14k

I have a 01 z with a 98 ls1 in it. With the 806 heads and the egr manifold. I had a tune up when I bought the car. Plugs wires oils.
I put lts on and have 1 high flow cat after the merge on the ypipe. I don't have the rear o2s hooked up since theres no bungs. The only codes I have are
p0140, p0160 (rear o2s)
p 0412, p0418 (!AIR)
And p1336 (crank pos. relearn)
It has not been tuned. Why am I getting 150 miles to a tank?? I drive conservatively to see how long a tank will last. I KNOW something is wrong. But no idea what. Any idea?

LS6427

iTrader: (2)

Get a tune.

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14k

I'm ordering a frost tune right now. Would the tune greatly improve my mpg?

And I'm ordering a new PCM and the tune so there's no downtime since the z is my dd. which PCM do I get? The 411 right??

garygnu

you need a tune.clean your MAF ,and the IAC.maybe you mite have a bad ground.have your front O2 sensors scanned to make sure they are working correctly.

Latch

iTrader: (8)

A catalytic converter that far back in the exhaust is going to clog prematurely. How long have you had that cat installed?

14k

Not to long. The cat was ok when I put the mangaflow cat back on about a month ago.
Maf is cleaned(2 weeks ago)
How do I clean the iac?
And a ground as in one of the body grounds?
The o2s are maybe 2 months old. What are the chances they went bad that fast?

LS6427

iTrader: (2)

Just spray the **** out of the IAC sensor with MAF cleaner....I've been doing that for 14 years, I still have my 1998 original.

You're most likely running real rich without having done a tune.

Good luck with the mail order tune. Sometimes they're good, sometimes they are terrible. If you can, get it on a dyno to tune it the proper way.

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indianass

iTrader: (3)

i'm in the same boat as you i've tried everything and still get bad gas mileage my car had a tune on it when i bought it a couple months ago so im thinking that has to be the problem my cam should be in and installed in a couple weeks im hoping the dyno tune will get me some better mileage.

14k

I hate it. 37ish miles = a1/4 tank then 105 the next 1/4 it's stupid.

sandsk8erz400

iTrader: (1)

^huh? the actual gas gauge isn't the best to go off of. And OP, is the city or freeway driving? If it's city, go fill up your tank, get out on the highway and just cruise 65-70mph for at least half a tank and fill back up. Do the whole miles driven divided by gas used. That's a much better way of checking your mpg.

14k

It's all city.
I was just saying the first 1/4 on the gauge lasts 37 miles the next 1/4 lasts Til 100 miles etc. I know it's not accurate but it gets on my nerves since gas is going up.

LS6427

iTrader: (2)

You definitely have an issue......my 427ci gets 230 a tank in the city.

Let it run down to E, on E. The fill it up until the pump stops by itself the first time. You should be able to get about 14-14.5 gallons in there.

And as mentioned....you have two new front 02's......have them checked on a scanner to see if they are switching properly. Lost of people complain about bad gas mileage, and lots of times it bad/failing front 02 sensors.

And NO.....you will not always get a code until they are bad where you can notice it. But it will make you run rich enough to totally kill your gas mileage. I installed a new 02 sensor a couple months ago, it was a dud, it happens. Only takes one bad one to kill your gas mileage.

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14k

I know i do. /:
I just filled up today. I'm going to run it Til the "check gauges" comes on. I think I put 12 gallons today when I filled up half way between E and 1/4

14k

Is not having rear o2s hooked up play a big role in this shittyness?

just finished ordering my frost tune. hope it helps alot.

LS6427

iTrader: (2)

NOPE.

Only way to know if the tune they send you is good, is too get on a dyno and check it out. Or you can drive the car on the streets if someone you know has the wide-band set-up that can hook up to your exhaust to check it out. Just feeling good won't tell you if you're running dangerously lean, rich is easy to tell, you'll smell gas and have bad gas mileage.

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14k

i know for sure im running rich. i smell gas all the damn time.
what about the engine itself it is a 98 with the bigger cam and the ls1 egr intake instead of the ls6 and smaller cam. since theres not egr on the engine could that be involved? i read the egr on the 98/00s kept emissions down.

LS6427

iTrader: (2)

If you smell gas than you're probably running rich...since you also have a gas mileage issue. Unless you have an evap issue. If its an evap issue you will smell gas right at your drivers door and drivers rear tire area when you step out and sitting still idling at times. But a bad evap won't cause bad mileage, it just stinks of gas all the time.

OH well, see if the new PCM/tune fixes it. But I would want to know if the tune is right and not running too lean, which could kill the engine pretty fast. Only way to make sure, as I said above....wide band 02 readings.

.

LS6427

iTrader: (2)

Have a freind rev the engine in PARK......put your hand right up against the exhaust, see if raw fuel spits out. If so, you're tune is just way way rich. I had a rich problem once, raw fuel would shoot out my exhaust like 6 feet and on to the ground, it was ridiculous.

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14k

i dont know anyone with a wideband setup what else could i check it with? or is that all

14k

wow... im praying that i get one of those "spot on" tunes everyone on here has.