1993 Mercury 175 EFI Bogging Issue

[Substation Electrician]

Hello, I am new here. I hope someone can help me out. My 1993 175 EFI has had some issues for the past couple of summers. It does run good on plane but it stumbles or bogs badly while trying to get on plane unless you push the throttle all the way down then it will go on and plane out. It also bogs badly trying to drive the boat on the trailer. It surges when coming off plane and the boat is settling down. Last year it would crank great when first getting to the river. It came out of the hole o.k. when the engine was cold. After running to a couple of fishing spots the engine would hit and die. It would spin over o.k. but leave a oil slick behind the boat. Giving the engine fast idle it would finally crank but smoked heavily for a moment then I could plane off and the engine seemed to run o.k. on plane. Same thing each time you would stop and fish for a while. It eventually got worse to the point it would not plane out even after launching the boat. The engine would bog and miss badly when placing a load on it but idle o.k. I had a mercury mechanic look at it and he said the stator and voltage regulator was bad. The stator and both voltage regulators were replaced. The compression was checked on all cylinders and was good. The fuel pressure was checked and was good. Carried the boat to the river. It ran much better coming out of the hole o.k. but still having a slight stumble or bog unless pushing the throttle all the way down. The volt meter reads 14 volts while on plane. Carried the boat back to the mechanic. Started checking the fuel system out. Replaced all of the fuel filters and a few fuel lines that were soft.
Replaced the fuel line from the boat to the engine with Mercury line and primer bulb. Ran the boat at the river with little change. I rebuilt the manual fuel pump myself, this made a really big difference in the cranking of the engine especially after running and sitting for a while. I still have a bog and stumble issue though that I can't seem to find. This morning I have been testing the coils. The local Mercury dealership seems to think I could have a issue with a coil breaking down or being bad. I found on each coil the primary side would read .1-.3 ohms and the output side would read 900-1000 ohms. I heated each coil with a hair dryer and tested again. The primary sided still tested .1-.3 ohms the output sides all increased a little in resistance to over a 1000 ohms. The number 5 coil increased to over 1100 ohms on the output side. What is acceptable? What is to high? I would like to have the engine load tested at a local dealer but they are a month or so behind. Does this sound like a fuel issue or an electrical issue? I also tried a different computer which was on a 200 horse EFI motor of the same era but had the same issue. Any ideas?

Thanks, Scott

 

[Dukedog]

think its gonna be fuel delivery somewhere. anything from faulty enrichner circuit, bad air sensor ta leaky injectors or anything in between. this can get touchy for tha novice. an oem manual is a must have if ya gonna attempt it yourself. coils, pre-opti. are probably tha most dependable 'lectric part on that motor. yours sounds more like a leaky injector/injectors, o-ring/o-rings but sure not limited to just those. seen tha ecu choke/primer circuit act stupid and cause similar conditions and so on. I can tell ya how to eliminate tha "automatic" part of choke/prime/enrichner (whatever ya wanna call it) and put it back in your control, like ona carb motor, if ya want.

guess it depends on how you feel about your mechanical abilities. don't think its gonna be just a "bolt on" part........ gl with it

 

[Substation Electrician]

Yeah I have wondered about the injectors maybe being dirty or leaking. I have ran some 4powerG through it but could not tell much improvement. Also tried a different computer from a 200 of the same era but no change. It ran like a scolded dog though wish I could have kept the computer.

 

[Dukedog]

yeah, ecu's can make a difference. pretty sure yours is analog. a little later digital usually works better and more dependable. think if ya get yourself a good oem manual it will help ya out a lot. probably more so than what ya get ona computer. being able ta touch something is way more better tha tryin' ta read between tha lines!

one thing that might help with tha startin' till ya get it straightened out. trim motor at least level. a tad positive might even be better when ya hit tha starter. those things automatically enrichen/prime every time tha key is turned.......

 

[Substation Electrician]

I would like to have a good manual but not sure where to get one. I will try trimming level if I don't find a solution.