Volvo Penta 4.3 GXI-G

[gusutavot800]

I have a 4.3 GXI-G with 340 hrs, regularly maintained and no major issues with it until now. After the engine over heated once, it started bugging at mid range ( 2800 rpm to 3800 rpm) at idle and full throttle runs fine, but at mid range is not. After inspecting ignition and fuel related components did a compression test and found 1 cylinder with no compression (20psi) pulled both cylinder heads out and found 1 exhaust valve seat had come off. Sent both heads to a machine shop and had them go over, they cleaned them re surfaced them put new seats, guides and seals. Installed everything, compression is at 150 psi on all cylinders with a cold engine but the problem remains the same, no change at all. I haven't checked the ignition timing because don't know which wires to jump to get the ecu to base timing. I'm at a dead end at this point and ran out of ideas, if anyone could help me I would truly appreciated.

Thank you

 

[Walt T]

Click your heels together three times and whisper "Verify firing order and then re verify" As for timing I believe it is set at 3000-3500 rpms. 3200 is what I think. 30 degrees total advance. As for the problem still there, if the above doesn't help check fuel pressure after verifying fuel filter is okay. I'd replace it if you haven't already. Cam/Crank sensor, knock sensor all come to mind.