PimpXS and wacky AFR

fasterthangas · Mar 5, 2025

I have a genuine mystery here. I'm using the PIMPXS in SD. Car was tuned and running fine.

Cold start shows AFR in the 13.0 range and as it idles; the AFR eventually goes to 18.0.

Fuel flow and pressure appear to be fine.

Plugs look great. I changed them for good measure.

During steady state cruise I slowly roll into the throttle and the AFR jumps to 16.0 or a tad higher causing a stumble.

When stabbing the throttle, there's a momentary lean spike and then it goes pig rich to 10.0

AFR is all over the place.

If anyone wants to view datalogs; I can email them.

Thanks!

90sickfox · Mar 5, 2025

How long have you had that wideband sensor ? They need to be re calibrated in free air every few months. Make sure there are no exhaust leaks before the sensor.

Noobz347 · Mar 5, 2025

Sounds to me like a vacuum leak.

fasterthangas · Mar 5, 2025

90sickfox said:
How long have you had that wideband sensor ? They need to be re calibrated in free air every few months. Make sure there are no exhaust leaks before the sensor.

The WB has been in place for probably 1000 miles over a year to two year span.

I use the AEM unit that doesn't require calibration that I know of.

fasterthangas · Mar 5, 2025

Noobz347 said:
Sounds to me like a vacuum leak.

That's always a possibility. I haven't come across anything suspicious as far as a vacuum leak.

Noobz347 · Mar 5, 2025

fasterthangas said:
That's always a possibility. I haven't come across anything suspicious as far as a vacuum leak.

Except this:

fasterthangas said:
Cold start shows AFR in the 13.0 range and as it idles; the AFR eventually goes to 18.0.

fasterthangas said:
During steady state cruise I slowly roll into the throttle and the AFR jumps to 16.0 or a tad higher causing a stumble.

fasterthangas said:
When stabbing the throttle, there's a momentary lean spike and then it goes pig rich to 10.0

fasterthangas said:
AFR is all over the place.

Do you still have EGR or other solenoids still in play, that might cause intermittent leaks?

Noobz347 · Mar 5, 2025

fasterthangas said:
PIMPXS in SD

This too.

fasterthangas · Mar 6, 2025

Noobz347 said:
Except this:

Do you still have EGR or other solenoids still in play, that might cause intermittent leaks?

I should have worded it differently. I haven't seen anything suspicious under the hood. I looked over the vacuum lines and catch can plumbing the other day. I didn't see anything suspicious. I didn't test the lower intake though. All smog equipment is removed.

Noobz347 · Mar 6, 2025

fasterthangas said:
I should have worded it differently. I haven't seen anything suspicious under the hood. I looked over the vacuum lines and catch can plumbing the other day. I didn't see anything suspicious. I didn't text the lower intake though. All smog equipment is removed.

I'm going to move this over to [General Talk] to get some more opinions.

I'm inclined to believe that your issue may be physical/mechanical versus a tuning issue.

If I'm wrong, we can always move it back.

fasterthangas · Mar 6, 2025

Noobz347 said:
This too.

???

Noobz347 · Mar 6, 2025

fasterthangas said:
???

I'm referring to the fact that you're running your rig in SD.

[Any] abnormalities/leaks in an SD system dependent on manifold pressure will create undesirable results.

It may also be worth your time to test the MAP sensor.

fasterthangas · Mar 6, 2025

Noobz347 said:
I'm referring to the fact that you're running your rig in SD.

[Any] abnormalities/leaks in an SD system dependent on manifold pressure will create undesirable results.

It may also be worth your time to test the MAP sensor.

The Pimp uses an internal MAP sensor. I'm not sure if it's replaceable. I'll check MAP readings on the datalogs. Thanks.

Noobz347 · Mar 6, 2025

fasterthangas said:
The Pimp uses an internal MAP sensor. I'm not sure if it's replaceable. I'll check MAP readings on the datalogs. Thanks.

Good to know. I am curious about that answer too.

fasterthangas · Mar 6, 2025

I did a smoke test on the lower intake. Smoke came out of the throttle body and the front China wall area. I pulled the upper and retorqued the lower. The lower stud nuts were very loose when torquing to 20 ft lbs.
Hopefully this does the trick.

PimpXS and wacky AFR

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