tripped...
The fuel pump not coming on is a sure sign that you don't have all circuits on line. Yes you can crank away with the key all day long and get nothing. You need power to the ECU so that it can tell the fuel pump to turn on. You probably have spark since most marine EFI is fuel only. The EFI gets its fueling event timing from the distributor/crank position sensor/whatever spinny thing.
 
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Thank you all very much for helping here! Slowly getting my head around the wiring loom. Engine number is OK163294.

Things I've have established so far, but still no success:
-ignition switch working correctly
-run switch/kill switch working correctly
-50a circuit breaker functional
-fuse block on starter motor OK
-starter slave solenoid OK

-NO POWER FEED TO COIL

so where could that leave the fault? If I could work back from coil it would be easiest right? Does the ecm feed coil or the other way round.

Thanks again guys!!
 
02batsea it was the battery! Thank you very much. Thank you all for putting in the time to read and help! Sorry to have wasted it what an idiot I am lol!

The battery I was using was putting out 12.4 volts which I assumed would be enough, and it was cranking over perfectly. Put a new one on before work this morning, 13.4 volts and straight away I had the proper beep alarm, fuel pump ran and she started as soon as I cranked.
What a bloody relief will be a happy day at work today!

I have spotted over the last few days that the big ground stud on the engine is rather rusted and my next job was to clean it all up. I'll definitely still be doing that because I wonder if that's causing a higher voltage needed due to the increased resistance??

Thank you all again!
 
Yay! Glad it was a relatively painless problem. Yes chase away as much rust and corrosion as you can. Use a spray preservative such as Boeshield to keep things from getting rusty.
 
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