Topic: A/F mix, cam

[damon54]

After reading some of the older posts,  I have a couple of questions about air fuel mixture.  It seems that running air flow improving mods ( 4.0 TB w/spacer, K&N conical filter, port matching the head and the intake) can add to problems with the engine runnning lean? (correct me if I am wrong)  Will that tend to balance out with larger fuel injectors? Throw in a more aggressive cam and what do you have?  I guess is it worth looking into better air/fuel management with those mods or will the engine computer be able to adjust to it?  Oh yea, does anyone running a performance cam have any trouble with rough idle?  The jeeps in pieces just deciding how to put it back together.

[Jeffy]

You really should get a WB O2 sensor to be able to monitor it.  Or else you'd need to dyno tune it.  Other then that you're just guessing which could get you in the ballpark or foul out.

[chrisfranklin]

A few days ago I ordered one of those wired-in, cheap IAT mods that are supposed to richen the fuel mixture.  Technically, you can just relocate the IAT sensor off of the intake manifold to a cooler location and maybe richen the mixture that way.  But, I wasn't overly confident there was such a thing as a "cool location" under the Jeeps hood.  And, there's no chips for 2.5YJs that I know of.

Even though I recenty passed CARB and wasn't planning on messing with the engine anymore, I figured I'd give this go (what with all the talk about 2.5 TJ chips here that was making me jealous  )  Mileage is probably going to go straight to hell, though.  AF ratio goes from probably 14.7:1 to 13:1.  WB O2 Sensor would be a nice (and expensive?) way to monitor all that

I may experiment with throwing the cone filter/pipe (and some kind of pre-filter) I had back on with this IAT mod and see if the mixture is rich enough to handle the higher airflow now.  I've been missing the highway performance I had before going back to the stock airbox and paper filter, what can I tell you. 

Makes me wonder though:  what do you need a MAP adjuster for if you can achieve the fuel curve-richening results with a mod to the IAT sensor?

[damon54]

I ordered one of those cheapo chips off of ebay and I still don't know what it's supposed to do.  The one I got wires up to the thermostat sensor though.  Will the computer richen the fuel mixture if it thinks the engine is cooler?  I've heard that the Mustang fuel injectors run rich on a stock jeep.  I thought about trying to balance the larger injectors with the 4.0 TB & spacer along with port matching the head and intake.  Probably going to have to get a WB O2 sensor like Jeffy said to see if it works.

[wrangler387]

I have a AEM conical filter on a short tube intake, spacer, 4.0 TB, pacesetter header, catless 2.5" exhaust.... My jeep still runs rich WOT... registers in the mid 11s afr wise on my PLX M300 wideband O2 with the stock ecu.

[damon54]

Will an adjustable MAP help?   I am still not sure how the map sensor works.  Isn't it supposed to adjust the A/F mix based on the pressure inside the manifold? 

[chrisfranklin]

I am in a guessing game contest as to what my AF ratio is currently.  Suppose it is normal since I passed the last emissions test. Tuning the 2.5 is too much dang work and $$ for the results you get.  Guess I just need to take the doors, top off, go off-road and dig it for what it is (defintely not something with a high-strung lancer evo engine or torque monster chevy big-block )

[aw12345]

Chris isn't that what a Jeep stands for to take the beast out in the dirt and play with it. 4 banger 6 banger they all crawl over a rock. Just enjoy the ride

Art

[damon54]

Some would like to crawl a little faster than  others.  Check out this link for how to build an adjustable MAP sensor.                    www.go.jeep-xj.info/HowtoMAPsensor.htm
It is for a Cherokee with the 4.0 but since it just manipulates the voltage sent to the computer I would think it would work on the 2.5 as well.