Merc 850 NO SPARK (Attn CDI Tech Support) et al....

[SeaKaye12]

I have a 1977 Mercury 850 that has no spark. Mine is the single power-pack model (no distributor; 4 coils...)

One of the things that I noticed lately when it was still running was that the tach would intermittently rise by about 1000 RPM...and then go back down again.

Now; in attempting to start the engine...I notice that the tach reads as much as 3000 RPM while cranking...

Do either of those scenarios mean anything to you?

Do you think that a problem with the tach could cause the ignition to fail?

Thanks for reading...

Chuck

 

[CDI Tech Support]

Re: Merc 850 NO SPARK (Attn CDI Tech Support) et al....

The tachometer itself cannot cause a No Spark issue. However, a rectifier/regulator can. And since the tach lead is attached where the rectifier/regulator is attached, your rectifier/regulator could very likely be the culprit, at least for the erratic tach.

Simply disconnect the stator's two Yellow wires from the rectifier/regulator. If you regain spark, replace the rectifier/regulator.

If still no spark, you may have two issues.

This should be our troubleshooting guide for that engine:

CDI Troubleshooting Guide

Shortcut:

Mercury 4 Cylinder

If not, obtain the serial# (or switch box part#), then check here:

Application Guide - Mercury

Then back here:

CDI Troubleshooting Guide


For the tach issue:

Battery Charging Issues, Regulator-Rectifiers and Tachometers

 

[SeaKaye12]

Re: Merc 850 NO SPARK (Attn CDI Tech Support) et al....

Well; further testing reveals two things:

(1) I have spark ONLY on Cylinder #2

(2) In reference to the trigger test that CDI references to; I get the following results:
Purple to White: OK (853 Ohms)
Brown to White/Black: Faulty (Open)
Purple, White, Brown and White/Black to Ground: All OK (open)

I do not have a DVA meter so I can't proceed further at this time.

Do you feel that the testing that I have done is conclusive in any way?

I definitely have a bad stator? Can I make any assumption about the switch box at this point?

Thanks for reading, Chuck

 

[CDI Tech Support]

Re: Merc 850 NO SPARK (Attn CDI Tech Support) et al....

Brown to White/Black is checking the trigger, not the stator.

Resistance is only reliable if the circuit reads Open or Shorted. If you've disconnected the trigger from the switch box & Brown to White/Black reads Open on the resistance scale, then replace the trigger. I would triple-check that measurement however, making sure you have proper contact.

 

[SeaKaye12]

Re: Merc 850 NO SPARK (Attn CDI Tech Support) et al....

I'm sorry; I meant to type trigger.

Another question though:

Is it necessary to have ALL the trigger wires disconnected when doing these tests; or is it OK to just dis-connect those wires that are being hooked to the meter?

Thanks, Chuck

 

[CDI Tech Support]

Re: Merc 850 NO SPARK (Attn CDI Tech Support) et al....

Is it necessary to have ALL the trigger wires disconnected when doing these tests; or is it OK to just dis-connect those wires that are being hooked to the meter?

Resistance checks should always be done with the component completely disconnected. Again, resistance is a highly unreliable measurement unless it's open or shorted.

DVA checks can be done on most triggers connected & disconnected. Check our respective troubleshooting guides to be certain.

 

[SeaKaye12]

Re: Merc 850 NO SPARK (Attn CDI Tech Support) et al....

OK. Well; thanks for putting up with me so far

I checked and re-checked the trigger tests and keep getting the same results; now with all the trigger wires dis-connected. I guess I need a new Trigger.

I then went on to follow CDI's testing procedure for the Stator.....and it was "in-spec" although the resistance on the red&red/white wires varied a little bit. The meter displayed varying numbers from 69-77 or so.... I don't know if this is significant.

Then; I went on to check the switch box; again using the CDI procedure.

This is where my next question comes in.

The CDI test for the switchbox again directs to check the resistance of the Stator. But on the print-out...the range for the Red&Red/White wires is said to be between 125-155. The Stator test itself said between 60 and 150.

