horrible mpg and weird idle drop

[Gerbil21]

Ok so as the title says I am getting 8-9mpg with almost 90% nyc driving

So far I changed:
Front & rear diff fluid
T case fluid
Trans. Fluid flush, filter and both shift solenoids
Engine oil (with 10w-30 by accident lol)
Power steering pump & fluid
Air filter
Spark plugs (acdelco 41-103) & coil boots
Coolant and t stat
Upstream O2 sensor

All fluids were top brand synthetics


I don't drive with ac on almost all the time but when I do it dosent reduce gas mileage (only about .2 mpg)

Ok so even after that I was getting 9.3mpg constant the highest I got was 12 after a long drive to jersey with ac on

Now afer I changed o2 sensor I am getting 8.8 - 9mpg I used o.e part number (I removed bolts for Manifold since I was going to replace it since the o2 sensor threads were messed up and after I tapped them they were to big (i used correct size) so I ended up taking off washer from o2 and it screwed in and then I covered it with thermosteel all bolts were torqued to correct 15lb ft. Three times as manual says but the last bolt on cyl. 6 broke but I still tightened it and it stayed in) so there are no exhaust leaks

I have cleaned tb twice already and pulled pcm fuses after o2 sensor and second tb cleaning

I am using dic mpg for measurments also I reset it after pcm reset and o2

I have stock 17" rims and non aggressive tires w/ no lift except for z71 springs and shocks in rear there is not a single leak on this car but yet I get horrible millage

In comparison my brother's 00 grand Cherokee gets 11.6 with highway commutes to work and city driving

My idle is steady but not smooth the gauge stays put but there is a slight shake but nothing like a missfire. You can feel the shake when you touch the engine and you can see it a bit (ive felt lots of missfires from my brother's jeep to my 05 p71) and this isn't it. It just idles a bit rough. Also when idling and I give it gas it slightly bogs down and then revs up it does the same with ac but its not bad also sometimes (not much) when idling it will drop rpm down then jump back up and stay steady

And one other thing is that I get a bit of blue smoke out of my pcv and feel no vaccum on resonator side I get the same smoke coming from the dipstick when engine is hot and I pull dipstick out. also I have not done compression Check yet but old plugs (41-103) aswell looked good

The only thing I can think of is the t stat and tune since when I replaced it I was getting the same mpg but it was a 160* t stat and op. Temp was low (it set a code also for low temp)
Now its ok but still bad mpg so I checked and the calibration # I found I also found online on a tune site so maybe the car was tuned for a lower temp? One other thing is that my shifter can move any time and pushing the solenoid on the side in didn't make a difference so what's wrong with it?

 

[Sparky]

Well, I can't imagine getting too great of MPG in NYC. I've not been there but it strikes me as a ton of stop and go. 12 to NJ (I'm assuming on the highway) is low though for highway mileage. Has it always been low or is this more recent? How many miles on the truck? Try doing a hand calculation for mpg, the DIC average numbers won't adjust very quickly on improvements as it is a running average, and hand calculation won't lie like the computer tends to do on cars.

The vibration could be worn/bad motor mounts. My 02 was vibrating badly a few years ago and the passenger mount was totally shot. It does the RPM drop when tapping the gas at idle sometimes, not sure why, but it has always done that for the 90k miles and 4 years I've had it. Far worse to the point of stalling when the throttle body was a caked up mess, but even totally clean it does it a bit.

Not sure on the smoke thing... blowby?

If it has some sort of weird tune it could really make it act weird. If the tune has been messed with like that I'd be tempted to get with PCM of NC to get it reflashed with a known good flash that would also be beneficial.

 

[Gerbil21]

Well, I can't imagine getting too great of MPG in NYC. I've not been there but it strikes me as a ton of stop and go. 12 to NJ (I'm assuming on the highway) is low though for highway mileage. Has it always been low or is this more recent? How many miles on the truck? Try doing a hand calculation for mpg, the DIC average numbers won't adjust very quickly on improvements as it is a running average, and hand calculation won't lie like the computer tends to do on cars.

