4.3 engine wont start

[Gerhard Peters]

I bit of background

I bought a cheap 1995 Bayliner boat a month ago with an unusable 4.3 engine that was not winterized (I knew this before I bought the boat so no surprise). I proceeded to remove the engine and bought a rebuilt long block engine.

The engine is back installed and the first thing I proceeded to do is a test for spark before even attempting to start it. I had a solid spark. Then attempted to start the engine and almost got it to run but then right away ran into problems with the carburetor. I ended up buying a rebuild kit for the carburetor and rebuilt it.

Now the engine won't start at all. Now when checking the spark it is very weak, nothing like when I tested it at first. I replaced the ignition coil thinking that would solve the problem but still a very weak spark. I'm testing at coil lead wire so it is not the distributor.

Any ideas on what to look for? This is the first time I'm working on a boat but my background is a car machinic even though it has been about 20 years when I quit car mechanics for a career switch of software development. So now mechanics it is a hobby.

 

[alldodge]

Motor serial numbers are always best, but

Being a 1995 I'll assume its a TBV ignition, and does it have a 2 (Merc) or 4 bbl (Weber) carb?

Have you run thru the TBV troubleshooting chart?

 

[achris]

...Being a 1995 I'll assume its a TBV ignition, ...

Being 1995 it's more likely TB-IV, but that's ok, the chart is EXACTLY the same for both.

Chris.........
(TB-V started on the V6s with the Vortec heads, mid 96....)

 

[Gerhard Peters]

The serial number is F287471 with 4 bbl Weber carb. I have the Thunderbolt ignition system but no sure if it is the IV or V

I have gone over the TBV troubleshooting chart up until the 12 volts at the coil (purple wires). I have 12 volts. As noted I have weak spark but not at first.

I'll go over the rest of the chart later on today

 

[Gerhard Peters]

Here is what I have. It is a Thunderbolt IV at step 3 where I unplug the Red/White coming from the distributor checking the lead coming from the ignition module I have 0 volts so according to the diagram I have a bad ignition module.

But with the bad ignition module would I still have a weak spark? I do have a weak spark as noted before

 

[Scott Danforth]

I always start at the battery and make sure every connection between the battery to the helm is clean and tight. this includes the 3-4 harness plugs along the way to the helm.

 

[alldodge]

The module does the ground and opening of the points (so to speak). The module is not doing it very well so you get a weak spark.

 

[Gerhard Peters]

Where can I find the Thunderbolt IV ignition module? Upon searching I can't seem to find any place that sells it

 

[achris]

Merc superseded it to the Thunderbolt V module... TB-IV modules are no longer available...

 

[alldodge]

They make a conversion kit (item 32) over $500

https://www.mercruiserparts.com/bam/subassembly/31486/1599/40

Can also look on ebay and Offshore only wanted section

Or can convert to Delco EST ignition

 

[Gerhard Peters]

According to the attached diagram, the ignition module and the sensor inside the distribution cap both have a ground. Mine do not have a ground. Are they grounded to the distributor or are there supposed to be ground wires to them?

 

[achris]

Read that article in full... The sensor with a ground wire is the new style. You have the old style. If you order a new one, the new style comes, complete with a couple of pigtails to adapt the new style to the old style wiring harness....

Chris
(Author of that article)

 

[Gerhard Peters]

I see that is the case for the new sensor but the ignition module also has a ground on the diagram which is the same as mine but mine does not have the ground.

Where can I find more information on converting to a Delco EST ignition? Is there a kit that I can buy?

 

[Scott06]

Many sell delco voyager ignition kits just google it, yes it comes as a kit. I think they're like $350, although more $ might be less work to get the ignition module upgrade as it's plug and play.

 

[achris]

I see that is the case for the new sensor but the ignition module also has a ground on the diagram which is the same as mine but mine does not have the ground.

You need to bring a ground wire from the harness, or run a new one from the engine block, up to the distributor. It was something I took a few months discovering when I first had my new 4.3LX. It would lose a few hundred revs off the top as the engine warmed up. I eventually found it to be the distributor body becoming resistive to the engine block and changing the bias on the module, thus changing the timing curve. About 6 months after I fed that back to Merc, all the new engines started coming through with ground wires on the distributor.

Use one of the screws that holds the module to the distributor as the ground wire point.

Chris......

 

[alldodge]

I see that is the case for the new sensor but the ignition module also has a ground on the diagram which is the same as mine but mine does not have the ground.

Where can I find more information on converting to a Delco EST ignition? Is there a kit that I can buy?

Just search delco voyager est and will find several kits
https://www.michiganmotorz.com/delco-voyager-marine-electronic-distributor-p-121.html

 

[Gerhard Peters]

I don't understand. What do you mean by the following

although more $ might be less work to get the ignition module upgrade as it's plug and play.

 

[Gerhard Peters]

I don't understand what you mean by this.

although more $ might be less work to get the ignition module upgrade as it's plug and play.

 

[Gerhard Peters]

I don't understand what you mean by this.

although more $ might be less work to get the ignition module upgrade as it's plug and play.

 

[Gerhard Peters]

Sorry for the last reposts. The posting did not take me to the second page so I thought it did not post when I clicked on Post Reply