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mercury black max xr2 losing one cyl spark at about 2200 rpm

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chevy83m

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hello all, I have a mercury black max 150hp v-6 xr2. it runs well at idle and also at full speed, however when accelerating it looses spark to the number 5 cylinder only. I tried switching the coil with another and also swapped the power pack, problem is still on the number 5 cyl. im using a timing light and the flashes stop on that cylinder only. tested it while in the water in gear. any advice would be very helpful. thank you
 
Ohm the wiring to the coil...there could be a cracked wire. When it is idling and using the timing light start pulling ang shaking one wire in the harness at a time to see if the flashes stop or skip.
 
wiring from the power pack to the coil is in good shape, did find a yellow wire leading up to the stator frayed very badly. never had an charging issues that i am aware of anyway. was getting dark so ill have to look for more wiring issues tonight. any chance it may be the trigger only affecting that one cylinder?
 
No, on a V6 the trigger works in three pairs of cylinders. So if the trigger was bad you would lose spark at two cylinders (one is triggered by a positive pulse and the other by a negative pulse from a given trigger pole).

No spark at 1 cylinder is almost always 1) bad coil on that cylinder 2) bad lead between coil and sparkplug or coil and switch box or 3) bad switchbox.

You can jury rig the switchbox and recheck the spark. Swap out the leads that feed your number 3 and number 5 coils. The motor won't start (or would be messed up if it managed to since it would be firing the wrong cylinder), but with a spark tester or a timing light you can note whether or not the problem moves. If it does that switchbox is toast (and if so you may consider changing both - they often die in pairs).
 
so I ohm tested the coils, trigger and stator. the stator is not testing good, all four ohm tests it fails. can this really be the problem though? only one cylinder loses spark. has great idle, starts easy and once over its fit and gets onto plane itll push my Ranger 360V to 59mph on speedo
 
red/blue tested at 4800 ohms supposed to be 5200 to 6500 according to the shop manual I have. also the test from the red and {red/white} wires to ground was around 37 ohms each, supposed to be closer to 125 ohms.
 
It seems the stator may have degraded some. Check the voltage output w/a DVA to be sure. You may have multiple electrical issues.
 
The stator voltage maybe low but it wont cause this as all it does is charge capacitor in switchbox which is shared by all three outputs. It either a SCR in switchbox failing or bia's circuit problem . Disconnect the stabilizer/advance module and the wht/blk jumper between boxes and test only to about 3000 rpm.
 
Yes, each switchbox look after 3 cylinders each.

Your numbers are a little out on the stator, but not enough that I would immediately be concerned. Depending on the air temp the ohm readings can vary pretty wildly.

If you have "no connectivity" at all when you are ohm checking a winding that almost certainly means something is shot, but if it's just "out of spec" that at least tells you that there is no break in the copper winding - in this case "excessive" ohms is far more of an issue then "not enough" resistance (less resistance means the copper wire wrapping is most certainly intact).
 
tested the stator and the trigger the same day so temp was about same. trigger ohmed good stator did not. my book says to do four tests, 1. ohm test red and blue, 2. ohm test red/white and blue/white. 3. ohm test from red to ground (this reading was in the 30ohm range), 4. ohm test red/white to ground( also 30 ohm range). I switched switch boxes and no change, also switched coils from another cylinder and no change. as the stator failed all 4 test im gonna bite the bullet and hope for the best. thank you all for the help
 
hello all, I am proud to say PROBLEM SOLVED. turned out to be the stator, now it even idles better and runs 55mph on speedo with alum 3 blade prop 23p. too bad the season is over but it will run good for striper season anyway. it is however a little harder to get started, but may just be cause its kinda cooler here in NY. thanks all for the brainstorming and info.
 
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