Timing Blips, Shudders at Speed... Caused by What?

[squeeler642]

Have had my truck running with the same tune for about a year now (daily driver, about 35k mi) with no issues. Recently started shuddering occasionally while the truck is moving (most noticable while at cruising speed) which occasionally throws a CEL with a P0101 MAF performance code. Nothing on the truck has changed, just started getting this code and noticing the shudder. Only once recently have I gotten a P2135 TPS code... my thoughts below.

- Truck is an 03 Tahoe with a 6.0L LQ9 swap with long tubes (so no cats) and an AEM WB O2 (plumbed into/logged by the tuner), and tuned by a performance shop in my area (Dallas, TX).
- MAF swap (new sensor install) didnt clean up the MAF data in my logs, but also doesn't seem to be the culprit as the MAF seems stable thru the blip. Throttle position sensor also looks pretty stable.
- Fuel system seems out of the question to me, as the inj duty and eq ratio seems good. Doesn't seem like it's low on fuel for any reason.
- The computer is obviously reacting to something, given that the eq ratio goes rich immediately after the shudder/timing blip. Can I better instrument/log this somehow?
- I have my most recent log attached, showing one of the more noticeable blips I am talking about at timestamp 5m38s.

Having listed the my symptoms/thoughts, this just reeks of "sensor issue" to me, given that the truck has been running fine for months prior to this step change. I'm just trying to figure out whether the problem is staring right at me in the data I have so far. Any advice or ideas for additional logging would be appreciated!

P.S. Have seen only one other post addressing something similar to this in the Gen 4 forum where they were talking about MAF flutter... New here to the forum and tuning, so please forgive if this is something that's already been covered elsewhere and I just can't figure out how to find the results I need. Trying to use this problem as a way to learn more about tuning/logging.

[ns158sl]

Maybe im blind, but i don't see the shudder? I looked at RPM and dont see any dip or rise. I guess I would log trans stuff. Does it feel like tq converter shudder?

[SiriusC1024]

If you're getting a CEL then address that before you go tweaking the tune.

[squeeler642]

Maybe im blind, but i don't see the shudder? I looked at RPM and dont see any dip or rise. I guess I would log trans stuff. Does it feel like tq converter shudder?

From what I have seen of trans shudder from the converter lockup, that doesn't sound like what this is. The trans stuff should be in that file I included if you wanted to look at that. I created a plot just now and fitted the scale min/max to the trans input/output/turbine RPMs, per your suggestion. You can clearly see some variation in all three (they correlate) where the engine RPM falls about 60 RPM. Those peaks/troughs match up timewise with the engine RPM.

Would something like a bad crank sensor cause something like this? Wondering if these symptoms could be explained any other way. What would cause the ECU to pull timing like it's doing here?

[squeeler642]

If you're getting a CEL then address that before you go tweaking the tune.

Agree completely. Not at all interested in getting into the tune on this. Tune has been running fine for about 10 months with all sorts of daily driving and some occasional abuse from my lead foot.

[2xLS1]

P0101 is a predicted air flow error, not necessarily a bad maf error. Try cleaning the maf. That can effect transmission operation/performance.

[SiriusC1024]

P2135

[2xLS1]

Just saw you changed the maf already. Did you use a genuine GM or parts store crap. I would still just clean the original maf before replacing it. In my experience they rarely go bad, just get dirty. I will take a cleaned genuine GM maf over a parts store replacement all day long.

[squeeler642]

P0101 is a predicted air flow error, not necessarily a bad maf error. Try cleaning the maf. That can effect transmission operation/performance.

Just saw you changed the maf already. Did you use a genuine GM or parts store crap. I would still just clean the original maf before replacing it. In my experience they rarely go bad, just get dirty. I will take a cleaned genuine GM maf over a parts store replacement all day long.

