Rough idle and poor gas milage, related?!
05-21-2015, 04:35 PM
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Rough idle and poor gas milage, related?!
1997 4.0 XJ with 150K miles bone stock!
Recent rig into our family and first time jeep owners, but having fun and the kids love it!
Fuel mileage is 10-12 mpg for city driving and I am a conservative driver! My wife isn't..and that's why we get 10 mpg sometimes!
Recent plugs, air filter, O2 (upstream), tested the MAP and it performed close to perfect, sprayed around the vacuum hoses and no change in engine load, starts right up and no funny shut-down backfire, etc. Decent running rig other than being a noisy 4.0 when cold and.....
...my odd idle issue. Idle issue is fairly identical to this guy's post on YouTube. He claims it was the CPS and I'm not saying it isn't, but I'm looking for every excuse not to pull it out, b/c it looks like a pain!
Could this rough idle be associated with fuel milage? I'd think yes, b/c the jeep would be firing at the wrong time.
I was thinking of checking timing on cyl 1 with my timing light and maybe even adjusting the distributor a little to see if it responded well.
A fairly new XJ owner looking for XJ advice. Thanks.
Recent rig into our family and first time jeep owners, but having fun and the kids love it!
Fuel mileage is 10-12 mpg for city driving and I am a conservative driver! My wife isn't..and that's why we get 10 mpg sometimes!
Recent plugs, air filter, O2 (upstream), tested the MAP and it performed close to perfect, sprayed around the vacuum hoses and no change in engine load, starts right up and no funny shut-down backfire, etc. Decent running rig other than being a noisy 4.0 when cold and.....
...my odd idle issue. Idle issue is fairly identical to this guy's post on YouTube. He claims it was the CPS and I'm not saying it isn't, but I'm looking for every excuse not to pull it out, b/c it looks like a pain!
Could this rough idle be associated with fuel milage? I'd think yes, b/c the jeep would be firing at the wrong time.
I was thinking of checking timing on cyl 1 with my timing light and maybe even adjusting the distributor a little to see if it responded well.
A fairly new XJ owner looking for XJ advice. Thanks.
05-21-2015, 04:42 PM
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Year: 1999
Model: Cherokee
Engine: 4.0
1997 4.0 XJ with 150K miles bone stock!
Recent rig into our family and first time jeep owners, but having fun and the kids love it!
Fuel mileage is 10-12 mpg for city driving and I am a conservative driver! My wife isn't..and that's why we get 10 mpg sometimes!
Recent plugs, air filter, O2 (upstream), tested the MAP and it performed close to perfect, sprayed around the vacuum hoses and no change in engine load, starts right up and no funny shut-down backfire, etc. Decent running rig other than being a noisy 4.0 when cold and.....
...my odd idle issue. Idle issue is fairly identical to this guy's post on YouTube. He claims it was the CPS and I'm not saying it isn't, but I'm looking for every excuse not to pull it out, b/c it looks like a pain!
Jeep misfire/stumble *** fixed *** oem cps sensor - YouTube
Could this rough idle be associated with fuel milage? I'd think yes, b/c the jeep would be firing at the wrong time.
I was thinking of checking timing on cyl 1 with my timing light and maybe even adjusting the distributor a little to see if it responded well.
A fairly new XJ owner looking for XJ advice. Thanks.
Recent rig into our family and first time jeep owners, but having fun and the kids love it!
Fuel mileage is 10-12 mpg for city driving and I am a conservative driver! My wife isn't..and that's why we get 10 mpg sometimes!
Recent plugs, air filter, O2 (upstream), tested the MAP and it performed close to perfect, sprayed around the vacuum hoses and no change in engine load, starts right up and no funny shut-down backfire, etc. Decent running rig other than being a noisy 4.0 when cold and.....
...my odd idle issue. Idle issue is fairly identical to this guy's post on YouTube. He claims it was the CPS and I'm not saying it isn't, but I'm looking for every excuse not to pull it out, b/c it looks like a pain!
Jeep misfire/stumble *** fixed *** oem cps sensor - YouTube
Could this rough idle be associated with fuel milage? I'd think yes, b/c the jeep would be firing at the wrong time.
I was thinking of checking timing on cyl 1 with my timing light and maybe even adjusting the distributor a little to see if it responded well.
A fairly new XJ owner looking for XJ advice. Thanks.
What brand O2S did you install? The 4.0 does not like Bosch O2S' for some reason. It came from the factory with NTK O2S', which you should use. Replace both O2S'.
The O2S Heater fuse in the PDC should be checked.
05-21-2015, 04:53 PM
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I have always been under the impression that upstream affects performance and downstream is there b/c the Feds want it there. I like on the East side of Oregon which 1) means we don't have easy access to Jeep factory parts (why I use NAPA) and 2) no emission testing!
I'll have to look into checking the fuse in the PDC....but O2's have voltage? Upstream is doing good and is not lazy...downstream...it's toast, but then again I believe it's only emissions? Thanks for the reply.
