Indeed. It's also very low output. See where a replacement gets me. If this one will come out !
What does it use as data if unplugged? It drives ok.
 
Looked back through my stored data of a working O2 sensor.
Screenshot_20231117_131629_Samsung Internet.jpgScreenshot_20231117_130502_Samsung Internet.jpg
Left: 1st O2 in red, second in green.

Right: Fuel trim long in red, fuel trim sensor in green, fuel trim short in blue.

Very different pictures !!
 
andyfreelandy said:
Indeed. It's also very low output. See where a replacement gets me. If this one will come out !
What does it use as data if unplugged? It drives ok.
Click to expand...
It should come out if you have an O2 sensor socket.
If there no signal from an O2 sensor, the ECM will flag a code, and run the engine in open loop, meaning it will fuel it based on information from the MAP, ATS, throttle position and CTS. If it runs well in open loop fueling mode, this would point to an issue with the O2 sensor.

That picture where it's graphed switching from low to high to low to high repeatedly is how an O2 should work. Your recent graph is all over the place.
 
Thanks. The location of the sensor on the engine side of the manifold means that a socket can't be used in situ.

Will try a ring spanner and if not then it's off with the manifold.
 
andyfreelandy said:
Thanks. The location of the sensor on the engine side of the manifold means that a socket can't be used in situ.

Will try a ring spanner and if not then it's off with the manifold.
Click to expand...
Looks like your on the right track. Some of the o2 sensor sockets have a hex head too which you can put the spanner on. Depends which type you have. I managed to get mine out with the manifold still in.
 
So the good news is that the sensor unscrewed easily.
Sensor 1, in the exhaust manifold, is now looking correct. See waveform. But sensor 2 is wrong. Permanent P0170 code and permanent EML.

Screenshot_20231120_155525_Torque.jpg
The fuel trim now, still wrong, looks like this...
Screenshot_20231120_155655_Torque.jpg
As I understand it, sensor 2 doesn't affect the ECU settings. So what could be causing the bad sensor 2 picture and upsetting the mixture settings??

One problem solved but not there yet !!
 
andyfreelandy said:
So the good news is that the sensor unscrewed easily.
Sensor 1, in the exhaust manifold, is now looking correct. See waveform. But sensor 2 is wrong. Permanent P0170 code and permanent EML.

View attachment 303093
The fuel trim now, still wrong, looks like this...
View attachment 303094
As I understand it, sensor 2 doesn't affect the ECU settings. So what could be causing the bad sensor 2 picture and upsetting the mixture settings??

One problem solved but not there yet !!
Click to expand...
Ok I didn’t read that properly, so edited my response. The code is for a fuel trim malfunction. What are your fuel trims saying?
 
Thanks. Will do. I doubt that this warm up will cure the P0170 and the EML which are evident from start up. The old O2 sensor that wasn't working allowed the P0170 to be cleared and it would then return again. With the new sensor it is showing as a permanent fault and won't clear.
 
andyfreelandy said:
Thanks. Will do. I doubt that this warm up will cure the P0170 and the EML which are evident from start up. The old O2 sensor that wasn't working allowed the P0170 to be cleared and it would then return again. With the new sensor it is showing as a permanent fault and won't clear.
Click to expand...
Ok, it may be the newer sensor is reporting better and hence the ecu picks up on the problem faster.
What brand is the new sensor?

Sorry when I looked at the pics it’s hard to see as I’m using a smartphone just now.

From what I can see in the pic the long term fuel trim is steady around -4% and the short term is actively adapting as I would expect with a range of about +2% up to + 6% roughly, and on average it is adding say +4% which puts the average amount of injected fuel adaptation back to zero when you calculate long and short term together. It’s normal for fuel trims to go positive or negative 5-10% say even a little more.

I’m gonna go read up on the fault code quickly to see what the description is as the trims are within normal range. You get the p0171 and p0172 system too rich and too lean codes when the ecu has to add or subtract 30% or more (percentage varies by manufacturer) in fuel trims.
 
Thanks for the help Ross.

My previous well working 1.8 displayed the fuel trim as attached.Screenshot_20231117_130502_Samsung Internet.jpg

Looks quite different. P0170 appears to be a general code for fuel trim errors without guiding you as to whether rich or weak.
 
andyfreelandy said:
Thanks for the help Ross.

