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CDI problem with a 75HP 1992 Mariner

S

sylvaing

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"Hi, my 75HP engine is startin

"Hi, my 75HP engine is starting to give me sporadic problem.

Here is the symptoms:

The engine has almost no power (even at WOT) until it reaches (slowly) 3,200 RPM at which point the RPM kicks to 4,000 and the boat speeds up fast. It started to do that suddenly while I was pulling a tube. With the tube attached, I was unable to get it over 2,200 RPM. I had to unload the boat to get it to reach the 3,200 RPM point.

That lasted for a few days then it started to work fine again. That lasted for a few weeks and now the same problem re-appeared :-(

By plugging just a spark plug at a time, I was able to diagnose that the lower plug (it has three) was not firing (ie, engine wouldn't start with just that plug while it would with any of the two other plugs). I switched plug and coil with the center plug/coil and the lower plug was still not firing while the center one was still working (although idling rougher than with it's original plug/coil).

The trigger resistance is within specs and there seems to be no broken wires.

The stator has two 'charge coils'. A low speed one and a high speed one. Could it be the low speed coil is on the fritz? Is this what the low speed charge coil is for? For below 3,200 RPM while the high speed coil is for above 3,200 RPM?

Thanks.

PS. Sorry for the long post. I try to be as precise as possible :)"
 
It could be. I have a similar

It could be. I have a similar problem on my 1986 90hp inline 6 except my problem appears to be the high speed stator. You could read out the stator with a multi meter. Thats what I am going to do when I get home on mine. I called a dealer about mine. He said the high speed kicks in around 2400rmps. I dont know where the cut out is for the low speed. Does it idle ok? It does sound like its the low speed part of the stator though or could possibly be the switch box that routes the power from the trigger to the coils. Did you check the plug wires???
 
"Thanks for the very quick rep

"Thanks for the very quick reply :)

It idles roughly since it's only running off two cylinders up until 3,200 RPM.

Yes, once I get back to the cottage, I'll check the resistance of both coils. I subscribed to the online maintenance manual for my boat so I have the specs for it (that's how I found out it had two charge coils).

Yes, I swapped the plug wires as well when I swapped the plugs/coils.

It can also be the switchbox, yes. I guess if I find the stator is behaving normally, I'll replace the switchbox. I don't know how to test if the switchbox is faulty or not.
"
 
"I connected the scope to the

"I connected the scope to the charge coils output and here is what I read:

Low speed charge coil: 300V

High speed charge coil: 150V

According to the chart, the low speed charge coil should have at least 180V while the high speed charge coil should be over 20V (I'm way over, can this be bad).

Mind you, the engine wasn't acting up last night. I'll need to check it when the problem occurs.

My current powerpack/stator is 332-7778A10/398-9710A28. If I have to change it, is the the replacement unit 114-7778/174-9710K1?

Thanks"
 
"Sylvain, not sure what chart

"Sylvain, not sure what chart you are referring to but here's the chart from the service manual. Depending what your rpms were when you tested, you numbers look quite "normal"..

215330.jpg
"
 
"I was using the online 'm

"I was using the online 'manual' from seconline. My RPM was at about 1,200 so I guess yes, they were ok. I'll wait until it does it again and check the voltages then.

Which service manual are you refering?

Thanks."
 
"The chart above is from the M

"The chart above is from the Mercury Factory Service Manual - while I do own a number of other "aftermarket" manuals, I have found that they do not always contain the same specs as those published by Merc..."
 
"Merc Part Number 90-136452

"Merc Part Number 90-136452

Available at any Merc dealer for about 70 bucks...

Here's what the cover looks like - if you are after a "genuine" factory manual, make sure it came right from Brunswick Corp (who owns Merc/Mariner)...

215455.jpg
"
 
"I don't know if Andrew wh

"I don't know if Andrew who runs this site sells the factory manuals, only noted he sells Selocs, but you could enquire.

Alternately, www.mercruiserparts.com (located in Florida) sells them for a little under 70 bucks. Probably numerous other sites that have them if you look.."
 
"Thanks, I'll look what he

"Thanks, I'll look what he has for manual. I checked mercrusierparts.com and they don't seem to carry any of my CDI parts. There are others though..."
 
A low speed failure would leav

A low speed failure would leave you dead in the water. A high speed failure will cause your problem or a bad switch box.
 
The chart above only does one

The chart above only does one check for the switchbox? Will that be enough to tell me if it's bad or not?
 
"Basically, if everything else

"Basically, if everything else is good, then the switch box is the problem - unfortunately it's one of those components that is proved bad by eliminating every other source..."
 
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