Lambda \ O2 sensor?
Discussion
A friend of mine has a 97 Golf 1.4. She mentioned that she has been having some issues. When she changes gear and gets back on the accelerator, sometimes the car hesitates and feels like it is going to cut out. She has had the car from new and mechanically it seems in really good order.
I thought I would help her out. It has done 150,00Km so instantly I thought Lambda sensor. I stuck a multi meter across what I thought was the signal wire and ground. Started up and had a reading of about 0.3v. This steadily climbed as the engine warmed up and got to about 0.55v. Then it just went crazy and started fluctuating all over the place. I saw readings of 0.1v to 0.8v.
I said that were it my car I would replace the sensor. She has had new plugs, dizzy cap, air filter and as I said, just generally looked after the car. I then asked had she notived a drop in economy... she laughed and said "yes, I thought there must be a whole in the tank".
So what do we think? O2 sensor or am I barking up the wrong tree. I know Lambda should be read with oscilloscope, but as I said, I got a steady voltage that slowly went up. I did wonder if I was just reading a heater contact, as it is a 4 wire sensor.
I thought I would help her out. It has done 150,00Km so instantly I thought Lambda sensor. I stuck a multi meter across what I thought was the signal wire and ground. Started up and had a reading of about 0.3v. This steadily climbed as the engine warmed up and got to about 0.55v. Then it just went crazy and started fluctuating all over the place. I saw readings of 0.1v to 0.8v.
I said that were it my car I would replace the sensor. She has had new plugs, dizzy cap, air filter and as I said, just generally looked after the car. I then asked had she notived a drop in economy... she laughed and said "yes, I thought there must be a whole in the tank".
So what do we think? O2 sensor or am I barking up the wrong tree. I know Lambda should be read with oscilloscope, but as I said, I got a steady voltage that slowly went up. I did wonder if I was just reading a heater contact, as it is a 4 wire sensor.
Yes, have been doing some reading, just confused why I got a static voltage up until the engine warmed up, but that is somewhat irrelivant. I could see the voltage fluctuating around a mid value, but from reading around VW lambda sensors, it would seem the voltages I was seeing pointed at the engine running too rich. Coupled with the occasional hesitency and the decrease in economy, really makes me think it is the O2 sensor.
The behaviour you're seeing at the lambda sensor is quite normal and (depending on the switching frequency, which you don't mention) could be showing you that all the basics are OK. Transient problems are quite unlikely to be caused by a lambda sensor and are much more likely to be caused by lack of transient enrichment (which is nothing to do with the lambda sensor).
It's hard to say this without seeming rude, and I'm honestly not trying to wind you up. To be honest I think you're wasting your time and her money trying to diagnose the problem with your current level of understanding.
These problems are usually quite easy to diagnose if you understand how the system works and have the right diagnostic equipment but you can't just jump in with a positive attitude and expect to find the problem. The engine management system is quite complex, and you have to have at least a basic understanding of how it works in order to diagnose problems with it. Without that you stand to spend a lot of time and money swapping parts that are perfectly OK, and possibly upsetting other things along the way.
It's hard to say this without seeming rude, and I'm honestly not trying to wind you up. To be honest I think you're wasting your time and her money trying to diagnose the problem with your current level of understanding.
These problems are usually quite easy to diagnose if you understand how the system works and have the right diagnostic equipment but you can't just jump in with a positive attitude and expect to find the problem. The engine management system is quite complex, and you have to have at least a basic understanding of how it works in order to diagnose problems with it. Without that you stand to spend a lot of time and money swapping parts that are perfectly OK, and possibly upsetting other things along the way.
Dont worry, I wont take offense. I posted here as I wasnt too sure and knew someone would know more than me. I realise now the behaviour is quite normal for the lambda. The frequency of change is very frequent, at least every half a second. As you said to me, and I to her. I am not a mechanic. I have for the last 3 years been able to maintain and solve my own issues with cars, but these have been my own issues on my own time. I will suggest she takes it to a good garage, and offer to be a b\s filter should they try to take her for a ride.
the throttle control housings tend to get pretty cruded up on these golfs causing faults like this, probably will req a clean out then setting back up using vag equipment to put the throttle back to its correct setting point as its controled electronicaly.
they also suffer from coolant temp senders and airflow meters so prob worth getting someone with good test eqip to check your components.
they also suffer from coolant temp senders and airflow meters so prob worth getting someone with good test eqip to check your components.
It sounds like its a fueling problem, and as an old school mechanic once told me, and my own 40 years of experience has borne out, 80% of fuelling problems are caused by the ignition system.
I have the same engine in a 99 Polo at only 55k miles, and it runs like a sewing machine, but at 150k km she really should be looking at replacing the plug leads, checking the plugs, and making sure the coil pack is OK. A weak spark or two would certainly cause hesitation.
Once the ignition system is proven A1 then its checking the fueling system, new fuel filter etc. When was the fuel filter last changed?
Only when all the basics are confirmed as working correctly should you start looking at ECU/ Lambda sensors etc. TBH I've never had a Lambda sensor fail, although I have been daft enough to change a few in the forlorn hope that was the problem.
HTH ,
Cheers,
Tony
I have the same engine in a 99 Polo at only 55k miles, and it runs like a sewing machine, but at 150k km she really should be looking at replacing the plug leads, checking the plugs, and making sure the coil pack is OK. A weak spark or two would certainly cause hesitation.
Once the ignition system is proven A1 then its checking the fueling system, new fuel filter etc. When was the fuel filter last changed?
Only when all the basics are confirmed as working correctly should you start looking at ECU/ Lambda sensors etc. TBH I've never had a Lambda sensor fail, although I have been daft enough to change a few in the forlorn hope that was the problem.
HTH ,
Cheers,
Tony
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