LY5 to LC9 Injector question

[Jonathan Motloch]

Good day everyone, 

 

About 4 months ago purchased a 2008 Silverado 1500 5.3 LY5 vin J . The prior owner had put a 2011 5.3 LC9 in the truck as the original LY5 had blown.  One day I noticed the engine acted as if it was stalling on sudden deceleration. To my surprise the the long term fuel trims were -16.7 % at idle sometimes ranging as high as -21% 
I went through the DTC for PO172 and PO175 . Suffice to say all of the parameters were passed. No exhaust restriction, no vacuum leaks, MAF reading is correct, receiving proper fuel pressure 43 PSI, injector resistance was 14 ohms on all but one injector at 13.9 ohms. O2 sensors are good. 
The only reading that is severely wrong is the MAP which reads 25.1 in Hg. I live nearly at sea level normally Barometric pressure is 29 in Hg here. 
I replaced the MAP sensor and the reading went to 24.8 , the pigtail for the sensor is spliced into the harness. 
I went through PO 106 all of the circuits tested normal 
*[ less than 5 ohms between low ref and ground] - reading was 0L 

*[ignition on 4.8 -5.2 volts between 5 volt ref and ground] - reading was 5.12

*[MAP sensor harness unplugged must read less than 12 kPa] - reading 10kPa

*[install 3A fused jumper wire between signal and 5 volt ref must read above 103 kPa] - Reading was above 103 kPa

signal circuit passed short to ground test

Found the pins on the ECM connector for the MAP pigtail. I tested for continuity between both ends for 5 volt, ground, and signal. All three had continuity. 
This lead the DTC106 instructions to say replace ECM which I did. The problem still happens. 

The check engine light has yet to come on

 

Which leads to my questions
1. Is there a major difference between the 2008 MAP sensor and the 2011 and where to go with diagnosing why the MAP reading is wrong key on engine off.

2. The LC9 engine used flex fuel 37 lb injectors where as the LY5 used 30 lb, upon looking at the injectors in my truck i believe he kept the flex fuel injectors on the LC9 and that is part of my fuel issue. What injectors should i replace them with the stock LY5 injectors Part#217-1621?

Any advice or ideas of how to proceed is much appreciated. 

 

[CamGTP]

Yes, the MAP sensor is different between a 2008 and 2011. The switch over was in 2009-2010 to the later style sensor. The linear and offset settings are much different between the two.

 

If the injectors are indeed different size, then yes you need to change them back or tune the computer. A tune can fix both of these issues if you owned HP Tuners or knew someone that did.

[Jonathan Motloch]

Thank you Cam GTP!

 

Okay so even though the MAP sensor pigtail is spliced into the 08 engine harness the ECM settings for the map need to be reset? 

[CamGTP]

Correct. I am going off memory here but in the calibration the 2008 sensor is 94/10.3 for the linear/offset and the 2011 is 121/-0.31 for the settings. Even though the harness pigtail was swapped the calibration is still running the 2008 sensor settings if it was not tuned.

 

If tuning isn't something you can do you can just swap the sensor and pins around in the pigtail as well as swap back to the other injectors.

[Jonathan Motloch]

Thank you, I will call a tuning shop!

[Japmaster]

On 5/12/2021 at 7:35 PM, Jonathan Motloch said:

Good day everyone, 

 

About 4 months ago purchased a 2008 Silverado 1500 5.3 LY5 vin J . The prior owner had put a 2011 5.3 LC9 in the truck as the original LY5 had blown.  One day I noticed the engine acted as if it was stalling on sudden deceleration. To my surprise the the long term fuel trims were -16.7 % at idle sometimes ranging as high as -21% 
I went through the DTC for PO172 and PO175 . Suffice to say all of the parameters were passed. No exhaust restriction, no vacuum leaks, MAF reading is correct, receiving proper fuel pressure 43 PSI, injector resistance was 14 ohms on all but one injector at 13.9 ohms. O2 sensors are good. 
The only reading that is severely wrong is the MAP which reads 25.1 in Hg. I live nearly at sea level normally Barometric pressure is 29 in Hg here. 
I replaced the MAP sensor and the reading went to 24.8 , the pigtail for the sensor is spliced into the harness. 
I went through PO 106 all of the circuits tested normal 
*[ less than 5 ohms between low ref and ground] - reading was 0L 

*[ignition on 4.8 -5.2 volts between 5 volt ref and ground] - reading was 5.12

*[MAP sensor harness unplugged must read less than 12 kPa] - reading 10kPa

*[install 3A fused jumper wire between signal and 5 volt ref must read above 103 kPa] - Reading was above 103 kPa

signal circuit passed short to ground test

Found the pins on the ECM connector for the MAP pigtail. I tested for continuity between both ends for 5 volt, ground, and signal. All three had continuity. 
This lead the DTC106 instructions to say replace ECM which I did. The problem still happens. 

The check engine light has yet to come on

 

Which leads to my questions
1. Is there a major difference between the 2008 MAP sensor and the 2011 and where to go with diagnosing why the MAP reading is wrong key on engine off.

2. The LC9 engine used flex fuel 37 lb injectors where as the LY5 used 30 lb, upon looking at the injectors in my truck i believe he kept the flex fuel injectors on the LC9 and that is part of my fuel issue. What injectors should i replace them with the stock LY5 injectors Part#217-1621?

Any advice or ideas of how to proceed is much appreciated. 

 

Seems as though the pcm is trying to do its job properly to trim the excess fuel.  I would change the injectors as they are either wrong sizing or have been capped for larger fuel capacity. I had same issues with my lc9 engine.