I am a newbe who posted this in the wrong section first, and if this question has been answered my oppologies. After several trys with this search engine I found nothing at all.

I have a 1990 740 Regina 4 cyl (new to the car and not sure if it is GL or what) Does have power windows.

Question: Are ECU brains interchangable as long as they are the same manufacture? Mine are Siemans and the original Volvo number is 8601056 the Seimans number is S101590202E. I found one in a junk yard that is Volvo #6842882 the Siemans # S101590202A. I drove the car home from the junk yard using the junk yard ECU. It did fine on the highway but when I came to a stop it sputtered and cut off similar to what the original does, except it started back easier.

My problem has been after car has been driven for 30 minutes or more it stumbles or completely shuts off when taking off from a stop. After pumping the gas it restarts and runs fine until the next stop. If I keep my foot on the accelerator (rpms above 1000) it usually does fine. I have a 3rd used Air Mass Control and it has done fine today. However the outside temp today is in the low 70 F. When I first started to work on this problem the temp was high 80's F to mid 90's F. I am not sure that would make a difference but it could.

Thanks and look forward to owning or blowing up this Volvo depending on whether I solve it's problems.

BTW I have replaced the Idle Air control valve (with used one that works) also the Air Mass unit (tried 3 different used and it seems to have fixed the problem). New Fuel regulator? on top of the fuel rail. And New fuel filter. I have not replaced distributor cap/rotor, plug wires or plugs, but I plan on it.

 

Well, the Regina ignition uses a MAP sensor, not a MAF sensor. I'm assuming you're swapping like for like. My 90 was a Regina before I put the V8 in it...or I'd run look what number is on the ecu. If the jy unit does no better but no worse, I'd put the original one back in and save the jy unit for back up. I'd do the basics that you haven't done yet before you start chasing gremlins. Caps, rotors and wires can cause a bunch of problems. You say you replaced the fuel pressure regulator? Did you get one for the Regina set up? Bosch cars use a 3 bar regulator but Regina's are only 2.5 bar.

 

I actually bought the FPR from a Volvo dealer to make sure it was right. I was told if you don't replace it it will ruin the fuel pumps so I didn't want to risk extra expense and bought it new. I agree about the basics but I am determined to fix the stalling problem first. Since it runs well except on take off and the problem seems like lack of fuel. If it was rich I could smell the gas but the smell is more like vapor lock or lean running. And yes I have exchanged like for like on the MAP. Sorry, I am a newbe and this car has parts and vaccum hoses like I have never experienced. It is warmer today so I am going for a drive to see if I have sovled it.