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mercruiser 488 starts but wont keep running

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Fabian Garces

New member
hi all, im new to the forum and got my first question, i got a mercruiser 488 3.7l that will crank, has gas, but starts from time to time, and when it does as soon as i turn the key from start to run it shuts off, ive changed the ignition coil already, spark plugs and wires; please help im about to shoot myself lol:mad:
 
Could be a faulty ignition switch. At the back of the switch, jump the red and purple wire. Start the engine then let go the key as usual. If she keeps running, it's the switch.
 
I also have a 1988 3.7lx (180 hp) and I had a similar problem with the key switch as woodieman suggested. In my case, the problem happened intermittantly. In some cases I would get a no start, other times it would try and fire with starter engaged and when key was released back to the run position it would cut right out. Maybe I'm wrong about your problem but it happened to me. Do you have electronic ignition (Pertronix?). If not, I highly recommend it! The engine will idle better, you will get a little more power, better fuel efficiency, easier cold start ups etc. Some of the older setups before the upgrades have a ballast resistor as Docksidemarineservices suggests. Do you still have the original rectifier (generator) and water cooled voltager regulator setup? If so, I would get the aftermarket alternator setup. However, some of the older guys like the original points setup but I immediately noticed a positive result after installing the Pertronix electronic ignition,Flamethrower 40,000 volt coil, 8mm wires,and a regap of plugs to .040 See if you can have someone turn the key while you hold a test light to the positive side of coil where your ignition circuit is connected. If the coil losses power then you probably need a key switch. jmmho
One last thing: Does your engine have a neutral safety switch in the shift controller? Do you have a throttle only button of some sort. maybe power is being interrupted between key switch and coil by faulty neutral safety switch.
Maybe this has nothing to do with your problem also, but figured you could check to be sure. good luck, Tom
 
1973 Browning Marine said:
I also have a 1988 3.7lx (180 hp) and I had a similar problem with the key switch as woodieman suggested. In my case, the problem happened intermittantly. In some cases I would get a no start, other times it would try and fire with starter engaged and when key was released back to the run position it would cut right out. Maybe I'm wrong about your problem but it happened to me. Do you have electronic ignition (Pertronix?). If not, I highly recommend it! The engine will idle better, you will get a little more power, better fuel efficiency, easier cold start ups etc. Some of the older setups before the upgrades have a ballast resistor as Docksidemarineservices suggests. Do you still have the original rectifier (generator) and water cooled voltager regulator setup? If so, I would get the aftermarket alternator setup. However, some of the older guys like the original points setup but I immediately noticed a positive result after installing the Pertronix electronic ignition,Flamethrower 40,000 volt coil, 8mm wires,and a regap of plugs to .040 See if you can have someone turn the key while you hold a test light to the positive side of coil where your ignition circuit is connected. If the coil losses power then you probably need a key switch. jmmho
One last thing: Does your engine have a neutral safety switch in the shift controller? Do you have a throttle only button of some sort. maybe power is being interrupted between key switch and coil by faulty neutral safety switch.
Maybe this has nothing to do with your problem also, but figured you could check to be sure. good luck, Tom
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thanks, yes my problem is the same as the one u had, it wont always fire up, and yes i have everything stock, except the coil and the ballast i just got, i just changed the wires and spark plugs along with the points recently as well still the same, checked for the neutral ign switch as u suggested, but was wondering isnt that switch meant to protect against starting with the gear engaged, in that case if it was bad the motor wouldnt crank at all, just my thought, and yes i have that crappy alternator with the voltage regulator on it
 
other thing i noticed, looks like my starter doesnt have enough juice to crank up correctly in order for the carb to get enough pressure to get gas into the engine, i just got a new battery today and it seems as if it just sucks the juice out of it inmediatelly, could this be a short somewhere and that being the cause my engine wont run? thanks in advance guys
 
Fabian Garces, sorry I don't know what I was thinking about the neutral safety switch on controller. Yes, that would interrupt power to the starter solenoid causing a no crank situation. In the run position of key switch, you should be getting power to your coil. (That will tell you if your switch is bad or good). But, in my case if I wiggled switch it would loss power intermittantly. (just a thought) Maybe take a voltage meter and see what kind of voltage you are getting at coil. What kind of coil are you using. I think if you are sticking with the original points set up you have to use a marine coil with 1.5 ohms of resistance but I am not sure about that. Somebody else on here probably can help you with that. (you need to know what coil has the right ohms of resistance. Also, you need to make sure that the little purple wire is hooked up to the choke or you might have problems with too much voltage. jmho. I think the wire is meant to drop voltage a bit so as not to damage the points setup. Something definitely sounds messed up with your wiring. Have you messed with wires at all? Do you have an external resistor or one built into the coil? The best thing for you to do at this point is to post your questions on "Discussion Forum breezeworks 470 talk" The site is dedicated to 470 owners and there are alot of good guys on the site that will steer you in the right direction. Again, I know it is expensive, but I would definitely get rid of the points setup along with the rectifier (generator) and water cooled voltage regulator and upgrade to aftermarket alternator and Pertronix setup. That could have alot to do with your problems at the moment. That charging system is notorious for overcharging and undercharging and maybe even possibly a dead short. Anyway, good luck, Tom
 
thanks tom but ive decided not to mess with this engine too much and got a mechanic for it since ive heard that they are garbage engines, so hope the guy can do the job before going nuts lol, but thanks to all that helped me try to find the problem
 
Depends what you want to do! If in a large vessel you would pretty much be running a barge. If in a small craft 16 to 18 feet, you should be able to scoot along pretty good. These motors are either loved or hated. Many issues such as front cam seals design issues, aluminum block with cast iron head, piss poor factory charging system, early models had 3 rather than 4 inch heat exchangers which would not keep them cool while running under heavy load, originally had point breaker system which I consider to be absolute rubbish (jmho), very prone to blowing head gaskets if overheated, some of the parts can be pretty hard to find (NLA), it is basically a antiquated engine system compared to the engine systems today, and the cost of rebuilding is pretty expensive unless you have your own machine shop. lol Now for a few positive notes: If Merc. had designed and built the engines with all the upgrades originally, alot of the problems people complain about probably would not have come to pass. Jmho Also, people got angry about having to do so many modifications to the motor, I guess after paying all that money for a boat that just was not reliable originally.(in some cases) You have to understand that the motors were designed to replace gas hog v-8s in the early 70's because of OPEC and the drop in boat sales. They started putting them in boats from 1974 until around 1990. They have alot of torque for a four cylinder engine and are fairly fuel efficient. There are a few guys that have been running the 470's basically since the early 70's and have had great luck but understand how to take care of the engine and know all of it's shortcomings. In your case, you are not trully sure of the condition of the engine you now have and have not stated the number of running hours on the engine or results of compression tests. To me, it sounds like you have all of the old components on your engine. It will cost alot of money to do all the upgrades that I mentioned so maybe you would be better to put in a 4.3 liter v-6. It is compatible with your drive if you have a 1:84 ratio.jmho all the best, Tom
 
this is a 30 foot boat twin, which first thing came to my head was how in the hell this 30ft can have these 4cylinder in here, the boat itself weights 8k lbs and yes is all original old components on the engine, but i dont really wanna spend too much upgrading it really since i have in mind putting at least an inline 6 cylinder that if i cant get 2 merc 350 to fit in there, but just wanna run it for the summer till i get 2 newer engines on it, thats why i didnt show so much interest towards changing the alternator unless the one i have is really messed up
 
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