spark advance problem Thunderbolt IV

jbt1

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I also disconnected the ground wire coming out of the electronic timing sensor just to see if it made a difference......would even pop......hooked it back up.....started instantly.....guess that pretty much says it's working. Also noticed that on my old sensor, the white/green wire was connected on the right side of distributor and the white/red on the left......new sensor has these colors reversed.....so I figured, what the heck.....reverse 'em and see.....not even a pop......put them back and all is at idle again.
 

achris

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Ok... You seem fixated on the ignition system, so here's how it works. The system consists of 4 main parts. The sensor in the distributor, the amplifier (mounted to the exhaust elbow in your case), the coil and the HT distribution system (dissy cap, leads, plugs)....

The amplifier is powered by the 12 volts when you turn the key to ON. When the key is OFF, the amplifier (and the entire ignition system) are completely un-powered. The module supplies a 12v line to the sensor (through the white/red wire) and the sensor is the signal to the amplifier as to when the rotor window goes past it. When the window goes past the sensor the white/green wire drops from 5v to ground. The sensor, as you have already found out, also needs a ground. That's all the sensor does, just flip the white/green between 5v and ground. It has nothing to do with the timing, apart from the initial timing you set with a timing light at idle revs. And that's done by rotating the distributor, not moving the sensor itself.

The amplifier takes the sensor signal (white/green) and based on the frequency of that signal, will apply an advance, or not. The amount of advance is based on the engine speed and the programmed curve in the amplifier ROM. If the engine is at cranking speed the ignition is advanced slightly, around 6 degrees. Once the engine is idling and up to about 1000rpm, the advance is effectively 0 from the initial timing setting. Once the engine reaches around 1000rpm, then the curve is applied, and the timing will be advanced. So, up until the engine reach around 1000rpm NO ADVANCE IS APPLIED.... If you don't have engine speed increase (up to around 1000rpm), it's NOT an ignition system problem. It may be the initial timing is wrong, or the carb is not set right, or you have a vacuum leak... But it is not the amplifier or sensor.

There are several different amplifiers, depending on the engine. The V8s have anything from 20 to 24 degrees of advance, depending on the model, and the V6s only have one, it advances 14 degrees. You need to make sure you have the right module for the engine you're working on. For the 200hp V8 it should have either 'V8-22' or 'V8-24' depending on whether you have an early model engine or a later model (distinguishable from the style of rocker cover). All the sensors are the same, both for the V8 and V6 and through time. They all do the same job... I've seen many people ripping hair from head over this sort of problem, and 99% of the time, it's something silly, like the wrong rotor (I have seen someone put a V6 rotor in a V8 engine and wonder why it didn't run right)... I have had many people swear black and blue that the plug leads are on on the right order, only to find they are not. And yes, they also checked them 4 times. Just saying....

As already mentioned, and I also noticed it, you make no mention of setting the initial engine timing with a timing light...

For your engine the initial advance should be 8°BTDC. And you really do need to set it with a timing light. Turning the distributor "about 10-15 degrees" just doesn't cut it.

Chris.......
 
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jbt1

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Thanks Chris! I understand everything you explained to the letter..... Appreciate you taking the time to explain and elaborate......Now.....I have a thought as you may have hit it out of the park with a comment......the distributor I received came with V6 cap & rotor as well as V8 cap and rotor as apparently they fit either configuration engine.......could it be as simple as the V6 rotor is being used instead of the V8 rotor?
 

achris

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Thanks Chris! I understand everything you explained to the letter..... Appreciate you taking the time to explain and elaborate......Now.....I have a thought as you may have hit it out of the park with a comment......the distributor I received came with V6 cap & rotor as well as V8 cap and rotor as apparently they fit either configuration engine.......could it be as simple as the V6 rotor is being used instead of the V8 rotor?

Count the shadows. Sorry, rotor windows. If it is a 6 cylinder rotor you're using, that might explain it :facepalm:
 

Fun Times

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Unfortunately post #11 shows there is a V8 rotor already installed.
fetch



also....no plugs on ignition amplifier/brain box.....wires go directly inside unit. It is secured to water manifolds with 4 bolts...how much better grounding does it need?
Some ignition modules use a "case" ground along with a ground wire in the harness to the module. It's best to ensure both have a good clean ground going to it if possible.

I was thinking you had the triangle module that utilizes the plug vs the box type module like this one,
http://www.ebay.ca/itm/Mercruiser-Ignition-Amplifier-Assembly-7804A-3-15248T02-/290609817651

http://boatinfo.no/lib/mercruiser/manuals/mercruiser9.html#/394
 
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jbt1

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well, at least process of elimination is something moving forward ..... i.e. correct rotor identification. Here's another thought, laying awake at night now thinking on this problem.....I decided to go to my installation manual and see if there is a procedure for setting initial or base idle speed......mind you I did nothing with remote cable adjustments or idle screw adjustments on the carb and boat worked as it should prior to tune up attempt with a couple of plugs not firing as they should as my only symptom ......setting "engine idle speed" is done with the boat in the water with remote control engaged and boat moving forward. Here's my thought looking at it from the standpoint that the situation was caused out of the water by removing and reinstalling a distributor......I did not go at this with the lack of acceleration as a problem.......so what I did has to have caused the issue.....if we rule out that we have a component failure; especially since the sensor in the distributor is just a fancy on - off switch and is sending on/off signals to brain box....i.e. spark plugs themselves, wires, electronic sensor, brain box, cap, & rotor all OK.....it either has to be a connection/wire issue or a mechanical adjustment/setup issue. I am wondering if the brain box is "lost" from an initial idle point and the best to do right now is to treat the problem as I need to completely establish the initial timing point of 8 degrees with a light and ensure the initial idle is 650 - 700 rpm. Once I know - for a fact - that my idles RPM's are spec...then we see what the brain does with that base info.
 

achris

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The amplifier does not 'know' where the timing is. All it 'knows' is that at x rpm it must apply y degrees of advance. But yes, setting the timing with a timing light is a good first step.

