Mefi 3 idle problems/throttle ??
 

I have a procharged 522CI( 1997 502 mag MPI) with a mefi 3. This past year you can start the boat and it fires immediately but then stalls. Then you have to push the throttle about half way and crank before it will start you can't cut the throttle fast or it will stall and have to repeat the part throttle start. I also noticed the plugs load up easier now. I changed out the IAC motor thinking that was the problem. I'm going to try and get the codes read soon. Just wondered if anyone else had this problem before.....Also, how do you clear the codes on a Mefi??

Look at it with a mefi program and see if something is screwed up, example, eng coolant temp sensor is bad and tells the mefi its -40 so it adds 35% extra fuel. I used to think it was screwed up that Tyler Crockett didn't graduate the temps and corrections all the way down but in reality you will never boat below 60 degrees motor temp so if mefi adds 8% more fuel at 60 degrees you put that 8% in all the way to bottom in case sensor shorts out or goes open and motor thinks its to cold or too hot. In your case maybe a local mefi tuning guy could drive in boat with you and see where problem is?

Would a scan show a bad temp sensor?? It ran fine before on the current tune. What you say makes sense.Thanks for the reply...Beginning to think I've been blacklisted on here....

The transom should be really black though, Right??

I am haveing the same problem with a MEFI-3 and have narrowed it down to the timing not advancing off base timing. I just started a thread asking for other ideas? Sorry I didn't see this thread first.... I'm hopeing it is just the ignition module. Should have a new one today and will post if it fixes the problem.

Ignition module was the cure for mine. Idols fine and doesn't stall any more.

The fact that it starts with half throttle leads me to believe you have too much fuel pressure at idle or perhaps leaky injector(s). Half throttle sends the ECM into flood clear mode (shutting off injector pulses). That's my first stab at the problem.

+1,,or the fuel pressure regulator's diaphram ruptured and is leaking fuel past it..

My regulator is plumbed after the fuel log. So that would cause a loss of fuel pressure i would think. It has gt has the correct pressure with no fluctuation. The plugs all look the same so I don't think leaky injector. The temp sensor does make sense. I need to get it fixed, I have the boat sold.....

I did not know that about the throttle!

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

whats the fuel pressure? is it different from the time it ran great?

The fuel pressure is the same as when it started fine. The tune hasn't changed. We messed with it to see if we could clear it up and ran it down pretty lean. We adjusted on the IAC motor to see if we could catch it before it stalled. Like I said , it's hard to imagine all the injectors leaking but that is the next step I guess. The fuel filter looks good so I can't see trash being a problem
.

If a ground was bad wouldn't it be all over the place instead of just idle?? I'll check it anyway though It always seem to be simple sh*t that gets ya.