Mercruiser 5.7 won't start

My 1988 Cobalt with 5.7 mercruiser suddenly decided to not start.Getting fuel, but no spark. I replaced the coil, but it didn't solve the problem. Any ideas?

Re: Mercruiser 5.7 won't start

looking at my motor which is close to the same thing, the ignition system (thunderbolt IV) is pretty simple. you got an ignition module bolted to the the port side riser somewhere, there's a hall sensor in the distributor and you got your momentary kill switch on the gear shift cable assembly.

i may be totally talking out of my *** because i've never fault traced the mercruiser ignition system but common sense would tell me to check the coil for 12v first, if it doesn't have power with the key on, fix it. next i'd check the kill switch, if it's stuck you ain't getting spark. then if the kill switch is ok i'd be looking at the ignition module, distributor hall sensor and wiring.

in my many years of working on cars i've only seen a couple of no-spark situations caused by the coil (barrel style coil i mean) yet that is the first thing everybody tries replacing. in a marine environment you are more likely to have a shorted coil from corrosion and such but it almost never happens with a car.

anyway, since you said you've tried a coil, we know it's not that. check for power at the coil and then check the kill switch, report back.

Re: Mercruiser 5.7 won't start

500dollar744ti said:

looking at my motor which is close to the same thing, the ignition system (thunderbolt IV) is pretty simple. you got an ignition module bolted to the the port side riser somewhere, there's a hall sensor in the distributor and you got your momentary kill switch on the gear shift cable assembly.

i may be totally talking out of my *** because i've never fault traced the mercruiser ignition system but common sense would tell me to check the coil for 12v first, if it doesn't have power with the key on, fix it. next i'd check the kill switch, if it's stuck you ain't getting spark. then if the kill switch is ok i'd be looking at the ignition module, distributor hall sensor and wiring.

in my many years of working on cars i've only seen a couple of no-spark situations caused by the coil (barrel style coil i mean) yet that is the first thing everybody tries replacing. in a marine environment you are more likely to have a shorted coil from corrosion and such but it almost never happens with a car.

anyway, since you said you've tried a coil, we know it's not that. check for power at the coil and then check the kill switch, report back.

Click to expand...

I checked the voltage at the coil, with igntion on, but zero voltage.

Re: Mercruiser 5.7 won't start

cobalt88 said:

I checked the voltage at the coil, with igntion on, but zero voltage.

Click to expand...

If you don't have voltage to the + side of the coil with the key in the run position, then you have a problem from the ignition switch the coil on the purple wire. Could be a connection, the ignition switch, the kill switch, or a broken wire. You are just going to have to trace the purple wire from the switch to the coil and find out where you loose voltage.

Re: Mercruiser 5.7 won't start

One thing you may check. Have same engine did have same issue, main inline electrical cable (plug) to engine was loose enough one day to not start eng. at all, another time enough to start and die start and die. Have secured cable and stopped bumping it around. again just one of the items to check.

Re: Mercruiser 5.7 won't start

cobalt88 said:

I checked the voltage at the coil, with igntion on, but zero voltage.

Click to expand...

not gonna start with no voltage at the coil. how about the momentary kill switch, did you check and see if it's stuck or not adjusted properly?