single issue left No Spark. ( boat cranking now, remote solenoid replaced)

The used e-bay harness fell through... But in the meantime figure, I am getting another opinion...

Well, my Second Mercruiser certified mechanic for this "No Spark" issue. also agrees that Everything he checks looks okay, and not a problem so Far,,
I guess I'll be ordering a new 700 top wire harness once he is done.
Apparently, there are not many "Set-ups" like this one with this type of ignition
 
John,

What exactly happened that started all this? You mentioned the starter relay fried....but other than replacing it....something else had to have triggered this set of events.
 
Nothing happened the last day the boat was put away.. The remote Starter solenoid was rusted not fried.
 
I started unwrapping the mess of wires in the harnnes.. nothing so far.. I was checking The Purple wires and got 12 volts though the big 9 pin plug from the ignition ( turns pink on other side).. I do not have 12 volts at the Purple on the Alternator 0r on the purple fedding the Diode from the Knock sensor that I also swapped for a known good sensor..mechanic didn't think 12 volts not at the Alternator was Significant.. maybe it's feed? It is a lot smaller wire than the opted Purple..
 
FYI, the one wire knock sensor doesn’t get 12v supplied to it.

A knock sensor generates its own AC voltage when it detects knocking and the ecm uses this as in input.
 
John,

I have reread this thread a couple of times and I am mystified that the problem remains that the coil is not firing. Specifically, is this a Mercruiser engine? If so what is the serial number? That really helps sort out the wiring diagram and the components.

Also what is the make of the distributor if it didn't come from Mercruiser?

You have replaced all the distributor components and if it is not firing.....the diagnostics would point to the ECM. The ECM tells the distributor to fire. You said you borrowed an ECM and plugged it in and it didn't work. Unfortunately, that approach only eliminates the ECM when you pull it off of a similar working engine.

If may be worthwhile to check the end to end continuity from the ECM plug to the distributor and see if those wires are okay before you take apart the harness.
 
The ECM that the Mechanic had was not an Exact match - Apparently I have a ECM-3
But plugged in and he said the basic functions should work..
I did look though his service manual and it would be nice to know what each side of the plug wire does and it's voltage.. I did find a basic schematic and did check the engine grounds and they where all good
 
John,

The Serial Number really helps. You have either a:
5.7L 2BBL or 5.7LX 4BBL 350 MAG ALPHA/BRAVO
In either case, there is no ECM or computer involved since it is a carburetor based engine. That really simplifies what could be wrong.

Most likely you have a Thunderbolt IV ignition system which is the same system I have on my boat. The device you may have borrowed could have been the ignition amplifier?

If the foregoing is true....then the no spark issue is self contained in the distributor. There are no external triggers. On a Thunderbolt IV ignition system, the signal to fire comes from the distributor pickup and routes through the ignition amplifier to trigger the coil. That's it ....no other magic involved.

Further, the no-spark problems associated with the system are:
-Power to the coil
-Ignition amplifier
-Distributor pickup
-Bad connections between components

What is weird is that coil you show earlier in the thread as well as the graphic are for an Electronic Fuel Injection engine. This is how you test a Thunderbolt IV system.

MERCSB92-11-illus.jpg
 
Its 5.7L 2BBL EFI with a Throttle Body ( not Carb) not Thunderbolt standard.. standard GM ignitionECM-3 .
I put in new coil, new Distributor pickup and Distrubutor Module.
 
John,

I don't doubt you but the serial number you provided and the references for marinepartsexpress and perfprotech don't show a TBI option. I rely on the Mercruiser diagrams to sort out a lot of problems and this would be a first for them not to have the build components right. I'm going to check a couple of other sources.
 
I'll have to check that serial number. I had a couple of numbers from other similar boats.
The diagram is accurate I have been using it for troubleshooting and yes the colors are the same and I did check all the fuses. Power in and out
Thanks
 
Update / Went down and got the serial number as much as I can read
OL 25966
 

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So now because of the limited space my first mechanic is saying the two options left as far as he thinks is either pull the engine so we check the barely accessible wiring or replace the harness, my other mechanic has gone through all the basic stuff and can't see an issue and also thinks it's a broken wire or the ECM...
 
John,

I appreciate the frustration.... Your second mechanic is more likely correct. With so much effort put in.....you have to take a step back.

If you have power to the ECM, then I would ohm out the wires to the distributor end to end from the ECM connector to the distributor connector. It's only 4 wires plus two to the coil.

The coil does not get 12 volts from the ECM. It comes from another connector.

You can also have the ECM tested. Pulling the engine won't solve the problem.

I can tell you that I have had my share of these issues working on boats. On older boats, it has been far easier (and less expensive) to ditch the TBI and go to a carb. Yes, you have to change the fuel pump and some wiring but the old school system does not require a computer to keep things going.
 
PlayDate said:
John,

I appreciate the frustration.... Your second mechanic is more likely correct. With so much effort put in.....you have to take a step back.

If you have power to the ECM, then I would ohm out the wires to the distributor end to end from the ECM connector to the distributor connector. It's only 4 wires plus two to the coil.

The coil does not get 12 volts from the ECM. It comes from another connector.

You can also have the ECM tested. Pulling the engine won't solve the problem.

I can tell you that I have had my share of these issues working on boats. On older boats, it has been far easier (and less expensive) to ditch the TBI and go to a carb. Yes, you have to change the fuel pump and some wiring but the old school system does not require a computer to keep things going.
Click to expand...

I did check the 2 wire distributor plug...will check the 4 wire..

RE: ECM.. The first Mechanic had another Known good ECM which was different than Mine But he said Mine is an ECM3. His has less fault detection...
His ECM which plugged right to my cables and He was able to go through it just like mine, checking codes etc with his computer... All looked good...
if he is correct about the ECM is probably good...

So, since all the Starting components have been changed or tested/swapped or Checked
I ordered the Mercruiser Harness from Amazon for $545 dollars this morning which give me a few more days before I get it to check anything ...
before I open the package and can't return it.
Oh, And of course I had my Throttle body rebuilt a year ago. The Boat was running very nicely after that...
Thanks Agin, John
 
Got power on the red/yellow wire ? Do check the 4 wires mentioned from ECM to Dizzy. 90 amp fuse on starter ?
This couldn't be as simple as an activated kill switch? More than likely you disturbed something when you R/R'd the slave.
 
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