Volvo Penta GXI B Starts and Stalls

[Chuckberg2]

Hello, thanks in advance for any help or advice
Have a 2003 VP 5.0 GXI B with 326 hours Ran good Thursday would start and stall on Friday, pumped throttle it threw an alarm code Map sensor 34 (Rinda Techmate) scan tool and it would stay running, not correctly but would idle all day. My first thought was fuel relay so changed that , no joy, Tested the map sensor and tested good, added New anti siphon valve, Fuel filter, pressure tested fuel 8 pounds low side 55 high side during priming and running and held 55 pounds high side when shut off, Changed IAC valve (shot in the dark) disconnected TPS pulled a low voltage code and audible alarm but it idled until Connected it back up and it shut the engine down, Disconnected batteries for 30 minutes and hooked back up.Tested every ground I could find, cleaned up made sure tight, checked J1 and J2 pins for continuity to ground and we are all good there, relays are getting the power they should be. the trim switch at the helm was shorted out, fixed that, added a new cap and rotor.
When the system goes into default mode due to a faulty sensor, does anyone know what other sensors are put into default mode to allow engine to run, just so i can narrow down how many I have to check? been after this a while, got the schematics and the service manual downloaded but keep going round in circles, only codes I am getting are self made to get the engine to idle so I could maybe diagnose with scan tool.
thanks

 

[Chuckberg2]

I want to add replaced the TPS after it shut the engine down after reconnect, still no good.

 

[four winns 214]

Wish I had a solution for you. I have same engine in a 2002 Four Winns. Runs great now, but I'm waiting for the electrical gremlins to appear. It is 15 years old and those things happen. Please post here if/when you find the fault.

 

[Chuckberg2]

Thanks Senior Chief, I certainly will, It is programming, not magic, if they (Volvo) laid out the series in progression how the beast thinks and responds, I think I could back track it down.
No Trouble codes until I force one, 30 years ago would be a key switch, or a fuel relay, $25.00 parts to $2,000.00 parts

 

[Chuckberg2]

Looking more and more like the ECM quit, still testing circuits in the main data cable for continuity so far all grounds are good, and no shorts to ground in the other pins, I am just not ready to pull the trigger without a difinitive yes thats it.

 

[Chuckberg2]

just an update, sent to Volvo to put on computer to scan systems, will let you know what they find.

 

[Chuckberg2]

Well we took it to a Volvo shop, it was the map sensor, the circuitry to the map sensor was fine, i could not get it to throw a code, so did not want to spend the $250.00 on a sensor unless I was sure. The Volvo certified software was well worth the $110.00 just the 5 week wait to hook it up for 10 minutes sucked.