Turns over ,wont start

makinwaves

Recruit
Joined
Oct 2, 2003
Messages
2
Hi, I have a 1988 mercruiser 5.7 liter 4 barrel 8cly. engine. Turns over for 10seconds and wont turn over any more .If I try again it will do the same thing. Starter seems to run slow. I charged Batterys over nite . ,allso used a booster battery same thing. while cranking I had a 12 volt meter across battery term., voltage drops to zero whlie cranking .I do have spark. I pulled each spark plug out one at a time no water came out of clyinder , I didnt turn motor over ,spark plug was little rusty. I have been following a trouble shooting section of a book I purchased. conections , motor grounds to battery ground and positive and starter conntections all clean , well after all that I am thinging of buying a starter . Do you think I am going in the right direction?
 

BMDODGE

Petty Officer 2nd Class
Joined
Sep 16, 2003
Messages
157
Re: Turns over ,wont start

i know GM starters can draw heavy current like that when the starter solenoid is bad (ground problems) but if it cranks for 10 seconds and your getting spark it should fire over. are you getting fuel ?? bruce
 

makinwaves

Recruit
Joined
Oct 2, 2003
Messages
2
Re: Turns over ,wont start

I am getting fuel I can see it spray when shift lever is pumped. If it is the starter, while turning over. could it rob enough current from the spark plugs to prevent ignition?. I think Im gonna buy a starter , but with my luck ,i will put it in and it still wont start. I dont beleive its the fuel because I sprayed starter fluid in carb ,no start no sence that it wanted to start. and I do have spark. Thanks for your reply .I will post back how I make out.
 

merc 140 pontoon

Petty Officer 2nd Class
Joined
Aug 23, 2003
Messages
129
Re: Turns over ,wont start

You may want to check the voltage at the coil positive post (CPP) with the key on and engine not running, and then during cranking. I would recommend looking at the wiring diagram for your engine, also. Mine has a resistance cable in the wiring harness, some others use one or two ballast resistors on the transom. The resistance is typically 1.8 ohms. The resistance across the coil is typically 1.2 ohms or so, for an externally-resisted coil. So the total resistance you measure in the circuit is about 3 ohms. The result, and the reason all of this is done, is that the voltage at the CPP is dropped from more than 12V down to 6 to 9V DC. This is to extend the life of the points. Well, let me clarify that a bit. The system could be physically designed to handle 12V at all times, but then there'd be no way to boost the spark during cranking. There's a wire from your starter to the CPP that provides 12V during cranking. Thus, the "crank assist" wire gives you CPP 12V during cranking. You should see 6 to 9V with the key on and the engine not running, and the voltage with the engine running is supposed to be less, although it seems to vary from person to person (boat to boat), from what I have heard. The problem my boat had was a little complicated. The resistance cable in the wiring harness had deteriorated over time. While it measured 1.8 ohms cold, it increased resistance when hot, so when the engine got hot, I would suffer a voltage drop at CPP. To complicate things, I have a Pertronix Ignitor conversion instead of points and condenser, and when the CPP would drop below about 7V, the electronic module would shut down, and the engine would die. This was partly due to the mechanic installing it incorrectly--the Ignitor positive wire is supposed to go to a 12V switchable source on engines that have externally-resisted coils, not on the CPP. I eventually re-wired the Ignitor to such a source (tapped into the harness), and after getting a lot of input from people who know a lot more than I do, bypassed the resistance cable and went to an internally-resisted coil. (I actually tried an external ballast resistor on the transom with the externally-resisted coil, but still had some problems.) With the internally-resisted coil and no resistance cable, I was concerned about no voltage boost during cranking (it always goes through the coil), but I have found my ignition problems are solved. It fires within about 1/3 of a second of cranking.<br /><br />Disclaimer--make sure you know what you're doing before you mess with your boat's wiring.<br /><br />Anyway, at the very least, take some CPP voltage readings, and you'll be closer to solving your problem.<br /><br />One more question: I have heard of people jumping the boat from a car, to see if the slow cranking is due to the boat battery or starter. Is this a good or bad idea?<br /><br />Steve
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
71,287
Re: Turns over ,wont start

One more question: I have heard of people jumping the boat from a car, to see if the slow cranking is due to the boat battery or starter. Is this a good or bad idea?<br />
Why Not ??????<br />If you can get within reach of your Jumper Cables....<br />It's Easier than Swapping Batteries.....
 
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