Kinda what I had found browsing documentation on those errors, so thanks for the confirmation there. I decided to try to rule this out, so I ran a new MAF and did the logging I posted here. No joy. TPS is probably next, but the TPS on it now is riveted onto the throttle body, so it'll be a new throttle body it looks like, unless I want to drill out the rivets to make the ACDelco TPS work. Could the TPS provide false readings to the ECU that the tuner just doesn't catch over OBDII due to its sample rate/bandwidth?

Also had the thought about OEM vs aftermarket junk for sensors like that. Might be worth trying an OEM MAF at some point. I was almost thinking the new MAF made the problem more frequent... I plan to switch back to the old sensor (after cleaning it) tomorrow and running it some more to see how that affects it. Who knows. Maybe I have a vacuum leak I don't know about from my warm air intake.

[2xLS1]

Look at the P0101 error table in the engine diag tab. Compare a 01 MY, 02 MY and 03 MY. You will see GM continued to tighter up the predicted airflow diagnostic for no apparent reason on basically the same engines/platforms. Again it is just a predicted airflow diagnostic. You can multiply the entire table to match the earlier year calibrations. I do on tunes I do. MAF codes can cause weird things to happen in the background when they set.

[squeeler642]

Look at the P0101 error table in the engine diag tab. Compare a 01 MY, 02 MY and 03 MY. You will see GM continued to tighter up the predicted airflow diagnostic for no apparent reason on basically the same engines/platforms. Again it is just a predicted airflow diagnostic. You can multiply the entire table to match the earlier year calibrations. I do on tunes I do. MAF codes can cause weird things to happen in the background when they set.

Interesting note about the changes from MY to MY. So you're essentially saying you widen the error threshold for the MAF error to match prior years? I guess I would be open to trying that to see if it resolves my issue, but isn't there theoretically a root cause of whatever parameter drifting outside the current value? Wondering what that could be.

[2xLS1]

Interesting note about the changes from MY to MY. So you're essentially saying you widen the error threshold for the MAF error to match prior years? I guess I would be open to trying that to see if it resolves my issue, but isn't there theoretically a root cause of whatever parameter drifting outside the current value? Wondering what that could be.

Dirty maf, non GM maf. If you are happy with the tune why do you care about predicted airflow.

[SiriusC1024]

Why talk about the MAF? There's no weird thing going on with it during the timing and commanded AFR blips. MAF changes are reflected in both MAP and TPS. Look at the log.
the log.png

[squeeler642]

If you are happy with the tune why do you care about predicted airflow.

The step change is what's getting me. Like why did it all of a sudden start shuddering? No issue for months, including the winter season, so it's not like IAT is throwing it off.

I guess I forgot to mention that it went into some sort of "reduced engine power" protection mode on me last week, but after letting it sit overnight before getting around to troubleshooting it, it wouldn't duplicate. WB was showing the afr super leaned out when I got on the gas, but I kinda attributed that to the protection mode.

[2xLS1]

Why talk about the MAF? There's no weird thing going on with it during the timing and commanded AFR blips. MAF changes are reflected in both MAP and TPS. Look at the log.
the log.png

Do you not understand predicted airflow?

[SiriusC1024]

Yes. That REP is from the TPS or TAC. Symptom of P2135.

[2xLS1]

The step change is what's getting me. Like why did it all of a sudden start shuddering? No issue for months, including the winter season, so it's not like IAT is throwing it off.

I guess I forgot to mention that it went into some sort of "reduced engine power" protection mode on me last week, but after letting it sit overnight before getting around to troubleshooting it, it wouldn't duplicate. WB was showing the afr super leaned out when I got on the gas, but I kinda attributed that to the protection mode.

REP is always ETC system problems.

[SiriusC1024]

Do you not understand predicted airflow?

You can't be serious.

Post #11
https://forum.hptuners.com/showthrea...ynamic+airflow

Post #128
https://forum.hptuners.com/showthrea...-airflow/page7

[2xLS1]

He said he is getting P0101 codes. This is not a GEN 4 discussion.

[SiriusC1024]

REP is always ETC system problems.

Well gee.