`89 mercury 40hp 4cyl - no spark on center cyl`s.

[ultra353]

Hi all, I`m new to mercury motors as well as electronic type motors. I`m more of a points/condensor type guy. Heres my question -top and bottom cyls have good spark, middle cyl`s are dead. Are the center cyl`s on the same type of cuircut that would cause both to be out? And what would you u suggest as a starting point to track down the problem? check the center coils on an ohm meter? all i have right now is a multmeter- ( no dva adapter, just read a bit on here on what they do ). All 4 cyl`s have 165 lbs compression .
It also has the tilt/trim and all i get is the 2 relays clicking when i try to use the button on the throttle or the button on the side of the motor- any suggestion on that as well. I just picked up this boat /motor combo and it sat outside for a while so i don`t have any history on it.

Thanks for any suggestions you might give me, i`m kinda lost on this electronic stuff so i`ll be bugging you mercury guys a bunch, Lol.

 

[Maxz695]

Re: `89 mercury 40hp 4cyl - no spark on center cyl`s.

Normally when two cylinders refuse to fire it,s the switchbox. First be sure to check for spark on the two suspected cylinders and see if there is at least a weak spark (orange) The spark at the distance of 1/4 inch from a ground should be a bright blue in color. If there is absolutely no spark check coil grounds and check all wires are not frayed broke or cracked. Make sure the plug wires are properly inserted into the coil and tightly secured on the plugs. Eliminate all possibilities before thinking the switchbox is faulty. A manual is your best freind and will guide you with trouble shooting and proper test proceedures to find if a componant is not working properly.

 

[ultra353]

Re: `89 mercury 40hp 4cyl - no spark on center cyl`s.

Thanks for the reply. i`ll check all the grounds/wiring first. Is there a proceedure for testing the switchbox?

 

[ultra353]

Re: `89 mercury 40hp 4cyl - no spark on center cyl`s.

Checked coils , they checked ok, (swapped coils and they all produced spark). I swapped the blue-blue/white and the red-red/white and on switchbox to see if the spark moves to the middle 2 cyl -no spark. top and bottom still produce spark. looks the stator has been replaced with a cdi unit. (If its producing spark does that mean its working )
Trigger brn-blk 824 ohms within specs
prp-wht 768 ohms out of spec.
I thought 1&2 and 3 &4 were on the same circuit. yet 1& 4 have spark.

 

[Maxz695]

Re: `89 mercury 40hp 4cyl - no spark on center cyl`s.

Try swaping the trigger wires on the switchbox to the firing cylinder to see if they all produce a signal for the spark. this will eliminate the trigger as the culprit. I at present have #3 cylinder not firing and know it,s the switchbox. Probably due to removing the plug wire while it was running (Big NO NO!) I had an old switchbox lying around that blew the Main capacitor but the diodes I guess where good where the trigger transfres to the coil and I,m using it to fire number 3 cylinder for testing. I have a new SB on the way. so 1 all coils are good the stator is goos as it,s sending current to fire 1 and 4 eleminate the trigger by doing my suggestion and that leaves the switchbox as the cause.View attachment 174018View attachment 174019View attachment 174020View attachment 174021

 

[ultra353]

Re: `89 mercury 40hp 4cyl - no spark on center cyl`s.

I swapped the trigger wires prp&wht with the brn &blk on the switchbox and still no spark on the two center cyl`s. Top and bottom still have good spark. So, i guess its the switchbox. I`m a bit concerned with the ohm`s reading on the prp/wht wires as there a bit low on the spec`s 768 ohm`s - spec is 800-1400 ohms.

 

[Faztbullet]

Re: `89 mercury 40hp 4cyl - no spark on center cyl`s.

Probably due to removing the plug wire while it was running (Big NO NO!)

Old wifes tale....

 

[Maxz695]

Re: `89 mercury 40hp 4cyl - no spark on center cyl`s.

Update on my carb situation... After a slow totall rebuild usign a copper wire to clear any debris it came down to using 3/8th hose from tank to the bulb although both call for 3/8ths Ethenol wins the battele over proper parts so what I did was go to 5/16ths and a 6 Gal reserve tank I use to mix and fill and althought the bulb is not fully tottally hard it fires and runs well without having to pump the bulb. Going to pull the tank inspect the pick up tube and replace all the 3/8ths with 5/16ths hose and never ever use ethenol gas again I,d rather ride to the Texaco and pay a bit more than to keep buying new unfreindly line for ethenol!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Running a bit more than fair with hope at the present moment. Happy here after all the $$$$$$$$ spent (crank pistons rings bearings hone sleeve carrier etc etc) temp had alot to do woth the lines expanding

 

[ultra353]

Re: `89 mercury 40hp 4cyl - no spark on center cyl`s.

Thanks Maxz695 for all the help. I got a good used box locally and now good spark on all 4 cylinders. I put a little fuel in the carbs and hit the key- fired right up. Good luck with your engine.

 

[Maxz695]

Re: `89 mercury 40hp 4cyl - no spark on center cyl`s.

Great to hear !!! I think I found my final stop in the road today being a bad coil I will not be able to test until at least tommorrow afternoon. View attachment 176991View attachment 176992

 

[Faztbullet]

Re: `89 mercury 40hp 4cyl - no spark on center cyl`s.

The ferrite core being broken will not cause a coil not to fire but can cause a double spark or inductive "buck" back into the SCR and damage switchbox on that cylinder...