Mercruiser 7.4L Starter/Elec Problem

[Rickhoff]

Started yesterday with the assistance of a battery jumper ... brand new off the shelf batteries(2) and still needed the jump. Today engine wont even turn over (just a click) even with the battery jumper. I would love to rule out the ground before moving on to the starter, can anyone confirm just where exactly the ground is bolted to the block, from my extremely limited view (prior owner added external exhaust) it appears to be attached at the back (transom) ? ! ?

 

[Bt Doctur]

Re: Mercruiser 7.4L Starter/Elec Problem

the negative battery cable is attached directly to the engine block. any convenient bolt will do.
check the slave solenoid first.

 

[Rickhoff]

Re: Mercruiser 7.4L Starter/Elec Problem

Thanks, I will check the solenoid, ... voltage meter I am assuming, what are the readings I am looking for ?

I guess what I was asking about the ground was not where can I ground it, but where do they ground it at the factory, is this engine typically grounded in the rear where I can not see it ??

 

[tpenfield]

Re: Mercruiser 7.4L Starter/Elec Problem

There should be a ground lead on each side of the flywheel housing leading back to the batteries. In your situation it sounds like something is draining the batteries. So you may want to hook up the multi-meter as an amp meter and see what sort of drain you are getting with everything off. Then maybe pull some circuit breakers if it is draining a lot to see if you can find the culprit. The mercathode should drain about 15-25 milli-amps.

 

[Rickhoff]

Re: Mercruiser 7.4L Starter/Elec Problem

Thanks, I will do a little hunt and peck in the fuse box when it cools down this eve, ... I still have no visual of the battery system ground on either side of the block, ... if I just want to test the ground, there is nothing stopping me from doing my own ground to the block from the battery where I do have access, just to rule out the simplest solution first .... right ??

 

[Fishermark]

Re: Mercruiser 7.4L Starter/Elec Problem

there is nothing stopping me from doing my own ground to the block from the battery where I do have access, just to rule out the simplest solution first .... right ??

That is correct.

It is also a good opportunity to check or replace your existing cables if there is any doubt about their condition.

 

[Rickhoff]

Re: Mercruiser 7.4L Starter/Elec Problem

tpenfield, Post-battery ground testing, I am on to battery drain testing as mentioned, did I hear that a fully charged battery should give me 12.2 amps, subtracting the mercathode draw as my target point with everyting off. If I have a reading less than that target, then start pulling fuses and looking for large increases.

 

[Rickhoff]

Re: Mercruiser 7.4L Starter/Elec Problem

Fishermark, how do I isolate and check pos cables that run to an A-B-Both switch (dual Battery set-up), and how do I do the same for neg cables that ground to the block back in the rear of the motor and are inaccessible.

 

[tpenfield]

Re: Mercruiser 7.4L Starter/Elec Problem

I am on to battery drain testing as mentioned, did I hear that a fully charged battery should give me 12.2 amps,.

Where would 12.2 amps of load come from? If all the 'stuff' on the boat is off, nothing running, etc. the only thing that may be draining the battery would be the mercathode at a very minor 15-25 milliamps.

 

[Don S]

Re: Mercruiser 7.4L Starter/Elec Problem

I think you are confusing amps and volts, plus I really doubt you know much about 12V systems in general.
Take the spark plugs out and see if the engine will turn over by hand. Not much since playing with electrical issues if the engine won't turn.
If all of your starter problems have been just something clicking, and not just slowly turning over then maybe your problem is not the starter.
Have a read of this thread on troubleshooting the starting system. http://forums.iboats.com/showthread.php?t=167035

 

[Rickhoff]

Re: Mercruiser 7.4L Starter/Elec Problem

tpenfield, my bad, no Im not getting a reading of 12.2 amps, nor would I expect to while testing the circuits you discussed above, .... It was a misguided question regarding voltage readings for a solenoid test I read in another thread, that I cant seem to find anymore ... sorry for the confusion.

 

[Rickhoff]

Re: Mercruiser 7.4L Starter/Elec Problem

Don S, you are correct, I am confused ... and the engine did turn over and start 2 days ago, .... I am still thinking electrical and I will read the link you provided, thanks!