Hmmm... 12-14 mpg...

[GLHSKEN]

93 IROC.... WHY???? thoughts appreciated. car runs like a top. What size is the exhaust pipe (stock)?? Thinking the cat is clogged... Good time to straight pipe that.

Any other thoughts??

[BadAssPerformance]

+1 to exhaust. Are the cams lined up?

[GLHSKEN]

Hope to hell so... slowe did the car

[BadAssPerformance]

I'm sure everything he did is right then... but its got to be something, that is pretty low MPG. What size injectors?

[chilort]

Knock sensor

[86Shelby]

Is the engine getting up to temp? My R/T sits around 18 mpg highway at 170*; 28 mpg at 190*

Any way to put a Wideband on it to see if the O2 sensor is fouled? Can you check to see what the fuel trim and O2 reading is at while cruising with a scantool?

A clogged cat is a posibility, rap on it to see if it rattles. Almost every one I have ran across has had a definite lack of power, some even misfired under high load due to the back pressure. If you have access to a infared temp gun keep the engine at a steady 2k rpm. While running, the exhaust should be hotter right after the cat if it's working right.

[Clay]

in my experience if the cat is clogged the car runs like dookie

[black86glhs]

Is the engine getting up to temp? My R/T sits around 18 mpg highway at 170*; 28 mpg at 190*

Any way to put a Wideband on it to see if the O2 sensor is fouled? Can you check to see what the fuel trim and O2 reading is at while cruising with a scantool?

+1 on the O2 sensor. Common poor fuel economy issue. Assuming nothing else wrong.

[Will Martin]

Check the O2 sensor wiring from the computer the sensor. Sometimes, because of the bad routing, the wires, after years of heat cycling, get a bit crisp and aren't any good. So a good signal doesn't reach the computer. If you can bend them and they seem a bit "brittle", you might want to put in some fresh wires (and O2 sensor).

[TurboSedan]

yowza, my trip computer shows about 24.5mpg delivering pizza in town and about 32mpg highway! mine does have a brand new NTK O2 sensor and a test pipe welded in place of the cat. i redid the O2 wiring (it was melted to ---- when i bought it) and routed it away from heat. i am running an estimated 7psi boost though - short vacuum line between compressor outlet fitting and wastegate can. car has stock injectors and FPR.

----------------------------
Joshua Mitchell
'91 Dodge SPiRiT R/T
'87 Shelby CSX #667
'98 Buick Regal GS

[GLHSKEN]

Thanks... Will get an oO2 to throw in. Can't hurt. They take the same one as the rest of the cars or a different #. I'll check the wiring as well.

[GLHSKEN]

Car is stock

[Scottmon]

Ken, sounds like it's not going into closed loop operation. Time to put a scan tool on it.

I've been getting 26 mpg suburban/rural secondary road driving out of my '93 IROC R/T and it's a 2.5 TIII with +20 injectors.

[Pat]

Thanks... Will get an oO2 to throw in. Can't hurt. They take the same one as the rest of the cars or a different #. I'll check the wiring as well.

Same. It's the typical TM 4 wire O2.

[GLHSKEN]

O2 sensor netted 3-4 mpg change. HMMM... Cat's rattling. Cut it off today. Could not see through it (no visible light) Guts floating around. Straight piped it. Car now fries the tires in 1st on acceleration. Was having trouble building more than 5 psi before.... We'll see after the next tank of gas...

[BadAssPerformance]

Sounds cool!

[GLHSKEN]

LOL.... Brants wants to take it to the strip now... running that well...

[glht_omni]

i am running a 3" and 15psi cal and even with 70% of spirited driving i average 24-26mpg and driving 5th gear intentionally staying out of boost i can see up to 42mpg at current driving and average 34-36mpg after driving 15 min each way to work cruising at 50 for the most part.
i love the mpg these r/ts can get when you want them to and how you still do good hard driving on curvy back roads!

[iTurbo]

Yep, my R/T gets very good gas mileage. Seems like it just gets better the more I mod it. I get about 25-27 MPG at work delivering pizza and have gotten 35-37 MPG on the highway. Over 500 miles on a single tank of gas...that was driving with NO boost, cruising at 70 MPH (~2250 RPM w/3.50FD). 3" cat-less exhaust, stg 1 cams, +20s, etc. SBEC is still stock.

One thing I've always wondered about other R/T owners....With a narrow-band A/F gauge, do your cars 'bounce' in O2 feedback very fast? It is like lightening fast compared to my 8v cars. It almost looks like it cycles lean-rich so fast the gauge is just a constant strobe/blur effect. Not sure if something is wrong or maybe because the SBEC is sequentially injected?

[glht_omni]

i did have a c2 a/f gauge in my 88 shadow and in my first r/t, the 8 valve you could watch bounce, the r/t was so fast it seemed like all the lights just flashed at the same time, like you said.
so i guess thats normal on a r/t.