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Discussion Starter #1
Hey Folks,

I have recently had a stint of low MPG on my 1995 VW Cabriolet. The vehicle has the following noted items:

  • Recently cleaned the MAF with CRC SensorKleen
  • 226 000 km/Odometer Reading
  • Changed Spark Plugs 100km's Ago (G-Power - NGK)
  • No signs of difficulty accelerating or unsteady idle or misfires
  • Check Engine Light never come on
  • No excessive oil burning from exhaust
  • New baffle and resonator - 500km's ago
  • Being using fuel injector additive to clean injectors
  • Airfilter is not clogged or excessively dirty

I noted that the spark plugs were a little fowled and had some carbon deposit on them. I believe this is due to high fuel/air ratio.

The question I have is to do with the Oxygen Sensor. I have read a few forums, but cannot get to the part where it explains if the Engine light will come on for a faulty O2 sensor or if it only lights up for one that is missing a signal. I checked the OBD-1 circuit by using a paperclip for #4 & #15 terminal and the light literally just goes off and no trouble signs are reported. I believe this is the 0000 code and therefore no issues have been reported.

Does this sound like a faulty O2 Sensor or could I possible be facing something else? I currently drive economically in and around the city. I get around 300-330 KM/tank. That seems very high for my type of driving and my restraint to put the peddle to the floor.

Please advise? Does the 95 VW Cabrio have one O2 sensor or is there a pre-catalytic converter and post-catalytic converter O2 Sensor? See attached photographs of the spark plugs, hopefully this helps.

Thanks
 

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The best way to tell is to crawl under there and see.

I could be wrong on this, but I believe it was the switch over to OBD II in 1996 that necesitated 2 oxygen sensors.

I'm looking at rockauto, where I buy all my parts, and I'm only seeing an upstream sensor. So I think you only have 1, you lucky duck. I have 2 in my 96 Golf and have to replace them both, plus splice in a broken wire.

How long were those previous plugs in there?

My Hanes manual says to replace the plugs every 30,000 miles, which is about 50,000 km.
 

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Discussion Starter #3
Thanks for getting back to me on this. I realized that after I posted this there was an autoparts website that had a schematic. There seems to be only one upstream Oxygen Sensor, which is before the Catalytic Converter. I guess I will get under the car and replace that or better yet, when I have an oil change next week; have them perform the Oxygen Sensor replacement once the car is up on the hoist, saves me the hassle of doing it myself and then they can perhaps let me know if the low MPG is due to this.

It does seem awkward that I have not as of yet had an idle or backfiring/misfiring issues. The previous twit that owned the car did very little maintenance and I guess was one of those people who only perform maintenance on a "Car is not working" basis. How much did you pay for your Pre-Catalytic Converter O2 sensor?

I'm expecting to pay around $40-50 if I can get away with that. I believe Bosch has them for the 1995 Cabrio.
 

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Thanks for getting back to me on this. I realized that after I posted this there was an autoparts website that had a schematic. There seems to be only one upstream Oxygen Sensor, which is before the Catalytic Converter. I guess I will get under the car and replace that or better yet, when I have an oil change next week; have them perform the Oxygen Sensor replacement once the car is up on the hoist, saves me the hassle of doing it myself and then they can perhaps let me know if the low MPG is due to this.
It's not too much of a hassle. It's easier than changing the spark plugs and wires. For mine, I needed:
  • Penetrating oil (WD-40 might do, I had Liquid Wrench)
  • I used a crescent wrench, but a real wrench may have been better.
  • New sensor

It took about 20 minutes, not including spraying the old sensor down with Liquid Wrench. By the way, spraying the penetrating oil is something you probably want to do at least a couple of hours before you remove the sensor. The day before is better, and yes, you can drive it in the meantime.

I've been told it's easier to remove the sensor when the car is warm, but I never considered it worth accidently touching the hot exhaust.

It does seem awkward that I have not as of yet had an idle or backfiring/misfiring issues. The previous twit that owned the car did very little maintenance and I guess was one of those people who only perform maintenance on a "Car is not working" basis. How much did you pay for your Pre-Catalytic Converter O2 sensor?
I don't think a bad O2 sensor by itself would necessarily show up as misfiring or backfiring. It's just one component in emissions. If it's not behaving properly, the computer will rely on other things to determine how to run the engine.

I paid $43 + shipping for one sensor. The O2 sensor for your 95 Cabrio looks like it's $42 for a no-name brand, or $65 for Bosch. Both are $3 shipping to my location. This is from RockAuto. I'm seeing $92-$155 from Napa.

If you get your own, be sure it has enough cable to it. RockAuto thought 7.5" was enough for my upstream sensor. :y:

I'm expecting to pay around $40-50 if I can get away with that. I believe Bosch has them for the 1995 Cabrio.
The only way you're going to pay that little is to do it yourself. ;) Any shop will probably charge you .5 to 1 hour labor to do the work.
 

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Well it seems as thought my MPG is still low, so its time to invest the money and get that O2 sensor fixed to hopefully try fix the issue. It is frustrating, seen as how this issue has been a recent problem.

Thanks for the advice. I will give the sensor a spray before and leave it for a few hours for the fluid to penetrate the Catalytic Converter. I wouldn't like to strip the O2 sensor and be faced with replacing the whole converter.
 

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Update on problem/solution

Hey,

So just to update on the situation. I took the car to a mechanic to see what I could get done. The car as previously mentioned was not too well maintained so some key items have been overlooked. There was a high carbon build-up where the manifold has the vacuum line entering the engine. I am not sure of what it exactly entailed, but the process took around 5-7 minutes and it flushed a whole smoke load of carbon out of the exhaust.

We then replaced the Cap/Rotor contact buttons and distributor cap. I had previously replaced the spark plugs, so we also replaced the spark plug distributor cables and replaced the fuel filter.

The performance was immediate. I could feel at least 15% more power, faster start, fuel consumption is back to normal. I think I got 125km's from a quarter tank. Its remarkable.

The mechanic said that with the 1995 VW Cabrio or the previous OBD-I vehicles that if there was an issue with the Oxygen Sensor, there would be an immediate signal to the ECU. So that is my update. Things look great.

Next job is to replace the shocks. I am not so aware of the shock process, but perhaps whoever is reading this can shed some light on the topic. I see that there is coils/shocks/struts. I believe I need to replace the shocks on the back, perhaps the coils too if neccessary; but will it be neccessary to replace the strut for the front suspension?

Thanks for reading.
 
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