1978 mercury 80 thunderbolt ignition problems

[jamiesthunderbolt]

i have a 78 80 hp thunderbolt. last week i was running wide open and it just stopped. got it home and found that there was no spark on #3 and #4 cylinders. i used a timing light to check. it will run but only if the fast idle is all the way open. i checked the stator and it seems to be ok except the resistance readings are about 20% higher that what the manual says. the trigger is brand new, i replaced a month ago because of bad wired. all wires seem to be fine but no spark on 3 and 4. all 4 coils resistance are great, and the plugs and wires are new.could the fact that i have spark on 1 and 2 but not 3 and 4 stear me to a specific part?

 

[Yepblaze]

Re: 1978 mercury 80 thunderbolt ignition problems

Your description makes me think you have ADI distributorless style ignition rather than Thunderbolt with a distributor.

At any rate, you need to test everything all over again and take nothing for granted, and don't assume that because something has been replaced it can't be faulty again.

 

[jamiesthunderbolt]

Re: 1978 mercury 80 thunderbolt ignition problems

it has a switchbox

 

[Yepblaze]

Re: 1978 mercury 80 thunderbolt ignition problems

They both use a switchbox.

 

[jamiesthunderbolt]

Re: 1978 mercury 80 thunderbolt ignition problems

im sure that it does not have a distributor.

 

[Yepblaze]

Re: 1978 mercury 80 thunderbolt ignition problems

Well then there you go it's ADI.

Perhaps the D stands for distributorless.

 

[achris]

Re: 1978 mercury 80 thunderbolt ignition problems

Well then there you go it's ADI.

Perhaps the D stands for distributorless.

Try 'discharge'...

 

[Laddies]

Re: 1978 mercury 80 thunderbolt ignition problems

Alternator Driven Ignition, your engine should have 4 coils. It probably is the stator but heres a simple test for it, just swap the red and red/white and the blue and the blue/white wires at the box and if it's stator the problem, the spark will goto 3&4 cyls. and will stop on 1&2.

 

[achris]

Re: 1978 mercury 80 thunderbolt ignition problems

Alternator Driven Ignition, your engine should have 4 coils. It probably is the stator but heres a simple test for it, just swap the red and red/white and the blue and the blue/white wires at the box and if it's stator the problem, the spark will goto 3&4 cyls. and will stop on 1&2.

That'll work.... if the fault don't move, it's the switchbox....