Awesome. I would wait till then before you go crazy and buy things. Soon as you can see it in closed or open loop you will know what is wrong. I MIGHT be wrong too...but the last time I read it needs all the o2 sensors for closed loop operation which would explain the very bad gas mileage.

Not saying it is just o2 sensors either, I had a problem with my knock sensors and that took my average down to a crappy 20 on the highway . Gonna get that fixed after I redo the transmission. Damn cars cost way to much. Either need to make more money or things be cheaper lol.

 

Well since I changed my iat sensor I did notice a change in my idle. Before it would sit at 500 and every now and then it would feel like a misfire and the rpms would drop to about 400. It was very noticable and I couldn't trace the cause. I thought it was my ypipe banging cuz when it would hit hard the rpms would drop. I put some heater hose to stop the banging fixed that but still they dropped. It would ONLY do it in drive idling. I just about gave up on it. But since the iat sensor change it hasn't done it. I let it idle in drive for about 10 minutes and nothing. Thanks a lot chrysler kid for your suggestion even tho it was for another problem of mine. Its to soon to notice a change in mpg but I'm happy with the results so far.
Does this sound right? Would the iat control how the car idles and a new one fix an idle only problem?

 

Like another commenter, my car is a '98 (auto) and it has rather poor mileage around town. On the highway I can get 25mpg if I stay under 75mph and have seen as high as 27mpg, but around town I'm only getting 16mpg lately. I think it's gotten slightly worse over the last several years too. The engine is unmodified and I replaced the driver's side pre-cat O2 when it threw a code a year or two ago. It actually just threw a low voltage code on the O2 after the cat on the same side just recently and I reset it and has yet to come back in the couple of months since. The car has new cats and I checked underneath and all the wires are safe.

I definitely need a new fuel filter as I have no idea how old the current one is. Actually the car just started doing this hard-start routine where it takes a few cranks and sometimes it will start right away, and sometimes it takes a couple of tries to start running--and the car always turned right over on the first try. It runs fine after that, but I'm hoping a new fuel filter might help. Cleaning the MAF would couldn't hurt either (although I'd think that would lead to a lean burn condition, if anything). I do smell gas, especially when the car starts running, but I don't see anything coming out the exhaust (though that is the source of the smell, the evap. is fine). I don't have any trouble codes.

I know with stuff like this, it could be a lot of things, but I'm open to suggestions. Cleaning is always good. I trust the plugs I put in there, so I don't expect they are to blame, nor has there been any kind of stumble or misfire. The fuel injectors could be a culprit and so too could the 02 sensors, but those are expensive to replace just in the hopes of better fuel economy.

 

What about a vacuum leak causing this? I did the !AIR but still have the hoses and the thing on the back of the manifold. I read that you need to cap it off but I haven't yet.

 

You are correct there are so many sensors in there your 02 sensors could be fine and MAF is dirty. I am NO EXPERT lol only a 19 year old kid that has ideas and makes them happen. Always things to learn and when I think I m right sometimes I am wrong.

If your computer isn't throwing any CEL for the o2 sensors it means more than likely it is switching over to closed loop. You would have to monitor the voltage from them to actually determine if there good. The front ones under normal conditions range from .2 to .8 volts. The after cat seems to sit around .5 volts. Due to the fact you said the engine is running smooth I am more likely to think it could be something else.

You said the fuel filter, I would start there. Hard cranks are no good. Cheap and easy and maybe that could fix it. Maybe some of the other experts will chime in?

 

Do either of you guys have a way to monitor your MPG realtime?

 

No I'm not. Just miles divided by gallons put back in

 

Okay my bet for you is the engine isn't going into closed loop so its running at a "default" A/F ratio. When I unplugged the o2s in my truck i noticed MPG significantly go down.

If you know anyone that has a simple performance monitor you could hook it up and see. Mine kicks into closed loop around 10 min after you start it (northern michigan is cold).

That doesn't look good. Maybe even this plays a part? Thats the one code you have for the crank.
http://www.trifectaperformance.com/t...ankrelearn.htm

Oh I don't quite know what the other codes are...Wish i could determine if they mess with MPG
p0412, p0418 AIR

 

When the front O2 sensor get old (more than 70K miles) they will switch at a slower rate... this can cause you to run rich.

