new maf cold air running rough

[brota]

hello
After dealing with some things last year I put the car away.
I noticed my original air intake was leaking so I added an ebay air intake kit with a new delphi maf because I was having MAF issues last year.

The car feels to be running a little rough almost didnt stay running but figured it was learning the maf.
I checked for codes because the light came on for few with a code 44.
I did run scan9495 and it appears my MAF is not dumping fuel like the defective maf I had last year.

The check engine light went off after a little but I didnt check if the code was still there.
Will a bad O2 sensor make it run rough? I assume 44 is the drivers side? I replaced with a bosch a couple of years ago. Are those o2 sensors good can they go bad with like 1000 miles on it?

I have attached my scan csv incase anyone can take a look at it and see if something jumps out.
https://black55chevy-my.sharepoint.com/:x:/p/brian/EcbRNCONKYpJu-nNC3NIjBgBgjGSJ4NiSFayxuv7J5nJTQ?e=fLdpl2

Thank you
Brian

[Injuneer]

DTC 44 = Bank 1 (driver side) O2 sensor lean. Could be a faulty sensor, faulty sensor wiring, or could actually be the result of the driver side of the engine running lean.

What do the long term fuel trims look like for BOTH Bank 1 and Bank 2? I'll look at the log later but don’t have time right now? By looking at both banks, it tells you if there really is a problem only on Bank 1 (indicating a problem that only affects Bank1), or if it’s a problem affecting both banks, but Bank 2 isn’t quite bad enough to set DTC 64 as well.

[brota]

38497

This is from right when the service engine light came on with car idling

[Injuneer]

Surprised you didn’t get a code for both sides. The LTFT's are maxed out, adding 25% extra fuel to keep it from running lean. Faulty MAF calibration, low fuel pressure, huge vacuum leak, or leak between the MAF and the throttle body, etc.

Do you have (or have access to) a fuel pressure test gauge? What was the MAF flow in grams/second when code set? Are you sure the rubber connectors for the inlet elbow are tight on the MAF and the throttle body ends?

I'll try and run through the data log tomorrow morning.

[brota]

The air pump hose may have been off when I was running the scan.
I have the new plastic delphi MAF.
I can test fuel pressure but it was fine last time I tested
I can verify the tubes are tight. I dont hear I leak I did with factory air inlet that is why I changed it.

What is the datalogger is that available online?

Thank you

[Injuneer]

The AIR pump supply hose connects to the inlet air ducting before the MAF. Disconnected hose would pull in unfiltered air, but it would still pass thru the MAF.

Not sure what you are asking about a “datalogger”. You attached a data log file from Scan9495.... what you called the “scan csv”.

[brota]

Sorry I misread what you wrote, I thought you said you would run it through a datalogger. I was hoping some software out there that you can parse the log through and tell you what was wrong.
I do appreciate you looking at this.

[Injuneer]

Never saw a data log with the fuel this screwed up. The problem seems to be worse at low RPM and low engine loads (low LTFT cells).

On Cell 16 (idle cell), the LTFT's are 160/160 and the STFT's are 194/197 in a typical frame of data. Since the fuel trims are multipliers, in series, the PCM is adding ~89% extra fuel, beyond what it would normally supply = almost DOUBLE. And still the Bank 1 O2 sensor is staying below 200 millivolts. When it stays below that level for 50 seconds, DTC 44 sets. The only reason DTC 64 isn't setting is because the Bank 2 O2 sensor creeps above 200 mV once in a while.

Either the "new" MAF sensor does not match the the grams/second vs. MAF output frequency (Hz) table in the PCM, or there is a huge amount of air bypassing the MAF. At idle, the MAF (at the end of the log) is reading 4.0 - 4.5 grams/second. The engine is idling at 850+ RPM vs. a target idle speed of 650 RPM in neutral. IAC is fully closed and still can't bring down the RPM. Air is getting there through another path. The MAF reading would typically be a lot higher (as much as DOUBLE) under those conditions.

The 160/160 LTFT's with high STFT's are still present in Cells 5 and 6. Cell 10 the LTFT's drop to 153/155 with STFT's around 128. When you get on the throttle, and the PCM enters power enrichment mode, Cell 15 LTFT's are only 134/134 (+4.7% fuel) and with the STFT's locked at 128 because its in PE mode, the O2 are reading in the 880 mV range.... a bit lower than you would normally see with stock tuning, but not seriously lean for PE.

Whatever is causing the problem, the "miscalibration" or the "leak" is limited to lower engine load and throttle positions. I'm still wondering if there is a leak between the MAF and the throttle body. A tear in the rubber coupling, or the coupling being rolled under and not fully on the bottom of the throttle body still seems possible. The leak volume is somewhat limited, possibly even closing up at high air flows.

[Injuneer]

Another thought - is the hole in the elbow for the IAT fully sealed by the IAT sensor? Do you have a hole in the coupling for the air supply to eh 95's vented Opti system, and is the blue 90-deg elbow in place?

