AFR's skyrocet when cruisng

[edmontontom22]

hey all, ive been having a issue while driving lately. reguardless of the gear i am in, if im cruising at a constant speed my AFR's will cut to 21.9 and i will have a surge of power loss and then it will cut back to having power and regular AFR's. This will continue to happen at all times and has been getting progressively worse over time. Also when accelerating above 4 thousand rpms, AFR's will be normal (11-12) ish and i will have a cut in power.

car is running off map sensors and vipec stand alone ems, turbo upgraded(t3/to04) walbro 255, fmic, exhaust etc and is set up for 15psi

Im not looking for a solution to my issue maybe just some guidance on things to check.

I just replaced my spark plugs with new iridiums(heat range 7), but the issue was still present before hand. I have an extra set of coils which i will try out and see if it makes a difference but is there anything else i should be looking into?

any help would be appreciated.

[compactfean]

First off, I hate to say it but get rid of those iridiums they can cause tuning issues. Gap them to 30-32. Bpr7e v power plugs are good for 20+psi so you could easily get away with 6 heat range, plus copper is a better electrical conductor than iridium . I'd also ohm check your coils, that will tell you if there good. Also check your o2 sensor voltage while cruising to see if it matches your wideband, maybe your ecu is getting incorrect information. Also, since you are speed density now, it is very important that your speed sensor, cts, and tps are all working properly. Another thing is who tuned the car? If the coolant temp changes or even outside barometric pressure changes and isn't tuned for those various conditions it will cause problems. That's why mafs is usually preferred for tuners as far as reliability and simplicity. Hope this info helps.

[edmontontom22]

thanks for the reply, i was unaware that the iridums were garbage, ill look into a set of bpr7e v power's, the car was tunned a reputable tunning shop here in alberta which is also a dealer for vipec ecu's. Speed sensor is not functional since i just replaced my transmission with a s13 transmission and still have the s13 speed sensor. But not to sure how that could be affecting my tune, could you explain?

One thing i did notice when swtich over to the iridums was that when the car was cold it had a rough time idling but once it heated up it perks up.

One last thing to add which point me towards timming/CAS is that when holding my car at a constant rpm level it cuts out then revs back up to the previous level.

[edmontontom22]

http://www.youtube.com/watch?v=KT_4xhzg ... re=related

this video is related to how my car runs when trying to hold rpms constant

[compactfean]

Nissan fuel maps are based on a "tp" value which is theoretical pulsewidth. The magical tp number at a given rpm is calculated from the cts,tps,maf,cas. The ecu then determines with all of this info how much fuel to add with a questimation of how much load is on the motor. Because the maf is not effected as easily as a map sensor as far as temperature, barometric pressure, example (if you change elevation you sometimes have to shut your car off and then turn key back on for the map to recalibrate and car magically runs better) or load the ecu doesn't need a speed signal. Hence the reason there would never be a check engine light or code because not having a working speed sensor doesn't effect emissions (when is why there's a check engine light)
Now because a map sensor can easily be affected by outside variables, they use the speed sensor and intake air temp sensor as well as the cts, tps etc.. To come up with the best "theoretical " load of your engine to put in the proper amount of fuel. All that being said it seems to me that you need to adjust tps and set timing from how you describe your symptoms.

[csramotorsports]

Ya sounds like something possibly related to your TPS. retarded question...but whats the abbreviation cts for?

[compactfean]

Coolant temperature sensor

[csramotorsports]

ah.