1985 5.7 Alpha One. No spark, i damaged something.

[redneckgenius]

I posted last weekend about my shift interrupt. I really had no understanding of it and took some bad advice from a different site and ran a jumper from the - coil post to the green white wire on the shift interrupt. It immediately killed the motor and I haven't been able to start it since. Got a chance to work on it today and checked ohms on coil and shift interrupt. Primary and secondary tested good on coil and interrupter tested closed with plunger depressed and open with plunger not depressed. I also unhooked black wire from interrupt switch and grounded it. Was told this is proper way. But, when I pull coil wire to distributor and ground it, I get no spark. I have power to dash, 50 amp breaker, and it turns over. Can someone point me in the right direction on this?

 

[Bt Doctur]

Re: 1985 5.7 Alpha One. No spark, i damaged something.

gren /white is for Thunderbolt system. on the back of the dist are 2 connections. red/white and green/white that come from the main module. the other green/white goes to the shift interupter,the other wire at the shift interupter goes to ground.
do you have power to the positive side of the coil with the key "on"
http://www.boatfix.com/merc/Techbk/94/94hsa2.pdf 2A-12

 

[redneckgenius]

Re: 1985 5.7 Alpha One. No spark, i damaged something.

I do have power to coil with key on. About 12.35 on each stud. While cranking motor, it drops to aboit 9.5. I troubleshot it per my Seloc manual section 5-9. At end of sequence, Seloc says replace coil and check for spark. If no spark with new coil, replace amplifier. Thank you, I feel a bit overwhelmed by this.

 

[achris]

Re: 1985 5.7 Alpha One. No spark, i damaged something.

I do have power to coil with key on. About 12.35 on each stud. While cranking motor, it drops to aboit 9.5. I troubleshot it per my Seloc manual section 5-9. At end of sequence, Seloc says replace coil and check for spark. If no spark with new coil, replace amplifier. Thank you, I feel a bit overwhelmed by this.

First up.... Seloc lies!!! It is so wrong about so many things that it can not be trusted to be right about anything....

Get yourself a copy of the OEM manual... In there is a troubleshooting chart for Thunderbolt ignition systems (section 4B, page 18)...

GM V8 1985-1988 service manual

Download, SAVE, and read....

Chris......

 

[redneckgenius]

Re: 1985 5.7 Alpha One. No spark, i damaged something.

Chris, thank you for the manual and advice. I did troubleshoot it per the manual and am at the second to last step. I have no spark at coil and the manual says try new coil for spark then look to amplifier. Am going to order coil today and cross my fingers. Thanks again.

 

[achris]

Re: 1985 5.7 Alpha One. No spark, i damaged something.

Just had a look at the wiring diagram for your engine and looked at what you did (effectively shorted the coil -, the gray, to shift 'kill', the green/white). I tried to find an internal schematic for the Thunderbolt IV amplifier (that way I could see the internal effect of that shorting) but there doesn't appear to be any on the 'net. Knowing that it may have put a dead short across the coil, and knowing that in points engines the shift interrupter does that anyway, without killing the coil, I'd say you killed the amplifier..... Sorry for the bad news. They are not cheap. The original part (390-7804A3) is no longer available and supersedes to -15248T02, which is over $450 from Merc. I did find one on the interwebnet thing http://www.boatusedpart.com/servlet/the-5910/Mercruiser-Ignition-Amplifier-Assembly/Detail

Chris......
P.S. Anybody with the internal circuit diagram for a Thunderbolt IV ignition amplifier.... I'd love a peek.

 

[Bt Doctur]

Re: 1985 5.7 Alpha One. No spark, i damaged something.

cant prove it but I think they were based on the Ford / Motorcraft electroninc amplifiers only because if the large square box.

 

[redneckgenius]

Re: 1985 5.7 Alpha One. No spark, i damaged something.

Chris, thanks for the direction on this. This was an expensive lesson to learn, but I will get better. Did find a new in box amplifier on eBay for $200. Also found my Mercruiser manual for $5. I'll post later this week if I get it running. Thanks again.

 

[achris]

Re: 1985 5.7 Alpha One. No spark, i damaged something.

Chris, thanks for the direction on this. This was an expensive lesson to learn, but I will get better. Did find a new in box amplifier on eBay for $200. Also found my Mercruiser manual for $5. I'll post later this week if I get it running. Thanks again.

Genuine or seloc/clymer?

 

[redneckgenius]

Re: 1985 5.7 Alpha One. No spark, i damaged something.

Genuine #9. Just like the download you linked for me.

 

[achris]

Re: 1985 5.7 Alpha One. No spark, i damaged something.

Genuine #9. Just like the download you linked for me.

 

[redneckgenius]

Re: 1985 5.7 Alpha One. No spark, i damaged something.

Got my new ignition amplifier and got it correctly installed and motor will still not run. I plan on trouble shooting it again per the manual, but am leaning toward coil. Been a frustrating and learning experience. Will post later in week if coil replacement is fixer.