Checked codes last night. No codes so I'm looking at the temp sensor or map sensor. It's cheaper to replace them than to haul it across town to know for sure.

The only problem I have with it being a temp sensor is this: The ECM takes reference from the temp sensor for a BPW multiplier to add fuel during cold operating temperatures and gradually decreases that value to near 1.0 as the engine comes up to operating temperature. There is a limit in this table at how rich or 'lean' the ECM can make the mixture. Even if the temp sensor gives a bogus value of say 0 deg Celcius, the multiplier value typically tops out around 1.35, and although it would create an artificially rich condition, it is still an operable condition and not a stall situation that you are experiencing.

Hope that makes sense.

I was told it would read down to -40 and dump up to 30% more fuel. When I half throttle it it kills the inj pulse and fires up......weird, I hope its this I have a map sensor also if not. May have to hook it up to Comp if this easy fix doesn't work....

Ken, I wasnt saying I think its the temp sensor necessarily but that was a example and why you should be scanning it and seeing IF any info is way off causing your condition , you can sorta test the map sensor by simply killing its vacuum with it running, if you remove its vac source while idling the ecu will think its at 100 map and boat will run even worse, Im not sure what the default if its unplugged is but you could unplug the wires to it and see what happened, you could also unplug the temp sensor wire with motor running and ground it so it goes to each end of the spectrum. I would have it scanned before you start throwing parts at it but when I say scanned I mean plugged into something that will show parameters NOT just read codes, Smitty

I had several people mention the sensors Smitty, I've got access to a comp it's just a 3 hour round trip with traffic, etc... If the coolant sens doesn't fix it i'LL PUT THE MAP ON IT. iF THAT DOESN'T WORK i'LL RUN IT OUT THERE FOR A SCAN...I'd rather spend $100 on parts than loose half a day in traffic You got you're boat out yet?? I've been thrashing the last 4 weeks trying to get this 33 up to standards..... I appreciate you're help Brother.

Looks like I'll need to hook it up after all....the temp and map sensor did not fix it.

The injectors will be sent off Monday to be tested, going to rule that out in the process of eliminations.

Everything checked out on the computer, No codes no issues with the tune....We pulled all kind of fuel out at idle and adjusted the AIC motor speed, etc....Still acting up. Would a bad coil cause this?? I find it hard to believe that 8 injector would leak at the same time and conditions. Would the fuel regulator do this? It's not leaking and it holds a constant pressure...Our A/F meter sensors where bad so I did not get a reading on that(Which would tell a lot)....but the plugs are black as hell borderline fouled at idle.

It sounds like your tune at idle is too rich if the sensors are good like you said.

When it stalls, is it like a rough idle from loading up and then stall or is it a clean/quick stall.

Ive never messed with the Merc stuff, but do you have a way to adjust the tune yourself?

Does the Merc stuff have an Afterstart Enrichment adjustment? Basically it gives the motor a little more fuel a couple seconds after it starts to help keep it running, like keeping the RPM's up in a carb'd deal. (just not needing increased RPM's to do the same thing). If that's too rich or too lean it will let the engine die after its initially started for a couple seconds.

Also get a new o2 sensor, without that youre kinda guessing which can get frustrating.

what does scanner pro report at Key on Engine Off. Look at the dash then check the item list? What's the reported BPW, IAC Position,, TPS voltage and percentage, (MAP) = KPA and KPA Raw, KPA Voltage. Compare your logs from when it ran great to when it started acting up.

Verify your ECU Ground