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Trouble shooting 502 EFI ignition issue

norcalLmo

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Hey Gang,
Looking to the RDP Brain Trust to figure out an issue I'm having with my 2001 502 EFI. The symptoms are when I turn the ignition key to RUN - the fuel pump and all gauges come on as normal, BUT when I turn the key to START - the starter doesn't engage/crank. I can 'jump' the Ignition solenoid and the starter cranks. When I put a meter on the 3-post ignition posts on the back of the ignition switch and turn the key to START my meter reads 11.5 volts on the yellow/red solenoid post??? I know I need 12volts so where am I losing voltage????
Any thoughts/recommendations would be GREATLY appreciated
 

Shlbyntro

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The 11.5 is just showing a standard voltage drop from load. I would look to your 2ndary start solenoid first. Its generally mounted on top of the engine near your ecm. You should see the same yellow wire/red tracer leading to it.
 

norcalLmo

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Thanks for the quick response - yup I've already replaced that and I get continuity from the keyswitch yellow/red post all the way to the yellow/red connector on the starter solenoid
 

norcalLmo

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I was told to check the tach to see if it's working properly - if not it would ground out the ignition
 

Shlbyntro

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That wouldn't really have anything to do with the engine not cranking. Really that little solenoid only needs to see 10v to engage the big solenoid on the starter. Next place to look would be the neutral safety switch. On sterndrives its usually located in the shifter handle. You should be able to bypass it for diag purposes by jumping the 2 yellow wires that lead up to it together
 

norcalLmo

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Already tested the neutral safety switch it is good and I bypassed it as well. Both 90amp breakers are good Getting ready to pour a Jack n Coke to get a better perspective LOL
 

Shlbyntro

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I would move to the 10 pin connector next
 

SBMech

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You are not looking for continuity, you are looking for amperage and voltage. A single strand of wire can give you continuity, and voltage, but no amperage under load.

You said you replaced the primary relay already, do you know if it's closing? If you can jump the solenoid at the starter and it cranks then the 50 signal is not getting there.

Usually goes ignition switch-neutral switch-starter relay-solenoid. You could have lost power at the relay, so it's not sending the voltage to the solenoid. Try jumping from the relay and backwards until you find where you are loosing the voltage.
 

norcalLmo

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Quick update: I do have constant 12vlt at the top post of the Starter Slave Solenoid (Red/Purple) - when I turn the key to START position I do get the 12 volts at the yellow/red post on the Starter Slave Solenoid but no crank at the Starter??? I can jump the red/purple and yellow/ red posts at the top of the Slave Starter Solenoid and the starter cranks over I've replaced the Starter Slave Solenoid and still same results. Is there a correlation to this "symptoms" if something like the trim limit switch is faulty???
 

SBMech

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Quick update: I do have constant 12vlt at the top post of the Starter Slave Solenoid (Red/Purple) - when I turn the key to START position I do get the 12 volts at the yellow/red post on the Starter Slave Solenoid but no crank at the Starter??? I can jump the red/purple and yellow/ red posts at the top of the Slave Starter Solenoid and the starter cranks over I've replaced the Starter Slave Solenoid and still same results. Is there a correlation to this "symptoms" if something like the trim limit switch is faulty???
Take a picture of the starter showing the solenoid/wiring and post it so we can be clear and on the same page.
 

H8Plow

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On the back of your starter there will be two large lugs (one is from the battery constant 12v, the other is to the starter motor after the solenoid receives a 12v signal, and lastly a 14 gauge solenoid wire (usually purple). Key on in the engine "cranking" position you should have 12v on the purple wire. If you don't have 12v on the solenoid wire, your issue is before the starter solenoid. The starter solenoid is NOT a slave solenoid or to be confused with the "circuit breaker" that is a 50 amp on top of the engine.

As mentioned before there is a neutral safety switch that will prevent the engine cranking while in gear. Double check with a DVOM for continuity between the two wires going into and out of the switch while it is in the neutral position and the in gear position. Make sure you have continuity in the neutral position and O.L. or open (loss of continuity) when in gear. I realise that you said you replaced it, however it could be defective or not properly installed.

Also, is this an IO powertrain configuration?
 

BDMar

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If you can jump the slave solenoid and it cranks, the problem is with the slave solenoid. Make sure it is closing when you turn the key to "start". Some of the solenoids require a ground wire also. If there are 2 small terminals and 2 large it will require a ground as well as the excite wire. Also, make sure to use the proper Merc solenoid. They make a bunch of different solenoids for different applications.
 

norcalLmo

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You guys FRIGGIN ROCK!!!!!!! Found the Yellow / Black small gauge ground wire on the Starter Slave Solenoid faulty and wasn't providing a good GROUND!!! Repaired it Turned the key and.....Vrooooom!!!!! THANKS AGAIN you guys REALLY appreciate it!!!!Be SAFE out there!!!!!!!!
 
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