emissions, poor gas mileage?

[utah_xj]

I have an 87 jeep Cherokee. It has the 4.0 I6, fuel injected. I am having a number of problems and don't know if you have any suggestions.

First off, I am getting 11 miles per gallon. I have a 4" lift with 33" tires. My engine has around 210,000 miles on it. I change the fluids and clean my filter regularly, also I keep my foot out of it when I drive, but I am sill getting really bad gas mileage! Is this normal? If not any Ideas?


Next problem...... My engine miss fires only at idle. I have replaced and gaped my plugs, new wires, new cap and rotor, checked my map sensor, new oxygen sensor, I have used "seafoam" in the intake, oil, and gas. I checked and replaced all of my vacuum lines (and did away with that vacuum connector) I replaced my fuel injectors, checked my fuel regulator. I did a compression check; all of the cylinders were within the recommended 20-psi variance. I swear I have done everything and still it miss fires at Idle. I'm about ready to give up!


Problem three...... Last time I took it in to get the emissions checked it failed miserably!!!!! I replaced my egr valve and my cat, it fixed the high rpm test but it kept failing the idle. I think it might have something to do with it miss firing if I can ever figure that out.

Do I need a new motor?
Please help!!!!!!!!!!!

[Papa Mo]

I cant help with the miss fire, but my 95 XJ got 17-19 mpg before I put on a 4.5 lift with 31" tires now my MPG has gone to about 13 mpg...

[utah_xj]

That’s good to know, I got the jeep stock but never drove it until after I put the lift and tires on. So I never new what kind of gas mileage I was suppose to get.

[OlneyJeeps]

CPS: dirty/cracked/bad connection
what is your fuel pressure (just found paparonbo's gauge, gotta get it back to him) if pressure to low, bad atomozation
is your spedo corrected for tire size (odo reporing fewer miles than actual)

[TwistedXJ]

Uth comes with the territory! I got 20 before and with the lift and 33's I get about 10

[utah_xj]

I just did a pressure check and I am running 30 psi with the regulator attached. The Haynes manual says I need to be at 31 psi. is 1 psi going to make a difference?

[utah_xj]

I checked my cps and its reading 235 ohms wich is also within spec. should I take it off and clean it?

[AZXJ]

have you changed your speedo gear ?

how is the PCV system ? 02 sensor in good shape ? last time the cat was replaced ?

do you have an NP242 transfer case ?

Dave

[utah_xj]

I havn't changed my speedo gear yet. I don't know which one I need to get for 33's. I have only had this lift and tires for maybe 2000 miles (don't know exactly since i havn't changed my speedo yet)

pvc system good

new o2 sensor

new cat 1000 miles ago.

[AZJeeps TJ&XJ]

Check the connection for the CPS, mine was loose and at an idle it would sound like a miss almost. As for passing the sniffer, if you just changed you cat, give a few more miles and make sure the 02 sensor has a good connection. Also a fresh tank of gas with no additives helps. What are the numbers that it is failling on? We can give you some better ideas with those.

[utah_xj]

I got it to pass the high speed but my idle is HC 1009, CO% 2.49 yea I'm almost off the chart.




I have the 231 Transfercase