Mercruiser 3.0 diagnosis / serial number decode

[Tube1]

Hi all, I picked up a beautiful ‘88 Chris craft cavalier with a 3.0 Mercruiser stern drive. The engine was rebuilt/replaced around 2017, so fairly new, as you can tell by the cosmetic condition of it.

I’m currently diagnosing a no crank/no start issue, but don’t have enough info gathered yet to ask a meaningful question about that (fuel/spark presence). One thing I noticed is the distributor wiring isn’t even close to what the factory service manual shows, but I guess I’ll have to verify myself by compression TDC in case someone rotated the distributor or something…

In the meantime I’m trying to figure out what drive unit I have, and whether I have the 3.0 standard or LX motor. My (drive) serial number on top of the carb flame arrestor is 0B934268.
(Engine serial number 0B840655)
There’s hundreds of threads describing how to find this SN, but not decode it.

I’d also like to know if this SN can say when the engine was made, but again, can’t find info on it.

Could anyone help me figure out my engine/drive specs from this SN?

TLDR: trying to know as much info about this engine as possible

 

[achris]

Unlike OMC, Merc serial numbers aren't encoded, they are just a sequential number. The number you provided is the serial number of the drive (and tells nothing about the engine), and that drive is 1986, with a ratio of 1.98:1. If you post the ENGINE serial number we can look that up and tell you about the engine... From the photo it has points ignition, that's the first place I'd look for a 'no start' problem...

Chris...

 

[Tube1]

Unlike OMC, Merc serial numbers aren't encoded, they are just a sequential number. The number you provided is the serial number of the drive (and tells nothing about the engine), and that drive is 1986, with a ratio of 1.98:1. If you post the ENGINE serial number we can look that up and tell you about the engine... From the photo it has points ignition, that's the first place I'd look for a 'no start' problem...

Chris...

Thanks Chris, I'll get this correct info and follow up today.

I did read that the ignition points being glazed over is a huge issue on these setups. This is my first time working on a distributor (I'm a baby compared to most of you guys on here, born in '99), but am really swift with this stuff and catch on quick.

My plan was to verify spark is coming from the coil to distributor using a spark tester. If that's present, then I will pull the distributor cap, clean the points, and verify the plug wires are attached in the correct 1-3-4-2 firing order by setting the engine to compression TDC and working clockwise around the rotor.

Does this sound like a decent plan? All I know right now is the spark plug wiring setup looks NOTHING like this diagram:



I also would like to test fuel pressure, but need to get a gauge first and figure out how to safely set it up on the carb feed line. I read some old posts on here saying the fuel supply line to the carb is the same as a 3/8" brake line.

 

[Tube1]

I located the engine SN, pic here.

Another thing I just verified is there is zero fuel making it out of the pump, to the carb.

What’s the proper way to verify that fuel is making it to the pump from the gas tank, unobstructed?

 

[Scott Danforth]

have you serviced the points?

 

[Tube1]

have you serviced the points?

No, but I plan to. I can’t find a part number for the replacement points on this distributor either.

 

[Scott Danforth]

No, but I plan to. I can’t find a part number for the replacement points on this distributor either.

take points to NAPA, guy behind counter will come back up with a new set of points and a condensor. pay the guy and proceed home

or simply file the points (required if they sit for any length of time), then set dwell and timing.

 

[Tube1]

take points to NAPA, guy behind counter will come back up with a new set of points and a condensor. pay the guy and proceed home

or simply file the points (required if they sit for any length of time), then set dwell and timing.

If I decide to file my points, are the areas circled in red what I should try to clean?

also, any good references for setting timing and dwell? all I can find on this website are expired links and unrelated discussion

 

[dubs283]

If I decide to file my points, are the areas circled in red what I should try to clean?

also, any good references for setting timing and dwell? all I can find on this website are expired links and unrelated discussion

Yes

The tune up info you seek should be on the engine. Your first post has a picture that shows the engine information sticker. It's red and located on the valve cover just below the shift plate

 

[Scott Danforth]

dwell is 32 degrees

 

[Tube1]

Trying to figure out this no spark issue and losing my mind.

I’m getting 12 volts consistently at the coil. Resistance measurement across the coil terminals is around ~2 ohms, from what I understand this means the coil is good. coil is making no park.

I removed the gray tach wire and still no spark.

So the coil has power, isn’t making spark, but continuity checks fine on it. I’m lost.

 

[ScottinAZ]

the coil needs a switch in order to fire. This is the points. If the coil has 12v and ground, but the points arent working, then you no get spark. either the coil is wired wrong, or the points arent doing their job

 

[Eric 3.7LX Alpha 1]

Have you checked out this one from the "ADULTS ONLY sticky"

How To: Troubleshoot a Points Ignition System​

How To: Troubleshoot a Points Ignition System

***Please read through ALL the information before attempting any procedure listed here and before asking ANY questions*** ***This tutorial is designed to explain step by step the proper procudures for troubleshooting a no spark issue for an engine with points ignition. If you are here, this...

forums.iboats.com

 

[Tube1]

Have you checked out this one from the "ADULTS ONLY sticky"

How To: Troubleshoot a Points Ignition System​

How To: Troubleshoot a Points Ignition System

***Please read through ALL the information before attempting any procedure listed here and before asking ANY questions*** ***This tutorial is designed to explain step by step the proper procudures for troubleshooting a no spark issue for an engine with points ignition. If you are here, this...

forums.iboats.com

Yes. I think the problem is I’m confused about the ignition process. I thought the ignition coil provided spark to the distributor, but it sounds like I’m not fully grasping this concept. So I need to check for spark coming out of the distributor FIRST? Then it reaches the coil??

 

[achris]

Coil produces the spark, which then travels along the lead out of the top of the coil to the distributor, which directs it to the right spark plug leads.

 

[Eric 3.7LX Alpha 1]

Spark comes from the coil, and enters the center post of the distributor cap. The spark is controlled from the points and condenser in the distributor. The rotor rotates and sends spark to the correct plug.

 

[ScottinAZ]

the coil produces the spark, which then goes to the distributor rotor, and out through the side terminals, wires and to the plugs. What you have is the points (also inside the distributor) that doesnt seem to be opening which causes the magnetic field inside the coil to collapse creating that spark. In this case the distributor does double duty, housing and opening the points which triggers the spark, and then distributing that spark to the appropriate plug

 

[Eric 3.7LX Alpha 1]

 

[Tube1]

Wow, you guys are helpful with these super quick responses. So I need to trace the ignition back even further by pulling the distributor cap and verifying the points are in good shape (not broken or corroded). Makes so much more sense now.

I’ll do that and update.

 

[ScottinAZ]

bingo, if the coil isnt being triggered, then it will not work. In your case, make sure the points are clean, and check the dwell. when this checks out, you should have spark