MPG has suddenly gone from kind-of-okay to worst

Sylvester said:
I've had a look, on how to change pre-cat O2 Nox sensor and the wire supposed to go through the floor to the ecu, next to the cccu, under the passenger seat compartment?
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The lambda I had doesn't have much more than a foot of cable going to the connector from memory, so I doubt you have to do anything inside the cabin - from what I understood, it is a case of taking off the exhaust manifold heat shield, and the sensor and the connector for it are right there. The above post is for a 1.6 FSi.

I agree with @PlasticMac though - in our case we had clear fault codes telling us that the lambda / wiring wasn't in good nick. An authentic lambda isn't cheap, and generics / ones where you need to splice the connector on are risky given the impact they can have on the way the car runs if anything is awry.
 
Robin_Cox said:
The lambda I had doesn't have much more than a foot of cable going to the connector from memory, so I doubt you have to do anything inside the cabin - from what I understood, it is a case of taking off the exhaust manifold heat shield, and the sensor and the connector for it are right there. The above post is for a 1.6 FSi.

I agree with @PlasticMac though - in our case we had clear fault codes telling us that the lambda / wiring wasn't in good nick. An authentic lambda isn't cheap, and generics / ones where you need to splice the connector on are risky given the impact they can have on the way the car runs if anything is awry.
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That's for sure, I definitely don't want to mess with that. I'm just gonna wait for the spark plugs to arrive, and the in meantime, I'll check how the ecu temps compare to the gauges. Thanks
 
If a sensor is faulty, as in open circuit, short circuit etc, you'll get a code/DTC.
But if it is just giving duff readings, logging is, I think the way to diagnose it.
It would be good to create a library of sensor data, from good and bad parts, to help diagnosis.
Mac.
 
Robin_Cox said:
The lambda I had doesn't have much more than a foot of cable going to the connector from memory, so I doubt you have to do anything inside the cabin - from what I understood, it is a case of taking off the exhaust manifold heat shield, and the sensor and the connector for it are right there. The above post is for a 1.6 FSi.
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You are spot on with that.
 
If you fancy running a log, ideally over a typical daily drive, these are the Groups I suggest, to give you an idea of what's going on:

Group 004
Block 1 Engine Speed
Block 2 Voltage Supply
Block 3 Coolant Temperature
Block 4 Intake Air Temperature

Group 030
Block 1 Bank 1 Sensor 1 Pre Cat
Block 2 Bank 1 Sensor 2 Post Cat
; 1xx - Sensor heater
; x1x - Oxygen sensor ready
; xx1 - Lambda regulation active

Group 033,
Block 1 Bank 1 Lambda Control
Block 2 Bank 1 Lambda/Oxygen Sensor 1 Pre Cat Voltage

VCDS (registered Lite, or full), will save the log, (in a sub folder of VCDS, called logs). Change the file type of the log to .CSV, then open it in a spread sheet application. (More info on logs here).

Mac.
 
PlasticMac said:
If you fancy running a log, ideally over a typical daily drive, these are the Groups I suggest, to give you an idea of what's going on:

Group 004
Block 1 Engine Speed
Block 2 Voltage Supply
Block 3 Coolant Temperature
Block 4 Intake Air Temperature

Group 030
Block 1 Bank 1 Sensor 1 Pre Cat
Block 2 Bank 1 Sensor 2 Post Cat
; 1xx - Sensor heater
; x1x - Oxygen sensor ready
; xx1 - Lambda regulation active

Group 033,
Block 1 Bank 1 Lambda Control
Block 2 Bank 1 Lambda/Oxygen Sensor 1 Pre Cat Voltage

VCDS (registered Lite, or full), will save the log, (in a sub folder of VCDS, called logs). Change the file type of the log to .CSV, then open it in a spread sheet application. (More info on logs here).

Mac.
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That's great info there, thanks a lot Mac. I had run the 004 before, almost knocked the wire off during driving, and I'm gonna try them again and the rest, to see what's coming up.
I'd received the spark plugs today, but they only sent 3, I didn't check they only sold 3 fot some reason, so now I gotta wait for another one. Cheers
 
PlasticMac said:
If you fancy running a log, ideally over a typical daily drive, these are the Groups I suggest, to give you an idea of what's going on:

Group 004
Block 1 Engine Speed
Block 2 Voltage Supply
Block 3 Coolant Temperature
Block 4 Intake Air Temperature

Group 030
Block 1 Bank 1 Sensor 1 Pre Cat
Block 2 Bank 1 Sensor 2 Post Cat
; 1xx - Sensor heater
; x1x - Oxygen sensor ready
; xx1 - Lambda regulation active

Group 033,
Block 1 Bank 1 Lambda Control
Block 2 Bank 1 Lambda/Oxygen Sensor 1 Pre Cat Voltage
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So I've just been out for a 30m drive, and the data it's worse than I thought :confused:

I've changed the 4 y.o. spark plugs, from Bosch 4 electrodes to NGK 3 electrodes. What I'd noticed, is the temp stay much longer around 88-90°C, BUT the car feels a little bit slower :oops: that might be placebo though.

For now I've only checked Group 4, and these came back (image).

Screenshot_20230625_232214_Chrome.jpg


Then the car gauge slowly moves around 90, but doesn't stay there for too long, never above 90 though.
When I'd stopped for a few minutes, the code reader showed rather fast climbing till 96°C, but car gauge stayed at 90°C. Then I drove off and the temp slowly reached the "15-30min" data again.

