Mpg went to total crap after k&n

[destroyer1362]

I replaced my stock intake w/ the k&n fipk mid summer and at first my mileage was bad bc I was driving it a little harder than I normally do, and the a/c was on. Mileage got a little better after I let up on the gas. Now the mileage seems to be getting bad again. I just checked it earlier today and now its at 10.14mpg!! No codes, no lights, and the fuel pressure is around 67-70psi minimum so the pump is good. The only thing I have noticed is the intake may not very snug to the TB so I'll probably seal it tonight. The only other thing I noticed is there is a lot of carbon build up around my exhaust tip. Any ideas? O2 sensor maybe?

 

[bowtiefreak]

I would say you are running rich. Truck is a '99 right? Something is wrong regardless. Get it sealed up better and re-check. I would think if it were the O2 sensor you would get a SES light

 

[destroyer1362]

2000, but yeah it's the same 5.7 as in the 98 and 99s.

EDIT:

Tightened it up, so cross your fingers thats all it was. Where the condensation from the exhaust lands behind the truck theres a black spot on the garage floor from all the carbon build up. Any other ideas on what else could cause a rich condition?

 

[SunlitComet]

o2 sensors would have popped a light. You may not have a MAF code yet but make sure your maf sensor is clean and not oiled over from a saturated air filter.

 

[19Yukon97]

Crap... didnt want to hear this. hope it gets fixed! i was gunna buy a k&n or a volant. dont like seeing that its hurting ur MPG! i get 16 and really dont want to get less... lets us know if you fix the problem!

 

[destroyer1362]

There was a pretty big gap between the tubing and the TB before I sealed it up. But if that doesn't make a difference would I be able to swap the maf from the z28 to see if it makes any difference? I think they're the same..

Nick, go ahead and buy one, I'm pretty sure it's not the filter but the fact I screwed something up here

 

[drowndindreams]

how do you calculate your mileage? i need to know!

 

[bowtiefreak]

I also second cleaning the MAF. A can of cleaner is like $8 and it cleans it up quickly

 

[SunlitComet]

would I be able to swap the maf from the z28 to see if it makes any difference? I think they're the same..

Only if you can verify the part numbers are identical. If you can get a scanner with live data stream to post I can give you specs on what you should see on what sensor if one of them is malfunctioning.

Also depending where this break was what your TB get in mass airflow and temperature might be different then what those sensors are measuring which will affect your running. For example if the break is after the air temp sensor it maybe picking up the temp or cold from outside but the vacuum in the ducting maybe sucking up engine heated along the way screwing things up. Dig?

 

[noJeepshere]

I have the K&N cai, and I get around 18 on the freeway, 14-15 mixed town driving, but my mileage goes to pot when the weather turns cold (read: 20f and below) My last tank ran me 11.5 mixed driving. But even in the cold if I do a roadtrip I'll still get 17 or so, it really just depends on how long the motor is in "cold" mode and dumping fuel in a cold motor.

I calculate mileage when I fuel up: miles driven (to the 10th) divided by the number of gallons used (to the 100th)

I would suggest cleaning your maf as it is prolly gunked up from an overoiled air filter, mine was similar when I put my intake on.