Chris.....
 

jbt1

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With that said Chris....what should cause the engine to increase in RPM from idle speeds whether in water or not from the 650 - 999 RPM range. Raw fuel only?? Thanks
 

achris

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Yes. Think about small engines, lawnmowers, chainsaws generators, etc. they don't have any spark advance, it's all done by increasing the amount of fuel available to the cylinders....
 

jbt1

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Very good.....that was my assumption....thanks! Here is the latest from work done yesterday as time permitted.......ensured all connections electrically were good, rechecked spark plugs wires, and included some more pics. Also disconnected throttle cable at carb. Started engine....idle speed about 850 according to tach on dash......if I go lower via idle screw adjustment on the carb, engines labors and quits. Engage drive (out of water) not much change to RPM and physical engine speed. If I increase throttle at carb very slowly, I do get an engine speed increase until about 1000-1100 tach RPM...at this point with continuing to increase throttle very slowly at carb....engine does slightly increase in engine speed, BUT RPM's on tach now drops considerably....to around 600 or less......if I increase throttle some more.....engine starts to labor, cough, and eventually will choke out and stop with tach showing about 400 RPM. So..........as I give the engine more raw fuel slowly, the RPM's do pickup until the tach shows about 1100 RPM and then as a still small increase in engine speed as fuel is added goes on, a noticeable drop on the tach is observed (1100 down to 600), engine begins to labor & miss and dies at 400 tach RPM....no additional engine speed increase is heard so it labors and levels off.

Here is another observation.....the rotor in the pre-owned distributor is rather sloppy.....probably a 2-3 degree movement....while my old rotor is rock solid tight with no slop and stuck on.....it is my understanding that Mercury may have lock tightened these original rotors on....so hence no movement at all. But would maybe excessive slop in the rotor create this bizarre issue??

I am also considering breaking off my old rotor, getting a OEM new one and installing the sensor & new rotor onto my old distributor and installing it back in the boat to see if there is a change in anything. Any thoughts greatly appreciated.
 

jbt1

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additional pics for all
 

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jbt1

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well I went and purchased a NEW OEM Quicksilver rotor.....installed it.......nice tight snug fit.....cranked her over.....fired right up....but NO noticeable change in performance. Perhaps I go the route of using the old distributor with the new rotor and pre-owned electronic sensor just to see what happens. After that...on the sale block she'll go! Very frustrating to say the least. Any and all thoughts appreciated.
 

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Fun Times

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Started engine....idle speed about 850 according to tach on dash......if I go lower via idle screw adjustment on the carb, engines labors and quits.
Might be time to connect a vacuum gauge and fuel pressure gauge to the engine to help see what is going on with the engine.

If I increase throttle at carb very slowly, I do get an engine speed increase until about 1000-1100 tach RPM...at this point with continuing to increase throttle very slowly at carb....engine does slightly increase in engine speed, BUT RPM's on tach now drops considerably....to around 600 or less......if I increase throttle some more.....engine starts to labor, cough, and eventually will choke out and stop with tach showing about 400 RPM. So..........as I give the engine more raw fuel slowly, the RPM's do pickup until the tach shows about 1100 RPM and then as a still small increase in engine speed as fuel is added goes on, a noticeable drop on the tach is observed (1100 down to 600), engine begins to labor & miss and dies at 400 tach RPM....no additional engine speed increase is heard so it labors and levels off.
Could be your coil may be breaking down not producing enough spark, a fuel pressure problem or carburetor problem. Remember this all could just be a coincidence that it may seem ignition related since you worked on it last.

Do you own a timing light? Set your timing then connect the inductive pickup to the high tension coil lead to ensure your getting a consistent unbroken spark. If it's broken spark, try disconnecting the gray wire off the back of the tachometer gauge.

Time to give up and sell it.
Don't give up so easily, we're just getting started here ;):). But please know there is no selling permitted here on open forums, it's only allowed here, http://www.iboats.com/sell-a-boat/ Thanks.:)
 

jbt1

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I understand and thanks! Sell her on CL if I decide that route. ** one thing I did notice worth mentioning since you bring up the coil......I went one by one and lifted each individual spark plug wire off of the dist cap to see if all plugs were firing.....which they all seemed to be......however, each and every wire when lifted caused an arcing between the two wire connections on top of the coil and the center main plug wire.....but only after the individual wires were lifted......as soon as they were reconnected.....arcing stopped........I did clean the top of the coil for any debris and such and it minimized the occurrences, but did not completely eliminate the arcing. I will have to obtain a timing light.
 

achris

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.... I will have to obtain a timing light.

If you don't already have one, how are you setting the initial timing? Or confirming that you have no advance? By the description of the symptoms, you have another problems, like FT suggested, coil or fuel problem... If you are trying to set timing and check timing advance without a timing light, all bets are off.... :facepalm:

Chris.......
 
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