PCM Sensors not setting

Tiny
JRCOX2
  • MEMBER
  • 1996 MAZDA PROTEGE
  • 4 CYL
  • FWD
  • MANUAL
  • 58,000 MILES
1996 Protege 1.5 5 speed. Bought the car wrecked. 53,000 miles on it and fixed the damage and drove it to work. Halfway to work it overheated. Put water in it and checked the oil- milky. Took it to a garage and they put and used engine in it. Also needed a PCM. They put one in it but I think that they put one in it from a automatic. None of my sensors would set so I can get it passed for inspection. I bought another used PCM, because a new one costs $450, made sure it was out of a 5 speed. It ran better and it idled @ 700 or so instead of 1200 rpms. Still no setting of sensors. Took it to a Mazda dealership and they said I had a bad rear O2 sensor and a "weak" catalytic converter. Put a new rear O2 sensor in it and could tell it was running better. Drove it some more but no sensor is set. This doesn't sound right to me. I have never once had a "check engine light" come on EVER. Shouldn't my sensors set and THEN the code come up for a "weak" or bad converter? This is sort of like a catch-22 isn't it? I have to have a perfectly running car for all of the computers to tell me something is wrong? I wouldn't mind paying $499 for the converter IF it would fix my car BUT it doesn't make much sense to me. And I hate spending money JUST GUESSING. Can you please help?
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Saturday, July 9th, 2011 AT 10:39 PM

3 Replies

Tiny
HMAC300
  • EXPERT
Your check engine light should come on as soon as you turn thekey on without starting. Check to see if the bulb is burnt out first or disconnected. Then check your grounds like battery and pcm/ engine grounds. One may not have been connected when it was repaired. A weak converter may be that it's not working correctly or it may be plugging up.
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Saturday, July 9th, 2011 AT 10:52 PM
Tiny
JRCOX2
  • MEMBER
My check engine light does come on when the key goes on. The check engine light does NOT come on AND there are NO CODES when the testers are applied. If I have a problem with the converter I believe there should be a code come up AND the check engine light should come on, isn't that correct? MY problem is the CAT, EGR and EVAP sensors WILL NOT SET. Something is WRONG and no one can tell me what it is.
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Saturday, July 16th, 2011 AT 6:54 AM
Tiny
HMAC300
  • EXPERT
A bad catylitic converter willnot set a code nor will it set one for egr or evap for a converter. You need to check vacuum at idle if it's 15" or so then suspect a bad converter and disconnect and see if vacuum goes up. It shold be around 20" if it does then it's a converter or blocked exaust causing the problem. Your fuel pressure could also cause the problem it should be 27-34 w vacuum connected to regulator and 40-45 withut vacuum connected this can be a kinked fuel line if low or high or a plugged fuel filter. The evap and eger sensors will only set if they read something wrong and they aren't. You could also have an AIR LEAK between the engine and Cat converter. Meaning exaust escaping and not letting you pass your inspection.
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Saturday, July 16th, 2011 AT 1:49 PM

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