The bottom line is, there's around -10°C between data reader and car gauge display. So during driving, the highest engine temp by reader was 79/80 °C, which isn't even close to 90°C :eek: No wonder the MPG isn't great...
Shall I check the Group 30/33 as well, or really seems the issue is the thermostat? Thanks

EDIT: @Andrew The RPM shows ~630 on gauge, but shows ~680 on the scanner. Could this prove something about reading values?
 
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Good Evening,

I feel you are missing the point. Surely if he two sides of the the temperature sensor are giving different readings for the coolant at the same point then that suggests to me the the temperature sensor is faulty. I know from your earlier posts it it is a genuine Audi sensor and only 6 months old but the evidence you present is undeniable barring something more exotic like a rogue temperature gauge, the thermostat is extraneous to this argument.

Sorry I cannot remember but I think you can monitor the gauge temperature somewhere under Instruments to rule out subjectivity, you really need this and G62 side by side in a log to scrutinise and post here in some form.

Andy

PS. I am not saying the thermostat is healthy or faulty, just pointless to think about until you know the G62 is working correctly.
 
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Sylvester said:
So I've just been out for a 30m drive, and the data it's worse than I thought :confused:

I've changed the 4 y.o. spark plugs, from Bosch 4 electrodes to NGK 3 electrodes. What I'd noticed, is the temp stay much longer around 88-90°C, BUT the car feels a little bit slower :oops: that might be placebo though.

For now I've only checked Group 4, and these came back (image).

View attachment 109658

Then the car gauge slowly moves around 90, but doesn't stay there for too long, never above 90 though.
When I'd stopped for a few minutes, the code reader showed rather fast climbing till 96°C, but car gauge stayed at 90°C. Then I drove off and the temp slowly reached the "15-30min" data again.
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That being said - this is a 1.4 AUA, not a tdi, and we are not in the depths of winter. I drove our AUA at the end of last week for 2-3 days. Ours - even when it wasn't fully healthy - always warms up to high 80s - 90 within a couple of minutes of running and stays up there constantly. Your two sensor channel-reading differentials look a bit wonky but (to me) I get the overall impression of over-cooling, suggesting that the radiator is in play much too early and constantly (noting the overspike when you stop moving and there is no airflow) and that therefore the thermostat behaviour is suspect at the very least.
 
The gauge readings should not be taken too seriously, as it's weighted to show 90C anywhere between 82 ish and 97 ish. The G62 should be your only reliable indicator but, as others have said it isn't.
Mac.
 
What you should do is directly compare the two outputs of the G62. They should be the same at any one time. If not change it. Otherwise (and maybe also) change the thermostat. As Mac points out, the "temperature" gauge is just a comfort gauge.

RAB
 
The discrepancy between engine speed via OBD, and dash is, I suspect, a dash problem. When the engine is off, but ignition is on, is rev counter spot on zero?
Mac.
 
Andrew said:
I think you can monitor the gauge temperature somewhere under Instruments to rule out subjectivity, you really need this and G62 side by side in a log
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RAB said:
What you should do is directly compare the two outputs of the G62.
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I've done the Group 4 check while driving, but I'm not sure how to set the other tests.
I'd like to check them for sure, as this G62 is the 4th one I've bought over the years. I've had changed them all due the similar unstable coolant temp issue.
1st was old oem, 2-3rd was cheap from ebay (they worked the worst) and 4th from Audi, this is the most stable one, and most expensive, but the coolant temp still moves as posted above. Cheers
Robin_Cox said:
... and that therefore the thermostat behaviour is suspect at the very least.
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PlasticMac said:
The G62 should be your only reliable indicator but, as others have said it isn't.
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So if the car reaches 96+ when stationary, and lower when driving, indicating the thermostat probably working fine and isn't sticking open/close? That's would be good news, but then leaves me with 4 faulty G62 in a row :oops: I probably would look for a known-working used one next. Cheers
PlasticMac said:
When the engine is off, but ignition is on, is rev counter spot on zero?
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Yes it is, only the fuel indicator moves before staring the engine, cheers.
 
Sylvester said:
I've done the Group 4 check while driving, but I'm not sure how to set the other tests.
I'd like to check them for sure, as this G62 is the 4th one I've bought over the years. I've had changed them all due the similar unstable coolant temp issue.
1st was old oem, 2-3rd was cheap from ebay (they worked the worst) and 4th from Audi, this is the most stable one, and most expensive, but the coolant temp still moves as posted above. Cheers


So if the car reaches 96+ when stationary, and lower when driving, indicating the thermostat probably working fine and isn't sticking open/close? That's would be good news, but then leaves me with 4 faulty G62 in a row :oops: I probably would look for a known-working used one next. Cheers

Yes it is, only the fuel indicator moves before staring the engine, cheers.
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I mean is the needle actually pointing to the "zero" at rest, not that it moves before the engine starts. If it's out by 50, rpm, if it's resting just below zero, that's the reason. It's only a few degrees. The needles don't have a physical stop, they are magnetically driven, so, if zero is out a bit, the whole range will be out by the same offset.
Mac.
 
Sylvester said:
I've done the Group 4 check while driving, but I'm not sure how to set the other tests.
I'd like to check them for sure, as this G62 is the 4th one I've bought over the years. I've had changed them all due the similar unstable coolant temp issue.
1st was old oem, 2-3rd was cheap from ebay (they worked the worst) and 4th from Audi, this is the most stable one, and most expensive, but the coolant temp still moves as posted above. Cheers


So if the car reaches 96+ when stationary, and lower when driving, indicating the thermostat probably working fine and isn't sticking open/close? That's would be good news, but then leaves me with 4 faulty G62 in a row :oops: I probably would look for a known-working used one next. Cheers

Yes it is, only the fuel indicator moves before staring the engine, cheers.
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Is the cooling fan working correctly in all speed ranges?
 
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