High Mileage Mazda 3, Engine clean, oil for long term
- Thread starter Johnnyz2
- Start date
On to performance question...
First, thanks everyone for the advice. I think I have my oil question answered but still wonder about the overall engine performance. Since a bunch of you seem to have the right knowledge, I’d like to get feedback on the sensors and engine performance. Apologies in advance for leaving the oil topic on this forum.
I’m going to post some of the scan tool images.
Some things to know:
First, thanks everyone for the advice. I think I have my oil question answered but still wonder about the overall engine performance. Since a bunch of you seem to have the right knowledge, I’d like to get feedback on the sensors and engine performance. Apologies in advance for leaving the oil topic on this forum.
I’m going to post some of the scan tool images.
Some things to know:
- The car has three “O2” sensors and two catalytic converters (the cats are in series)
- #1 is a heated wide band sensor at the exhaust manifold.
- #2 is in between the two cats (might be heated).
- #3 is after the second cat (might be heated).
- All of these scan tool tests were taken before I posted to BITOG
- They show “throttle snaps”
- One or two slower throttle ramps and declines
- A few show full throttle acceleration (car moving) and computed load (I read that is a good test for a wideband sensor)
- Some steady state images are included as well.
- The images were loaded in time sequence.
- One shows removal of vacuum tube to simulate leak. That test caused the engine to stall out.
- I’m learning how to read these things as I go and there’s a risk that I’m misinterpreting the data. It’s also the reason I’ve included so many images - I’m not certain which would be most useful.
- LOOK CAREFULLY: The tool does not always assign the same position or graph line color to the same sensor; so, for each image, double check the graph headlines and/or legend
- As someone already said, the computer seems to be managing things as expected and none of the readings indicate anything very far off. Does everyone agree?
- 02 #2 regularly shows a higher voltage than a similar sensor would if working correctly and in the exhaust manifold. I don’t know what should be expected in this situation (behind the first cat).
- Some graphs suggest that O2 #2 lags a bit; however, I wonder if that’s expected after a cat.
- A few graphs seem to suggest that O2 #2 has an effect on ST fuel trim.
- Considering 02 #2 is after a cat, the variability of it surprises me. Especially compared to 02 #3. Perhaps that’s expected in this setup though.
- I won’t be able to borrow the scan tool for too much longer. Please suggest specific tests which might be useful and/or specific combinations of sensors to test.
- For example, I still want to double check timing etc. against throttle snaps and hard acceleration.
I don't see anything obviously wrong with the O2 sensor readings.
Keep in mind that since you're not applying much load to the engine, the fuelling will always be commanded to be stoichiometric. The only thing the sensors will be responding to is the lean condition caused by fuel cut when letting off the throttle, and they seem to be doing that with around 1 second of delay since the throttle was cut. This seems like a normal delay.
Do some data logging while driving, after applying high throttle, to see how the sensors respond to a rich condition. Log knock and misfire as well.
The first log on your second post shows the manifold pressure failing to increase with throttle/load. It even goes down slightly. It seems to be working fine in the other logs. Keep logging MAP to see if something weird is going on with the sensor.
Keep in mind that since you're not applying much load to the engine, the fuelling will always be commanded to be stoichiometric. The only thing the sensors will be responding to is the lean condition caused by fuel cut when letting off the throttle, and they seem to be doing that with around 1 second of delay since the throttle was cut. This seems like a normal delay.
Do some data logging while driving, after applying high throttle, to see how the sensors respond to a rich condition. Log knock and misfire as well.
The first log on your second post shows the manifold pressure failing to increase with throttle/load. It even goes down slightly. It seems to be working fine in the other logs. Keep logging MAP to see if something weird is going on with the sensor.
Thanks. You might have missed them....the images which show 2:58 and 3:09pm, on the top left corner, are hard accelerations. 2:58 shows full throttle accleration from stop signs, first gear only. The 3:09 one shows full throttle from stop with a gear shift from 1st to 2nd. Both show computed load values to 90 and 95%. But on those I was not measuring MAP.
I'll repeat that with the additional data.
Sadly, in the meantime, I've got a new issue while draining the oil. Will post separately for that.
Okay, the O2 sensor readings look good to me on those logs. Absolute Throttle maxes out at only 90%, and load only goes to 95%, but that might be normal. I'm thinking that Relative Throttle should be going to 100%, and so should Accelerator Pedal Position, so log these all at the same time to make sure they're normal.
In addition to the above, I'd log the following parameters for high throttle pulls.
RPM
Engine Load
MAP
Mass airflow
Equivalence Ratio (lambda)
Ignition Timing
Knock Retard
If there's a long term knock correction parameter, log that too. I'd do some longer pulls through 3rd gear, and some pulls at 50-75% throttle.