Like I said; mine is in the 70 range (with the variation)

Is there something I'm missing that accounts for the difference in the ranges?

Thanks again for reading,

Chuck

 

[CDI Tech Support]

Re: Merc 850 NO SPARK (Attn CDI Tech Support) et al....

Again, resistance is a highly unreliable measurement unless it's open or shorted. The stator needs to be checked using DVA measurements in order to verify it.

There is no 100% test for any switch box/power pack minus sending it to us to be checked using our tests. The best one can do is check DVA from the switch box/power pack output (usually at the ignition coils) to ground.

Unless you can verify DVA, at this point, I would only replace the trigger.

Our two trigger replacements for that engine are as follows:

part# 134-6452 (if the linkage arm is straight) List price $96.00

part# 134-6454 (if the linkage arm has a 90 degree bend) List price $118.00

We sell direct or you can purchase through iboats.

 

[SeaKaye12]

Re: Merc 850 NO SPARK (Attn CDI Tech Support) et al....

I just received the trigger from CDI. Part # 134-6452.

I notice than when installing it, the trigger arm does not have the bend in it like my OEM one has.

It installs OK, but when the throttle arm is at the idle position, the trigger arm hits against the end cap assembly.

I'm puzzled over this. Do you think that I have the wrong trigger? I've included a picture that might help explain what I'm talking about. Should I expect lynch and synch adjustments to remedy this?

I acknowledge that CDI also has the trigger #134-6454, but the bend in the arm on that one appears to be down, an opposed to bending to the left.

CDI tech; what do you think?

Thanks, Chuck

 

[ifeeltheneed4speed]

Re: Merc 850 NO SPARK (Attn CDI Tech Support) et al....

I am just curious to know if you checked the wiring coming from your stator and trigger arm??? Not just look at what you can see but actually remove the plastic covers from wires and cut a piece of insulation off the wires. I have own 3 of these engines and ALL wiring MUST be replaced even prior to turning the engine over. I have never had to buy a single part. It always came down to bad wires. Not saying this is part of your problem but it is the best place to start. If you have'nt already changed all of your wiring, now would be a good time to do so. These engines are made to blow the switch box and or rectifier if you have a bad wire in the ignition system. I just finished tearing one down. The previous owner tried to do a "patch" job but missed the worst part 3"'s from stator. Everyone has wire lying around. Cut the entire wire from component and resolder. I recomend using heat shrink tubes or liquid tape. Its better to change a wire that costs .10 cent rather then a switch box that runs $200. Mercury in my oppionion is the best motors ever built! They are one of the easiest to work on. Also, if you dont already have them, you can find ALL the diagrams for this motor for FREE on google. I apoligize if my comment has offended you! If this info doesnt help you, maybe it will someone else. I hate seeing people throw money away.

 

[SeaKaye12]

Re: Merc 850 NO SPARK (Attn CDI Tech Support) et al....

Hi ifeeltheneed4speed....

Actually I think you are correct. I now believe that the actual cause for my engine's failure to run is indeed a broken (disintegrated) trigger wire. The issue is right up where the wires go into the sealed unit trigger. Even my neighbor who has decades of experience working with miniature circuit board soldering seemed to think it was touch and go in trying to repair that.

I ordered a new trigger essentially just because of Mercury's crappy wires. At some point I would like to hear just what was wrong back in those days at Mercury. What was the problem with their wires anyway? I have other engines (JhonnyRudes) of similiar vintage or even much older that have no such issues with the wiring. Mercury ought to be ashamed of themselves....

I have now completely re-wired the engine with a CDI internal wiring harness. A few years ago I re-wired the harness myself...splicing and heat-shrinking and all. It worked fine for a few years; but now I figured it was time to just start over and eliminate what I have always felt was a recipe for getting stranded someplace.

I now have a new Stator, new trigger and new wiring harness. Hopefully the PowerPack will continue to be reliable. We'll see.

Thanks for the reply,

Chuck