1989 5.7 350 Mercruiser ignition replacement help - possible upgrade to DUI unit

[vetting]

I have a 1989 Mercruiser 5.7 and the Thunderbolt IV ignition has left me dead in the water 3 times now (good thing I have a kicker). 1 time was a coil, one time with rotor busting, and one time with the timing advance module flaking out (actually more than once with this one). Starting to have issues with the timing advance module again so its time to replace it. I was thinking about going with a DUI (Davis Unified Ignition). The timing advance module is the V8-22 unit. Outdrive is an Alpha One with shift interrupt. Right now it stumbles over 1300 RPMs and sometimes before since it isnt advancing the timing.
Was wondering the following:
1) Do I just buy the DUI unit from Summit/Jegs and get it back up and running properly an then maybe get specific weights/springs from Davis Unified Ignition when I can?
2) What model do I actually need?
3) What is a good timing light that I should purchase to time the motor? Always just borrowed one from a dock neighbor before.
4) How do you hook up the shift interrupt?

2nd motor pic was with the cover off.

Thank you in advance for you help!

 

[Scott Danforth]

I would look at a Delco Voyager dizzy over the DUI

 

[Scott06]

X2 on the delco its an OEM quality complete set up, the usual go to for replacing merc unique part$. It is capable of working with the shift interrupt and common enough that any reasonably talented mechanic should know how to service it vs the less common DUI. Also has total timing of 25 so should be in the ballpark right out of the box for 5.7

Here is a ink to install instructions http://marineengines4less.com/images/companies/1/EST Ignition Instructions - ME4L.pdf?1431462059320
Listing for kit

GM EST Electronic Distributor Kit

GM V8 EST Electronic Distributor Kit Delco EST Replacement Billet Distributor Kit Fits GM V8 5.0L, 5.7L, 7.4L, and 8.2L marine engines Kit includes Billet aluminum EST distributor assembly, distributor mounting gasket, ignition coil, sparkplug wires,

www.michiganmotorz.com

 

[alldodge]

It's hardly ever the coil, and if the rotor breaks then it wasn't installed correctly

Looking at the spliced wiring on the motor, that is what's causing the problems. The module wiring appears to be spliced, and have no idea what the red wire is doing on that side of the carb.

 

[Scott06]

Looking at the spliced wiring on the motor, that is what's causing the problems. The module wiring appears to be spliced, and have no idea what the red wire is doing on that side of the carb.

those look like alternator wires

 

[440roadrunner]

It's hardly ever the coil, and if the rotor breaks then it wasn't installed correctly

Looking at the spliced wiring on the motor, that is what's causing the problems. The module wiring appears to be spliced, and have no idea what the red wire is doing on that side of the carb.

Another thing that can ruin a rotor is "spark punch through" and other spark damage, caused by open plug wires, poor/ damaged plug connectors and even defective plugs and in cases where internal engine problems such as leaking valves cause an extreme lean condition.This causes spark voltage to climb and "start looking" for a good place to flash over.

So far as a different system, make certain it is designed and approved for marine use AND HAS the proper advance curve, whether electronic or mechanical, for your application.

 

[vetting]

It's hardly ever the coil, and if the rotor breaks then it wasn't installed correctly

Looking at the spliced wiring on the motor, that is what's causing the problems. The module wiring appears to be spliced, and have no idea what the red wire is doing on that side of the carb.

Thats just from when I reglassed the bunks on the sides and had everything tied up and out of the way.

 

[vetting]

those look like alternator wires

That actually the trim unit power - i had the trim tied up and out of the way and had it disconnected when I was glassing. That was a pic from years ago.

 

[alldodge]

ok, thanks
The TB ignition is pretty solid. If it does have trouble it either works or it doesn't. It won't stop working and work again later. The Dizzy module can get intermittent from a bad ground, and is the reason Merc came out with a new module with 3 wires instead of 2

 

[vetting]

Just got back from the boat with some updates. I started right up and timing at high idle was 9 degrees. It ran for awhile but it was rough. Tried to go back to normal idle and the boat cut out and then wouldnt restart. Its the same issue I had last year that I fixed by messing/cleaning the plug on the timing advance module. Let it sit for awhile and then it fired right up and ran fine. Hooked a timing like back up and ran it up to 1500 RPMs and timing advance was at 12 degrees. Got it up to full operating temp and it started right back up 3 times in a row. Here are some updated pics of the motor with everything in its proper place. Its all the same symptoms I had when I had to constantly mess with the timing advance plug to get the boat working correctly last year. I also did notice that pushing down on the shift interrupt switch didnt stall the motor.

 

[nola mike]

Just got back from the boat with some updates. I started right up and timing at high idle was 9 degrees. It ran for awhile but it was rough. Tried to go back to normal idle and the boat cut out and then wouldnt restart. Its the same issue I had last year that I fixed by messing/cleaning the plug on the timing advance module. Let it sit for awhile and then it fired right up and ran fine. Hooked a timing like back up and ran it up to 1500 RPMs and timing advance was at 12 degrees. Got it up to full operating temp and it started right back up 3 times in a row. Here are some updated pics of the motor with everything in its proper place. Its all the same symptoms I had when I had to constantly mess with the timing advance plug to get the boat working correctly last year. I also did notice that pushing down on the shift interrupt switch didnt stall the motor.

When it's running rough put the timing light on each wire and see if it's firing regularly. What's the timing advance plug?

 

[vetting]

When it's running rough put the timing light on each wire and see if it's firing regularly. What's the timing advance plug?

The plug that goes into the timing advance module on thunderbolt IV system on the passenger side riser - mine is the v8-22 version.

 

[nola mike]

The plug that goes into the timing advance module on thunderbolt IV system on the passenger side riser - mine is the v8-22 version.

Ah. "Ignition module". Or apparently official name is "ignition amplifier"

 

[vetting]

I did end up going with the Davis Unified unit (ended up having to buy 2 of due to Fedex "delivering" the first one when it actually wasnt. Before the install I also upgraded the shift interrupt to the new style with the bracket. Didnt realize my shift interrupt hasnt been working for awhile. Install went fairly smooth after got the timing sorted out. It was purple wire to the + and then the grey tach along with the shift interrupt wire (green/white) into the other spade on the new distributor. Fired right up and dialed it at 8 degrees. I wasnt able to take it for a official full RPM rip due to wind this weekend, but it seemed to run a lot better. I'll post an update once I'm able to do a full run.

 

[achris]

I wasnt able to take it for a official full RPM rip due to wind this weekend...

I hope your flatulence clears up soon.

 

[vetting]

Here are pics of the completed install. It really cleaned up the back of the motor. Shift interrupt (white/green) hooked into the tach wire coming out of the main harness and purple hooked into the + side of the Davis unit.