Volvo RWD 900 Forum

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Stumbling and intermittent rough running 900

Stumbling problem with my 95-940. a normally aspirated 2.3. I was on the interstate which went from 3 to 2 lanes and a slow down. The engine ran rough and stopped. I found the fuel pump relay (new style blue in the front row) very hot. I changed the relay and was able to get it started, it ran very rough but by pumping the gas pedal once it got to 2000 rpms it smoothed out. Now I get rough running sometimes. I have changed the plugs, plugs wires, cap and rotor. I changed AMM with one from my 93-940 93 runs fine 95 starts but if I try hard acceleration at about 30MPH it bogs down for a second or two and then takes off. No check engine light.








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    Stumbling and intermittent rough running 900

    LH 2.4 or Rex/Regina?








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      Stumbling and intermittent rough running 900

      Bendix injection not Regina. I forgot to mention before the hard starting and rough running. I replaced the AMM with a used one that I had which cured most of the problem.








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        Stumbling and intermittent rough running 900

        This seems to be the classic sign of the single in-tank pump failing. The anecdotal evidence seems to indicate they last an average of 150K miles.

        The only other, unique to that ignition system, issue that does not pop codes but can cause stalling and weird running issue is microscopic between the coil-integrated power stage and the coil. This does not sound like your issue but it is free to to do an a good idea anyway. I think the FAQ's has the disassembly and cleaning procedure.








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          Stumbling and intermittent rough running 900

          I'm afraid I spoke too soon. I drove it for a couple of miles after changing the ECU and it seemed ok. My wife left for the store and had a bad miss on acceleration. Is the coil-integrated power stage Rex/Regina? I think I said Bendix earlier but should have said Bosch. Round coil on passenger side.








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            Stumbling and intermittent rough running 900

            OK, I am completely confused on what you have. Does it have a round or square coil?








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              Stumbling and intermittent rough running 900

              Sorry Round coil passenger side on the brace to the strut tower.








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                Stumbling and intermittent rough running 900

                OK, in spite of the no check engine light pull the codes for both ignition and fuel. If everything is 1-1-1 then be have to look at this a little differently.

                A fuel pressure tester on the Schrader valve could (almost) elliminate fuel pressure as a concern. I think Autozone type places have started carrying these as loaner tools.

                Everything about your symptoms seems to point toward the AMM but said you swapped in a know good replacement so it is unlikely to be the cause. That said, pins in the AMM connector have been known to be corroded enough to not pass the meager current the device uses and pins have been know to get push back in the connector no longer making proper contact.

                After that I would lean toward either the crank position sensor or ignition power stage. The CPS should probably be changed out if you have not done it over 100K miles but certainly is the insulation have cracked where the wire meets the sensor. The Power stage should be unbolted and new thermal paste applied if you have not done it in the last 50K miles...it costs only $3 and takes only few minutes.

                There are other odd causes possible but these (plus the RSR if you year has one) are the more common issues. This is assuming you have more that 1/4 tank of gas during all these issues.








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                  Stumbling and intermittent rough running 900

                  I was grabbing at straws trying to cure my stumbling problem. I changed everything that was suggested or on the FAQ's. After all the changes cold engine ran ok after one mile on hard acceleration it would stumble until 3000 rpm then smooth out. The cure was the coil. Thanks for your help.








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                    Stumbling and intermittent rough running 900

                    That is VERY rare with the Bosch coil but can happen. Luckily, since it is so rare the coils have no street value and can be had cheaply.

                    Thanks for reporting back.








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                  Stumbling and intermittent rough running 900

                  Codes are 1-1-1 I have changed the radio suppression relay, crank position sensor and the ignition power stage. When I run diagnostics the RSR does not operate, I have bypassed it but maybe this points to a wiring problem. Plenty of gas fuel pressure ignition on 45 PSI engine idle 38 PSI, but I have not run it down the road with the gauge where I could see it. I will try that next.








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          Stumbling and intermittent rough running 900

          Thanks for your help. Turned out to be the ECU lucky I had a spare. Fuel pressure looked good ignition on 44 engine running 38.







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