1989 5.7 Mercruiser 350/ Alpha one

Ok guys here we go again! Had my 89 Cobalt this weekend and was a disaster! First dipped in the water wouldnt even turn over just clicked. Tapped on starter and it slowly turned over. Changed battery with battery out of suv. Started fine then throttled down ran great for about 5 min then just died. Got it started and it ran but at 10 mph wot. It acted like it was starving for fuel, however, before we took it out I installed a new 19p prop hydrofoil and new water/fuel separator(10micron) filled up with gas with the 10% ethanol which I have always done. The last time we had it out it started dying on me but would restart and run fine thus made me think to change water separator.
So i took the line off the carb to make sure it didnt have a filter and just a screen which it did just have a screen. Took off water separator and was filled with fuel like overflowing when i unscrewed it ( which is may be normal)
Please give me all the help you can. I am trying not to take it to the dealer and get my head ripped off.
OH and it never ran hot.
I am not sure if i have a fuel problem or ignition problem or something completely different.


These are the things ive heard:
Bad ignition coil
using gas with ethanol


Thanks in advance for ALL your help.

Toby
1989 Cobalt 19BR 5.7 Mercruiser/Alpha one

Re: 1989 5.7 Mercruiser 350/ Alpha one

Also I put Lucas Oil gas treatement in before I filled up. Not sure if this matters, just trying to give you all information to try to get some direction.

Thanks again

Re: 1989 5.7 Mercruiser 350/ Alpha one

When you unscrew water/fuel seperator, you should dump in a clean container so you can look for debris or water. The water will be easy to recognize as it settles on the bottom.
If the boat only runs at 10 mph WOT, and is probablly running really bad, that is typically a sensor telling you your drive resevior is empty or there is a low oil psi/ over temp issue. Investigate those items.
Factory, I dont think an 89 model has the low speed alarm though.
When you changed batteries and then took out for a run, did you swap batteries back? If your altrernator is not charging and you are running with a bad battery, I could undertand the poor running condition. The engine needs 12volts to operate.

Re: 1989 5.7 Mercruiser 350/ Alpha one

Speakrdude said:

When you unscrew water/fuel seperator, you should dump in a clean container so you can look for debris or water. The water will be easy to recognize as it settles on the bottom.
If the boat only runs at 10 mph WOT, and is probablly running really bad, that is typically a sensor telling you your drive resevior is empty or there is a low oil psi/ over temp issue. Investigate those items.
Factory, I dont think an 89 model has the low speed alarm though.
When you changed batteries and then took out for a run, did you swap batteries back? If your altrernator is not charging and you are running with a bad battery, I could undertand the poor running condition. The engine needs 12volts to operate.

Click to expand...

Ok thank you for the info I will check those things. I didnt swap batteries back. One thing that I found strange is when it died the first time and would just click when i tried to start it(before I swaped batteries) I put the boat battery in the suv and it started right up. I also had lights and radio just wouldnt turn over. After i swapped batteries it turned over started but wouldnt idle in neutral and ran poor.

Re: 1989 5.7 Mercruiser 350/ Alpha one

Really kind of sounding like a loose battery connection, either Red on the starter post or black on the block. Typically, if a battery connection is loose, and you have a strong battery, you'll get heat and lots of it at the loose connection point. Smoke, wires and/or lead melting.

Re: 1989 5.7 Mercruiser 350/ Alpha one

Speakrdude said:

Really kind of sounding like a loose battery connection, either Red on the starter post or black on the block. Typically, if a battery connection is loose, and you have a strong battery, you'll get heat and lots of it at the loose connection point. Smoke, wires and/or lead melting.

Click to expand...

Ill check that as well. Would that cause it to run rough and only 10mph wot, backfire and die?

Re: 1989 5.7 Mercruiser 350/ Alpha one

Only if the ignition system was not getting its +12volts. So, yes!

Re: 1989 5.7 Mercruiser 350/ Alpha one

Speakrdude said:

Only if the ignition system was not getting its +12volts. So, yes!

Click to expand...

Thanks again! I will check all these thing out and let you all know. If anyone thinks of anything else please feel free to post.