i have been stumped the past few days i have a 03 ford ranger 4 cylinder, before i bought it, it was going through coil packs and would run fine for a couple weeks then run on only 2 cylinders when I bought the car we tested the ECM and it was giving a weak single to cylinder 2&3 but giving a good single to cylinder 1&4. after that i buy a new ecm and program it and it still has the same weak single to cylinder 2&3, i re-ran new wires but no luck, it threw no misfire codes
Change all 4 spark plugs and see if that improves things.
Compression test the engine before spending any more on parts. Confirm the engine is mechanically OK.
A weak 2 and 3 makes me think you have a blown head gasket.
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Possibly a leaking valve. A leak down test would find that problem also.
A leaking valve would only effect one cylinder.
Tester
Are you sure? I’m trying to recall if my experience with adjacent cylinders failing due to one having a leaking valve were always on carbureted engines. But my memory is failing me and fuel injection could lesson if not eliminate the problem come to think of it.