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-   -   fuel economy going crazy with cai! (http://www.jeepgarage.org/f108/fuel-economy-going-crazy-with-cai-46025.html)

benny82 08-13-2012 07:40 AM

fuel economy going crazy with cai!
 
Hey guys i fitted a k&n cai and a modern muscle ported throttle body a couple of days ago to my pentastar and it went great but yesterday i noticed fuel average went up to 25-35 L/100km and that bar that goes up and down acting strange ,when idol that bar goes right up. Anyone no whats going on?? air leak in the cai ,throttle body not the same or the ecu and air flow sensor not working please help!

armoredsaint 08-13-2012 05:05 PM

Re: fuel economy going crazy with cai!
 
did you disconnect your - cable?

benny82 08-14-2012 12:42 AM

Re: fuel economy going crazy with cai!
 
no i didnt i thought it was just a safety thing like working on a car unisolated ,the k&n instructions didnt say anything about the computer has to reset, i dont want to call the dealer they might say void warrenty!

Doc_d 08-17-2012 09:07 AM

Re: fuel economy going crazy with cai!
 
V6 or Hemi? I haven't looked at my Hemi yet to see if it's a mass air flow system or a speed density system.

If it's a speed density system it means that it isn't measuring the phsyical amount of air entering the engine like a mass air flow system does with a MAF sensor. Instead it estimates the amount of air entering the system based on known volumentric efficiencies of all the parts involved (including the throttle body).

So if you put on a larger throttle body, the system is completely misjudging the amount of air entering the engine which may lead to miscalculating the fuel economy.

If it is a speed density system then this is what is happening. It thinks X amount of air entered the engine based on estimated volumentric efficiencies of all parts involved (including the throttle body). But your larger throttle body really let 1.2X amount of air in. It calculates that it needs Y amount of fuel for X amount of air to hit it's target air/fuel mixture (probably stoich at idle/light cruise). It injects Y amount of fuel. The O2 sensors read that the mix is too lean. The ECU adjust short and long term fuel trims until it is now injecting 1.2Y amount of fuel. So now the computer thinks that it must inject 20% more fuel than it should normally have to. I wonder if that somehow feeds into the fuel economy calculations and is throwing it off.

This is just a guess. And if your engine is using a mass air system (i.e. if you have a MAF sensor) then this wouldn't apply.

ekaz 08-17-2012 11:29 AM

Re: fuel economy going crazy with cai!
 
Disconnect the negative battery cable for 15-20 minutes, let everything reset and then drive it. It'll need to do some re-learning


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