1996 Mercruiser 5.7 Bravo Ignition Upgrade Questions

[jprkcr97]

Hi, I have a 1996 5.7 Bravo in my Bayliner 2252. Just replaced the long block and been sorting through issues. It had a misfire which started around 3k rpm. Verified timing was good and has new plugs and wires. Good fuel pressure ~ 4-7 psi. Was thinking this may be a faulty ignition module, which is no longer available. Is there a good thread or anyone have insight on what to buy and how to wire it. The current module is a NipponDenso with 8 terminals in the single plug.

 

[jprkcr97]

I see this one on Amazon...has anyone used this? https://www.amazon.com/gp/product/B07MF4WZSR/ref=ox_sc_saved_title_1?smid=AAJLT181W8SQO&psc=1

 

[Bondo]

Hi, I have a 1996 5.7 Bravo in my Bayliner 2252. Just replaced the long block and been sorting through issues. It had a misfire which started around 3k rpm. Verified timing was good and has new plugs and wires. Good fuel pressure ~ 4-7 psi. Was thinking this may be a faulty ignition module, which is no longer available. Is there a good thread or anyone have insight on what to buy and how to wire it. The current module is a NipponDenso with 8 terminals in the single plug.

Ayuh,.... Welcome Aboard,...... I'm guessin' carbed,.... In that case, that's where I'd start,.....

Generally speakin', the ignition works, at all rpms, til it dies completely,.....

Post up the serial number of the motor,so we know exactly what you've got,....

 

[Scott Danforth]

If you haven't checked the ignition trigger

That may be the only part of the Thunderbolt system that may be an issue. They redesigned from a 2-wire sensor to a 3-wire However it's a work or doesn't thing

I agree with Bondo, look at the fuel system first

 

[jprkcr97]

Wow, thanks for the quick replies!
A couple of other notes:
1. The tach started reading crazy...would go all the way around, then sit at around 5k rpm, when I know it's running around 3k-3500. I replaced the tach with a new one and it is doing the same thing.
2. The last time I took it out, I decided to test the interrupt switch that attaches to the driver. I pulled the cable which flipped the switch and it shut off. Then I couldn't get it to refire after. I even tried cutting the wires and hard wiring them together. No fuses were blown.
Yes, it is carbed...Quadrajet. I tried adjusting the secondary opening spring and that made it more responsive, but still has the miss.
I am going to try to upload some pictures and a short video.

 

[Scott Danforth]

It won't fire with the interupt switch wires shorted together

That is how the shift interupt system works. Shift interupt switch kills ignition to make the motor stumble as you shift. Shorting out the switch just kills the ignition

Sounds like you may have a bad shift switch adjustment and a flakey tach

 

[jprkcr97]

It won't fire with the interupt switch wires shorted together

That is how the shift interupt system works. Shift interupt switch kills ignition to make the motor stumble as you shift. Shorting out the switch just kills the ignition

Sounds like you may have a bad shift switch adjustment and a flakey tach

Sorry, not the shift interrupt...I'm talking about the kill switch at the helm.
Also, as mentioned I already replaced the tach and it is doing the same thing.

 

[Scott Danforth]

Check your wiring at the ground buss

Go thru the Thunderbolt trouble shooting guide in the sticky

 

[jprkcr97]

Check your wiring at the ground buss

Go thru the Thunderbolt trouble shooting guide in the sticky

Thanks for the tips. Wow, the sticky is very informative and I'll definitely go through it before I spend any more money! I had knee replacement surgery a few weeks ago and had to throw the boat into storage before I could do any more troubleshooting. I'll get it back out soon and go through the steps for sure.