Code P0174 &P0171 65 miles after LS Swap installed.

[Nodnarb76]

Hello all just finished up my LQ4 4L80 swap on my 87 Suburban.
Everything was great until this afternoon check engine light came on. Took it to Autozone and they scanned and got codes P0174 & P0171, fuel trim lean on banks 1&2.
They told me most likely a bad MAF sensor. Before I bought one decided to get people's opinion here. Here is what i am thinking: when I installed my swap, I had to mount th MAF directly to the throttle body and then mounted an new K&N air filter directly to the MAF. I've heard that it's not a good idea to mount it that close to the throttle body, would that set these codes?
Also because I mounted my new K&N filter to the MAF, Could some oil from the filter have gotten on the MAF and given me these codes? This may explain why the CEL came on after 65 miles of driving instead of when I did my first startup, just long enough to have oil come off the filter.

Opinions?

[clinebarger]

What I do is....Scan the PCM for High LTFT & STFT readings (Lean) with he engine running, If they are high +15 or higher.......Unpin the Yellow wire from the MAF, Start the engine (It will set a P0101) & monitor the Long & Short Fuel Trims, If the fall back to Zero +/- 5....Suspect a faulty/dirty MAF OR the MAF in the wrong/bad location, My Camaro set lean codes using a stock tune truck PCM because where the MAF is located about 6 inches forward of the throttle body. A custom Tune fixed mine, If the same is true for you....Relocate the MAF closer to the stock Truck location.

If unpinning the Yellow wire has no effect on LTFT/STFT in closed loop, Suspect a Vacuum Leak.

Running open exhaust will also cause a Lean reading by the O2 sensors.

[Nodnarb76]

Originally Posted by clinebarger

What I do is....Scan the PCM for High LTFT & STFT readings (Lean) with he engine running, If they are high +15 or higher.......Unpin the Yellow wire from the MAF, Start the engine (It will set a P0101) & monitor the Long & Short Fuel Trims, If the fall back to Zero +/- 5....Suspect a faulty/dirty MAF OR the MAF in the wrong/bad location, My Camaro set lean codes using a stock tune truck PCM because where the MAF is located about 6 inches forward of the throttle body. A custom Tune fixed mine, If the same is true for you....Relocate the MAF closer to the stock Truck location.

If unpinning the Yellow wire has no effect on LTFT/STFT in closed loop, Suspect a Vacuum Leak.

Running open exhaust will also cause a Lean reading by the O2 sensors.

Won't be able to get to a scan tool, that will read fuel trim until Tuesday when I get back to work. Plus I'm not sure how to unpin a wiring connector. I need to learn though, also need to get a 98 diesel accelerator pedal for my swap and re-wire it too.

Until Tuesday my plan now is: Clean MAF with MAF cleaner if that doesn't work, replace MAF and keep receipt. If that doesn't work, then spray the mess out of the intake manifold and brake vacuum hose with brake cleaner, and see if the idle changes.

If this doesn't work still will have to wait until Tuesday to get a scan tool.
Thanks for telling me what to look for.

[truckdude239]

Mine on my 02 suburban 5.3 was intake leaks i now have the same codes in my 71 cq0 with 4.8 i smoked it same thing intake leaking

[Nodnarb76]

Still can't get a scan tool until Tuesday. This morning I disconnected the battery to reset the light and removed and cleaned the MAF. Found a loose hose clamp at the throttle body/coupler. Once I put it back together no CEL.
But today when driving it came back on, when I was accelerating pretty hard getting on the interstate. Sprayed brake cleaner all around the intake manifold and no change in idle. Ordered a new MAF, and parts to move the air filter and MAF away from the throttlebody today, hopefully this does the trick.

[Nodnarb76]

I got a hold of a scan tool today and checked fuel trim:

[clinebarger]

That looks to be "Freeze Frame" data (Though not familiar with that scan tool), Its shows what the data stream was reading when a code trips.
+25% on both LTFT's will set those two codes.

Access the Live Data & unplug the MAF & watch LTFT's.

Intake Vacuum leaks are easier to prove out with the engine cold, Check with carb cleaner on the first start of day.

[Nodnarb76]

Originally Posted by clinebarger

That looks to be "Freeze Frame" data (Though not familiar with that scan tool), Its shows what the data stream was reading when a code trips.
+25% on both LTFT's will set those two codes.

Access the Live Data & unplug the MAF & watch LTFT's.

Intake Vacuum leaks are easier to prove out with the engine cold, Check with carb cleaner on the first start of day.

Good idea. Will try that tomorrow morning. Thank you for the help.