Took some co2 reading tonight.

 

No matter what I did, the left side was always twice the reading of the right!

 

e.g. Left read 3%co2 and the right read 1.5%co2.

 

When switching the sniffer, the change was almost instant and the difference always the same!

 

This may sound daft, but listening to the exhaust note up close, the left side sounded like.. puff puff puff and the right sounded like.. pop pop pop!

The difference was very noticeable. Any relationship do you think??

 

So! my question is.. What would be the key features to check, that would most likely cause this fault?

Took some co2 reading tonight.

 

No matter what I did, the left side was always twice the reading of the right!

 

e.g. Left read 3%co2 and the right read 1.5%co2.

 

When switching the sniffer, the change was almost instant and the difference always the same!

 

This may sound daft, but listening to the exhaust note up close, the left side sounded like.. puff puff puff and the right sounded like.. pop pop pop!

The difference was very noticeable. Any relationship do you think??

 

So! my question is.. What would be the key features to check, that would most likely cause this fault?

 

lazy lam sensor

Thanks znut.

 

Is it possible to check this by way of their resistance using a multi-meter?

do you have Cats still on the car ? as you said there is two different sounds coming from the exhaust system ... if u do you could have a blocked/collapsing cat and this would all so give you false readings on the O2 banks

lazy lam sensor

 

What's one of them?

Hi Mark,

 

I have just fitted a Mongoose cat-back system in conjunction with a Japspeed front section.

The only cats I have left are the ones in the cast elbows at the turbos.

Maybe a slight blow in one of the exhaust tubes mate?

Maybe a slight blow in one of the exhaust tubes mate?

 

Good point Steams!

 

I will check it out at the week end.

If that checks out, where else do I look?

You could try unplugging both of them and see how it runs then. Daft question but were you checking them with the revs at 2k or above?

You could try unplugging both of them and see how it runs then. Daft question but were you checking them with the revs at 2k or above?

 

Will do. Also, I was at idle when checking. 850rpm.

If you were at idle then you won't get a reading off the o2's mate. Engine needs to be above 2k before the ECU will use them (and at temp). Warm the car up then take it upto to 2k and test again. They should pulse back and forward. If both are pulsing nicely then they're fine.

 

I'm thinking that you may have a slight blow from the exhaust but saying that your idles a little high too if the engine was at temp.

If you were at idle then you won't get a reading off the o2's mate. Engine needs to be above 2k before the ECU will use them (and at temp). Warm the car up then take it upto to 2k and test again. They should pulse back and forward. If both are pulsing nicely then they're fine.

 

I'm thinking that you may have a slight blow from the exhaust but saying that your idles a little high too if the engine was at temp.

 

Arh, that rules out the O2 sensors then?

As for the rpm, that was a typo error! Should have read 750 rpm.

The engine had been idling at temp for good 20 minutes.

If it is an exhaust blow, which side should I check first, the high reading or low?

put something over the end of the exhaust for a few secs you will hear if that side is blowing, quick and easy to find out which then.

put something over the end of the exhaust for a few secs you will hear if that side is blowing, quick and easy to find out which then.

 

Cheers DBnathan. Will try that at the weekend also.

welcome mate, will be interested in the results.

The ECU is in closed loop mode at idle above a certain temperature, ie O2 sensors are activated at idle:

 

 

For a stock JDM Auto ECU 41P13: O2 activation temp is 50°C; lean trigger voltage 0.21v; rich trigger voltage 0.58v

 

Let me know if you've got a different ECU and I can check the specifics.

 

The 2000rpm is an arbitrary value specified for diagnostic purposes in order to achieve approx 1 change rich to lean (or vice versa) every 2 seconds, and to ensure no other sensors (eg IACV) have a bearing on the results.

Hi Noz,

Thanks for your input mate.

As far as I know, I am fairly certain that I have a stock UK manual tt 1992 and that the ECU is standard also.

If I get chance to check tomorrow I will post some more specific information if that's ok?

So if I understand correctly, it could still be a fault with the O2 sensor?

Hi Noz,

Thanks for your input mate.

As far as I know, I am fairly certain that I have a stock UK manual tt 1992 and that the ECU is standard also.

If I get chance to check tomorrow I will post some more specific information if that's ok?

So if I understand correctly, it could still be a fault with the O2 sensor?

 

Wont really know until you test it mate.

If it's a manual UK TT ECU with stock chip then the O2 activation temp is even lower at 25°C. Lean/rich voltages the same as above.

 

It could be an issue with an O2 sensor. There is a simple ECU diagnostic check you can perform (I may have posted the sequence elsewhere) which gives fault codes and O2 sensor switching. Alternatively, you can get a full diagnostic check done.

P.S. I'm heading to the West Mids tomorrow if you're in need :laugh:

Thanks for the info Noz, and the kind offer. unfortunately I am working tomorrow and won't get home until the afternoon.

What sort of costs would I be looking at if you we're to do a check on them?

Maybe once I am taxed for the summer I could come over to you?

PS. Would I be able to use Data Scan software to check them?

PS. Would I be able to use Data Scan software to check them?

 

Yes, you can use Datascan to determine the voltage outputs from them, which is what's important. Lambda sensors can fail without throwing a code.

Yes, you can use Datascan to determine the voltage outputs from them, which is what's important. Lambda sensors can fail without throwing a code.

 

Cheers Noz.

Might give datascan a go.

Mind you, I don't really understand half of the things I'm looking at when it's hooked up if I was honest. lol

Looks like I will be taking a trip to Leicester when the weather picks up.

 

Assuming I am hooked up and the engine is up to temp, should I see the voltage fluctuate indicating rich to lean?

put something over the end of the exhaust for a few secs you will hear if that side is blowing, quick and easy to find out which then.

 

Tried this today, blocked each side with my hands and no sign of any blowing.

I was surprised how much force was needed to block the things off!!

Cheers DBnathan. At least that's one concern out of the way.

 

The next thing I tried was to disconnect the o2 sensors, made no difference at all! ?

 

At the moment I am just about to check that I have voltage to them and that I have resistance on the heater circuits.

After that I will try Data Scan. Should I see the 02 readings fluctuating madly? I think the last time I tried to check them both gauges just sat steady no matter what I did.!!

I can't remember the exact figures mate but they should pulse up and down smoothly about once a second or so. Smooth is the key I think.