Mercruiser 5.7 non-fuel injection, wont start when hot

[Mike C 123]

Hello All,

I took my boat out yesterday. Initially, I didn?t have enough battery to get it started, so we pulled one from the truck to jump start it and it fired right up and ran strong all day until we stopped for a swim. When I wanted to start up the boat to re-anchor, the boat would not start up. It was getting at least some fuel in the carb and at one point it seemed like it wanted to start. I had the engine cover off for about an hour before trying to get it to start before calling for a tow and it wouldn't even start using starting fluid sprayed into the carb.

We finally called for a tow. In the process of being towed back I tried starting it again with on luck.

However, when we finally got back to the dock 3.5 hours later I decided to give it one more try and it fired up right away. I turned it off again, and it had a hard time restarting. But the next four on-off attempts it would start with no problem. It was running normally at all throttle levels before and at the dock.

I have the approximate 1995 aged Mercruiser 5.7 non-fuel injection Chevy 350 version of the engine. Any ideas of where to start troubleshooting this problem?

Many thanks,
Mike

 

[Don S]

Re: Mercruiser 5.7 non-fuel injection, wont start when hot

Do you have spark?
Fuel to the carb?

Have a serial number for your engine, or do you know if it has Thunderbolt IV or V on it?

 

[Mike C 123]

Re: Mercruiser 5.7 non-fuel injection, wont start when hot

Do you have spark?
Fuel to the carb?

Have a serial number for your engine, or do you know if it has Thunderbolt IV or V on it?

Hello Don,

Thanks for the reply. I don't have the engine serial number handy or know if I have Thunderbolt IV or V, but I will try to get out to the boat tomorrow to get it. The iginition is on a 1995 boat and has never been replaced if you can tell by year?

We took off a a few spark plug wires and tried to get a spark using a screwdriver grounded to the dist cap -- no spark. I am fairly certain it is an electric issue somewhere. We could see fuel moving as expected with the throttle.

We also sprayed in starter fuild into the carb, so I think I can rule out a fuel issue. We happened to have a multimeter with us and seemed to only be getting 7 volts into the ingition coil (I think that's what it is called) at the time it wouldn't start.

Thanks,
Mike

 

[bonzoscott]

Re: Mercruiser 5.7 non-fuel injection, wont start when hot

I would check the battery. I think it's toast. Also clean cables - both ends. You may clean the connections with success before buying a battery.

 

[Don S]

Re: Mercruiser 5.7 non-fuel injection, wont start when hot

We took off a a few spark plug wires and tried to get a spark using a screwdriver grounded to the dist cap -- no spark. I am fairly certain it is an electric issue somewhere. We could see fuel moving as expected with the throttle.

To check for spark, remove the coil wire from the center of the distributor cap. Hold the end about 1/2" from a good clean ground (unpainted) and crank the engine. You should get a bright blue/white spark that snaps across the gap.

 

[Mike C 123]

Re: Mercruiser 5.7 non-fuel injection, wont start when hot

I would check the battery. I think it's toast. Also clean cables - both ends. You may clean the connections with success before buying a battery.

Hello bonzoscott,

We brought the one that started the engine with us just in case the battery was bad and tried to use it as well. Same result.

After the original battery charged while we had it running, it was cranking over just fine. This was the same battery that sucessfully started the engine once we got back as well. Normally, I just get a clicking noise when the battery is low or bad. Didn't get a clicking noise, it was turning over just fine, just not starting...until it cooled down a few hours later.

 

[Mike C 123]

Re: Mercruiser 5.7 non-fuel injection, wont start when hot

To check for spark, remove the coil wire from the center of the distributor cap. Hold the end about 1/2" from a good clean ground (unpainted) and crank the engine. You should get a bright blue/white spark that snaps across the gap.

Thanks again, Don. I'll try that when I am at the boat tomorrow to get the engine #. However, I suspect that it will spark as expected when it's cold. I'll post back with findings.

Thanks again!

 

[NHGuy]

Re: Mercruiser 5.7 non-fuel injection, wont start when hot

Next time you start it watch the battery gauge. It should show around 14.7 volts when the motor is running. Fully charged resting voltage is almost 12.7 volts. If you can take the battery to a real tester and get it's cranking power tested that should tell you something. Hopefully it's within 10% of new rating.
The troubleshooter for TB IV (don't know whether yours is IV or V) says the coil positive should have 12v with the key on and a fully charged battery. Did you say 7 volts with key on, or with key on AND cranking? If it was key on and cranking that's a partially charged battery voltage with the starter spinning. A fresh battery starting a modern car drops to 10 or 9 volts if I recall.
If it was 7 volts key on, NOT cranking, then go through the electrical contacts, wire brush them and snug them back up. There aren't that many on the motor and they are easy to reach. Don't forget the grounds on the ignition harness. Also don't forget the contacts under the dash at the keyswitch and at the shifter. The ones at my shift/throttle are the hardest reach. Use some brass brushes in there, they don't overdo the corrosion removal and they are inexpensive. I think I bought a bag of them at Harbor Freight for 4 or 5 bucks.
If you still have trouble after that, clean up the the master plug. I do the master plug with rolled up bits of emery cloth, then use a knife edge to split the male contacts ever so slightly. They should have no corrosion on them when you are done. They don't have to be super shiny, but they can't be powdery or green either. It wouldn't hurt to put a SMALL dab of dielectric grease on them before assembly. Just use the tiniest bit in each hole so there can be no path of contact between them. Do that with the shaft of a snipped off q tip or something else small. If you get too much in the gaps between the contacts, wipe it dry.

