Ugly71C20

I have a 71 Chevy C20 that I swapped a 2003 silverado 5.3 with a nv4500 behind it into using LT1swap.com's PCM reprogram. After 200 miles on the swap it started stumbling, being gutless and running supper rich. I plugged it in and I am getting P0101 and occasionally P0135/P0155. My scanner is pretty simple so it doesnt do live data unfortunately but I put a multimeter on the MAF output wire and it is reading 0Hz no matter what I try.

Things I have tried:
Swapped in 2 new Delphi MAF's
Rewired MAF plug
Checked for vacuum leaks
Cleaned throttle body
New intake manifold gaskets
Verified ignition hot and ground to MAF
Verified continuity/resistance to PCM from MAF
The IAT is getting its 5v reference and has continuity back to the PCM

What am I missing here? Any ideas? I am stumped

Heres the thing... so ugly its almost cool

lsxRanger94

Turn the key on and check wire at the iat for 5 volts. If there is no 5 volts there, you will have to check for 5 volts coming out of the computer with the key on. If still no voltage coming out of the pcm on this circuit with the key on, then chances are the PCM is at fault and will need to be replaced. Otherwise it's a harness issue. check for continuity to ground on reference wire,

Ugly71C20

I tested it again and got the 5v reference on the IAT and a good ground for the IAT as well. I think I might have had the key off or my wires mixed up when I tried yesterday. Checked the MAF side of the plug again too, it's getting 12v ignition hot, a good ground and the signal wire is at 5v key on engine off. The signal wire drops down to about 4.2v at idle.

I thought the MAF was a frequency thing not a voltage thing so I never tested the voltage at the signal wire.

Still getting all three codes

busta9876

iTrader: (3)

Focus on the P0135, P0155, those are related to the oxygen sensor heater circuits. make sure you have KEY HOT 12v+ to the PINK wire at each oxygen sensor. make sure your oxygen sensors are for 2003 5.3L engine. The 2002 sensors have same plug and will plug in, but will result in heater codes.

The Oxygen sensors must reach a certain temperature to send proper signals to the PCM.

Ugly71C20

Ill check that out. They should be for a 2003 unless the parts store gave me the wrong sensors.

Here is the freeze frame data I got the last time I took it on a test drive. Isnt the MAF value low?
Fuel Sys 1 CL
Fuel Sys 2 CL
Calculated Load 8.6%
Coolant Temp 188.6*F
STFT B1 -23.4
LTFT B1 -5,5
STFT B2 13.3
LTFT B2 24.2
Map 20.4 inHg
RPM 1329
MPH 34
MAF 2.6Lb/min
TPS 19.2%

busta9876

iTrader: (3)

wow your fuel trims are all jacked up. One side going positive, one side negative. This usually happens when o2 sensors are plugged into wrong side of engine.

There are 4 wires going to each oxygen sensor. The wires on the DRIVERS side should include a PURPLE wire with a WHITE stripe.

The wires going to the PASSENGER side o2 sensor should be SOLID PURPLE, no stripe.

Also, if there is any Y pipe on the exhuast, need to be sure the o2 sensor ONLY samples the exhaust gases from just the side its on. If a passenger side o2 sensor samples gases mixed from both sides, you can have issues as well.

busta9876

iTrader: (3)

If you do find your wiring switched up, correct it, and leave battery unhooked overnight so it will reset fuel trims. This can also be done with some good scan tools.

Ugly71C20

I just checked the o2 sensors they are on the right sides, they are getting 12v ignition hot and have continuity back to the pcm on the purple wires.

There is a y pipe but the closest sensor is about 2 feet from it

pdsq98gt

Also make sure the injectors are wired correctly. If they somehow got switched bank to bank it could cause those weird fuel trim readings.

Ugly71C20

I will double check but the way the harness is laid out for the tps and throttle body actuator plug it can really go on one way

Hart_Rod

iTrader: (3)

swap o2 sensors side to side and see if the fuel trims switch. Did you happen to change your air intake setup? Also, you might want to try a new set of plugs.

Ugly71C20

I pulled the ground over night to reset the PCM, put a new set of plugs in it and swapped the o2 signal wires side to side at the PCM. I also picked up a scanner that can do live data. Its still running supper rich but the fuel trims are back at 0. Looking at the oxygen sensors Bank 1 bounces around between .030 and .040 and Bank 2 is .440. MAF .9lb/min TPS 5.5%. Not sure what most of this means. The O2 codes are gone but I only drove it a mile or so after the reset so the O2 codes might come back. The MAF P0101 is still there. It was pretty gutless still and stalled on me when I got off the gas to turn around.

What should I look for in the live data?

4wheels

0.030 to 0.040 for bank 1 O2 sensor voltage means something is likely wrong with the O2 sensor or the O2 sensor wiring. 0.030 to 0.040 volts would mean a very lean condition (lots of excess oxygen).

0.440 volts is normally although it should be going up and down centered around 0.440 once it is in closed loop (down to around 0.200 and up to around .700).

Earlier you mentioned checking the MAF with a voltmeter. These are frequency type MAF sensors so you can't check the signal based on voltage. The sensors read from about 1000 Hz to 10,000+ Hz (to give you an idea of the measurement range).

P0101 is either sensor problems or a calibration problem. P0101 indicates that measured airflow (from the MAF) doesn't match the calculated airflow (basically from the VE table).

Assuming the calibration is fine things that cause a mismatch and set a P0101 are: bad MAF sensor, wiring problem to MAF or MAP (but it looks like you are getting signals on those sensors so that probably isn't it), air leak after the MAF sensor. Since one bank O2 sensor is giving odd readings you might want to check if any vacuum fittings, hoses etc. are broken or missing on that side.

Ugly71C20

Alright I will go through all the O2 sensor wiring tomorrow and see what I can find. Ill look into the vacuum lines and ports again too.

As for the MAF, I thought it was a frequency thing too, even went out a got a new multimeter so I could test it but never could get a read from it (with 3 different MAF's, new wiring at the plug and verified signal/ground/12v). Maybe I am testing it wrong? Multimeter in Hz positive lead on the signal wire, negative lead to a good ground?

240dan

Start with the 02 sensors first then work your way back to the MAF issue. In other words, get the o2 sensor problem fixed, unplug the MAF, and focus on the VE table, THEN go back to the MAF. If you've checked the wiring/grounds, and the MAF itself, then it's computer time.

Regarding your 02 sensors: when I first built my car, I installed new Bosch 02 sensors. The car ran but the fuel trims were off. After a lot of screwing around I took it to a pro tuner and he said I needed to lose the Bosch 02s and install some OEM 02 sensors. He was right, problem solved.

Ugly71C20

Finally got some time to work on the truck. I swapped in 2 delphi o2 sensors and redid the ground on the back of the passenger head which is the ground for both the passenger o2 and maf. No luck, still getting P0101, P0135 and p0155. Its gutless and stumbles when you let off the gas to start slowing down.

Looking at the live data it doesnt seem to swap over to closed loop even after a trip around the block and 5 min idling in the driveway. Watching the o2 sensor values bank 1 will hover around .440-.445v. Bank 2 sits at .440-.445 at idle but bounces from .020/.030 to .770/.820 if I put it up to 1000 or 2000 rpm. The short term fuel trims stay at 0.0.