Carver Owners Forum

Engines 2001 mx6.2 merc mpi......I would like to use this thread for this type of discussion for anyone.....In a short while, hopefully, I will be getting the boat ready and want to go thru each engine and check harness plugs,grounds etc because at the end of the year the port engine would try to stall the odd time when you pulled the throttle back quick..otherwise ran like a champ, great fuel mileage etc.......I will clean the plate on the Tb, lube the linkage, and check the iac filter etc....have new iac's and tps for both....there does not appear to be any codes as there is only one beep when ignition turned on. I will get tech to check for codes after all that. So I guess the question....what is in charge of controlling the fuel when you pull the throttle back to idle quickly.?????thanks guys......

Checking the readings with Merc diagnostics will help. I think you're on the right track with the IAC and filter. Since you already have a new one, try replacing it and only it first then try to duplicate the problem before you replace another component. You can also swap a component from one engine to the other and see if the symptom follows the part. That will leave no doubt but again, swap only one part at a time then run the engine.

bud37 wrote:Source of the post ....what is in charge of controlling the fuel when you pull the throttle back to idle quickly.....

The ECM/computer controls fuel delivery at all times based on data received from all the sensors. It takes this data then refers to an on-board table to determine how long it should open the injectors for.

bud37 wrote:Source of the post
I will clean the plate on the Tb, ....

It is not really the plate that is the issue (well, I guess if one got REALLY gunked up!)... but it is the sensor in the throttle body. Not sure of the exact model on yours, but if there is a wire running across the opening then clean that CAREFULLY.

That's what senses the flow of air and density so that the ECM can meter out the right fuel.

The IAC is also a good suspect. If you bump it in and out of gear a few times and it dies that's what I'd check first.

Vacuum leaks could also be giving the engine trouble and having the IAC and ECM work "overtime" to keep things in shape.

There is really no issue in and out of gear, smooth ,no drama, it is only when you pull the throttle back fast......example would be docking and you need to blip the throttle, have to pull back slow or it acts as if it will stall or sometimes does.....trouble with this is it does not show the same every time.
There is no wire (mpi), sensor is in the manifold......the only thing that was different about this side was the flame arrestor was filthy, I cleaned it but made no change....there was actually a bit of crud on the edge of the throttle plate.......Mathews finally scored, nice.......

Okay I have been thinking ( could be dangerous).......let me know if this is right so far, now the injector pulse widths are controlled by a chart/map programmed in the ecu......so if the sensor for the engine temp fails , does it fail so that the ecu thinks the engine is cold all the time and then over fuels accordingly, and the same for the rpm sensor, would it fail showing high rpm or low and create the same scenario.....I get that you would see a failure code, just like to know why and how.......

RE: " if the sensor for the engine temp fails , does it fail so that the ecu thinks the engine is cold all the time and then over fuels accordingly..."

You should have two temp sensors... coolant temp and intake air temp... but either way...

Could fail either way (short or open). However, the ECU should be able to determine that it failed because it is way outside of "normal" temperatures, for example showing a temp of 400 degrees or minus 100 degrees. Once the ECU detects that out-of-range condition, then it "assumes" something safe... and will usually skew to a slightly richer fuel mixture.

RE: "and the same for the rpm sensor, would it fail showing high rpm or low"
RPM sensor is different. It's just sending pulses as the crankshaft turns and counting the pulses. If it fails, then the ECU doesn't even know if the engine is turning and probably won't start at all.

Viper wrote:Checking the readings with Merc diagnostics will help. I think you're on the right track with the IAC and filter. Since you already have a new one, try replacing it and only it first then try to duplicate the problem before you replace another component. You can also swap a component from one engine to the other and see if the symptom follows the part. That will leave no doubt but again, swap only one part at a time then run the engine.

I agree., am a great supporter of the change only one thing at a time camp......I will check every connector first as this was the side with the plugged deck drain.......

I would have thought that the intake air temp would have a much smaller effect on the fuel pulse width than the engine coolant temp, yes /no??.....a question, is there a head temp sensor in this package??........

bud37 wrote:Source of the post I would have thought that the intake air temp would have a much smaller effect on the fuel pulse width than the engine coolant temp, yes /no??.....a question, is there a head temp sensor in this package??........

All inputs together make a difference in pulse width control. Air temp is just as important. Air temps have an effect on fuel burn so the ECM needs to compensate for that.

No head temp sensor.

Do you have serial number handy for your engine that you can post?