Zirconocene

Hi there all-

I'm working on diagnosing my '90 S4 which has been stumbling a bit. Late last week on the way home, the car just died twice while driving. It started back up with no issue but it's bumming me out that the car is not as reliable as I'd like it to be. There have been other times where I can feel that the engine just stumbles while cruising, and yet other times where I press the accelerator and it takes just a bit for the engine to respond. This engine is hard to feel what's going on, as it's typically running in a pretty relaxed state, meaning under 2500 rpm on the high side of things. I think these things would be far more obvious on a higher strung engine.

The other weird thing that happened this morning, which has never happened before, is a couple of weird surges right as I was parking the car once I got to work this morning. I can promise you that my foot was on the brake when that happened and not the result of too large a foot.

So far, I have not installed a WBO2, so the only AFR data I have is from the standard O2 sensor.

There's a lot to investigate via other means (fuel pressure, vacuum, ignition bypass lights, TPS, probably a lot of other things I don't know about yet) but I thought that I would start with hooking up the SharkTuner and logging data while I drive around on various trips.

I'm just starting to look through the data and the first thing that jumps out at me is that the coolant temperature STARTS at about 130 deg F. This is on an engine that has sat outside all night and most of the previous day. This seems like a problem but I'd like to verify before I start throwing parts at the engine.

The AFR across all the RPM ranges that I ran the car was constantly less than 12 but I don't know how much I can trust that data given that it's not from a WBO2 sensor.

If it sounds like I don't really know what I'm talking about, you're right!

ETA: Both data files are the same, just different formats

All help is appreciated.

Thanks

FredR

Looks as though your temp2 sensor is buggered.

That would explain why you are running rich as the brains think the car has not warmed up.

Temp2 has two channels, one for the LH and one for EZK. As I recall the first of the two temperature readouts [the seemingly "failed" one ] is the LH channel so hence the rich fuelling problem.

You should see two column lines with the same temperature number but that is just not the case. The headings are not aligned so that makes it a bit more confusing trying to tell which column line is which. The temeprature measurement that is working shows 180F or 83C after about 3 minutes- a typical warm up period - that is a suspiciously low temperature unless someone fitted a 75C thermostat and if so sling it and get the 83 C unit.

FredR

Hang on a minute- just saw the XLS file and that is giving different numbers. one channel is in degrees C the other in degrees F- no problem but not sure why they are different- but it is warming up and giving values on both channels so not the temp 2.sensor
Have you any idea why the data variance between the two files? The first file is typically what is seen in ST2.

Zirconocene

Well, the txt file is what ST2 output, and then I fooled with making the columns right for the xls file, but I didn't touch any of the data itself.

I did notice that there is a slight difference in the readings (to/from the LH and EZK? Either way, there is a difference) but I don't know what's normal, I only have experience with this car.

The txt file is the straight output from ST2, though. I'll have another look and see if I can make heads or tails of what's going on.

Cheers

FredR

You might see a slight difference between the two channels of 1 degree that amounts to a rounding error but that is all.

Without a WBO2 the AFR numbers are meaningless I would suggest.

The XLS file version looks fine and easier to make sense of- I have seen this problem before with data extracted from ST2 and pasted into a text document - why it happens I do not know but probably a formatting issue..

The temperatures recorded look too low for an 83C thermostat- would make sense if there was a 75C thermostat fitted..How you have managed to get one column line in centrigrade and the other in degrees F baffles me- I assume they are readouts from the two separate channels. As to why your initial start temperatures are that high [54C] I have no idea but it sure looks suspect- it is just not that hot in Pennsylvania surely?

Other than the above I cannot spot anything remarkable- presumably you were driving an automatic and quite gently at that. ..

Zirconocene

Correct on all counts!

I don't know what other tomfoolery has gone on with different components, like the thermostat, but there are records in the engine bay of (relatively) recent water pump and timing belt replacements, so I would assume that other work was also done concurrently but, of course, I can't be sure.

Temp 2 sensors are not very expensive (I found a Hella part for $12, and the Bosch part for $27) so that's an easy choice to put on the car and see what happens.

I also have a new O2 sensor that I plan to install when I get room on my lift and install the WBO2 sensor, in case that helps or changes things.

The other cause for stumbling that I read about today indicated that it is a symptom of a dying LH which...gah.

Cheers

Billu

Agree, those temps seem low. Some people think they’re saving their engine by running at lower temp.
Also, I would check resistance of the temp 2 cold and at temp, first at the controller, then at the sensor.
I had issues with my 80 (Ljet) and found a previous owner had added a potentiometer in the line to adjust mixture.

hacker-pschorr

If your LH and MAF have not been rebuilt, I'd start there before chasing your tail with any other random sensors. The LH rebuild is an upgrade and the MAF is a wear item that needs to be serviced.

Oh and, quadruple check all the grounds and the positive connections on the battery. The side of the battery terminal with those extra wires can be loose while the battery hold down is still tight. This is a direct power feed to the LH and any iffy connection here will cause all sorts of random issues.

Lower combustion chamber temps lowers the detonation threshold. Lower intake air temps, coolant temps etc... all help accomplish this. That's why E85 is such a wonderful performance fuel, it burns so cool detonation is almost nonexistent.

That's besides the point though, once the Temp 2 sensor is sending a signal of 160F or higher, it's off the warm up enrichment map and he's reaching those temps in less than two minutes of driving. The sensor still could be faulty due to the 130F temp after sitting a day, that's odd.