[brota]

I will look at the sensor maybe that is loose.
I had to put a small hole in the silicone to for the opti vacuum.

I know back in the day you could spray gumout to find a vacuum leak is that still true on fuel injected?

I will go run some more on it

Thank you

[brota]

thank you for looking into it

[BALLSS]

never heard of using "gumout" to test for vac leaks around manifold....starter fluid, yes.

The MAF is directional...I assume you have it installed so the arrow points towards engine?

Maybe that new Delphi style blade MAF is bad. FWIW I tried one and it worked fine...does not mean everyone is though

Fred is infinitely more versed in understanding data logs than me but a rich condition is often due to a vacuum leak after MAF

Maybe your "ebay intake" is not sealing as it should

you mentioned you had "MAF problem" before which apparently prompted you to replace MAF...are you sure the wiring to it is good and you have plugged in the connector the right way

[SSlowBoat]

hello
After dealing with some things last year I put the car away.
I noticed my original air intake was leaking so I added an ebay air intake kit with a new delphi maf because I was having MAF issues last year.

The car feels to be running a little rough almost didnt stay running but figured it was learning the maf.
I checked for codes because the light came on for few with a code 44.
I did run scan9495 and it appears my MAF is not dumping fuel like the defective maf I had last year.

The check engine light went off after a little but I didnt check if the code was still there.
Will a bad O2 sensor make it run rough? I assume 44 is the drivers side? I replaced with a bosch a couple of years ago. Are those o2 sensors good can they go bad with like 1000 miles on it?

I have attached my scan csv incase anyone can take a look at it and see if something jumps out.
https://black55chevy-my.sharepoint.com/:x:/p/brian/EcbRNCONKYpJu-nNC3NIjBgBgjGSJ4NiSFayxuv7J5nJTQ?e=fLdpl2

Thank you
Briandoes the new maf have a screen? sure your "fleabay" cold air isn't sucking closed? these engines need a 3.5" Intake to breathe (maf diameter)

Sent from my SM-N950U using Tapatalk

[brota]

yes it has a screen it
it is metal pipes

[SSlowBoat]

yes it has a screen it
it is metal pipesthere are couplings on it...

Sent from my SM-N950U using Tapatalk

[brota]

Hello
well got it back together fire damaged was only a few tubes.
I verified the cold air was tight.
I fixed any hoses that looked questionable.

Tested fuel pressure it was about 43, 38 running held pressure for about 30 min.
Check engine did not come back on with lean condition.

Here is the latest log.
https://black55chevy-my.sharepoint.com/:x:/p/brian/Eebfp9paWQ1CnKwykyh26WgB0_GKrK4bFf7eaD0eXOPmPg?e=8 UMTV8

I was driving it, it seems to hesitate somewhere between 1200-2000.38529

[brota]

tested vacuum lines again by spraying carb cleaner around nothing seemed to make the engine surge.
Anyone have an idea why the car hesitates at around 1200?

Thank you
Brian

[Injuneer]

I'll try and take a look at the data log. I was away over the weekend.

[brota]

Thank you I do appreciate it.
The hesitation seems to be a common lt1 issue but nothing really solid as a fix.
It doesnt happen when the car is cold, which is strange.

[brota]

the issue is still there when I unplug the MAF, it only seems to happen underload not in park

[Injuneer]

At idle, the LTFT's are back to rational numbers 130 Left/126 Right. Seems like you have eliminated the vacuum leak.

The problem I see is that the car has not been driven much, and the LTFT's in the seldom used fuel trim cells are still up at ~150-160. When you roll into the throttle in the 1,000-1,500 RPM range, the PCM moves to a cell that still has the ~160 LTFT's in it and the engine is suddenly running excessively rich. The PCM is gradually moving these 160 LTFT's down, but you haven't driven enough for all this to work itself out.

Clear the LTFT's by pulling the PCM BAT fuse (under hood fuse box in 1995) for 30 seconds. Drive it over a wide range of throttle position/RPM so the LTFT's can fully develop. Then see if the hesitation is still there.

It's not going to show up with the car sitting still and playing with the throttle, or with cold engine. The PCM doesn't use the cells that are causing the problem until it's in closed loop and the car is actually being driven under load.


The hesitation seems to be a common lt1 issue but nothing really solid as a fix

Totally disagree with that statement. There is nothing inherent to a properly running, properly tuned LT1 that makes it prone to hesitation in that RPM range.

[brota]

Thank so so much I will try this out, I do appreciate you taking the time to look it over. I have driven a little more since this report was taken so I will keep driving.



=Injuneer;
Totally disagree with that statement. There is nothing inherent to a properly running, properly tuned LT1 that makes it prone to hesitation in that RPM range.
Well googling around hesitation at 1100 or 1200 came up