Closed Loop uses the front O2S's.

 

THIS ^^^

Rear O2s DO NOT affect MPGs. They are there to monitor cat efficiency...ONLY!

 

AHHH I said I wasn't gonna post anymore but would you like me to make a youtube video and show you realtime what these sensors do.

1. Your car needs all the o2 sensors or o2 simulators to go into closed loop. I can go ahead and make a video and show you that my truck WILL NOT go into closed loop with the rears unplugged.

Idk if my truck is just a weird one, oh wait it isnt. A ten minute search on google found me DOZENS of examples about people replacing their REAR o2 sensor and it makes a difference to the engine. Not saying its crucial to MPG performance because it would make sense that it uses the front ones for the most part. But there there and if all you think they do is monitor cat efficiency your nuts.

Funny part is there NOT even there for that. They are there to monitor the levels coming out of the cats and make changes based on that information to make it run with as low emissions as possible and make the cats as efficient as they can be...These things aren't designed with MPG in mind, just low emissions and it WILL make the engine run however it needs to achieve these goals. My understanding in all the research I have done is they work together and if there messed up then it just doesn't work.

I won't be able to make the video right now but I could. Showing that mine won't go into closed loop with the rears missing, fronts missing, 1 front, 1 rear lol idc. I want it all documented for when I make my new MPG system anyways. I need to video document everything so when I get 40MPG I can tell people how to do it. Already at 30 just 10 more can't wait to get building.

 

So I got a scanner to check the voltage on my o2s
B1S1 - .739
B1S2 - .444
B2S1 - .179
B2S2 - .444

Now could this be the cause in my **** mpg? Looks like b1s1 is fine and b2s1 is sucking dick.

 

The static voltages don't tell us anything...

when the PCM is trimming, the front voltages (B1S1, B2S1) will switch from above 700mV to below 300mV and back several times per second.

 

Ok. How exactly do I find out the voltages that tell I'd the sensors are getting the correct voltage??

Do I look under b1s1 etc trimming instead of voltage?

 

If you have a scanner that supports fast mode you can see the voltages rapidly changing.

If you have a software-based scantool (e.g. AutoTap, EFILive, HPTuner) you can save the log to your laptop and look at the waveforms using the software that comes with these scantools, and you can measure/count the number of cycles per second.

You can also look the the long term fuel trims, any value substantially away from 0% would indicates problem; and 0% does not necessarily indicate good health.

 

Under the trims on the scanner I had it showed the fronts at 0% and the backs at 99.5% I know cuz they aren't hooked up. But it wasn't showing the live switching.

 

Few things you could read if you wish...I find it interesting. It might help you be able to test them. I see it defaults the rears to .444 so I think its safe to say I was very wrong in what I said. I just assumed because mine messes up your prolly would, not a particularly smart move when your arguing with people that have been on the forum forever. Anyway I would have a read there and if these links fail to help just google "o2 sensor testing" a few pages pop up. Anyway let us know!

http://mr2.com/TEXT/O2_Sensor.html

http://www.autodiagnosticsandpublish...or-testing.htm

 

Update: engine coolant sensor still out of stock locally. And I got a code for o2 2/1 low voltage. Why? Do I just need to replace that sensor and my mpg will be fixed

 

Heh, this is the exact code I got, but for bank 1, sensor 2. I checked for damage to the wiring and it all looked fine so I cleared the code and it has yet to come back in the 3 months since. Because I already had one (1/1) go bad on me and this was the second code involving O2s and my car is high mileage, I just decided to replace them all. The remaining 3 should arrive on Wednesday. You can save a bundle on 'em from Amazon. I paid $93.90 for 3 (no tax or shipping) versus $221.82 from Autozone with tax. Bosch uses the same 13444 model for pre- and post-cat on both sides with OEM harnesses.

 

I cleared the code and it came back later today. So I need a replacement. I just remembered one day a few weeks ago before I finished my exhaust (just ypipe plus 2ft of pipe) I got stuck at a light that had a puddle that appearently got water in the exhaust and wet the sensors cuz the car ran like total **** for a few miles Til the water was evaporated.