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Originally Posted by blinkwatt
Well I talked to a local independent shop today and they said if it is the o2 sensors and I dont have money for all four,I should be able to at least order a pair and change out the ones before the cats. Then I can later order the other o2 sensors after I have more money. The shop is higly recommended for Porsche work but I have never personally used them. Does this information sound realible? By the way MNBoxster you should be teaching car classes,your o2 sensor thread us amazing. Is there a way I can test them without a blow torch though?
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Hi,
Personally, I can't see replacing only the Fronts as a solution. The reason for this is that the DME compares the readings between the Front and Rear O² Sensors, and then Bank to Bank, to determine what MAP to select. You could actually create worse problems. It would arguably be better to replace one entire side, but maybe only slightly because again, the DME could go into Default MAP from the other side alone. Are the codes you're getting relative to one Bank of Cylinders? Or worse from one side? But, you still won't be doind the Car any favors driving it this way. As mentioned, see if you have someone who can Spot you the Cash, this would be best.
There is a Test which you can do on the Car, but it's not, IMHO, any easier. Here are some fast and reliable diagnostic procedures which you can use to check out the O² Sensors in situ.
The following symptoms will help tip you off to a failed oxygen sensor:
Surging and/or hesitation
Decline in fuel economy
Unacceptable exhaust emissions
Premature failure of the catalytic converter
You will need the following equipment:
A handheld volt meter (digital VOM or Digital Multimeter)
A propane enrichment device, such as a Propane Torch (Unlit)
An oxygen sensor socket
It should take less than 10 minutes to perform a diagnostic check.
- 1. Verify the basic engine parameters, integrity of the electrical system (supply voltage), fuel delivery, mixture performance and internal mechanical considerations (eliminate any other possible causes for the poor running condition).
2. Treat the rich mixture performance as follows:
a. Disconnect the O² Sensor lead to the control unit.
b. Run the engine at 2500 rpm.
c. Artificially enrich the fuel mixture by directing propane into the Side Intake until the Engine speed drops by 200 rpm. Or, with electronic fuel injection, you can remove and plug the vacuum line to the fuel pressure regulator.
d. If the voltmeter rapidly reads .9 volts, then the oxygen sensor is correctly sensing a rich mixture. But, if the voltmeter responds sluggishly, or if it stays below .8 volts, then the sensor should be replaced.
3. Test the lean mixture performance as follows:
a. Induce a small vacuum leak.
b. If the voltmeter rapidly drops to .2 volts or below in less than a second, then the oxygen sensor is correctly measuring the lean mixture. But, if the voltmeter responds sluggishly, or if it stays above .2 volts, then the sensor should be replaced.
4.Test dynamic performance as follows:
a. Reconnect the sensor lead.
b. Set the mixture to specification.
c. Run the engine at 1500 rpm.
d. The sensor output should fluctuate around .5 volts. If it doesn't, replace the sensor.
Diagnosis
To check the performance of the oxygen sensor, run the vehicle engine at about 2000 rpm to ensure that the sensor remains hot throughout the test procedure. Do not remove or disconnect the sensor lead in order to test it as this will eliminate the "closed loop" signal to the DME and result in a non-cycling voltage condition. Connect your test leads so as to read voltage from the signal wire to the DME. With vehicles that use a heated oxygen sensor such as the Boxster (four wire), it may be necessary to bridge the connector leads and tap into the signal wire with an appropriate test probe at the connector plug in order to obtain the signal. The Multimeter will allow you to read the electrical response of the oxygen sensor to changing exhaust gas oxygen content as a measure of its performance.
A properly functioning oxygen sensor will exhibit a rapidly fluctuating voltage signal alternating between approximately .2 and .8 volts in response to varying residual oxygen content in the exhaust stream. Look to your scope's time reference line for a desired lean-to-rich and rich-to-lean time of less than 300 milliseconds. A response time greater than 300ms. means that the sensor should be replaced.
It is important to recall that these values are valid only when checking a sensor operating in "closed loop" in a hot exhaust stream (350°-800°C). Sensor age, degree of contamination, mixture setting, and exhaust temperature all have an effect on response time.
Without this rapid electrical response to changing exhaust composition, the DME cannot accurately correct the fuel mixture. A sluggish sensor is either contaminated or beyond its intended service life and must be replaced. Hope this helps...
Happy Motoring!... Jim'99