D-booster

As the title states..I get anywhere from 230-280 miles on a full tank. around 230 when I mash here and there, and around 280 if I take it easy.

I'm tuned on crome pro and AFR's are in the 14.8-15.2 from idle to crusing. 12.0:1 AFR low boost(1-8 psi) and 11.5:1 AFR high boost( 9-15 psi).

Here are some things I notice thats been happening for a while now...
engine backs fire when I'm off the throttle at high rpm ( loudness depends on how high I rev).
Engine back fires when I shift to secound or when I lift off the throttle and slightly get back on it.
exhaust smells even when E-cutout is closed. (like its running rich)
power output seems lower than before especially on the lowend and highend midrange feels normal.
Hesitation and jerking under light throttle around 21-15 vac
And just the other day my wide ban is starting to read low 13's afr under low boost and low 12's afr under highboost, so I stoped boost'n for now.

I replaced my plug wires about 5 months ago ( blue ngk's)
replaced Cap and rotor about 9 months ago
replaced spark plugs about 3 weeks ago (ngk's 7's)

Fuel filter and fuel pump was replaced when engine was built about a year ago.
I will be replacing my used RC550's low imp. with some new RC550 sat.
Some how I feel that maybe Crome tune got jacked up some how or maybe my wide ban is giving a lean reading when its not.

Let me know if you guys had a similar problem and what was done to fix it, thanks.

VtecCarHauler

That's not bad mileage. About 23 plus mpg if you have a 10 gallon tank.

D-booster

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by VtecCarHauler &raquo;</TD></TR><TR><TD CLASS="quote">That's not bad mileage. About 23 plus mpg if you have a 10 gallon tank. </TD></TR></TABLE>

My boi gets about 320 on a full tank and we have almost the same setup minus ram horn and RC550 Low imp.

D-booster

on average with out boosting here and there its more like 250 miles on a full tank.

inspyral

That's pretty decent mileage for mixed city/highway driving. I usually average in the low 20s MPG with mostly city driving and a decent amount of boosting. I usually get mid 20s MPG with a mix of city/highway, high 20s with mostly highway, and 30+MPG with all highway driving. Fuel economy on boosted cars generally depends on how and where you're driving, assuming your tune is good(which it seems like it is). If you're comparing fuel mileage with your friend, you have to consider the differences in your setups, driving style, as well as whether or not there's a difference in your tank capacity.

For example, my cousin has a 350Z Track, and my friend has a G35(whichever trim level comes with the Brembos) which have essentially the same engine. The guy with the G35 is somewhat of a miser and pretty much babies it everywhere, always shifting before 3k RPM, etc. My cousin likes to drive his car the way it was meant to be driven, and usually shifts between 4.5-5k. The G35 gets close to 30MPG, and the Z gets around 20MPG, and it's pretty easy to see that most of that difference is due to driving style.

wakedoe

I'm a bit of a noob, but those symptoms sound like bad spark, don't they?

SOHC_MShue

my sohc gets 34mpg with some hard boosting here and there

wakedoe

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by SOHC_MShue &raquo;</TD></TR><TR><TD CLASS="quote">my sohc gets 34mpg with some hard boosting here and there </TD></TR></TABLE>

That's an IHI turbo you're running right? Did you rebuild it, or is it straight off the donor? How quick does it spool? Sorry for the thread jack.

D-booster

I totally agree with ya, but my other problems with back firing and hesitation makes me feel there's more to have than 250 miles. I've been told that its better to run saturated injectors so thats what i'm gonna try along with a new tune. I still don't know why my engine is now back firing. When I lift off the throttle and the car is coasting with the clutch still engaged what AFR's i'm suppost to see? cuz right now I see AFR's in the 17's.

wakedoe

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by D-booster &raquo;</TD></TR><TR><TD CLASS="quote">I totally agree with ya, but my other problems with back firing and hesitation makes me feel there's more to have than 250 miles. I've been told that its better to run saturated injectors so thats what i'm gonna try along with a new tune. I still don't know why my engine is now back firing. When I lift off the throttle and the car is coasting with the clutch still engaged what AFR's i'm suppost to see? cuz right now I see AFR's in the 17's.</TD></TR></TABLE>

You're def. having ignition problems.

nowtype

Tune leaner in cruising conditions.

D-booster

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nowtype &raquo;</TD></TR><TR><TD CLASS="quote">Tune leaner in cruising conditions.</TD></TR></TABLE>

how much leaner? i'm already crusing at 15.3:1 and adding 1-2 deg of timing to the area's to cope with lean burns
also should I replace my distributor, I bought it used when my engine was assemble..maybe the ignighter is going bad?

JDogg

you dont need to add timing when you run it leaner

D-booster

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JDogg &raquo;</TD></TR><TR><TD CLASS="quote">you dont need to add timing when you run it leaner</TD></TR></TABLE>

Thats what I read up on PGMFI.ORG...they had mention about adding some timming under lean conditions when tunning for crusing AFR's. I don't know... maybe I misunderstood when I read it or maybe you can explain why adding timming does'nt help under those conditions.

