Hey guys I have an issue. I've done some searching and it seems that stumble and shaking is usually caused by too much fuel. My problem is that under crusie control, when set to about 65, when accelerating up an incline around 5-0 in of vac my car starts to shake and stumble. I checked the knock on the commander and its highest value was 95. It only happens with the use of cruise control when holding 7-0 in. of vac for an extended period of time. My plx-m300 reads about 13.5 at 7 in of vac and 12 at 0. Am i running too rich at this low vac level? I am running stock injectors, stock spark plugs, catback, hi-flow, intake, pfc and 12 psi. If any other information would help diagnose the problem, please let me know.

I also have one other issue. My wideband reading seems to be off sometimes. Under highway cruise sometimes the afrs will read from 14-14.5 and other times 17-20. When totally off of the gas decelerating in 5th it reads "lean" then changes to "air". Also at idle my the display shows from 17 afr to "lean". In summary at idle and at cruise with high vac, 14-17 my wideband continually shows very lean readings and under full decel with no brakes it reads "air". Can anyone help me with this? I thought the plx-m300 required no setup and was plug and play. I've checked and replaced my exhaust gaskets and made sure the wideband was completely in the bung.

Thanks in advance for any assistance.

 

This is completely normal. When you decelerate in gear, the car cuts fuel to save gas and prevent backfire. If you have a pfc, you can see this happening when the injector duty cycle goes to zero.

 

Wow, im slow. That totally makes sense for decel, but what about idle. It reads very lean i.e. 18-20. Any clue about the shaking? Thanks,

 

I hope that your air pump is either removed or disabled. If not, it will give false leaner AFR readings due to air dilution of the exhaust gases. Most noticeable at idle. The air pump works up to about 3000 rpm.

If you are reading richer than AFR 15 at 65mph, you are way too rich.
I run 16-16.5 AFR from 45 - 100mph cruise. It really cleans up the plugs and exhaust.

 

That may be it. I don't have the air pump removed. It is left on for the next time i have to pass emission, which will hopefully be the last. To disalble it can i just removed the tube from the cat, plug the hole, and let the pipe inject air to the atmosphere?

 

I did some searching at it seems the my options are to remove it or unplug its connector. There seems to be some descrepancy as to whether unplugging it will
1. destroy the cat
2. cause the airpump to fail if left unplugged for an extended time period
Does anyone know if either of those is true? There don't seem to be any difinitive answers.

 

Think easy! Disconnect the electrical plug for the AP.

It will not hurt the cat if only removed for AFR tuning.

 

Will do, thanks again Chuck

 

Chuck is the man!! After unplugging my airpump i my idle afr now reads correctly @ 13.5. So now i can tune my cruise and idle areas. Hopefully there will be no ill effects to the airpump if it is disconnected for an extend period. Anywho thanks Chuck