www.iFourWinns.com

One possibility is the analog input that measures the voltage from the MAP sensor is not working correctly on your ECM. Watch this video on how to check your MAP sensor.

http://www.youtube.com/watch?v=B8EVhFc5Yqw

Use a vac gauge and your volt meter to check MAP voltage at the sensor and at the pin on the ECM harness. They should be the same if your wiring is good. If you have access to a data link tool, then you should be able to read the voltage sensed by the ECM using the monitoring tool as well. The values given by the guy in the YouTube video should be correct for your engine. If you get the correct voltage values at the sensor and the ECM pin, but something different sensed by the ECM then it appears the ECM input may be faulty. The MAP sensors are so cheap ($30 to $70) that is might be worth just replacing it and see what happens.

Here are some good resources:

DELPHI MEFI3 EFI Service Manual:
http://www.pleasurecraft.com/manuals/L510004.pdf
See PDF page 27 and 32 for MAP sensor data and page 118 for a wiring diagram showing the MAP wiring to ECM.

Buy a new MAP:
http://shop.advanceautoparts.com/webapp/wcs/stores/servlet/product_Map-Sensor-Delphi_25986788-P_414_R|GRPSENSAMS_906709620____#
If you don't have an Advance Auto Parts nearby, then go to your local parts store and tell them you want a MAP sensor for a 2000 Chevrolet Silverado 1500 with the 5.3L engine. This is one of those few marine parts that is interchangeable with automotive parts so don't feel like you have to buy it from Volvo for $200. It's the same part. I would stick with AC Delco or Delphi branded parts if you can.

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Jim
Richmond, Virginia
2005 Horizon 230 w/ Volvo 5.7GXI Duoprop
Towed by: 2007 Chevy Tahoe 4x4 LTZ

Jeepman,
That MEFI service manual is an excellent reference. Page 182 also has diagnostic procedures. As jvthundercat recommended, check the connections from the wiring to the ECM, it will be terminals 3, 18, 19, 27.

Since the MAP issue follows the ECM, I'd guess that the problem is either the ECM connector or internal to the ECM. If it was MAP or wiring I would think it would stay with the engine but stranger things have happened that don't make sense.

_________________
Terry
Current: 07 Crownline 255 CCR cuddy - 350 Mag MPI/B3 "Casi Cielo"

Previous:97 245 Sundowner 5.7GI/SX

Tow vehicle: 1986 GMC 2500 Camper Special 454/TH400

You could try swapping the MAP sensors and see if the problem swaps with it.
Rob

_________________
Anything Worth Doing Is Worth Overdoing
2001 Horizon 180

I'm with you on this but the MAP input into the ECM is a simple voltage measuring device. It should be very reliable and should not require calibration. From a probability standpoint, it is more likely to be a wiring or sensor issue. The fact that it follows the ECM obviously suggests it is internal to the ECM though.

Is there any chance someone flashed the ECM and updated it? They might have flashed it with the wrong software (fuel map) for your engine. You said you have had engine work done recently maybe this is a possibility?

The definitive test is still to send a 0 to 5 volt input to the ECM's MAP input pin and see what it is measuring using the data link tool. Your volt meter and the ECM should read the same within a percent or two. If they don't and you have checked the wiring, then you have confirmed it is internal to the ECM and you will have to replace it.

_________________
Jim
Richmond, Virginia
2005 Horizon 230 w/ Volvo 5.7GXI Duoprop
Towed by: 2007 Chevy Tahoe 4x4 LTZ

It's been a little while, but I just wanted to give some updates incase someone else has similar issues. I had the suspect ecm reprogramed, but it didn't help at all. Same problems, same symptoms. Finally tested the reporgrammed ecm at a local go-fast marine shop, and got some answers. He explained that it looks like the controller has a bad driver in the computer that can not be repaired for a reasonable price. The ecm thinks it's working correctly (which makes it almost impossible to diagnose), but is incorrectly changing some of the sensor values.
Unless you can find a good used mefi 3, (ebay, etc.) then I need to replace it with Mefi 4b. Looks like the exact same controller, but the pins are in different order. So, either new wiring harness ($600) or change the wiring on the connections. This shop recommended a few suppliers that they work with. I ordered the new mefi 4b controller and new connectors for $748.00 I will be hooking it up sometime next week, I check back with results. $750 sucks, but it's better than the $2400 that FW wanted.
At the go fast shop, I saw some incredible rigs. 1100 hp 555s, double superchargers, 135 mph fountains, really cool stuff! We were laughing about dropping new power in our boat. For only $100K he thinks our 328v could hit 80! Tempting

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Lakebum
2006 378 Vista
Nashville, TN
Current
04 Hustler Cheetah
06 Seadoo sportster 150
Past
06 378 vista
328 vista
240 horizon
21' glastron
20' celebrity

Glad you found a "reasonable" solution. I'd like an 80 MPH 328......

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2001 Horizon 260 - 7.4 Volvo GSI DP

FINALLY, PROBLEM SOLVED!! Got the new mefi 4b ecm on Friday, repinned the connectors and hooked up the new computer on Sat. Cranked the engine and it purred just as smooth as butter. Push the throttles forward and it matched the other engine perfectly. Went out for a ride and accelarated like it did before. I changed the plugs and added injector cleaner to help clean out some of the carbon build up from running so rich. It was a good weekend.
If anyone else has ecm/controller problems, I've aquired a few service manuals for engines, efi, ecm, and ignition pdfs.
Most service techs and dealer service departments will tell you that you have to get a new wiring harness if you change mefi from 1-4. That's not true, I've got the wiring diagrams to work around it.

_________________

Lakebum
2006 378 Vista
Nashville, TN
Current
04 Hustler Cheetah
06 Seadoo sportster 150
Past
06 378 vista
328 vista
240 horizon
21' glastron
20' celebrity