Logo
FULL SITE MENU

Very High Voltage ( Is this the Problem) ?

T

TGBTG7701

Member
Problem- hard to start, dies at below 1200rpms, will not stay running after a long run.

I have been trying to pinpoint my issue with my 1991 Mercury 40hp 4 cylinder. I have found quit a few things that where wrong and have changed them, first being adding a voltage regulator and doing away with the rectifier. Someone had installed a 16 amp CDI Stator, but left the OEM rectifier, CDI states you have too use a regulator not rectifier with this stator. This corrected my issue with battery charging, but not how it ran. The next thing I checked was ohm my stator and trigger, stator checked out fine, dead on the allowed specs, trigger I am not sure I have a spec of (Purple to White 800-1400, I got 0.864 and the same for Brown to White/Black).

Built a DVA adaptor and here is where this got all out of range, voltage to coils between 280-230 volts, (highest #1 lowering as you get to #4). Blue to Blue/White 260 volts (180v +) Red to Red/White 85 volts (25v +). Trigger wires 61-68 volts (4v +).

I marked TDC of each cylinder on the flywheel, and checked with a timing light (#1 showed 2-1)(#2 showed 3-2)(#3 Showed 4-1)(#4 showed all bunched).

The trigger looks kind of rough, the epoxy has a crack, but plastic housing is fine, found a few broken wires, soldered on new heat shrink the joint.

CDI states this stator has to be used with a flywheel with glued on magnets, but I have a bolt on. I talked with CDI tech support, the guy said he thinks a bolt on magnet causes a drop in voltage, but I think that may be the other way.
 
I'm looking over your numbers and they look fine.

If you didn't change your ohm meter setting when testing the trigger might have an issue there. Spec is 700 - 1000 ohms (both sets of measurements). The 800 to 1400 is a little high in resistance. The 0.864, or near full continuity (unless you bumped the meter from X100 to X1000 ohms which would make it 864 vice .864 ohms). However, in both cases you have "continuity with some resistance" which tells me the bobbin itself has integrity, at least the winding is not broken. A cracked case (housing) could allow some (power) to escape to ground which would result in a lack of fire at one or more plugs.

You don't note the rpm that you tested the stator but can assume it was at idle/just a little north of idle (you say will stay running at 1200 rpms) or at cranking speed. Given the your numbers are likewise in the range for what I have in the service manual for the 4 cylinder 40 - I'm not sure what you have for "spec" on the numbers you note above as being "high".

If your "hard to start/won't run under 1200 rpms" was stator related it does not appear to be your low speed side of the stator which is putting out a very healthy 260 volts (210 - 310 range normal) - the high side, which is there to supplement power at higher rpms is, likewise, putting out 85 volts (25 - 90 normal) and your coils in 280 - 230 range, those are fine as well (would expect 160 - 275 depending on exact rpm) - bottom line, lot's of power getting to the coils to be upconverted to give you a solid spark assuming the coils are ok, not cracked etc (and have you checked them - lots of power coming but doesn't mean they are working properly.

Have you checked with a timing light or confirmed you have spark at all the plugs? If so that would indicate the trigger is doing it's job and the coils are working.

So looking at your ignition tests I don't see any immediate red flags there. The trigger might be suspect if it has a cracked case, but the numbers look ok to me.

Have you ruled out fuel related issues? The hard start, won't stay running at normal idle speeds and dies after a long run (presumably when it returns to idle?) could all be symptoms of carbs, gaskets or seals either not letting enough fuel in (clogged idle jet etc) or allowing extra air in or air/fuel/oil out through a bad seal.

You seem to indicate you got this motor from (somewhere) and are working your way through issues. Do you have a good history on it or are you starting from scratch??
 
Thank you for your help, the specs I got where from CDI trouble shooting ligature, I also have a service manual in PDF form, kind of hard to read. The motor came for a guy that works on only Mercury outboards in his spare time, he has been at it since 1954, he is quit an older gentleman, he may have over looked something. I have had the motor over a year, but it started the issues within the last six months. He went through the motor, rebuilt the carbs, new seals, it still has over 145 psi +/- 3 on all 4 cylinders. I have had the carbs off myself, they where very clean, but I went ahead and cleaned them once they where off. I installed better quality fuel line than what was there, I found a leak on the side of the power head, line that connects #1&2 and 3&4 bleed line, behind the electrical control panel. The motor is clean as new, and I have not found a single leak after these repairs. I was leaking before these repairs, this helped a lot, but still having the problem. While I had the carbs off, I adjusted the floats to service specs, using a caliper, the cams on the carbs have the correct clearance and the air mixture is 1- 1/4 to 1- 1/2 turns.

I have noticed every so often I will get a back pressure (puff sound) it comes from under the flywheel, but seal seems to be good on crankshaft under flywheel. The motor will sometimes run 3-4 trips and never do it, but then sometimes it will do it several times all at once, motor is running horrible when it does this.
 
Starting to suspect either the top seal or the O-ring in the top bearing carrier. Both can be replaced without a major tear down. I'd do this and see if it's the problem. And while you're at it, I'd replace that damaged trigger coil.

Jeff
 
Jeff, Thank you for the help, I agree and will do this. I do have one question, how does the bearing carrier remove? I removed the four bolts and tap on it, but it was not moving, if there something I am missing? I looks as if there is a metal spacer between it, I assume that is reusable.

Again thanks for your help.

Keith
 
145psi give or take 4-5 psi between all four cylinders. The guy I got it from went through the power head completely. I do have some oil leakage under the flywheel, so I am going to pull the upper bearing cap and replace the Oring and shaft seal.
 
Loosen the top 4 bolts (to on each side) holding the crankcase to the block and the bearing carrier will come out. Pry evenly on all sides to avoid jamming it.

Jeff

PS: The crankcase joint will seal back up after you retighten those bolts. Done it numerous times.
 
A leak at the upper end of the crank could account for all the issues you note. Anytime your gas/air/oil is going anywhere "but" the cylinder it's going to run like crap :)
 
Thanks for the help,

I was able to get the bearing carrier out, it took a little time and patience. The bearing spins freely, but seems to have some wear, I ordered another bearing along with my seals. I found three coils with cracked ferrites, you can't fix these, correct?
 
I wouldn't try and fix the coils - maybe you could, have never tried - have always figured once they start cracking they are probably on their way out anyhow. It would be one thing to band-aid them together during a remote trip, but really, for the cost (and the potential of being stranded if they really go), best just to swap them out.

I would however, replace them with Sierra Coils instead of the OEM ones from Merc.

The Sierra's list for less than half the price of the OEM ones and they work great. This website sells them for about 33 bucks a piece (if you don't have a local source).
 
Back
Top