MAF sensor and O2 sensor bad?

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Michael Gain

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Sorry for the delay. Fan, thermostat, and fan relay were replaced at the same time. I am guessing that the sensor is faulty. Hence, reading low temp and potentially explaining my burnt oil. (Not too excited about potentially overheating the engine every time I drive it). It definitely takes longer than 5 minutes to register 1/2 way on the temp gauge.

New MAP/T sensor and rear vacuum line installed (different color internal o-ring and fits a little more snug). I also figured out how to release the MAF connector pins.

MAF connector:

IMG_20210328_132454.jpg



Brown/pink wire's pin:

IMG_20210328_132621.jpg

IMG_20210328_132534.jpg


I cleaned it up with some connector cleaner and elbow grease, but could not really clean out the inside.

New fuel trims and timing advance. Still reving in park:

Screenshot_20210328-135049.png


Timing advance was 57.5 degrees for 1500 rpm and 2500 rpm. Seems pretty high, but I have not had a chance to research that much. For a forced induction engine, I always thought timing advance should be no more than 15 degrees.

Screenshot_20210328-135152.png


New intake air temp sensor and coolant temp sensor will be here tomorrow.
 

jlglr4

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Fuel trims at idle don’t look bad. A little lean, but well within normal range. They get less lean at the higher idle, but still not bad. I assume this with the engine warmed up. That shot with the idle trims shows 731 rpm. Is that the surge in the idle, or is that a normal idle level. Its a little higher than mine normally idles at.

It’ll be interesting to see if that ECT sensor fixes the issues. Seems like everything could still tie back to that sensor.

I don’t think a bad ECT will cause you to run too hot (running a little lean or maybe with extra advance on the timing might cause you to run a little hot, but not likely enough to overheat). Thermostat will still open and close at the same rate regardless of the ECT sensor readings.
 

Michael Gain

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Unfortunately, these metrics are on the cold engine. I'll get some warm metrics on my way home today. I will say that the MAP/T sensor did not fix the idle bog.

For clarity, my idle does not surge like the other post. The 731 rpm was because the engine was cold. My idle only reduces, I experience a nice shake, and then it returns to basically where it was. Over the last couple of weeks, I noticed it happens more during stop-and-go traffic. Slight pressure on accelerator pedal and then to brake. Once the vehicle comes to a stop, the idle bogs and car vibrates. Sometimes it will keep vibrating, other times it will return to "normal".

The only reason I mention overheating related to the ECT is because I THINK the thermostat is electrically controlled. Unless there is another sensor in the thermostat. Notice the pigtail coming off the thermostat:

Screenshot_20210329-081022.png


If it is electrically controlled, a faulty ECT sensor may cause the thermostat to open early (taking forever to warm up) or not open soon enough (causing overheating); or display the incorrect temp on the dash gauge.


If I have time tonight, I will swap out the other two sensors lol.


Fuel trims at idle don’t look bad. A little lean, but well within normal range. They get less lean at the higher idle, but still not bad. I assume this with the engine warmed up. That shot with the idle trims shows 731 rpm. Is that the surge in the idle, or is that a normal idle level. Its a little higher than mine normally idles at.

It’ll be interesting to see if that ECT sensor fixes the issues. Seems like everything could still tie back to that sensor.

I don’t think a bad ECT will cause you to run too hot (running a little lean or maybe with extra advance on the timing might cause you to run a little hot, but not likely enough to overheat). Thermostat will still open and close at the same rate regardless of the ECT sensor readings.
 

jlglr4

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I had forgotten there was any pigtail on it (just changed it 8 months ago - memory is getting bad). So, it must be electrically heated. My understanding is that these are still temperature controlled, but the ECM can influence the opening and closing using a little heating element inside. Even if that circuit were to completely fail, I believe the t-stat would still be open at whatever the max set temp is, and closed when cold, so it shouldn’t overheat. Still, I understand your concern and hopefully that new ECT sensor will help.
 

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