350 mag no spark

I have a 350 mag MPI serial number OL374697. It recently died on the lake. Got it home and the fuel water separator would not refill. I replaced the fuel pump and now it refills. Now it seems I have no spark. I have checked all the fuses under the dash and the lanyard switch. Any other ideas?

Re: 350 mag no spark

Start at the coil with the key on and go backwards with a volt meter or test light and see where the power is.

Re: 350 mag no spark

Can anyone direct me to a troubleshooting manual for my serial number. Getting ready to dig into this and some reading material/guidence would be greatly appreciated. Thanks!

Re: 350 mag no spark

H2Onut said:

Can anyone direct me to a troubleshooting manual for my serial number. Getting ready to dig into this and some reading material/guidence would be greatly appreciated. Thanks!

Click to expand...

Ayuh,.... Lotsa Great readin' in the Adults Only section, at the top of this forum,...

Re: 350 mag no spark

Bond-o said:

Ayuh,.... Lotsa Great readin' in the Adults Only section, at the top of this forum,...

Click to expand...

Thanks Bond-o, I looked there first but didn't see anything specific to the MPI ignition set up. From what I have read so far I beleive it to be a Thunderbolt V. Knowledge is power so before I break out the Volt meter this afternoon I am trying to dig up some info. I will look again to make sure I didn't miss something.

Re: 350 mag no spark

H2Onut said:

I have a 350 mag MPI serial number OL374697. It recently died on the lake. Got it home and the fuel water separator would not refill. I replaced the fuel pump and now it refills. Now it seems I have no spark. I have checked all the fuses under the dash and the lanyard switch. Any other ideas?

Click to expand...

Knowledge is power so before I break out the Volt meter this afternoon I am trying to dig up some info.

Click to expand...

If you haven't even broke out your meter, how did you check the fuses and lanyard switch? Looking at them only confirms they are still there, doesn't mean they have power to them.

The basic troubleshooting says the first thing you do is get your meter out. Wouldn't surprise me that your fuel pump wasn't the problem either. Most like a corroded or loose connection.

Have you checked the ignition relay on the engine, or the fuses? There is a block of 3 fuses. Check them with a meter.

Re: 350 mag no spark

Don S said:

If you haven't even broke out your meter, how did you check the fuses and lanyard switch? Looking at them only confirms they are still there, doesn't mean they have power to them.

The basic troubleshooting says the first thing you do is get your meter out. Wouldn't surprise me that your fuel pump wasn't the problem either. Most like a corroded or loose connection.

Have you checked the ignition relay on the engine, or the fuses? There is a block of 3 fuses. Check them with a meter.

Click to expand...

I checked the under dash fuses visually. I checked the lanyard switch by turning the key on and cycling the switch. I figured shutting off the lanyard switch would kill the fuel relay for safety reasons, sure enough it does. If you turn on the key and cycle the switch it initiates the fuel pump to run for about 2 seconds every time. It is working and it was still there.

I have since checked the three fuses with an ohm meter. I have also bench tested the two relays (they are identical) by powering up the coil and verifying contact continuity. Before I posted I had looked in the distributor and it looked normal. I have since taken the module (coil to create an expanding and collapsing field) and examined it under a magnifying glass. The coil has three small uninsulated leads under it. They were heavily corroded with rust which obviously shorted them out. I cleaned the corrosion off with contact cleaner and re-assembled the module. Motor still would not start. Question is did the short kill the module or the ECU. Hopefully just the distributor module ($79.00) from a local shop. If it is the ECU well.............

I appreciate the help and also hope my problem helps others in the future. I will update tomorrow after I install a new module.

Re: 350 mag no spark

I figured out it was the module inside the distributor. Turns out mercruiser has redesigned the module so that the 3 uninsulated leads are now covered in encapsulant. The shop I got the module from said the old design was prone to corrosion between the leads like mine had. The new design should not have this problem.

It is easy to tell the difference the old design had 4 screws the new design only has 2. If anyone has the old design you might want to consider putting in a $79 module as a preventive maintenance item to avoid a $100+ tow. I wish I would have.