My previous well working 1.8 displayed the fuel trim as attached.View attachment 303112

Looks quite different. P0170 appears to be a general code for fuel trim errors without guiding you as to whether rich or weak.
Click to expand...
Ah ok, glad you posted the known good 👍 😊
The difference is the problem wave is more frequently active than the known good.
Best to check the hardware before going any further now. It could be reacting to the actual readings from no1 sensor.
I would first check intake and exhaust for leaks.
If that shows nothing check fuel pressure at rail meets requirements.

Looks like it may be reacting to an intake air leak to me. This could be anywhere after the throttle body like throttle body seal, manifold gasket, injector seal, pcv hose etc.
 
Check the pcv hose that goes to throttle body isn’t blocked with crud. Sure that happened to mine at one point.
 
Just had a thought! It happens sometimes.
A few weeks before I got it it had a new timing belt.
Would a tooth out of sync cause this?
Worth checking anyway I guess.

Also, when driving it makes a droning noise (like an aircraft going over) at about 3k rpm. Could that be an air leak or bad timing??
 
andyfreelandy said:
Just had a thought! It happens sometimes.
A few weeks before I got it it had a new timing belt.
Would a tooth out of sync cause this?
Worth checking anyway I guess.

Also, when driving it makes a droning noise (like an aircraft going over) at about 3k rpm. Could that be an air leak or bad timing??
Click to expand...
I would check the above first as it’s easier.
Then if you think the timing might be out it’s easy enough to check. It is an easy belt to do but I guess anything can happen.
I think it’ll be a breathing problem most likely, intake exhaust etc leaking tbh.
Plenty other things to check later if not, but I’d start there.
 
So here's a thing. Decided to check timing belts, leaks in inlet and MAF sensor.
Last time I started it the engine warning light was on and had permanent P0170 code.
Moved car to do checks. No engine light.
Timing is correct on belt.
No sounds of leaks, ripped hoses or gummed breather.
Inserted a substitute MAF.
Ran scanner, no fault codes and O2 second sensor now behaving. Fuel trim looked good too. See below
Screenshot_20231122_140932_Torque.jpgo2 sensors.

Screenshot_20231122_141055_Torque.jpgfuel trim

I then did what I always do and tried to reproduce the fault. Refitted original MAF.

Same pictures.

Left it and test drove. Lovely and lively.
So was it ok when I started it? Not sure. Could the engiine have needed run time to get the second o2 sensor sorted or cleaned ?

When fully warmed up the fuel trim showed the following. Which confused me a bit as I thought the the short and long sort of cancelled numerically to zero??

Screenshot_20231122_142745_Torque.jpg
Clearly this one doesn't although the shapes look good. Anyone explain please ??
This might be a mystery that reappears. Or maybe the second o2 needed cleaning to do its job ? Although, again, my understanding is that the second o2 doesn't affect engine management?
 
Last edited:
andyfreelandy said:
So here's a thing. Decided to check timing belts, leaks in inlet and MAF sensor.
Last time I started it the engine warning light was on and had permanent P0170 code.
Moved car to do checks. No engine light.
Timing is correct on belt.
No sounds of leaks, ripped hoses or gummed breather.
Inserted a substitute MAF.
Ran scanner, no fault codes and O2 second sensor now behaving. Fuel trim looked good too. See below
View attachment 303230o2 sensors.

View attachment 303231fuel trim

I then did what I always do and tried to reproduce the fault. Refitted original MAF.

Same pictures.

Left it and test drove. Lovely and lively.
So was it ok when I started it? Not sure. Could the engiine have needed run time to get the second o2 sensor sorted or cleaned ?

When fully warmed up the fuel trim showed the following. Which confused me a bit as I thought the the short and long sort of cancelled numerically to zero??

View attachment 303232
Clearly this one doesn't although the shapes look good. Anyone explain please ??
This might be a mystery that reappears. Or maybe the second o2 needed cleaning to do its job ? Although, again, my understanding is that the second o2 doesn't affect engine management?
Click to expand...

Hi there, glad your making progress. Your o2 sensors and fuel trims look nice, well within expected range.
Yea fuel trims long/short are calculated against each other. As if the long term is adding 5% and the short term removing 5% then 5 add -5 is 0.
What has happened could be explained by two things.

1) there is an intermittent problem that currently isn’t a problem hence the good readings. An example of the intermittent problem could be a sticky evap valve maybe not closing fully sometimes upsetting the mixture but maybe evap valve shut right later, and all ok for now.

2) when you delete all the fault codes the ecu again carries out the system monitoring checks I.e lambda evap etc. Maybe that fault code is held in memory until the system passes the lambda and evap monitors.

Cheers
 
Last edited:
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