96 Mariner 200 EFI surging and loss of power. Please help!

[Adam21986]

New member, this will me my first post. I have a 96 Mariner 200 EFI on a 96 Procraft SP200 bass boat. I am a tournament bass Fishermen and run the boat at least twice a week hard. The oil injection was removed when purchased in 96 (I bought from original owner with 98 hours) I run rec fuel and mix 50:1 plus some TCW 3. Friday I had accidentally went heavy on oil mixture in tank 2. I always run heavy but this was more than usual. Saturday after a full day on Okeechobee ran roughly 55 miles, on my way in I switched to tank 2 about 3 minutes later the motor began to surge and also struggle to hole shot. It was intermittent, I could run up to 68 mph and then it would bog down to 60 then surge back up. It did this at all speeds and rpm. Never died. I went home and pulled the plugs, they were fouled. I put new plugs and ran it Sunday, same problem, intermittent surging and hard to get on plane. Sunday afternoon I drained all fuel out of both tanks, cleaned VST and hp fuel pump filter (both which were clean) I by passed the fuel tank and ran 2 gallons of rec fuel 50:50 mixed with seafoam from a gas can also cleaned plugs. Monday I ran the boat again, the surging stopped but it will bog down on hole shot and not get in plane (rev to about 3k then bog down. Can get on plane with passenger on bow) so it didnt surge but would hold me at 60 mph, twice it cleared up and ran clean up to 67mph then pull me back to 60. Also it now burns (or wastes) twice as much fuel maybe more. Checked plugs, fouled again. Tested fuel pressure was at 35. I checked compression exactly at 130 on all 6. It's a clean low hour well maintained motor. I am wondering if a injector is stuck open and getting to much fuel. Ran again today same symptoms but never cleared up and harder to plane. I am considering pulling injectors and having them cleaned and tested but I wanted to check here first. Any help is greatly appreciated!! Thank you!!
SN OG373534
1996 Mariner 200 Magnum EFI
96 Procraft SP200

[revlimiter]

I wouldn’t think injectors would be intermittent, but not a bad idea to have them run thru the machine. Make sure all your sensors are still plugged in, check for any loose connections or grounds. Wonder if you don’t have a stator getting weak.

[EuropeanAM]

Welcome to BBC!

Moving your post to the CORRECT Forum for you.

Check and record fuel pressures:

-At idle
-Under Acceleration
-15/30/60 seconds after engine shutdown.

When was your Pulse Fuel Pump last rebuilt?

Important note: 50:1 is the correct mix for this engine. It's actually HEAVY for idle/low RPM operation. DON'T compound this by adding more oil to the equation- there comes a point at which the fuel does not flow across injectors and passages correctly (and what was meant to avoid a lean condition actual begins to CAUSE a lean condition).

[Adam21986]

Thank you for the replies and helping move the post to the correct location! I appreciate the fuel oil mixture information as I did not know and have been running to much oil. I will do the suggested tests and post the results. Thank you for helping!!

[Adam21986]

Also the pulse fuel pump was done two years ago.

[EuropeanAM]

Might want to reference this thread (very important items ALL be addressed simultaneously... the "try this first and that later" approach very seldom works).

FUEL LINES AND PERFORMANCE PROBLEMS

[Adam21986]

FIXED. Ambient air temp sensor failed confusing ECU. Replaced and running great

[revlimiter]

Glad you got it fixed! I’ve not found oil mixture to make a lick of difference on how they idle when all’s running right, all the way down to 32:1.

[EuropeanAM]

FIXED. Ambient air temp sensor failed confusing ECU. Replaced and running great

If like the ones I've seen it was reporting like 1.5 Billion Degrees F......