MasteRX

Okay, i am having a problem with my car running lean on low RPM acceleration, but the problem can occur throughout the RPM range sometimes as well. My A/F ratio guage will often show no lights indicating a really lean mixture on acceleration even under light throttle until the secondaries come on. Sometimes I am lucky and it doesnt do it. It won't do it unless the car is warm, when it is cold it runs like a dream. Also, often when it is not running lean, the fuel ratio will bounce around from way lean to almost rich, up and down, continuously; this condition only happens under steady throttle. I believe it is related to one of the sensors, but I was wondering if anyone else had any experience with this. Please help me out.

Also I had a question regarding the proper resistance values of the TPS. I was looking at an '88 mazda manual and it said that the proper values were as follows:

terminals A-B:

idle: approx 1 ohm
full throttle: approx 5 ohms

terminals A-C:

idle: approx 5 ohms
full throttle: approx 5 ohms

On my TPS the values for terminals A-B are within range, but for terminals A-C the idle value is correct, but at full throttle it goes to just 1 ohm. Is this faulty? Or is there a typo in the '88 manual I am looking at? It seems silly that the value is not supposed to change from idle to full throttle.

All responses appreciated.

Keith

The manual is wrong. You (and your car) are correct, sir. While you were at it, did you check if the resistance varied smoothly from 1 kohm to 5 kohm without any jumps to 0 or Infinity? If there were none, your TPS is good and correctly adjusted, and that is not your problem.

The most suspect on my list would be the Oxygen sensor. When they are going bad, they tend to always read lean and respond very slowly, which is what it sounds like yours is doing. Also, the ECU doesn't pay attention to it until it warms up, so your car would be fine cold. Thirdly, you are reading off of the sensor on your guage, which would mean that your car is actually running much richer than your guage indicates. I would replace it, after all it is the reference for your A/F guage, and if the indications remained the same, you could then feel confident that your readings are reliable. Have fun!

Irv, Keith's dad

Scott 89t2

it should bouce back and forth under normal driving.... that is your ecu working.

HAILERS

I don't disagree with anybody, but I do agree with the normal condition of the bouncing from rich to lean. Thats just the ECU trying its best to find stoic, or maintain it. I use a volt meter taped into the 2d wire on the ECU to monitor my o2 sensor and that baby at steady throttle jumps on either side of stoic constantly. If the throttle is depressed enough that the tps reads above 4.5 volts(its max output) then the 2d reads a steady reading like .7 or so. But the main reason I wrote is to ask MASTERX if you still have your air pump and acv active on your car?? If you get time will you please give me an answer? Also this site http://autometer.com/hp/index.html under products tips/faq there is a writeup on air fuel gauges, o2 sensors etc. Sure would like to know if you still use the airpump and acv.

MasteRX

Update: I had a hunch that it might be related to the boost sensor so I disconnected it, and now my car runs fine. It does run a bit rich all the time though, so I want to get the boost sensor replaced soon. I wonder though if disconnecting the boost sensor really just compensates for another problem that is still there? Well, I'll keep my fingers crossed.

HAILERS

In closed loop the af gauge should go up and down. When you depress the pedal enough, the tps and the tps voltage goes above 4.5 volts, the ECU goes into OPEN LOOP. The ECU at that time does not use the 02 sensor anymore and relies on *maps* for fuel delivery, therefore you then do not have the up and down on the af meter. If you are in the closed loop scenario, the ECU looks at the 02 sensor and makes rapid corrections to the mixture. If it shows too rich, it sends less fuel, when it sees lean, it sends more fuel. It does this rapidly. Thats why you see the meter constantly going up and down, and why you see a constant reading when in open loop. Also if you are in closed loop and let off the gas or back off the gas, you see a lean condition because the ECU sees through the tps and the boost sensor that less gas is needed so it leans off the mixture. You took off the boost sensor plug and the ECU has gone to a fail safe mode or value. Probably going to do what you see, run a touch rich. You can test the boost sensor with the manual that is on line if you have a Mittyvac or some kind of vac pump. The autometer.com site has a good explanation of how the gauge works. If you buy another boost sensor I suggest the wreck yard. Maybe 10-bucks max.