The vibration could be worn/bad motor mounts. My 02 was vibrating badly a few years ago and the passenger mount was totally shot. It does the RPM drop when tapping the gas at idle sometimes, not sure why, but it has always done that for the 90k miles and 4 years I've had it. Far worse to the point of stalling when the throttle body was a caked up mess, but even totally clean it does it a bit.

Not sure on the smoke thing... blowby?

If it has some sort of weird tune it could really make it act weird. If the tune has been messed with like that I'd be tempted to get with PCM of NC to get it reflashed with a known good flash that would also be beneficial.

Thanks for the quick reply.[emoji1]
Also 12mpg was a while ago since I don't do much long trips on the highway but that is what I've been getting since I got the car with 134k miles so far I've put exactly 1111 miles on it lol and about 900 since oil change
Also if its motor mounts I can live with that and the idle drop isn't a big concern either but weird

Also I am going to get the tune soon as for the smoke idk but I doubt blow by since it has not gotten worse and doesn't seem to have much issues and It drives good and oil is good too I would expect oil to smell different at least.

 

[KNBlazer]

what brand O2 sensor you use? I highly recommend like a broken record to only use GM or AcDelco.... on the temp, you might want to check it with a scanner that does live data...depending on the year of your Truck, check your fuel pressure regulator.... lastly, you should probably remove your thermostat and replace it, not sure if there are options to go lower on our trucks... I think you have the OE temp stat....

as for the smoke, probably a good idea for a compression check....

 

[Gerbil21]

what brand O2 sensor you use? I highly recommend like a broken record to only use GM or AcDelco.... on the temp, you might want to check it with a scanner that does live data...depending on the year of your Truck, check your fuel pressure regulator.... lastly, you should probably remove your thermostat and replace it, not sure if there are options to go lower on our trucks... I think you have the OE temp stat....

as for the smoke, probably a good idea for a compression check....

I used acdelco o2 sensor and yes there is a lower temp t stat. The one I pulled out was a motorad and it said 160. I put in a stant also I have a 05 so there is no pressure regulator

And yes I do need a compression check also I check temp readings with live data app. And it was a few degrees cooler that intake temp when cold and smoothly went up until op. Temp and gauge went along as well

 

[KNBlazer]

I used acdelco o2 sensor and yes there is a lower temp t stat. The one I pulled out was a motorad and it said 160. I put in a stant also I have a 05 so there is no pressure regulator

And yes I do need a compression check also I check temp readings with live data app. And it was a few degrees cooler that intake temp when cold and smoothly went up until op. Temp and gauge went along as well

Your truck is a 6 cylinder, right?

 

[Gerbil21]

Your truck is a 6 cylinder, right?

Yes

 

[freddyboy61]

What is your temperature gauge reading when fully warmed up? It should be at or near the 210* mark. If you had a 160* stat in there before, you may have a clogged catalytic converter. 160* is way too cool for the engine, the PCM will be dumping extra fuel in the mix.

 

[Gerbil21]

I am running at 210 and I checked it with live data also what would be a good way to check the cat?

 

[freddyboy61]

Best way is to check the backpressure in the exhaust by removing the O2 sensor on the exhaust manifold and check the pressure there. I believe it should be somewhere around 3 PSI. Maybe someone else can chime in with a confirmed number.

 

[Texan]

I agree with Fred, but I do not know the max. PSI.
Some folks try driving it with the O2 sensor out, to see if that improves the performance.
Good luck.

 

[Gerbil21]

I agree with Fred, but I do not know the max. PSI.
Some folks try driving it with the O2 sensor out, to see if that improves the performance.
Good luck.

Driving with the downstream o2 out?

Also what is a preffered tool for checking pressure

 

[Wooluf1952]

No. The up-stream O2.

 

[Gerbil21]

No. The up-stream O2.

