91 4.3 Mercruiser with thunder IV HELP!

[topherolsen]

Hey everyone after looking at a ton of posts on here for the last week or so im still stuck I have a 91 Merc 4.3 with the thunderbolt IV modual carb..etc well a week ago i could start it up and it would run ok two days later it would start but seemed like it wasnt getting any fuel so i replaced the fuel pump .. ok ... so now were gettin fuel and not getting any spark from it period i went through the process of pretty much replacing the whole ignition system new thunderbolt modual..new distributor.. new distributor cap..new ignition coil..wires.. and im not getting anything i have read and been told that the oil pressure switch could be a culprit but there is just the single post coming out of it and as far as i know nothing has been attached to it for the month that we have had it. If anyone has some advice for me i would really appreciate it thanks oh sorry The starter DOES turn the motor over just doesnt get the spark to start up

 

[cooter2506]

Re: 91 4.3 Mercruiser with thunder IV HELP!

Definitly not the oil pressure switch. Thats has nothing to do with spark, just fuel pump. Do you hae a safety lanyard on your control. Sounds like it might be disconnected.

 

[topherolsen]

Re: 91 4.3 Mercruiser with thunder IV HELP!

No we dont have one unfortunatly i have checked for that as well and i guess the boat didnt come with that

 

[cooter2506]

Re: 91 4.3 Mercruiser with thunder IV HELP!

Ok is control in neutral?

 

[Fun Times]

Re: 91 4.3 Mercruiser with thunder IV HELP!

Hey everyone after looking at a ton of posts on here for the last week or so im still stuck I have a 91 Merc 4.3 with the thunderbolt IV modual carb..etc well a week ago i could start it up and it would run ok two days later it would start but seemed like it wasnt getting any fuel so i replaced the fuel pump .. ok ... so now were gettin fuel and not getting any spark from it period i went through the process of pretty much replacing the whole ignition system new thunderbolt modual..new distributor.. new distributor cap..new ignition coil..wires.. and im not getting anything i have read and been told that the oil pressure switch could be a culprit but there is just the single post coming out of it and as far as i know nothing has been attached to it for the month that we have had it. If anyone has some advice for me i would really appreciate it thanks oh sorry The starter DOES turn the motor over just doesnt get the spark to start up

Try doing post #2 in this link. http://forums.iboats.com/showthread.php?t=320755

 

[topherolsen]

Re: 91 4.3 Mercruiser with thunder IV HELP!

Yes it is It has the throttle only control as well as the regular It is in neutral and we have played with it a little also I have read some posts on here about the throttle sensor but i didnt think it would cause my problem but where im at now im open to anything

 

[cooter2506]

Re: 91 4.3 Mercruiser with thunder IV HELP!

Check with BoatTeck's post. That link was the one I was looking for for ya. It will tell you where your problem is.

 

[topherolsen]

Re: 91 4.3 Mercruiser with thunder IV HELP!

Hey we went through that whole process last night i beleive i printed it so we cold try it all still no luck Thats why were a bit stumped as far as i know we have tried mostly everything

 

[cooter2506]

Re: 91 4.3 Mercruiser with thunder IV HELP!

Ok where on that diagram do you not have voltage?

 

[topherolsen]

Re: 91 4.3 Mercruiser with thunder IV HELP!

Hey were running through that process again to double check i have an added question for ya i picked up a new distributor along with the coil modual etc yesterday and the new one is somewhat differant than the old one same serial number but the ignition sensor inside is all covered up while the old one is pretty open seems like its updated the old one had the white/red white/ green and the post for the ground under it the new one has the red/white green/white and a black coming out of it along with the same ground post under it also im assuming its another ground but i have been told otherwise

 

[Fun Times]

Re: 91 4.3 Mercruiser with thunder IV HELP!

Hey were running through that process again to double check i have an added question for ya i picked up a new distributor along with the coil modual etc yesterday and the new one is somewhat differant than the old one same serial number but the ignition sensor inside is all covered up while the old one is pretty open seems like its updated the old one had the white/red white/ green and the post for the ground under it the new one has the red/white green/white and a black coming out of it along with the same ground post under it also im assuming its another ground but i have been told otherwise

Have you installed the new dist, And now it is not working?

 

[topherolsen]

Re: 91 4.3 Mercruiser with thunder IV HELP!

Hey no it was a problem before I touched anything so I just bought a whole ignition setup and it came with the new distributor

 

[Don S]

Re: 91 4.3 Mercruiser with thunder IV HELP!

Sounds to me like you are throwing a lot of money (aka parts) at your problem without knowing what is actually wrong.
With no spark, the first thing you would do is pull out your trusty OEM service manual (Not Clymers or Seloc, that's just more money wasted)
Then find the chart that looks like this and follow the flow chart.

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[Fun Times]

Re: 91 4.3 Mercruiser with thunder IV HELP!

While cranking does the rpm gauge move up? Also try unhooking the gray wire to the rpm gauge then try to start it. Do you have timing light? hook it up to the coil wire it self and turn it over and watch the light to see if it sparking.

 

[Bt Doctur]

Re: 91 4.3 Mercruiser with thunder IV HELP!

1: lanyard safety switch(man overboard switch)
2: remove all the wires from the neg side of the coil except the gray that goes to the module, try starting. may be a bad tach
3: unhook the green w/ stripe at the shift interlock,test. may be a bad switch
4: run a jumper directly from the battery to the + side of the coil, test.
post results.

 

[topherolsen]

Re: 91 4.3 Mercruiser with thunder IV HELP!

Hey guys . Sorry its been a while since my last post well we figured it out and it was a very very easy cheap fix sadly after i had spent a few hundred bucks. But uh there was an inline fuse coming out of the ignition that wasnt making contact with one of the sides ...touched em together and voila spark! Got the timing all ironed out again and yet more issues!!! We get up to about 2000 rpm's and it was bogging down at first i thought it was either a blocked exhaust or fuel problem but decided to do a compression check and if i remember correct 1- 80 psi 2 -65 psi 3-90 psi 4- 20 psi 5-90 psi 6 -70 psi so..... im uh lookin for a motor found a 4.3 for pretty cheap outa a s-10 so im hoping i will have some fun on the lake eventually this summer

 

[180shabah]

Re: 91 4.3 Mercruiser with thunder IV HELP!

Those are some seriously low compression numbers.

I had a head gasket let go on a civic one time, I was surprised when all four cylinders came back with about 40psi. surprised because I had just driven it home, about 230 miles. Besides constantly pumping exhaust in to the coolant it actually ran pretty good.

Back on topic - is the donor engine the same vintage as your current 4.3?

 

[topherolsen]

Re: 91 4.3 Mercruiser with thunder IV HELP!

Hey guys Finally got the new motor put in ... Went with a 4.3 from a 91 s10 pretty good deal we have got everything swapped over but now for more problems!!! We put the old starter on the new motor and the terminals on the solenoid were spinning and it was just pretty tired so i found a new one from a guy i have got other parts from. Well we put the new starter in and it tried to turn over for about 2 seconds then just started humming ?? well we pulled it back off and pulled the starter apart and i have no idea what its called haha but this plastic part inside with a bunch of teeth a few areas were grinded down asked a local guy about it and he said that will do it so i replace the part put the starter back in it turns over for a few min and back to the humming Does anyone know what the issue could be why its chewing the starter up ??

P.S The part im talking about is a circle the long pin that the bendix goes on slides inside of it and it has three small gears that catch the teeth on it!