New data and More scan tool captures.
New Data:
Set 1: Fully warmed up engine. Various tests both stationary and moving without the scan tool doing a recording.
Set 2: Fully warmed up engine. Various captures from recordings, shown in sequence, of full acceleration testing. Most are multiple gear changes (see RPM to see how many gear shifts).
Set 3. Engine: After an ECU reset with some immediate driving. Testing done on a cooled engine, after initial idle/trim ressetting already started but still with thought to capture ECU resetting the idle etc. Wish I had thought of that earlier; however, this still shows some of the process.
Some notes:
New Data:
- Fuel pressure measures within spec and does not drop when the engine is running.
- Spark gap testing: All four coils will jump a 2cm gap, which is supposed to be about a 30kv output. The jumps are more orange/red than blue; so, not full power from what I've read but should be adequate. There may have been some misses in jumping the gap but it was hard to see.
- All coils, except one, measure the same. The one that does not has about a 10MegOhm connection from one of the pins to the spark plug connector while the other 3 do not. That suggests that the control transistor for it is no longer functioning as it should. Despite that no codes whatsoever.
- No codes for any of the scan tool testing either.
Set 1: Fully warmed up engine. Various tests both stationary and moving without the scan tool doing a recording.
Set 2: Fully warmed up engine. Various captures from recordings, shown in sequence, of full acceleration testing. Most are multiple gear changes (see RPM to see how many gear shifts).
Set 3. Engine: After an ECU reset with some immediate driving. Testing done on a cooled engine, after initial idle/trim ressetting already started but still with thought to capture ECU resetting the idle etc. Wish I had thought of that earlier; however, this still shows some of the process.
Some notes:
- ECU is detecting and adjusting for knock on hard acceleration in more cases than was showing up previously.
- The mid/center O2 sensor has more impact on fuel trim that I would have guessed.
- As someone noted before, the MAP can go negative at the same time the MAF is going positive with slow ramp/decline of RPM (see set 1). It does seem to occur a small amount in other cases too.
- Watch out for the color changes and sensor changes in the images. I found that the tool will only show 12 graphs together at once and that led to some variability in options as I captured the various image sets.
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The lack of power you're feeling is probably caused by the knock retard. 5 to 8 degrees of ignition timing retard is a lot, and will be very noticeable. The large timing correction only seems to occur up to mid-rpm.
The wideband O2 sensor reading remains close to stoichiometric for several seconds after applying max throttle. I'd expect it to respond more quickly, but I don't know at what load/rpm this engine starts targeting richer fuelling. Try to find some datalogs of a similar engine. Start logging commanded/targeted fuelling if you can, so you can compare it to the wideband reading. The sensor could have a delayed response, but I don't think this would cause a lot of knock.
I'm still leaning towards an issue with the MAF sensor. The knock retard starts at low rpm and moderate load, where rich fuelling shouldn't be necessary to prevent knock. High positive trims caused by a bad MAF will affect both target ignition timing and target fuelling, which is likely to cause knock.
I'd start by cleaning the sensor, resetting the ECU, then take some logs at WOT to see if it helped. If not, rinse and repeat with a new MAF sensor, then again with a new wideband O2 sensor. If you can log knock sensor noise for individual cylinders, and only one cylinder is knocking, I might suspect a bad injector on that cylinder.
The narrowband sensors shouldn't relate to knock, and the MAP sensor seems fine. Fuel pressure is probably fine since the fuelling is plenty rich enough at high rpm.
The wideband O2 sensor reading remains close to stoichiometric for several seconds after applying max throttle. I'd expect it to respond more quickly, but I don't know at what load/rpm this engine starts targeting richer fuelling. Try to find some datalogs of a similar engine. Start logging commanded/targeted fuelling if you can, so you can compare it to the wideband reading. The sensor could have a delayed response, but I don't think this would cause a lot of knock.
I'm still leaning towards an issue with the MAF sensor. The knock retard starts at low rpm and moderate load, where rich fuelling shouldn't be necessary to prevent knock. High positive trims caused by a bad MAF will affect both target ignition timing and target fuelling, which is likely to cause knock.
I'd start by cleaning the sensor, resetting the ECU, then take some logs at WOT to see if it helped. If not, rinse and repeat with a new MAF sensor, then again with a new wideband O2 sensor. If you can log knock sensor noise for individual cylinders, and only one cylinder is knocking, I might suspect a bad injector on that cylinder.
The narrowband sensors shouldn't relate to knock, and the MAP sensor seems fine. Fuel pressure is probably fine since the fuelling is plenty rich enough at high rpm.