Last edited by Hawks; 05-21-2015 at 05:00 PM.
05-21-2015, 07:45 PM
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Year: 1999
Model: Cherokee
Engine: 4.0
NGK (OEM one from NAPA). I checked the voltage on my friends graphing scanner and the upstream is acting like it should.
I have always been under the impression that upstream affects performance and downstream is there b/c the Feds want it there. I like on the East side of Oregon which 1) means we don't have easy access to Jeep factory parts (why I use NAPA) and 2) no emission testing!
I'll have to look into checking the fuse in the PDC....but O2's have voltage? Upstream is doing good and is not lazy...downstream...it's toast, but then again I believe it's only emissions? Thanks for the reply.
I have always been under the impression that upstream affects performance and downstream is there b/c the Feds want it there. I like on the East side of Oregon which 1) means we don't have easy access to Jeep factory parts (why I use NAPA) and 2) no emission testing!
I'll have to look into checking the fuse in the PDC....but O2's have voltage? Upstream is doing good and is not lazy...downstream...it's toast, but then again I believe it's only emissions? Thanks for the reply.
The downstream O2S plays an important role in fuel economy, as it sets the goal voltage for the upstream O2S, as well as monitoring the catalytic converter efficiency.
I recommend that you change the downstream O2S.
08-21-2015, 07:57 PM
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UPDATE on MPG (improvement)
Howdy,
Here's the update on my MPG improvement.
Driving conditions = 60% HWY 55-60 MPH / 20% around the town / 20% gravel roads with steep grades headed to the fishing hole
I did not change the downstream O2. I did some more looking and it looks like the 97 downstream does not contribute to the fuel trim. 98 an on may (and probably do…). I have been on regular fill-ups since this thread posted using Texaco (Techron) fuel.
I tested my MAP, CTS and looked at my clean TB. All sensors were OK. Fuel pump pressure was great and a new upstream O2 (NTK, I was mistaken earlier) did little for improvement. I did not get to any other sensors because I think I got it. I have not changed the downstream and with the MPG I am getting I may not get to it.
I tend to over analyze too much when it comes to car repairs so I took a step back and decided to 'fix the cheapest first'. I bought a bottle of fuel injector cleaner (Techron), put it in a tank that was 1/4 full and filled the rest up with regular (87 octane Texaco fuel). I noticed a smoother idle (though still a bit rough) almost immediately. I ran that tank through and got 17 MPG. I felt good about that, but knew I could get better. I changed the PCV's and made sure all hoses were tight and put in new plug wires. Since the origin of this post I have done weekly fill-ups. I am getting anywhere from 18.5-20.1 MPG. My lowest was 17.5 MPS in that time, but I credit that to pulling a trailer to the dump.
Culprit = dirty fuel injectors.
I have a set of plugs I'll throw in it as soon as we slow down at work.
I have debated getting some of those Bosch injectors with the 4 ports. I don't think they'll increase it much more, I just think mine are still a little dirty.
Thanks for the help and I hope this post helps someone else! Clean those injectors!!
The only other thing I did that may help is I listened to a lot of Rock and Roll on my drive to work.
Here's the update on my MPG improvement.
Driving conditions = 60% HWY 55-60 MPH / 20% around the town / 20% gravel roads with steep grades headed to the fishing hole
I did not change the downstream O2. I did some more looking and it looks like the 97 downstream does not contribute to the fuel trim. 98 an on may (and probably do…). I have been on regular fill-ups since this thread posted using Texaco (Techron) fuel.
I tested my MAP, CTS and looked at my clean TB. All sensors were OK. Fuel pump pressure was great and a new upstream O2 (NTK, I was mistaken earlier) did little for improvement. I did not get to any other sensors because I think I got it. I have not changed the downstream and with the MPG I am getting I may not get to it.
I tend to over analyze too much when it comes to car repairs so I took a step back and decided to 'fix the cheapest first'. I bought a bottle of fuel injector cleaner (Techron), put it in a tank that was 1/4 full and filled the rest up with regular (87 octane Texaco fuel). I noticed a smoother idle (though still a bit rough) almost immediately. I ran that tank through and got 17 MPG. I felt good about that, but knew I could get better. I changed the PCV's and made sure all hoses were tight and put in new plug wires. Since the origin of this post I have done weekly fill-ups. I am getting anywhere from 18.5-20.1 MPG. My lowest was 17.5 MPS in that time, but I credit that to pulling a trailer to the dump.
Culprit = dirty fuel injectors.
I have a set of plugs I'll throw in it as soon as we slow down at work.
I have debated getting some of those Bosch injectors with the 4 ports. I don't think they'll increase it much more, I just think mine are still a little dirty.
Thanks for the help and I hope this post helps someone else! Clean those injectors!!
The only other thing I did that may help is I listened to a lot of Rock and Roll on my drive to work.
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