1980 Pontiac LeMans Station Wagon - G-T-faux (stuck with it, and can't shake it... like a bad case of herpes)

[fleming442]

Did it work? You done yet?

You're definitely the man with this stuff. Lots of numbers! You should become a tuner in your spare time. From what I've seen my buddy going through with his ZR1, it's an invaluable skill when it comes to LS engines in today's world.

 

[motorheadmike]

Did it work? You done yet?

You're definitely the man with this stuff. Lots of numbers! You should become a tuner in your spare time. From what I've seen my buddy going through with his ZR1, it's an invaluable skill when it comes to LS engines in today's world.

The code is written, but still needs to be uploaded. The rain has been heavy lately, not that I am afraid of getting the car wet, but the humidity and lack of AC makes me a big wussy. It is supposed to be dry this afternoon so we'll take the wagon to pick up the girls.

Thanks for the compliment but I have zero interest in doing this for money. Maybe, once I retire in 21 years... then they'll be vintage and I can charge triple!

 

[motorheadmike]

Ran the new tune - no change. Decided to start clean and do a Write Entire and change the OS to the factory one with a segment swap for a 4L80E - no change. I've started turning off and zeroing out things that could be influencing this condition (cat over temp (COT) or deceleration fuel cut off (DFCO) and so on).

If I get some time this weekend I am going to try CLSD and OLSD to see if the "OL - Accel/Decel" condition persists regardless of the engine mode. I am really not happy.

But, I think I fixed the P0106 code.

 

[fleming442]

So, the code is clear. Is there a driveability issue? Could a different MAP sensor possibly solve it?

 

[Texas82GP]

You have every right to be frustrated. Hang in there. You're a sharp guy. You'll get it sorted.

 

[motorheadmike]

So, the code is clear. Is there a driveability issue? Could a different MAP sensor possibly solve it?

Unfortunately I have already swapped out the MAF, TPS, and MAP in an attempt to rule out a malfunctioning sensor. The scanner supports that they are operating in spec. The trouble is that the car runs perfectly at idle, at low speeds, cruising at speeds up to ~60mph, and at WOT. It is essentially anything over 60mph and ~2200rpm where it arbitrarily drops the Fuel System Status (banks 1 and 2) into "Open Loop - Accel/Decel" and richens everything up to act as though it was in Power Enrichment (PE) despite still being in a commanded Closed Loop.

It is just plain weird.

Anyway, I have things set up to start logging the Fuel Trim Cells (FTC) vs the LTFT Boundaries (MAP and RPM) to try and isolate the issue better. FTCs are better explained here: https://www.hptuners.com/help/vcm_editor_parameters_gm_eng_fuel_loop.htm and https://www.hptuners.com/help/vcm_editor_tuning_how_to_advanced_ve.htm

Additionally I changed my LTFT Boundaries to better reflect the table above, rationale is similar to this: https://forum.hptuners.com/showthread.php?742-LTFT-boundries Before I had only about 4 cells referenced; odd to say the least. I am also going to look into reducing the Equivalence Ratio in PE from 0 to 2500ish RPM to 1.0 to see if this has an influence.

It is quite the process.

 

[motorheadmike]

Solved it. Finally. At least I got to go for a long drive.

 

[motorheadmike]

So this morning before heading out to sign my oldest up for the Winter skating session I decided take a moment to rotate the MAF sensor/mount away from the engine and from sitting directly over the PS fluid reservoir. Simple right?

Wrong.

Triggered a P0101 for MAF Performance - LOL.

Which is weird because the MAF housing has a large cell screen in it to improve laminar air flow across the sensor - so orientation should have no bearing.

However, it is possible that moving the MAF away from the heat source and no longer being saturated caused it to get skewed. It went from being "untouchable" last night in the previous position to just "warm" this morning.

I'll check the MAF error and fuel trims later.

 

[motorheadmike]

Here you can see the distribution of FTCs actual vs. theoretical. FTC 22 is the one for WOT - important to note that the distribution of FTCs 0-15 isn't perfect; but it is close.

View attachment 93787

 

[motorheadmike]

Ram-Err.