!988 Mercury 5.7 350 magnum spark issues

[Bigal13]

Hello long time reader first time poster. I have a 1988 5.7/350 magnum im not getting spark to the plugs. Last weekend i splashed the boat after a little finagling i got it running and drove it around for a while ran good, coming back into my slip i throttled down to pull in and the motor died and would not start again. I was having fuel issues earlier in the day so I automatically assumed it was a fuel problem. Long story short i have fuel now squirting into the carbs but now have no spark to the plugs. Its an accel 6800-e dizzy and an msd coil. I'm leaning toward it being the electronic module in the dizzy, but not 100% sure is there a way of testing this or is it something else ie pick up coil, tach ??

 

[Bigal13]

Re: !988 Mercury 5.7 350 magnum spark issues

Any help would be greatly appreciated.

 

[Cj7jeepoffroad]

Re: !988 Mercury 5.7 350 magnum spark issues

Does it have a shift interupt?

 

[Bigal13]

Re: !988 Mercury 5.7 350 magnum spark issues

yes that ok

 

[Bigal13]

Re: !988 Mercury 5.7 350 magnum spark issues

sorry that is ok, from the meter

 

[joewithaboat]

Re: !988 Mercury 5.7 350 magnum spark issues

I have had numerous Mallory distributors, in cars. My Dad had one in a boat that i wrenched on. Module failures are reasonably common.

My theory is that they are sensitive to stray voltage. From say using an electric welder on the exhaust system of the car. We lost the module 2 times in that boat in maybe 10 years. One time it had been jumped with battery cables the other with a battery charger. They seem to fail, sometimes, soon after using either.

The guys where i bought my modules, SuperShops (no longer in business), said they were one of there biggest selling items.

Id carry a spare.

Hope that's it for ya!

 

[Bigal13]

Re: !988 Mercury 5.7 350 magnum spark issues

Went down to the boat last night this is what i got. Any ideas?


ohms 0.687 on pick up coil from +/- on module
ohms 0.9 from ign coil on module
ohms 0.8 from +/- on ign coil
ohms 0 @ shift interupt from terminal to terminal

volts 12.07 @ + on ign coil
volts 12.07 @ + lead to coil on module
volts.002 @ red+ wire from pick up on module
volts.0007 @ green- wire from pickup on module
volts 12.07 from tach terminal to ground - on ign coil

12.07/ 9.06 voltage drop from ign coil on start up

 

[Bigal13]

Re: !988 Mercury 5.7 350 magnum spark issues

going back down tonight to recheck. I want to make sure that I replace the right part, It doesnt make sense to try this, this and this, without knowing first.

 

[Bigal13]

Re: !988 Mercury 5.7 350 magnum spark issues

If everything is checking out what am i missing??

 

[Bigal13]

Re: !988 Mercury 5.7 350 magnum spark issues

Nobody, huh.

 

[joewithaboat]

Re: !988 Mercury 5.7 350 magnum spark issues

Check to make sure the trigger wire ti the tach is not shorted to ground. On aftermarket tachs they are usually blue. Not sure about factory boat tach.

Does the boat have a kill switch with a lanyard?

If that's not it, replace the module.

 

[Bigal13]

Re: !988 Mercury 5.7 350 magnum spark issues

Check to make sure the trigger wire ti the tach is not shorted to ground. On aftermarket tachs they are usually blue. Not sure about factory boat tach.

Does the boat have a kill switch with a lanyard?

If that's not it, replace the module.

No i do not have a kill switch. I replaced the ignition coil still nada gonna try th module next

 

[Scott Danforth]

Re: !988 Mercury 5.7 350 magnum spark issues

lets go back to basics.

is there spark from the coil? (between the coil wire and ground)
if there is spark, you have bad wires or cap/rotor
if there is no spark, then focus on coil or dizzy.

then put the meter across the coil leads, switch it to DC frequency. have someone crank. the meter will record the coil pulses. if the pulses are present, bad coil. if the pulses are not present, something in the dizzy is awry.

next check out the coil pickup and module.

also, it looks like your battery voltage is a bit low. the voltage drop while cranking may be dropping out the module. if I recall correctly, they drop out at 9 volts.