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Hi:
I am a Volvo owner of many years, I have had 240, 740, 740 turbo, 760 and a 780. I love the car. My kids drive them too! I am retired, so I tinker around. My mechanic experience is self-taught. I have put in a turbo, removed and replaced 16 valve heads, done the brakes and played with all the sensors, distributor, bushings, trailing arms and other suspension, kick-down cables and transmission filters and flushes etc., but I have never experienced the problem I now have.
I have a 1989 740 B230 (plan Jane) that has a very sensitive knock sensor. It arrived one day many months ago and I am stumped. The only code I get is 143. It is classic, in that at about 3000 rpm it will cause check engine light to come on. But it doesn’t always happen. It usually happens in hot dry whether, but has happened in damp weather. You can almost sense when it will come on. Days go by without incident, then bang. I have re-set the code far too many times to count – afterwards it idles well, will perform well. Once check engine light comes on it creeps to cruising speed, but gas consumption is not significantly affected. Octane booster additives make no difference.
I have put in a new one with no luck. I have rewired the thing. I have cleaned all connections in that circuitry. I have replaced the air meter. I have replaced the ICU (ignition system control unit)(under dash at steering column). I am careful with the torque of the item (8-10 lbs). I have checked the O2 sensor for micro voltage comparison (it is a new O2 sensor). I did find that my timing was off (about 3 degrees), but even correcting that has not improved the condition. Volvo experts at dealers and other friendly shops have said I have tried everything they would do. This I doubt, cause I have trouble believing after 169,000 miles it (my car) wants to drive me bonkers. My distributor is good/clean and gapped. I have new rotor button. I have new and accurate gapped spark plugs. The wires have good continuity. All connections (involved – that I know of) have been cleaned and dielectric grease applied. I have re-tensioned the timing belt. The throttle position switch is accurately set. . I have replaced master ECM (inside kick panel at passenger location). I have even switched gas caps. The idle motor is good and clean. There are no leaks in the crankcase ventilation system (the oil trap and flame trap are clean). The guidance I get is that only in desperation should I change out the FCU (so I have that to do – if and when??). I get excellent mileage, just degraded performance when check engine light is on.
I have used new parts, old parts, re-used certain parts, all for naught. Of course I could be just unlucky (but doubt my luck is all bad), but I still get the same (and only one) code - 143. I have a Bosch system.
Any ideas? I would really appreciate some feed back. I have confidence I will solve this but I feel I am now looking in the wrong places and I do not know where to look now. Thanks much.
CRD
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