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1986 5.0L 8 cyl ignition problem

C

col421

New member
Hi all I hope you gyus and gals can help
I have a thunderbolt iv ignition problems with my (new to me)1986 5.0L carberated 8cyl merccruiser alpha one thunder bolt IV ignition.
This is what I know, Coil is good, Ignition sensor in distributor is new. The white/green wire from the ignition amplifier plug on the risor going to the ignition sensor in the distribtor was unseated and pulled slightly from the plug. I removed the plug from the ignition amplifier and redid them all to ensure a positive contact with male connectors in the igniton amplifier and she fired up beautifully. Now I could be boating for an hour or maybe 2 then POW. No spark. I'll shake the plug going into the ignition amplifier and cross my fingers and she might fire up if she doesn't Ill start to steam home on my kicker and try again to start the main and she will fire up after about 3 or four tries.
I'm fustared with situation and would like to replace the ignition amplifier and wires. I need to buy a few parts but am not sure what to buy. I'm not sure if my motor is GM or ford, big block or small block. or maybe replace the whole dam thing with something like this:
http://bpi.ebasicpower.com/p/MALYLM512DV/Distributor+Ford+V8+302+MBI+RH
It says Distributor Ford V8 302 MBI RH. I'm not sue if this part would fit my motor and would like help in identifying what parts I would need.
Any help appreciated. Thx
 
Perform the test when it quits. You may just have a wire defect in the harness to the ign. amp. Make sure all of the grounds are clean and tight.

Tests for Thunderbolt Ignition:


W/ignition key on AND BILGE WELL VENTILATED OF GAS FUMES!!!


Check the kill switch first!


#1 - Connect your voltmeter neg. lead to the engine ground and pos. lead to the white/red wire terminal at the dist. It should read 12 volts.

#2 - If 12 volts are present, remove the coil spark wire from the distributor and connect it to a spark gap tester to ground. Remove the white/green lead from the dist. terminal. Turn the ign. key to on and strike the white/green lead to ground. If there is spark, replace the ignition sensor in the dist.

#3 - If there is no spark, substitute a new coil and repeat test #2. Now if you get spark, install a new coil. NO SPARK, replace ign. amp.

#4 - In #2, if there is No voltage present, disconnect the white/red wire and check it again for 12 volts. If 12 volts is present, replace the ignition sensor inside the dist. cap. If no 12 volts present w/it disconnected--ignition amplifier is shot and must be replaced.
 
Ok Ill try the above test but if its a defect in the harness to the ign. amp I dont tink the above test will identify that. The above test assumes the wiring is in good working order does it not?
I too believe its a defect in the wiring/connection in the ign. amp and the 5 wire herness leaving the ign amp. Ive done everthing possible with what I have to ensure continuity in the wiring from the ign amp and the harness but still having positive contact issues as is evident when I shake or move the harness at the ign amp and it fires up perfectly. An Ign amp cost almost $400 dollars and it doent come with a wring harness and Plug. Thats why I was leaning towrads getting rid of the whole thing and replacing it with one of these: http://bpi.ebasicpower.com/p/MALYLM5...+V8+302+MBI+RH I just dont kno if my motor is GM, ford, right hand left hand ect.
I believe I could kill a few birds with one stone with this new component by getting rid of the wiring harness completlty, eliminating any pssible distributor issues and replace the Ign amp at a a lower cost of just an ignition amp. I just dont want to order the above part and it not fit my motor.

Col
 
get a complete kit dist,wires,coil works good get it from michigan motorz.com i had a thunderbolt lv two!!! takes about 45 mins to install time it and your on the water!!
 
Before removing the distributor, crank the engine enough w/the dist. cap off so you can see when the rotor is pointing at the position of #1 cylinder spark wire stud on the cap.
 
Merc has ONLY used GM since the late '70's early 80's,

NO ford v8's in the merc line up for decades.

A 1986 is a GM ONLY!!

Nothing wrong with fixing his ignition. all that needs to happen is to fix it!!


The thunderbolt Ignition is one of the BEST marine ignitions ever designed!!
 
guyjg said:
I think it is a small block chevy 305 cu. in., 5.0L. Does it have MR44T spark plugs? Yes? Chevy. Fords are 302 cu. in. and used C83T plugs. Get the serial number off the engine tag and call a dealer. Look it up below.

http://www.mercruiserparts.com/selectModels3.asp?type_id=8
Click to expand...

The serial number is OC875119 it uses MR44T spark plugs wich would mean its a Chevy right? Ok so using your very helpful link I can see that the ignition amplifer costs $339.00 and the Harness Is No Longer Avail. I personally think the problem lies between the mating female plug in the harness and the male pins inside the Ign amp. I believe the female connectors have lost their elastisity and motor vibration open them. But I could be wrong. My first choice wouls be to install a new harness but I don't know where to get one. What do you suggest?
 
mikey43 said:
get a complete kit dist,wires,coil works good get it from michigan motorz.com i had a thunderbolt lv two!!! takes about 45 mins to install time it and your on the water!!model #107-c 319.00 plus shipn
Click to expand...

Thanks for your response but I dont see an igition amplifier and harness in this kit. I dont think this kit would solve my problem unless I'm wrong.

Thx
Colin
 
To Chiefalan

So if I understand you correctly there is a new system that bypass's the ignition amplifier and harness that will work on my 1986 5.0L LX 305 V8 GM Alpha one with thunderbolt IV igition?

If that is true what would I search for on Ebay or any marine parts store?

Is the kit metioned above the proper kit for my boat?

Thx for your help on this guys

Colin



chiefalen said:
i agree thunderbolt was one of the best ever devised. but they last about 10-11 years. Lucky to get 20 + years out of them.

If it's only the pickup then your lucky , however in my dealings with it i'm sorry to say it isn't.

I wish you well.

But the new system with coil and bypassing all the bull on the riser is the way we have been going in my circle of friends.

Not that i RECOMMEND the hei unit one piece with coil one wire in one wire out and one wire to the tach. 80 bucks delivered to your house. Many on ebay right now .
Click to expand...
 
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looseplay said:
I was having problems with mine 1996, I went with HEI problem solved, I needed a module so I saved by going HEI problem solved
Click to expand...

When you say "module" do you mean an ignition amplifier? and could you point me the direction to what (part number) HEI unit I would need to bypass my ignition amplifier and harness.

Thx
Colin
 
So what I did today was went to a scrap boat yard and found a wiring harness for ign ampilfier. Every Ign amplifier was already gone so I wasn't able to get one there. I installed the harness and had no issues today. For the 2hrs I was out she worked perfectly. I hope this has solved the problem. Thx everyone for the help. I learned alot.
 
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WOW someone actually took the advice and it worked.

As far as this unrelenting push for aftermarket non marine ignitions, I would strongly reccomend that this stops!!!

ONLY MARINE IGNITIONS SHOULD BE RECCOMENDED!!

Having NON PROFFESIONALS install AUTOMOTIVE ignitions is a big NO NO!!

Very dangerous...............

I looked at the links posted and did not see any marine.........

If one chooses to to do this it is best kept off this web site. Too many "newbies" and "unauthorized" back yard mechanics who may not understand the potential effects...................

JUST SAYIN..............
 
Can you explain exactly where the danger lies and how this can lead to catostrophic failure. I believe you when you say it can. I'd just like to know what events could occur.
 
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