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Fuel Control Unit + Ignition Control Unit? 850 1993

posted by  Buddha001 on  Wed Oct 13 05:22 CST 2004
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Hi All,

I've recently had my check engine light come on repeatedly with a fault code pointing to the TPS. I've had it replaced twice now within the past year only to have the check engine light come back on. Lately, the car has also had some problems idling (it sometimes will just sit there and fluctuation, drop to 500 rpm, go back up to 1250rpm) and when driving can seem sluggish and like its going to lose power after 2500rpm. If I press the gas pedal all the way down it kicks and gets back to normal, but as soon as I release the pedal it seems to go back to doing the same thing again. This is random however, since it only does it sometimes. It's perfect sometimes and problematic at other times.

I took it into my local indie here (Nordic Motors in San Carlos, CA) and they said they swapped out the Ignition Control Unit and Fuel Control Unit w/another 1993 850 and only then did it work properly. However, I'm skeptical as I've called dealers, IPD and FCP Groton and all say that those parts are rarely, if ever, in need of replacement. Guy at IPD said I was the first person since 1993 to even ask about it.

So, do any of you share my skepticism? If you do, what other possibilities do you think there are? I was thinking possibly MAF sensor, dirty throttle body or stuck air flap, do any of those make sense? I'd appreciate any comments/suggestions. Thanks in advance!

Nigel.








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    Fuel Control Unit + Ignition Control Unit? 850 1993

    posted by  someone claiming to be ksg on  Wed Oct 13 07:47 CST 2004 [RELATED]

    To me your ideas make sense. I too have heard from pro mechanics that most control modules seldom go bad - one person said he had seen it "once or twice in my career". (I do know of exceptions such as early Ford and GM electronic ignition modules). More often it is a bad connection or external sensor.

    On a Volvo 240 I had similar behavior (after a very short while the car would not idle beyond a couple of seconds after starting) which was traced to the MAF sensor. On that car disconnecting the plug to the bad MAF sensor resulted in a smooth idle but barely enough power to get the car to move at all (i.e., in limp-home mode, no fuel enrichment with increased air flow). I don't know if that diagnostic test would work with the 850. If you try it you will get the check engine light which you will then have to reset.

    Is it possible the throttle body shaft is badly worn? On a much older Volvo 164 I had, the TPS was built in such a way that it would not stay aligned if the throttle body shaft was loose or ran out.








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      Fuel Control Unit + Ignition Control Unit? 850 1993

      posted by  Buddha001 on  Wed Oct 13 12:33 CST 2004
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      Yeah, even the mechanics that came up with this diagnosis said they haven't had to ever change these things out. However, they said they had another 93 850 come in and they swapped out both modules and put them in my car, one at a time. It wasn't until they put both of the other car's units into mine that mine worked properly. They then took my units and put it into the other car and they said that within minutes the Check Engine light and all other symptoms that I was happening started occurring on that car. I'm fairly sure I can trust these guys that they're not lying about this part. When I asked about the ideas I had, they said they had looked into everything and even tried putting in a new MAF sensor which didn't help things any.

      So, at least to me, that's pretty compelling that something is wrong with these damned things. Anyone else think it still could be something else? I asked them about a warranty on this and they said that if they swap out these units and it turns out not to be problem or that they are somehow defective too, they'll replace them. I'm guessing I just have bad luck or something. :(

      Nigel.








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        Fuel Control Unit + Ignition Control Unit? 850 1993

        posted by  porkface on  Thu Oct 14 09:46 CST 2004
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        last visit: Fri Oct 24 09:12 CST 2014
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        i have not run into this on any volvo, both ecus fix the car. that being said, the evidence points to that being the problem. highly unusual and i can't think of any circumstances, other than bad ecus, that would change that. i would seek out a 2nd opinion and don't mention the ecu swap with a known good car. if they come to the same conclusion, i guess go for it. or, order the motronic books for your car from volvo and see what they have in common. keep us posted, please. chuck.








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          Fuel Control Unit + Ignition Control Unit? 850 1993

          posted by  Buddha001 on  Sat Oct 16 06:56 CST 2004
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          Hi Chuck,

          So the mechanic found a couple ECUs from a wrecking yard and swapped them into my car and the check engine light apparently turned on even faster then with my parts. I'm pretty sure these guys did a good diagnosis as they tried swapping out everything they could before going to the ECUs. I've been taking my car to them for a year now and they've never tried to screw me. In fact when I took it in for the check engine light, they replaced the TPS sensor and it came back on. I took it back in and they had it for a few days swapping things out and they couldn't find anything, but they did solder a couple wires they thought had some loose connections. They probably put about 10 hours of work just driving it around and screwing with things but didn't charge me because they couldn't figure it out.

          They're currently looking for some better ECUs, so until then I'm w/o my car but at least they're making sure it works before they give it back to me. If anyone knows where I can find some decent used ones (since they apparently never go bad, except for mine), I'd appreciate it. Not sure I can afford brand new ones right now (one is about 1K and the other is about $825 new).

          They too said that they've never ever had to replace both the ECUs. I guess I have bad luck, but hopefully it'll get fixed soon. Will keep everyone posted on this one.

          Nigel.







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