Well I can't since I cemented it in lol the threads were messed up

 

[Texan]

You asked a good question that I do not have a answer for as I have not had this problem.
But, a tool for this could be purchased or borrowed at a parts store.
I would be inclined to find a old sensor and cut/drill the guts out of it and thread a small pipe
into it and use a hose and a gauge that reads low PSI (0-10).

Edit: it may not be grounded.

 

[Gerbil21]

You asked a good question that I do not have a answer for as I have not had this problem.
But, a tool for this could be purchased or borrowed at a parts store.
I would be inclined to find a old sensor and cut/drill the guts out of it and thread a small pipe
into it and use a hose and a gauge that reads low PSI (0-10).

Edit: it may not be grounded.

I will try that since I have the old sensor

 

[Gerbil21]

Just wondering but can anybody check there live o2 sensor data and compare it to mines

 

[Gerbil21]

just got back to 9.3mpg today i will do a o2 sensor live data check later today when its fully cold and when its at op. temp

is there anything specific i should be looking for with these trucks? stft, ltft, tps, etc? do they naturally run lean?

 

[Gerbil21]

Any one have live data to compare? I use car gauge pro and it is the best obd app anywhere not only can I see things that no other app would even get close to but I can send commands as well also anyone know why my shifter dosent lock?

 

[KNBlazer]

one of the o2 sensors should be in the high (.775-.900) it should be changing back and forth... the other o2 reading should be low (around .300 also changing, but staying low)

I don't have access to truck, otherwise I would help you out with live data...

****Correction**** the high number should not be changing, at least not that much, that would be the CAT o2 Sensor... the other sensor should be changing rapidly between .100 or so to .800 ....

 

[Blckshdw]

One other thing is that my shifter can move any time and pushing the solenoid on the side in didn't make a difference so what's wrong with it?

anyone know why my shifter dosent lock?

Are you able to move the shifter when the ignition is off as well? When the ignition is on, and you depress the brake pedal slightly, do you hear a click or no?

 

[Gerbil21]

Downstream should be low or high? Aa far as I know the upstream will always be switching from about .02 to .80 quick and the downstream should be steady but not shure if high or low or right inbetween

 

[Gerbil21]

Are you able to move the shifter when the ignition is off as well? When the ignition is on, and you depress the brake pedal slightly, do you hear a click or no?

I am able to move it any time and there is no click ever. Sometimes I remote start it, leave the keys inside and move it up a spot then tap on the brake to turn it off also I have a jeep key lol only for ignition I have no door key

 

[KNBlazer]

Here's a link to a video I took last December after swapping o2 Sensors......

http://youtu.be/3cUCVI02l-Q

 

[Gerbil21]

Here's a link to a video I took last December after swapping o2 Sensors......

http://youtu.be/3cUCVI02l-Q

Thanks I will compare that to mines later

 

[Blckshdw]

I am able to move it any time and there is no click ever. Sometimes I remote start it, leave the keys inside and move it up a spot then tap on the brake to turn it off also I have a jeep key lol only for ignition I have no door key

Faulty brake switch maybe? I know I not only hear the click when I hit my brake pedal, I can also feel it in the shifter handle.

Shot in the dark, you can try lifting up the brake pedal with the toe of your shoe, see if there's any travel, and a 'release' click at all. Although that still wouldn't explain being able to shift the transmission with the ignition turned off. That sounds more like that solenoid on the side of the console is stuck pushed in or something.

Edit: Some troubleshooting steps.

 

[Gerbil21]

Faulty brake switch maybe? I know I not only hear the click when I hit my brake pedal, I can also feel it in the shifter handle.

Shot in the dark, you can try lifting up the brake pedal with the toe of your shoe, see if there's any travel, and a 'release' click at all. Although that still wouldn't explain being able to shift the transmission with the ignition turned off. That sounds more like that solenoid on the side of the console is stuck pushed in or something.

Edit: Some troubleshooting steps.

