1996 Mercury 200efi slight power loss at wot NEED HELP!

**Coltons33** · 04-07-2020, 06:06 PM

Hey everyone I am needing some help I have a 1996 Mercury 200efi that is having a issue. First off the facts all compression test 126-130 .had injectors cleaned and put back is it has Carson reeds. The bot runs good and smooth but one the boat gets on pad it’s running good but then it looses some power and and won’t run wide open and on pad . But then if I let off and roll back into it the power will be their and then cut back out. But it doesn’t die. Also I have checked fuel pressure it’s running at 36-39 at wot. Someone please help me I want it to run the best it can.. and yes it had a brucato. Computer on it. If y’all need any more info I will answer the best I can please help.

**Coltons33** · 04-07-2020, 08:23 PM

And just to be clear it is like a loss of around 5-600 rpm and then u can let off and roll back in and the power is their. And their is no skipping that I can hear.

**billybob** · 04-08-2020, 02:25 PM

What I would check first is temp. sender on port head. If you are running without thermostats, it is possible motor gets too cold, and puts it back in enrichment mode. That would drop you about that much RPM. Enrichment is controlled by tan/black stripe wire. Run motor to where it happens, then unhook that wire. Second step in same test, is to ground that wire to ground with jumper. It may possibly be that temp. sensor is going bad, or that circuit in ECM is going bad. Try those tests first, then reply on thread. There could be other things going on, but try that first.

**Coltons33** · 04-08-2020, 06:09 PM

So on that sensor mine has 4 wires that come out one watch is black one that is all tan and 2 that are tan with the black stripes the one on the other head only has one wire and it’s tan with blue stripe . How do I know what one to unplug?

**TEXAS20225** · 04-08-2020, 11:16 PM

two tan/ blk stripe are air temp sensor wires that go to sensor in plenum these two cause a lot of trouble they can put way too much fuel in the motor the other one is actual heat temp sending wire to temp gauge i doubt thats it but maybe those things can be a pain in the well u know

first are all the" BOXS" gone (idle stabilizer) check your plug wires they could very well be it breaking down under load pre mix or auto oiler u could have a switch box double firing or similar problem or a host of other things i built plenty of those in my business before i went fishin and lost the directions to my house

**Coltons33** · 04-09-2020, 06:23 AM

Billy Bob and Texas the sensor bob was tlking about is it that one with all the wires and how should I test that? Their is also a sensor on that same port side gear that plugs in what one is the one that needs to be tested and how I can’t find how on youtube

**billybob** · 04-10-2020, 05:01 PM

The single wire sensor on stbd. head, is overheat. It is an off, on switch only. It only ever completes a circuit when motor overheats, will sound horn. On port head sensor, has 4 wires. 1 black wire is ground. 1 tan wire is temp. gauge for dash. 2 tan black stripe wires control fuel mix for cold motor. when you have your problem, unhook both tan black wires, and rerun motor. Then if that makes no difference, ground both wires, and rerun. All that will tell you is if that is the problem, with powerloss. Try those tests first, then repost, if that does nothing. This is exactly why I am not a fan of older EFI outboards. They are getting to the age where you may have to replace ECM, At a cost of about $1,500.

**Coltons33** · 04-10-2020, 08:24 PM

Billybob how would be the best way to ground those tan with black stripe wires when they are unplugged. What the best way to do that in ur opinion I’m going to the lake Tomorrow to do these test.

**billybob** · 04-11-2020, 09:16 AM

Just use a jumper wire, with an alligator clip on each end.

**Coltons33** · 04-25-2020, 09:18 PM

Ok guys so unplugging that didn’t work also used alligator clips and that didn’t change anything however. I was going down the lake and it was doing the same thing and all of a sudden the rpm started to climb like it was headed over to 5600 then it die back to 4800 then surged again and then the motor shut down. And it came completely off plane motor not running. Hit the key fired right back up and did 4800-5000 the whole time didn’t do the other part again. But when it did the big surge I could tell it was running good and if it would have kept up those rpm that thing would have been fast . Obviously the problem is electrical what other things do y’all think I need to check now.