'91 Grand Am Check engine light

My '91Grand Am (2.5L vin U), with 103k miles has a check engine light. Checking the code is rich exchaust. Fuel consumption is high, about 18 mpg instead of normal 27 mpg. Since the weather is warmer the engine runs a lot hotter than normal (it used to do that only in 90+ degree weather). Looking at the symptoms, it seems that the car gets too much gas in the engine. This could be many things, but I was thinking to try the Coolant Temperature Sensor first. This only makes sense if the temperature gauge inside is linked with another Sensor, since this gauge seems to work fine. My question is if this is true and if there are some other possibilities that I am missing. Thanks in advance!

Reply to
Sdraijer
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Not sure about your particular application, but the temperature sensor for the gauge is often separate from the one for the ECM. I would not replace parts in the hope of fixing it, at least connect a scan tool and see what tripped the light. Could be an oxygen sensor or any number of other parts or connections.

possibilities

Reply to
Lee Richardson

Right, the scanner says "Rich exhaust", but because the car has a high fuel consumption, I trust the O2 sensor to be working fine. A CST is $6, IOW cheaper than a 15 minute brainstorm for other possibilities.

Reply to
Sdraijer

Checked the resistance over the CST and all seems nice within specs (guessed the engine temperature). Had the engine running without the connector hooked up and error code 15: CST - low temp detected. That is as expected because low temp -> high resistance. So, that systeem seems to be fine. Any ideas for the next step (e.g. how to check the presure of the fuel presure regulator)?? I expect the engine gets way too much gas in the cylinders, just looking for ways that this could happen (and only giving error code 45 - rich exhaust)

Reply to
Sdraijer

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