bley49

I know its a muscle car and all but when you're 17 and pay for things yourself mpg is important. So my 85 Z51 is stock except for a chip and exhaust, transmission(automatic) is brand new, idle is set properly now, no vacuum leaks, everything works fine etc. Currently going 21 miles a day with 16 being freeway @ 70mph I'm averaging 15mpg is that typical or can it be improved? Edit: I only get on the gas when getting on the freeway because the on ramps I have to use are short.

Tom400CFI

Car should do much better than that. My Silverado does better than that.


What are your other driving habits? Are you smooth/staedy on the throttle? Do you look (plan) ahead? Keep the RPM low? My '92 has a different motor, but my average mpg is in the 24 range.

http://www.fuelly.com/car/chevrolet/...m400CFI/129334

I'd consider getting rid of that chip and and putting a stock one back in.

John A. Marker

dump the chip unless it was custom made for the car by dyno tuning. My 85 stock was getting 26.2 on the freeway and 19-21 around town....automatic 3.07 rear end gears.

vader86

Dump the chip.

I suspect you have an O2 sensor problem, they do not always give a SES light or engine code when they are on the way out.

bley49

I'm pretty smooth when driving and easy on the gas the chip was on the car when I got it thanks for the advice I'll get rid of it my actual mpg is about 12 city and 21freeway which is pretty bad

hcbph

86 L98 - basically stock except for 5 speed manual. 22-25 mpg around town and up to 32 mpg highway. You can do better.

bley49

I was off in my average on my commute still 12ish around town but got more like 23-24 on the freeway average came out to 17.5 so dump the chip I will.

ghlkal

I agree that you should check the sensor in addition to returning to the stock chip.

ex-x-fire

Is the engine running cool? Your gonna use more gas if it never reaches & maintains 190-200 degrees.

bley49

The temp is perfect around 185-190

N42375

Bley49- If you are not leaking fuel out of an injector, then you are most likely running too rich. The computer should set your air/fuel ration at apprrox 14.7 to 1. Did you remove a spark plug yet? It could give you the clue that the engine is running rich. My 90 coupe with auto averaged 27.1 MPG on my last 2000 mile cross county trip. With a full tank, my computer shows a range of over 520 miles. What is your max range number with a full tank? Are your exhaust pipe tips looking sooty/ dark?

bley49

No leak but plugs are new saw nothing wrong there, tailpipes are clean but it seems the engine floods a little when's it warm so it takes longer to turn over when the engine has been ran in the past few hours

Geardo

my 87 auto 3.07 geared gets 25mpg at 70, and my 93 LT1 6spd 3.45 gears gets 32mpg at 70

BadUmp

I haven't had my '93 (w-2.59 axle) long enough to get in any long road trips, but over the 1500+ miles I've logged locally it's averaging 18.5 mpg. Which is better than I've ever gotten from day one locally on my damned '03 4 cyl S10 run-about.....

3JsVette

'85 4+3 Headers and cat back exhaust 28 MPG highway.
As the others have said put the stock prom back in and go from there.

bley49

Thanks guys you're all very helpful I'm glsd I found the forum I'll see about getting that chip out asap