LC1 reading lean under WOT

[kchaazz]

So, a couple months ago, I was pulling a log, and I noticed that my WB gauge was reading lean in the 12- 13:1 range at wide open throttle (Im targeting 11:1 AFR in that load range). I backed off the throttle right away and began to troubleshoot. Wideband is an LC1, installed per instructions with the output shared between the EGRT and DB gauge, and it worked fine for well over a year before this started. After all the things Ive checked, Im leaning toward a bad sensor, but Im still not sure because the thing reads 14.7- 15 at idle and cruise, and goes to 22.xx under decel as it should. The basics are as follows: Denso 660cc injectors, Jay Racing in tank 340 fuel pump, FP 18g, fuel lab filter and afpr. Base pressure is 38psi, base timing is 5* BTDC, plugs are BR7ES, gapped to .024, wires are good, NGK. Im using Tunerpro RT to tune, and everything is set properly regarding the 2g maf comp, injector comp and deadtime, but if anyone is familiar and interested, I can send a copy of my adx, bin and xdf for inspection. The car runs absolutely great, other than not wanting to get into boost.

1. Tried a known working maf from a friend
2. Boost leak test, no leaks
3. Bought a new fuel pump, no change
4. Bought a new fuel pressure regulator because my old one seemed to fluctuate and was leaking a little fuel into the vac line
5. Tried a new gauge on the fpr, just to see if the gauge was a few psi off, no change there either
6. Checked voltage at the pump, its 13.xx
7. Set boost to just 9- 10 psi and still the afr didnt change
8. Set the load cells in the fuel map to 9.0:1 just to see if anything would change and there was still no change on the gauge at wot.
9. Pre sensor exhaust leaks- I took the manifold off, and took it to Bogussvo, and he found that the flange at the head side was warped, so he surfaced it for me. I also thought that perhaps the brand new DP flex section I put in was leaking, so I put the WB sensor upstream from it, but still there was no change.

10. I did a free air cal per the innovate instructions with no change
11. Changed the fuel lab element, no change
12. I even put in a set of stock 450cc injectors, set the comp and dt for them and nothing changed

 

[kchaazz]

Alrighty, I know this is a pretty tough one, so I think Im going to try a new WB sensor and see if it clears up the problem cause thats the only thing I can think of...

 

[Kevin Jewer]

It is possible for sensors to read fine at idle/cruise but fail to operate properly when hot (WOT). A common failure mode for the typical bosch sensors is to read 13.5-14.5 at WOT no matter what AFR actually is. It will usually return to normal readings as soon as you let off the throttle. An over heated sensor will also read lean but it takes a pretty agressive setup to get into that territory (i.e. 90-100 lbs/min through a 3" exhaust pipe).

 

[kchaazz]

Good deal, I was almost certain it had to be a fuel delivery issue but Ive checked and re checked everything I possibly could! The sensor is only 50 ish dollars at the local parts slingers, so Ill give it a try and post back.

 

[kchaazz]

I put in a new sensor for the lc1 this morning. After a free air cal per the instructions, I set my fuel map to target 9.0:1 afr just in case and took it for a spin. Damn thing hits 11.9- 12:1. As a test, I set the map to target 11.9, and it tried to hit 13- 14:1. SOmething is really wrong and Im al out of ideas now...

 

[kchaazz]

As a final check before I buy a new wideband controller, I decided to check the TPS and coolant temp functionality, though Ive never known the CTS or TPS to be used for open loop fueling directly.

The TPS: I was able to adjust it to read .50 volts, manual says .48- .52 acceptable.
Resistance: pins 1- 4: 4.3K Ohms, manual says 3.5K- 6.5k acceptable.
Resistance: pins 2- 4: Closed- 620 Ohms, Open- 4600 Ohms, manual says 1100 Ohms closed, 5600 Ohms open.
This is way off, so its certainly out of range and should be replaced if the manual is to be taken seriously.

On to the CTS: I checked it at approximately 80* F, it reads 600ish Ohms. Manual says that at this temp, I should see 2200- 2700 Ohms.
So, would changing these fix my open loop troubles???