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fuel trim errors 850 1996

posted by  Lobito on  Wed Sep 1 15:54 CST 2004
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I am infrequently getting CEL warnings regarding fuel ratio errors on my wife's 850 Turbo wgn. Car is running fine, just have the annoyance of the light coming on and worrying my wife :-) I have had to reset a couple occurences of both P0170 long term fuel trim and P0171 - system too lean. When I watch the real time fuel trim reading while at idle, WOT, and part load it looks to be normal but my long term is way out there at about 22-25%. Over the past year I have replaced both O2 sensors, looked at all of the usual vacuum leak suspects, and used a stethoscope to listen for vacuum leaks while engine was running. All of the normal "tune-up" items were done within the past 18 months -- new plugs, wires, cap and rotor, air filter, fuel filter. Anybody that has any helpful tips, let me know. Thanks








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    fuel trim errors 850 1996

    posted by  someone claiming to be bl on  Wed Sep 1 16:48 CST 2004 [RELATED]

    I had a similiar problem on an 96 850 NA engine this spring. I kept getting a long term FT error (are you using Alex Peper's software?) but my other code was "system too rich". To make a verrrrrry long story short, the O2 sensors were wrong. I changed them myself. As they were new, they were overlooked by my regular mechanic as a source of the problem. After he tried numerous other things w/o success, I finally took it to a different indy who found the problem right off. Apparently, many mechanics and o2 sensor vendors have charts showing the wrong sensor number for that engine. He changed them (again) and presto, the car has been perfect since. Won't go into how much this episode cost me. Just a thought.

    bl








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      fuel trim errors 850 1996

      posted by  Lobito on  Thu Sep 2 05:22 CST 2004
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      I'm pretty sure the O2 sensors were correct. I ordered them from IPD and checked the part #'s as I installed them. I guess anything is possible though. I have a scanner from Scantool.net and am using their software. Seems to work fine. It would be nice if it could reset the service light as well but that's a Volvo specific thing.








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        fuel trim errors 850 1996

        posted by  someone claiming to be bl on  Thu Sep 2 10:31 CST 2004 [RELATED]

        You're probably OK on the sensors then. I'm an idiot for not checking the #'s when I made the swap. Pepers's software is supposed to reset the service light on 96-97 850's although I haven't tried it yet. As the sensors are right, I'm kinda out of ideas as to your fuel trim error. There is a forum on volvospeed.com that is specific to the 850. You may find more ideas or the answer there. Good luck

        bl








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          fuel trim errors 850 1996

          posted by  Bjorn Smeds on  Wed Sep 15 13:46 CST 2004
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          I had same code on a volvo c70, checked for vacuum leaks but wasn't any, ended up changing the air mass meter, and no more codes... Sometimes if an air mass gives the wrong signal, usually during part load, the oxygen sensor will notice that the fuel mixture is too lean and try to compensate for it, but if it is way off it can't and therefore will trigger the fault code.

          If possible try to hook up a volt meter to the front oxygen sensor and check the readout during acceleration if it goes down and stays low. If it does there is really only 2 things that could be faulty, Air mass or low fual pressure/clogged filter.

          Only bad thing is the Air Mass meter is kinda expensive to buy just to try it :) so if you know anyone that has a volvo with the same one on , you could try to swap it.

          Bjorn Smeds / Swedish Motors LA







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