1990 3.0 mercruiser ignition voltage issues

[Samjam63]

Hello Guys really looking for help I have a mercruiser 3.0 4 cylinder, last year I had various issues. it previously had sat out of the water for 4 or 5 years then I bought it as a project floor had rotted it’s a Capri bayliner. Anyway floor got replaced it was serviced I launched it to water, straight away it over heated. My own fault for not doing full checks anyway I ended up pulling it out of the water I replaced engine water pump, thermostat, the stern drive water pump, starter motor all spark plugs and filters, and turned out my head gasket had blown. so I got the head resurfaced and replaced the gasket. End of the summer season I got it back in to the water for one quick test run after all the work was complete and all was good. Pulled it back out the water parked it up for winter, it was left uncovered through the winter months engine bay filled up with fair bit of water before I pulled the bung on the back nothing drastic. This season I hoped I’d get a full season to actually get the boat in and enjoy it troubled free after splashing the cash and getting the work done last year. So had it all antifouled battery charged up ready to go. I went to run the boat up on the hose at home to give it a run before I launched it. And this is where my new problem started, I connected my hose to the stern drive got in the boat flicked the key all was good went to start the boat it cranked over About 3 revolutions or so then cut off completely, lost all power my dash and gauges but tilt trim had power fine. But nothing up to the dash it had an aftermarket ignition already on it from previous owner my initial thought was that was the issue I had a play around under the dash whilst playing I had a slight burst of life to the dash and on crank a slight half revolution then gone again. So popped to the store got myself new ignition connected it up and still nothing, head scratching started more. I’ve searched high and low on the net over forums hoping to find an answer seen similar issues but yet to find a fix answer tat could help me. We did crank the starter by arcing the starter terminals together and actually got the motor started and running for about 5 seconds it was running sweet, then it cut of like I’d switched it off at the key which I didn’t but wouldn’t fire again just cranked, fuel is getting to the plugs fine but we’re getting no spark to the plugs since. I then pulled the main harness plug apart reading people have issues there I was getting 12.5volts into the harness but only about 2.5 out. I thought perhaps the pins weren’t making good contact so I tried cutting the red and purple power wired and connecting them
Together that way but same thing only reads 2.5volts played around abit checked under the dash at the fuse panel we discovered we getting 12.5 bolts to the fuse panel after some tinkering but once switching the Ignition to power on volts drop back down to 0 basically. switch ignition off 12.5 come back. Then if I switch the bilge on the volts drop the same to basically 0 and like I said no gauges working. And not getting a spark to plugs when cranking starter with direct feed. I’m really not good with electrics at all it’s my least knowledgeable trait I’ve had help from my brother who is more knowledgeable but still he’s non the wiser where the issue lies, wondered if the new ignition was possibly faulty to but I shouldn’t have thought so. Hopefully I’ve made myself fairly clear as to what we’ve tried so far, I seem to have power most places I should have and the circuit breaker hasn’t been tripped off at all at anytime. Any help from someone that’s had similar problems would be appreciated im kinda on the verge of throwing the towel in on the boat as I really don’t have the funds to keep putting in to it, and it has a block coil pack on it which I don’t remember the name but I know they’ve discontinued making that type, I’d have to buy an all new distributor type unit if it happened to need a new coil which I don’t want to have to go down that route but I don’t believe that is the problem though but maybe someone could help. Sorry for the long message. Tia

 

[achris]

Hello and welcome to iboats.

Having read your story, let me summarize.

Mercruiser 3 litre (no year or serial number provided. Could be anything from 1969 to 2017).

Sat for 4 or 5 years. You serviced it but it overheated when you ran it.
You replaced a bunch of parts, then discovered a bad head gasket, and had that repaired. Everything was good.

You laid it up for winter (did you winterize it, or at the very least drain the water out of the block and manifold?). Forgot to pull the bung and the engine bay flooded (how far up the engine did the water get?)

Now you have a problem with power. 12v without power draw, nothing when anything is trying to draw power. That sounds like a bad connection. Use a meter and track back to where the 12v doesn't disappear when the switch is turned on, the component immediately after that is the problem.

Do you have the (Merc factory) service manual for the engine? In there you'll find a wiring diagram. Assuming some idiot hasn't decided that Merc don't know what they were doing and changed everything, that should help you find the problem pretty quickly.

Chris......