Adding a resistor to an L-Jet car is a common "fix" due to those sensors reading low. I once setup a testing station using ice cube trays and tested over a dozen new Temp 2 sensors. All of them were in range per the WSM but some were way on either side of the scale. I put in the one with the highest resistance.

Speedtoys

I hope youre not replacing the normal O2 with a Wide Band...that doesnt work so well.

Install a bung for the WB, always. The NB simulator setups never work quite right.

Bulvot

I have a lot of SharkTuner logs, but only one that captures anything close to the cold startup temperatures. The car wasn't fully cold, but the ECU recorded a temperature of 103 Fahrenheit at startup.

I don't recommend having expensive parts rebuilt (LH/MAF) until after you've done the easy tests. I prefer diagnostics rather than parts replacement, personally. Since you have the SharkTuner, you can be a lot more confident in your diagnosis.

For the AFR, I assume that what you're really seeing is the SharkTuner's conversion of the voltage it sees (or doesn't see) on its WBO2 input, vis-a-vis whatever AFR slope is configured in the software. In other words, ignore that column. Without a wideband O2 sensor plugged into the SharkTuner, that column is meaningless and unrelated to anything going on with your car.

Instead, look at the O2 sensor adjust. If it's near or over 20%, then your ECU believes that the fuel mixture needs more/less fuel than it is able to adjust for. I see quite a bit in that range in your file. That means that either there is too little fuel, or the O2 sensor is misreporting and the computer is over fueling. Most telling is at idle, which you have a chunk of at the end of your drive/file. You're off of the throttle, according to the ECU, but your idle is fluctuating a little, and your O2 sensor adjust rolls up to 20%.

Strangely, you seem to be missing a chunk of time. I see your time count go from 605.6 to 647.8. That's almost 40 seconds of missing data. When the data comes back at 647.8, it takes about 7 seconds for the computer to max the fuel out.

I didn't look for any other missing time periods, but even assuming that's an anomaly unrelated to the car (stop/start log on computer, computer froze, etc), the fact that it maxed out the fuel at idle is concerning to me. The MAF signal is fairly steady, but the RPM's are going up as the fueling goes up. To me, that's pointing to the O2 sensor misreading the fueling.

However, there is another strange thing there. Before that missing time gap, your MAF readings were 105 to 115, roughly. After the time gap, they drop to 85 to 95, roughly. And, your RPMs do the opposite. They jump up a bit. And your coolant temperatures also jump up.

Your battery voltage remains consistent, so I don't think that it's a result of the radiator fans coming on and drawing power.

Looking a little earlier, around the 590 time mark, I see that your idle RPMs are quite high. I'm going to guess that you have an automatic and it was in gear at that point, and then you put it in Park? That in gear idle seems a bit high to me, though.

And then there is the ignition advance jump. It happens around the 600 second mark. And then drops off after the time gap. I'm wondering if the advance caused it to burn hotter and warm the motor up.

There is definitely some strangeness going on. I would want to observe the fuel and ignition maps during the idles. To see which maps and which points in the maps the ECU's are using. To make sure that they are not using any of the warm up maps, for one.

You may want to try resetting your adaptive O2 adjustment in the SharkTuner. To give it a fresh start at the O2 adjustments. If your O2 sensor is bad, and the adaptive adjustments have saved an over fueling map, then even though your O2 sensor adjust looks reasonable, it could still be over fueling and causing the stumbling and delayed throttle response. To be sure, you could disable adaptive adjustments in the SharkTuner and see if that makes a difference. If so, then it would be another indicator that the O2 sensor is the issue.

To me, the log files point to one of the following:

O2 Sensor
MAF
LH

You should be able to test the O2 sensor, but replacements aren't expensive and if yours hasn't ever been done, I would be tempted to replace it as a maintenance item.

For the MAF, you can unplug it and then idle the car and log that. Running with the MAF unplugged is a pretty well known scenario on here so you can read up on how it should perform with it unplugged. The logs will also confirm what the computer is doing and eliminate that variable.

For the LH, unfortunately there isn't an easy test. The most sure and no cost way is to swap your LH with a known good one from another properly running car. You could also do some exhaustive diagnostics that may or may not be conclusive, but at that point you're better off sending it to a rebuilder who will test it prior to rebuilding.

I think that it's also worth confirming that your grounds are good, figuring out why there was a big time gap in the logs (maybe something happened in that gap that would help you figure out what's happening), seeing which parts of the fuel/ignition maps are being used, and confirming good fuse/relay connections. If you've never cleaned your CE panel, it might be worth considering. It may have no improvement on this situation, but it's easy to do and won't hurt. I say "confirm" with all of this, because there's no sense in redoing work if you've already done these things.

Personally, I would start with the map monitoring, then the O2 sensor, then the MAF, and then the LH. In that order. And address things that seem to be likely culprits as I go.

If you can easily install a wideband O2 sensor in parallel with the narrowband, that would go a long way to diagnosing the O2 sensor. Especially if you can swap them back and forth between banks.

The temperature sensor reading is likely a red herring. It might just be that your particular sensor has a lower limit that's higher than mine. The temperature readings that you're getting at full warm seem reasonable, so I wouldn't chase that quite yet. If it were me.

Also, on the logging, you shouldn't select all of the checkboxes. It slows down the data transfer frequency. Just select the ones that you need, and only one of each type (not both items in both LH and EZK). My recollection is that the manual recommends using the LH variables when possible. Supposedly it is faster.

Good luck and let us know what you find.