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Participant

Join Date: Jul 2008
Posts: 2

engine trouble warning lights

07/04/2008 1:39 AM

on '93 Mazda MPV engine check light on dash stays on. Came on at 130,000k Trouble appears to be exhaust system centered any suggestion other than big bill at shop for new system?

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Join Date: Dec 2006
Location: Sask. Canada
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#1

Re: engine trouble warning lights

07/05/2008 12:11 AM

In my limited knowledge of OBD 1 systems, the exhaust only has the O2 sensor hooked in to the system and it has its own code so it should be easy to diagnose. The only other exhaust component that may cause trouble is the Catalytic Convertor and that would show up as poor fuel economy, hard to start and no power under acceleration, etc and it can be checked with an exhaust gas analyser (or your nose if you have a sensitive sniffer).

I would suspect that at 130,000 miles, the culprit is more likely to be ther fuel filler cap. Fuel tank pressure is hooked into the OBD system and often shows up randomly as the cap may still seal from time to time. Not only that it does take a few run cycles to shut the light off if it is the fuel cap, so it would appear totally unrelated to filling up or to just putting a new cap on to try it out. Depending on how much you drive, the cap would have to be on for a week or so before the light would go out.

If it is the O2 sensor, it shouldn't cost much to replace and if it is the catalyst, then that can be expensive. Many people cut the catalyst out if it fails, but you should check your state's laws about catalyst removal.

One other solution that is not recommended, but is cost effective. If the system checks out fine and the light still stays on, take the bulb out of the dash so the light doesn't bother you.

writer

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#3
In reply to #1

Re: engine trouble warning lights

07/05/2008 11:15 PM

Thanks so much for your input. I Live in a smaller community with no Mazda dealership so have to use what is available. They are good general mechanics but for diagnosis I'm afraid I'm on my own or head to the big city. This info has saved me $$$$.

Thanks again. Don Scott

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#2

Re: engine trouble warning lights

07/05/2008 3:24 AM

You really need to go back and have the code identified exactly as to what it is, to start with. "Exhaust system centered" is rather vague. I will assume that it is a reference to lack of O2 sensor voltage movement; the sensor(s) are not moving back and forth across their threshold voltage properly. The problem here is that this may be no movement, or movement not quick enough, or movement too quick.

This problem can be caused by a host of problems: bad O2 sensors, fuel supply/pressure problems, injector problems, vacuum leaks, improper air/fuel ratios, other sensors providing incorrect information to the ECM, resulting in improper outputs to the "reaction" components (again, fuel supply/pressure, as well as ignition), etc., etc., etc.

Gas cap is not probably an issue here: Most ODB I vehicles (generally, pre 1995) do not do onboard vapor control system testing. I am not sure about Madza, but I would guess they did not.

Have your shop (or another, if they can't or won't) do a proper complete test sequence: not just pull codes, but examine the ECM data stream, plus check fuel and ignition systems for proper operation. Just pulling a code and trying to "shot gun" the repair by throwing parts at it usually results in wasted $$$ and no repair.

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#4

Re: engine trouble warning lights

07/06/2008 1:19 AM

If is just a light on the dash, you could buy a code reader and reset the sensor or you could cover the light with black tape and dismiss it from your mind.

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