 

[Bt Doctur]

Check the connections at the starter

 

[Samjam63]

Hi guys sorry thought I’d put the year down it’s 1990 fairly old motor, I’ve checked with a meter as far back as the wiring harness plug and when switching ignition or bilge on voltage is dropping there. The starter was brand new last year, I’ve checked the terminals couple times now everything is tight and looks to be good. I was thinking if it maybe something to do with the dash fuse panel being faulty but unsure and didn’t want to go out a replace that if it didn’t need it. Had tried pulling individual fuses to see if anything on there was triggering the problem but had no different results. I’ll go out and check voltage at the starter and alternator with meter could it be alternator issue that could cause it? Alternator was working always but strange how getting no spark at the plugs, yet it did start with power to the starter but only for short time before cutting off again

 

[Samjam63]

So just checking my bolts at the battery read 12.5 at the alternator 12.5 at the starter 12.5 but at the main plug harness 0volts when it’s connected so I’m assuming the issue is somewhere at the dash that’s drawing all the power down

 

[brian3127]

I had pretty much the same problem this weekend. for me it was one of the 20 amp push button breakers at the dash. I replaced it and haven't had a problem since.

 

[nola mike]

I’ll go out and check voltage at the starter and alternator with meter could it be alternator issue that could cause it? Alternator was working always but strange how getting no spark at the plugs, yet it did start with power to the starter but only for short time before cutting off again

Not too strange. In the start position the normal ignition circuit is bypassed.

So just checking my bolts at the battery read 12.5 at the alternator 12.5 at the starter 12.5 but at the main plug harness 0volts when it’s connected so I’m assuming the issue is somewhere at the dash that’s drawing all the power down

No...The issue is upstream of the problem. The power draw with the ignition on could be from the gauges, choke, or ignition system with the ignition on. But those are supposed to draw power. Not sure which wires you're checking on which side of the harness. You should have 12v going from the starter, through the 90a breaker, through the red or red/purple wire to the helm and fuse panel. Find the connection where you get 12v on one side and less/0v on the other when ignition is on.

 

[Samjam63]

I been out there again I decided to disconnect the fuse panel under the dash completely I sanded down everything and changed a few connectors connected power and earth back up checked it, 12 volts connected all the individual connectors to gauges testing voltage still whilst connecting was all good until I connected the bilge and ignition both of them dropped voltage to 0 again when in on position, I think those are the only working accessories on the boat don’t think the nav lights or blower switches ever worked since I owned the boat but I know the bilge deffo was and ignition. So I guess I know the fault must be a bad connection engine side, the big circuit breaker fuse on the engine doesn’t seem to be tripped at all as I attempted to push it and won’t move. One thing also noticed is that if I try to short the starter using just a screwdriver on the terminals getting nothing where when I tried it a week or so ago it would turn over that way. but I guess I had the ignition to on position so that would be why perhaps when off position it would turn over I’m guessing. I’ll go back out double check connection on alternator starter ect and the main ground, everything has seemed good wires and tight from what I’ve checked so far haven’t removed anything though maybe I’ll try a new ground and see. And get back to you. Appreciate the help so far like I say I’m a novice when it comes to electrics I know very little which is also frustrating when things electrically go wrong. I spoke to my local auto electrician and told him the issues he seems adamant it’s a bad connection somewhere from what I explained that’s why I tried the fuse panel first.

 

[Samjam63]

so I seem to have found my problem, I run jumper wire from battery to starter had power to starter still not to dash so I tried to run jumper cable from starter power connector to the breaker circuit that joins to starter as I had 12 volts on one side of ther circuit breaker but not the side coming off starter. So with the jumper cable from starter to that non voltage side of the breaker bingo I had power to dash and turned it over fired straight up! So happy, I stuck my hose to the drive and ran it up checked my voltage and realized not getting charge rare from the alternator now annoyingly, really hoping the alternator hasn’t packed up it could well be the original alternator I replaced everything else last year accept that looked in to replacing it but was going to cost 250-300! As last year I wasn’t getting a charge reading either when I first bought the boat and was going right through it but last year I took the little cover on the back of the alternator off and saw one of the 3 connectors was off I reconnected it and then I had a charge rate so I stuck with that alternator, I just checked for the same issue but connectors were all on although that one seemed a little loose then the other 2. But I’ll take a better look tomorrow, but my guess is I need a power cable from starter to circuit breaker I’ll have to go to the auto shop get a new one made up and investigate the charge issue some more. But thanks mike, brian, and chris for your advice and help so far really appreciate it.