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Old 02-14-2012, 08:59 PM   #21
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Andrew, not sure if you've seen this PDF but it details both the TB IV and V ignition systems. http://www.boatfix.com/merc/Servmanl/16/16B4R2.PDF

Scroll about halfway down the doc - TB V info starts on page 16.

According to this document the knock sensor is down low on the starboard side of the engine, just before the starter motor.

Dan
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Old 02-15-2012, 11:46 AM   #22
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Thanks for that Dan.

I have seen similar instructions in my manual, but not with a picture of where the Knock sensor is located.

I had assumed it would be on the port side, near the oil sensors, and you would think I would have noticed it on starboard side, but have not. The other thing is that I did not think it had a knock module, as it is not attached with the ICM, so will have to check all this again, but could well be a source of the timing not advancing.

Unfortunately I am away until Monday, so will have to check it then and advise back.

Another thing is that I have tried previously to diagnose the problem using the flow chart for the TBV ignition. I have spark, so probably doesnt apply. Got to the 4th point, unplugging red/white wire and checking for 12 volts. Mine read only 10V. Is this a problem, or am I barking up the wrong tree, because I do have spark.


Thanks again for the help.

Andrew
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Old 02-15-2012, 01:17 PM   #23
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No problem Andrew.

10V instead of 12V certainly indicate there's an issue but I have no idea how tolerant the ICM/KCM are of under-voltage. Certainly warrents investigation though. Based on this statement " The 12 volt signal from the ignition module to the distributor is carried thru the WHITE/RED wire “8”, to the distributor sensor and back to the ignition module thru the WHITE/GREEN wire “7” " I'd think if you were seeing only 10 on the W/R then you'd also see only 10 on the W/G. Regardless, if you are seeing full battery voltage at the 12V supply to the ICM and KCM on the Purple wires, and you've verified/cleaned the grounding contacts, then your ICM is, at least, suspect.

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Old 02-15-2012, 07:11 PM   #24
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That was the answer I expected, but didnt want to hear!!

Ill update when I am near the boat again.
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Old 02-17-2012, 12:19 AM   #25
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So I have talked to another mechanic about this, since I have come to the conclusion my other mechanic has no idea what he is on about.

He said possibly the ignition sensor, as they can go. He also mentioned that it could be caused by the Alternator. If unhooking battery overloaded Alternator, it could have caused some damage, and will cause ignition to not function properly. He said would have to try another alternator to see if this is the case.

Anyone else heard of this happening?
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Old 02-17-2012, 01:51 AM   #26
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I would confirm that possibility..... There is either an internal or external regulator in this system and it's quite possible you "made it angry" by disconnecting the battery while it was running. It's plausible.
With a bad regulator you can get 20+ volts and melt a battery or the opposing 10 or less.....and the entire system will be jacked especially if you don't have a good battery to compensate.

PS even if you did have a good battery... and the regulator is jacked.. you probably don't anymore....
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Old 02-17-2012, 12:40 PM   #27
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It's an easy test Andrew.

Engine off: Check battery voltage across + and - batt terminals. Should read just a bit more than 12V.
Engine at idle: Same test as above but reading should be above 13V but below 14.2 (ish).
Engine at 2000: Same as with engine at idle.

If your readings are as above the battery is probably fine and the regulator is fine too. The Alt has an internal regulator which is designed to produce a more or less constant output voltage at all RPM's. I suspect that specification can be found somewhere. So as long as the regulator is producing voltage within its specified range it's fine. In my experience that range is above 13V and below 14.2.

He's right in that disconnecting the battery with the engine running can cause the regulator to go nuts but doing so usually kills the regulator, but it can certainly damage other electronics. However, if that were the case then replacing the alt/regulator isn't going to fix any damaged components.
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Old 02-18-2012, 08:43 PM   #28
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Thanks for the advice.

So if engine off/ running battery test checks out ok, should there be any need to try another alternator? If I can get my hands on one I will probably try anyway, but if I have to buy one in, then I will be a little hesitant to spend money on something that may not be a problem (if it tests ok).

Will try this today if I get the chance.
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Old 02-20-2012, 01:43 PM   #29
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I see absolutely no need to replace it if it tests out ok, but perhaps you have a place you can take it (after removing it of course) that can test it.

Dan
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Old 02-21-2012, 07:14 AM   #30
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UPDATE

Ran Dan's test today
Engine off- 12.2V
Engine Idling- 13.9V
2000RPM- 14.2V

Above readings would suggest to me that the alternator should be ok, but let me know if you think otherwise.

I have found a couple more tests that can be done on the alternator in my manual, so will try them in the next couple days, however I would think problem is now isolated to Ignition sensor, ICM, or the below issue that I found. Correct me if Im wrong.

Another few observations I have made today:

Least importantly- Boat does not have a knock sensor. Checked all around both sides of the block, nothing near the starter motor, or on the port side.

More importantly- Pur/Yel wire on starter motor had come off. This wire leads to the oil pressure sensor, electric choke and FUEL PUMP!
I had noticed that I had not been hearing the fuel pump buzzing away after engine had been shut down, but assumed it was ok because the motor would still run. I held the wire against + terminal, and fuel pump immediately started buzzing away.

I have attached wiring diagram- I assume power comes from Purple wire into oil sensor, into Pur/Yel wire.

Now the questions that come to mind are:
1: Was the fuel pump running without this wire hooked up? Why did I not hear it buzzing when shutting engine off?
2: If not, was the carb/motor able to siphon fuel up from the tank?
3: Why was I getting 12V at the electric choke when the engine was running, and why was the choke coming off?

I dont think this is the main cause of my problems, as if the carb was short on fuel, it would have coughed spluttered and died if fuel starved, however it is a problem still that needs to be fixed.

Sorry, another big rant from me, just trying to give all info and thoughts as I find them.

Andrew



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