5.7 mercruiser wont start

[swampy2646]

ok this senerio has been posted on here many times before.....i rebuilt a new long block it ran fine. last week boat sputtered and died. figured i was a victim of ethenol. at some points the boat started but ran like ****...stalling, wouldn't take a load, dumping fuel like crazy. figured the needle seat went, but when beched tested carb (sorry to say q-jet) at 10 psi, held fine. cleaned filters, even put a new mechanical fuel pump on. now problem seems to be ignition. no, or very little spark comong from coil. did the whole flow chart thing, by-passed instruments, ignition switch, laynard, shift interupter,tried a new sensor, tried a new ignition mod. swapped out coil, probed modoule harness for continuity, every thing shows voltage. even did a compression test all good. any ideas????

 

[jtybt]

Re: 5.7 mercruiser wont start

What ignition system and year?

TB ignition uses special coil.

 

[swampy2646]

Re: 5.7 mercruiser wont start

it was originally a 1991 thunderbolt, put a new coil in when i rebuilt it and just to eliminate it i put the old one back....same results

 

[Don S]

Re: 5.7 mercruiser wont start

Did you check the coil wire

 

[swampy2646]

Re: 5.7 mercruiser wont start

yeah don, swapped that out also...this one is a real stumper.

 

[Don S]

Re: 5.7 mercruiser wont start

Hook your volt meter directly on the battery and crank it over. What voltage does it show while cranking?

 

[swampy2646]

Re: 5.7 mercruiser wont start

i'll try that tomorrow. where are you going with that? thanks ,pete

 

[Don S]

Re: 5.7 mercruiser wont start

Weak battery, corroded cables, low voltage = slow turning, weak spark, and no start.
Other than that, no where.

 

[swampy2646]

Re: 5.7 mercruiser wont start

re-did the main grounding stud when out of boat, all cables and batteries good.

 

[Don S]

Re: 5.7 mercruiser wont start

Do the voltage check ............ PLEASE

 

[deadstick]

Re: 5.7 mercruiser wont start

ok this senerio has been posted on here many times before.....i rebuilt a new long block it ran fine. last week boat sputtered and died. figured i was a victim of ethenol. at some points the boat started but ran like ****...stalling, wouldn't take a load, dumping fuel like crazy. figured the needle seat went, but when beched tested carb (sorry to say q-jet) at 10 psi, held fine. cleaned filters, even put a new mechanical fuel pump on. now problem seems to be ignition. no, or very little spark comong from coil. did the whole flow chart thing, by-passed instruments, ignition switch, laynard, shift interupter,tried a new sensor, tried a new ignition mod. swapped out coil, probed modoule harness for continuity, every thing shows voltage. even did a compression test all good. any ideas????

sounds like a fire issue! try new distributer cap and roter button. if you are showing lil or no fire at ther coil you could have a problem with the pickup in the dist. make sure you have all ground straps tight from wirring harness. i have seen a roter button do some crazy things... but if you have no fire or weak fire it is coil, pickup, module or +, - ...deadstick

 

[Don S]

Re: 5.7 mercruiser wont start

sounds like a fire issue! try new distributer cap and roter button.

Lets see now, he has weak/no spark coming from the coil BEFORE it gets to the cap and rotor. So how could that cause the problem?

 

[deadstick]

Re: 5.7 mercruiser wont start

Lets see now, he has weak/no spark coming from the coil BEFORE it gets to the cap and rotor. So how could that cause the problem?

How do you classify weak fire. most people try to judge the fire by looking at the spark in the middle of a sunny day and you just can tell. or he could have been in the driver seat turning the key and looking back to see if he could see the spark.

if it has fire try dist. cap or roter button. IF NO fire coming from coil, check fireon the + of coil. you can take the distributor out and take coil off and bench test it to see.... this will eliminate any other factor like a ground or kill switch.

If the motor is turning over normally we can assume the battery terminals are not corroded or loose.

 

[swampy2646]

Re: 5.7 mercruiser wont start

hey Don,in going over the flow chart involving the spark gap tester, maybe im missing something...if you have spark, change ign. sensor....no spark eliminate the coil, then its the ign mdl. what are you supposed to find if everything is good,.......its got to be one or the other, right?

 

[Don S]

Re: 5.7 mercruiser wont start

if you have spark, change ign. sensor....no spark eliminate the coil, then its the ign mdl.

That doesn't make any sense at all to me.
If you have spark, why would you change the ignition sensor????? If you did change the sensor and then didn't have spark, my thought would be that the new sensor was bad because you had spark before???????????

If everything is good by the chart, then you have spark?

 

[swampy2646]

Re: 5.7 mercruiser wont start

Don, i did voltage test with load 10.7 volts. getting back to troubleshooting chart...it clearly says if spark at coil change sensor. already tried that but it didnt solve the problem so i put the old one back. but it all circles back to that being the problem?? do i buy another one and try it again? maybe it was the wrong one, it was a different style, had pig tail harness not just posts. what do you think?? thanks Pete

 

[wca_tim]

Re: 5.7 mercruiser wont start

Don, i did voltage test with load 10.7 volts. getting back to troubleshooting chart...it clearly says if spark at coil change sensor. already tried that but it didnt solve the problem so i put the old one back. but it all circles back to that being the problem?? do i buy another one and try it again? maybe it was the wrong one, it was a different style, had pig tail harness not just posts. what do you think?? thanks Pete

the one with the pigtail replaces the one with the posts. just a newer style and part number...

 

[swampy2646]

Re: 5.7 mercruiser wont start

thanks tim, every test points to that being the problem, but it wasn't. any ideas?

 

[swampy2646]

Re: 5.7 mercruiser wont start

my engine seems to be flooding. i realize that it is not burning fuel it is getting. my question is if it is dumping fuel would there still be spark out of the coil? thanks, pete

 

[deadstick]

Re: 5.7 mercruiser wont start

my engine seems to be flooding. i realize that it is not burning fuel it is getting. my question is if it is dumping fuel would there still be spark out of the coil? thanks, pete

im not sure what you are asking. it can pump fuel without firing out of the coil. have you fixed the firing problem?

please be careful. this is very dangerous. if you have pump the cylinders full of fuel and you remove the sparkplugs to spin it over, it could fire and become a big ball of fire! i have a friend who spent a few months in a burn center.
deadstick