Thanks for the pages I will look through them also no the solenoid is not stuck, I have removed the center counsel and pushed it in and no difference (is it normally out?) Also when looking at live data it shows me when brake switch is active and it does work so it cant be that

 

[Gerbil21]

Ok nvm it does click but does nothing

 

[Blckshdw]

Could be electrical, rather than mechanical then. I guess that puts you at step #4. I don't know where the park lock solenoid is located exactly offhand, but shouldn't be too hard to test it for power, or disconnect it, to see what happens.

 

[Gerbil21]

If that's the one on the shifter than it's easy just got to remove the center counsel and it's damm anti theft connector inside lol.

Also it clicks from the shifter not the brake

 

[Gerbil21]

Just a update I got up to 9.7mpg after a bit of highway driving yesterday but now with all city I'm at 9.5 also upstream. o2 reads good and downstream stays at .80mv after hot and idling

Any other nyc people? What do you guys get?

 

[KNBlazer]

Just a update I got up to 9.7mpg after a bit of highway driving yesterday but now with all city I'm at 9.5 also upstream. o2 reads good and downstream stays at .80mv after hot and idling

Any other nyc people? What do you guys get?

that I think is very low... B4 o2 sensor was replaced, I was getting 14.5 mpg, with new sensor went up to 16mpg....

are you calculating your mileage by pumped gallons and mileage driven?

 

[Gerbil21]

No I was using dic I keep forgetting to count miles and fuel . Also is fuel used on the dic correct or no. I read it uses info from injector pw to calculate it.
How much city driving do you do?

 

[Gerbil21]

Some graphs
First two are cold start

Load & rpm


Load & timing


Stft & ltft


Timing & stft


Rpm & stft


Load & timing


Load & rpm

 

[KNBlazer]

No I was using dic I keep forgetting to count miles and fuel . Also is fuel used on the dic correct or no. I read it uses info from injector pw to calculate it.
How much city driving do you do?

mostly highway 75% - 25% city....I wouldn't trust the DIC, lol.... reset it and see if it gives you different numbers on your next trip..... last year, I rented a van that had DIC, gave me mileage of 16mpg, it was completely off... at the pump and crunching the miles driven I was at 12.5 mpg....

 

[Gerbil21]

mostly highway 75% - 25% city....I wouldn't trust the DIC, lol.... reset it and see if it gives you different numbers on your next trip..... last year, I rented a van that had DIC, gave me mileage of 16mpg, it was completely off... at the pump and crunching the miles driven I was at 12.5 mpg....

Dam it sounds like gm wants people to feel good about there gas guzzlers lol, I will calculate it tomorrow when I get gas to 1/2 tank

 

[KNBlazer]

Dam it sounds like gm wants people to feel good about there gas guzzlers lol, I will calculate it tomorrow when I get gas to 1/2 tank

It was a 2012 Chevy Express van.... this week rented a car, got stuck with a Ford Focus and its mpg calculations were spot on give or take .5 mile....

 

[Gerbil21]

It was a 2012 Chevy Express van.... this week rented a car, got stuck with a Ford Focus and its mpg calculations were spot on give or take .5 mile....

Well that's good ford can do something nice since there's usually something wrong with them

Edit: then again they do get better mpg I had a 99 blazer with 74k that got 15mpg all highway and I had to drive within a block distance of a gas station for city mpg [emoji1]

 

[Blckshdw]

I wouldn't trust the DIC, lol....

This. ^^^^

Calculate your MPGs yourself at the pump. Then you'll really know what's going on.

 

[gmcman]

The downstream sensor when good and hot should be ideally around .500, and steady...give or take but .800 is high......means it's a rich reading and could be from fuel or possibly the hydrocarbons related to the blue smoke from the breather.

The upstream should dance all around and change at 1 Hz or faster.

You definitely need a dry and wet compression test, please post results.

Do you have access to a vacuum gauge? You can test the port at the TB or on the intake manifold. The port on the intake may or may not draw vacuum. Which brings another question.....is this port capped off?

The cat could also be clogged or just not working well based on the high downstream voltage.