 

[Don S]

Re: Mercruiser 5.7 non-fuel injection, wont start when hot

We also sprayed in starter fuild into the carb, so I think I can rule out a fuel issue.

I assume nothing changed and it didn't fire when you sprayed in starting fluid?

We happened to have a multimeter with us and seemed to only be getting 7 volts into the ingition coil (I think that's what it is called) at the time it wouldn't start.

You did you test it, I have seen so many people using the meter improperly I just don't know if you tested correctly or not.?
Black test lead of meter to a good clean ground, and Red test lead to the + terminal of the coil is how you do voltage tests.
Testing voltage from + to - tells you nothing.

 

[Mike C 123]

Re: Mercruiser 5.7 non-fuel injection, wont start when hot

Next time you start it watch the battery gauge. It should show around 14.7 volts when the motor is running. Fully charged resting voltage is almost 12.7 volts. If you can take the battery to a real tester and get it's cranking power tested that should tell you something. Hopefully it's within 10% of new rating.
The troubleshooter for TB IV (don't know whether yours is IV or V) says the coil positive should have 12v with the key on and a fully charged battery. Did you say 7 volts with key on, or with key on AND cranking? If it was key on and cranking that's a partially charged battery voltage with the starter spinning. A fresh battery starting a modern car drops to 10 or 9 volts if I recall.
If it was 7 volts key on, NOT cranking, then go through the electrical contacts, wire brush them and snug them back up. There aren't that many on the motor and they are easy to reach. Don't forget the grounds on the ignition harness. Also don't forget the contacts under the dash at the keyswitch and at the shifter. The ones at my shift/throttle are the hardest reach. Use some brass brushes in there, they don't overdo the corrosion removal and they are inexpensive. I think I bought a bag of them at Harbor Freight for 4 or 5 bucks.
If you still have trouble after that, clean up the the master plug. I do the master plug with rolled up bits of emery cloth, then use a knife edge to split the male contacts ever so slightly. They should have no corrosion on them when you are done. They don't have to be super shiny, but they can't be powdery or green either. It wouldn't hurt to put a SMALL dab of dielectric grease on them before assembly. Just use the tiniest bit in each hole so there can be no path of contact between them. Do that with the shaft of a snipped off q tip or something else small. If you get too much in the gaps between the contacts, wipe it dry.

Hello NHGuy,

Thanks for the reply. The 7 volt reading was taken with just the key on, not trying to start. We didn't take a reading while trying to start it.

What is the "master plug" that you referenced above? I am not familiar with that term, but I'll clean it if I know how to find it.

I don't think it is a battery. I mentioned that I pulled one from a truck to jump start the boat, but I brought the truck battery with us in case the battery was bad in the boat. I did try swapping the truck battery with the boat battery when we ran into an issue, but it still wouldn't start. The same battery for the truck did start up a Ford 7.3 diesel when we got back.

When I got back to the marina after the tow, I was able to start the boat using the boat's battery I jump started before.

I really don't know why the boat battery was dead to begin with, it started up just fine less than a week before and nothing electric was turned on when I parked it.

I appreciate your help!

Thanks again,
Mike

 

[Mike C 123]

Re: Mercruiser 5.7 non-fuel injection, wont start when hot

I assume nothing changed and it didn't fire when you sprayed in starting fluid?.

Affirmative, nothing changed with starting fluid. The boat started up later without it.

You did you test it, I have seen so many people using the meter improperly I just don't know if you tested correctly or not.?
Black test lead of meter to a good clean ground, and Red test lead to the + terminal of the coil is how you do voltage tests.
Testing voltage from + to - tells you nothing.

I personally didn't test it for the reason's you mentioned, but my engineer friend did. He knows what he's doing.

I do owe you the engine # from my boat. I unexpectidly had to work all Saturday, but I will get it tomorrow.

Thanks again!

Mike

 

[sptjet90Reflexx]

Re: Mercruiser 5.7 non-fuel injection, wont start when hot

After it warms up does it continue to run until you shut her down? or does she just stall at operating temp and fail to spark until cool?

 

[christoner2002]

Re: Mercruiser 5.7 non-fuel injection, wont start when hot

Just a thought, do you have a tether switch on the throttle control? Looks like a little on/off switch that you could connect a lanyard to. Could it be faulty? It will not let it start, by shutting the ignition system off. Was towed about 30 minutes before I looked down one day, to see mine was in the off position. I may not be that, but worth a look