I have seen as low as 9.8 momentarily, can hear it crackle then it goes lean like it should. In my logs this whole operation is lasting about .4 second.

 

For mine, when i let off the throttle (in gear) it stays at 10.3 after a quick spike to 50-60 right as I get off the throttle. It doesn't fluctuate or anything from coasting down 6000 to 1000, any gear....no change.

 

ya this lift off phenomenon is still a mystery to me. during logging I noticed my 4 knock sums would be EXACTLY at the moment of lifting of throttle (0%). Which puzzled me because I would think all air would stop but fuel still being delivered, and because of the accel enrichment map it would also work for deacceleration as well. People told me its really a knock and not a phantom knock and that I should worry about it. I dont see how the heck it can run lean from lifting off the throttle, it just dont make sense.

 

I am at like 12.6-13.5 as soon as I let off

 

thats the injector over-run delay i talked about in my original post. it will typically last .5-1.0 secs, depending on the engine and it's ECU. During this time, there is a lot more fuel than there is air(throttle plate is closed), therefore it's completly normal to see a rich condition during this time.

It's also important to understand that if the ECU was in open loop during a pull, it will continue to stay in open loop during decel depending on several circumstances.

CJ

 

Just checking if anyone's made any progress on this?

 

I put a different turbo in my car and it made a significant difference in throttle lift richness. the turbo was basically the same, slightly different wheels. used the same ign and fuel maps.

I can't figure the correlation. You have a quantity of metered air that has been given fuel. The fuel is getting there but the air is not. As to why there is a difference pre and post turbo instillation makes no sense. The only other variable would be the new intercooler.

Makes sense when the throttle has closed, the figured air mass isn't allowed to get to the cylinder. The gas does because the ecu can't keep up with the change in air intake. Would the same situation happen when the throttle is reduced (not closed)?

 

There is always some time based lack of correlation there because of the meter's distance from the cylinder. Accel and decel fueling make some attempt to mitigate this, but I wouldn't be surprised if it can't do it all of the time. I'd also speculate that perhaps setups like AEM with a MAP sensor right in the manifold are easier to tune for accel/decel, since the only lag time is really the distance between the injector and the cylinder, with no throttle plate to interfere. But I'm half asleep here and reserve the right to be wrong about any of this...

 

I run a PFC ecu, with a MAP i also go slighly richer before it goes lean.

Another thing, where is your O2 sensor? This could be causing it? I.e. slower.

 

I don't know if it's the O2 sensor since it's sitting pretty much where the stock one was in the O2 housing.

I've attempted to adjust timing in the lower load areas, adjust my fpr, rescale my maf, and adjust latency on my injectors (880 PTE). My car is running smoother, but the problem still hasn't gone away. I'm going to check my PCV and ISCV next.

This has been happening since I was just on 272/272 cams with the usual mods prior to cams about 2 years ago. I appreciate all the input. I was just wondering if anyone's discovered anything since this thread has been quiet for a while.

 

I figured out the issue with mine going rich off throttle. The slide bracket behind the valve cover with two bolts that hold the throttle cable. The tension was too taught not allowing the throttle plate to fully close after letting off the gas.

A way to tell if this is your issue is after you let off the gas and it goes rich stick your foot behind the gas pedal and lift. AFR's go lean?

I repositioned the cable placement on the bracket and all is as it should be

 

You should be able to see that in the TPS signal as well.

 

I worked on this a little more. There are two scenarios that help to remedy the stalling, but doesn't resolve going rich before O2.

When I lift it goes rich then goes to O2 just like the OP described. I've adjusted the stepper table up 5 values across the board, which keeps the revs hang a bit and prevents the car from choking out to near stall.

The second scenario that I tested was decreasing my injector latency primarily in the 11 and 14 volt ranges, which keeps the STFT higher. (All LTFT values are still 100 on Evoscan.)

In both cases my car doesn't stall anymore, but it still goes rich before going to O2. I feel like I'm putting bandaids on a physical problem.

Although I'm recirculating, the car is behaving like I'm VTA. I'm going to swap out my BOV, and see if that helps at all. (I've already cleaned the throttle body, IAC motor, PCV, adjusted the idle adjustment screw, and checked the throttle cable while removing and re-installing the TB. None helped.)

 

When logging with the LC-1 and EvoScan, I get a reading of 10.3:1 when the injectors cut out. This isn't the actual AFR value, as the Innovate XD-16 gauge will read free air at the same time (as witnessed in a friend's car).

the rich condition before going to O2 is an actual issue though ... I always assumed it was simply the OL/CL crossover delay.

 

I'm having the same prob...everytime I lift off the throttle, my XD-16 will show very rich O2 readings (10.5 to 12.5) for maybe 2-3 seconds before going lean (18.0 to 20.9) for the remaining duration of the decel. The car doesn't stall but its quite irritating to see it react opposite to what it should under decel. Also, this happens regardless of whether the lift off is during cruising (close loop) or WOT (open loop).