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Discussion Starter · #1 ·
Well I have a 1991 stealth RT Turbo. It has been getting terrible gas mileage since I bought it a little over a month ago. I am currently getting 8 MPG. I replaced the front oxygen sensor (they gave me a rear one with the longer cable, but the same harness, so I figured they were the same), I also put in champion copper plugs, and put an EGR gasket on. (It didn’t have one before)

My dash has no lights lit on it other than the SRS light and the SPORT TOURING light. Before all this mess, I had 5 codes. They were for the front oxygen sensor, 3 codes for the MAS, and one for the speed sensor. I inspected my ECU, made my own bracket to mount it (there was no hardware in my car, it was sitting there loose) and I don't get the codes anymore. Than I did the work described above, and I am still getting shit gas mileage.

Any tips?!?!?!!?
I can't afford to buy all this gas

Thanks in advance,

Joey
 

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chunsangp
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Check your fuel components. 8mpg sounds very terrible though...

Also what's your plugs' gap?? If you aren't modified, shouldn't be lower than 0.039 and if you are modified, 0.028-0.039 should be fine but as your gap gets lower, the mileage gets worse AFAIK.
 

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Grandpa
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I'm sure your not, but just to clarify....Are you going WOT all day?

As I assume your not an idiot, and don;t drive WOT all day 24/7, that it is something else.

How long was the car sitting around? With the way you described the ECU, it sounded like it hadnt been driven in a long time.

Possibly clogged fuel injectors, not spraying correctly, or a clogged up fuel filter.

Most of the time its O2's w/bad gas milage, but I see you installed new ones.
 

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Discussion Starter · #5 ·
About the oxygen sensors...

Back when i got the ECU codes, it had a code for only the front one. So I replaced the front one. I replaced it with a nippendenso, whick looked identical to the rear one, which has the same harness as the front one, just a longer cable.

And I am not going WOT all day. I usually cruise at around 1.8-2.2k RPM. And I haul ass like maybe once a day, usually trough 1st and 2nd.

I will check out those fuel components soon.

First I gotta look it up on stealth316 though.

Joey
 

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Rollin, Rollin, Rollin
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1,249 Posts
maybe you should get an AF guage so you will have an idea if the computer is adjusting the ratio or is it stuck full rich all the time.

Do you smell gas when you come to a stop, have you noticed that there are never any cars directly behind you?:confused:

8mpg....that is totally nutz!!

I don't think you mentioned how the car drives, how is the pwr?
 

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I am the 1.85% =
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You need to change the rear O2 Sensor. That is most likely your problem.

Even though it is not tripping a code does not mean that it isn't bad. I was getting 10MPG in my 91 RT TT with no codes whatsoever. I changed both O2's and now I get 25 highway and 18 city. (I drive hard)

In order to trip the Check Engine light, the ECU must read the sensor as bad. It does this when the sensor reads a faulty value steadily for a certain amount of time (5 min or so) However, even a bad sensor can vary in its signal voltage enough for the ECU to see it as working properly. If you got a code saying the front was bad, then I am most certain the rear is also dead but still tricking a variable signal to the ECU. It is unlikely anyways for just one sensor to go bad, they usually wear out in 60k miles or so.

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You can also test the O2s with a multimeter. Connect at the upper harness above the front valve cover. + to the yellow wire and - to the green (or vice versa, I cannot remember) set the meter to measure mV. Take a reading with the car cold and then when it is fully warmed up. The voltage should go from closed loop (.1-.2 mV) to .8-.9 mV when warmed up. If the number is still low when the car is warm, then the sensor is most likely dying causing the car to dump in fuel to warm up the engine and prevent it from running lean.

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If this does not fix your problem;

Fuel filter
Air filter
clogged cat(s)?
clogged injector(s)?

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The ECU wasn't bolted in? Maybe you just have one f'ed up ECU. Could be going bad, but I do not know why it would account for such low gas mileage.


Good luck

Beep me on AIM (RickyNigro) or post here if you have any Qs about what I said, it's late so I might not have made sense.
 

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Discussion Starter · #11 ·
Thank you very much. all of you were very informative. I think I will go ahead and change that rear 02 sensor. It will only cost me another 60 bucks or so. I am gonna go with another nippendenso. Acually it is the same part number as the one I put in the front! they will accually get me the right one! (I still have one I need to return today that is the wrong one)

I bet you guys are thinking I should take the 40cm one and put it in the back where it goes, and than get the front one, and put it in the front. But have any of you changed the front oxygen sensor? I think that extra 20cm of wire aont hurt anyone.

Joey
 

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Discussion Starter · #12 ·
Well I returned the oxygen senso, and oredered the right one. I will get it tomorrow.

To answer earlier questions:
ChunsangP- My plugs are gapped at .037
VR4 Maniac- I have the ol' resistor-LED codechecker. and here are no codes

I accually thouht about getting an air/fuel gauge. I also lightly considered an aftermarket fuel controller, like an HKS AFR or something simillar. But if I can get good gas mileage for under the 400 bucks those electronics would cost, I am all for it.

Joey
 

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Discussion Starter · #14 ·
Slasher-
I don't know a great deal about timing. And I have no idea whether base timing is correct or not. But the only things that sound wrong with the car is its throwout bearing and an average severity lifter tick. It also revs very smoothly. So I wouldn't think the timing is off.

I got the rear oxygen sensor about 20 minutes ago, I am going to go install it.

Joey
 

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My rear O2 sensor just fell outta the car a couple days ago

<A href=http://www.3si.org/portal/forums/showthread.php?s=&threadid=116096>Click here for the full story</A>

and I've been getting shit mileage ever since. It's going back in tomorrow :)
 
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