JDogg

generally leaner mixtures are more unstable than rich ones, therefore they need less timing

also, at cruise you have alot of timnig advance, this advance will create torque in the wrong direction, so more may not be better

usually there is an area around the best timing for mileage thats about 10deg wide where you wont see much if any difference at all.

also make sure you dont have any exhaust leaks before the o2 sensor, that will cause a false lean condition and you will actually be running very rich and not know it.

lean it out till it starts to stumble/drive funny, then slowly add fuel till the stumble has cleared away.

D-booster

This may explain why the car stumbles at very light throttle when crusing, Well I know I don't have an exhaust leak cuz I've checked. I guess I would have to wait for the the new RC550's to come in and possibly replace the distributor while I'm at it. Thanks for the advise JDogg.

JDogg

if its TOO lean your mileage will be crappy too

but around town, 230-280 is pretty typical

nowtype

Um, are we kidding here Jdogg? You don't need to add timing when you remove fuel? Really? Because I'm pretty sure fuel burns fastest between 12-13:1 AFR and anything richer or leaner requires advance. So between 14 and 15:1 AFR mixture, the 15 will run better with more advance. Also any stumble you speak of may be tuned out via timing adjustment because that stumble can be created because of the ignition event taking place too late. Lastly, an O2 leak will not result in a huge difference as the exhaust is exiting, not allowing more air to enter the exhaust stream, thus resulting in just less exhaust. An O2 sensor measures a comparison of parts of the exhaust mixture so less mixture, but the same consistency will result in the same readings which is exactly what occurs when there is an O2 leak.

SOHC_MShue

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by wakedoe &raquo;</TD></TR><TR><TD CLASS="quote">

That's an IHI turbo you're running right? Did you rebuild it, or is it straight off the donor? How quick does it spool? Sorry for the thread jack. </TD></TR></TABLE>
Yup the vf39 ihi turbo. I didn't rebuild it and its showing...thing blows all kinds of oil into the charge pipes. It spools fairly quick...full 15psi a little after 4k.

D-booster

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nowtype &raquo;</TD></TR><TR><TD CLASS="quote">Um, are we kidding here Jdogg? You don't need to add timing when you remove fuel? Really? Because I'm pretty sure fuel burns fastest between 12-13:1 AFR and anything richer or leaner requires advance. So between 14 and 15:1 AFR mixture, the 15 will run better with more advance. Also any stumble you speak of may be tuned out via timing adjustment because that stumble can be created because of the ignition event taking place too late. Lastly, an O2 leak will not result in a huge difference as the exhaust is exiting, not allowing more air to enter the exhaust stream, thus resulting in just less exhaust. An O2 sensor measures a comparison of parts of the exhaust mixture so less mixture, but the same consistency will result in the same readings which is exactly what occurs when there is an O2 leak.</TD></TR></TABLE>

Ok...thats sounds like something I read at Pgmfi.org forum. Also... Would you still disagree that an Exhaust leak can affect O2 readings if say...the leak was befor the O2 itself?

JDogg

sure thing buddy, go tune a few hundred cars then talk

and go ahead and tune the stumble out of a car running at 18:1 with timing, see how good your mileage is

most stockish hondas get best mileage at around 15.5:1 with between 35 and 40 deg of timing.

D-booster

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JDogg &raquo;</TD></TR><TR><TD CLASS="quote">sure thing buddy, go tune a few hundred cars then talk

and go ahead and tune the stumble out of a car running at 18:1 with timing, see how good your mileage is

most stockish hondas get best mileage at around 15.5:1 with between 35 and 40 deg of timing. </TD></TR></TABLE>

I'm not disagreeing with ya, I'm just a lil confused. I'm not a tuner, and wont consider myself one cuzz i've only tune my car and a friends. I'm just trying to gather some knowledge from the pro's like yourself and few others on here.

JDogg

i was refering to Nowtype

nowtype

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by D-booster &raquo;</TD></TR><TR><TD CLASS="quote">

Ok...thats sounds like something I read at Pgmfi.org forum. Also... Would you still disagree that an Exhaust leak can affect O2 readings if say...the leak was befor the O2 itself?</TD></TR></TABLE>

Doesn't matter as long as air isn't entering the exhaust stream from outside, which it shouldn't because air flows from high to low pressure zones.

As for Jdogg, congrats on making a bunch of false statements and backing out like "well I tune cars for a living so I don't need to defend myself". Obviously at 18:1 AFR you are going to have unstable combustion. Who is talking about 18's AFR? I surely never made a mention of such lean conditions. He is talking about mid 15s AFR and a stumble. In which case he should not need to add more fuel and should be able to atleast make an attempt to fix the stumble by advancing timing. If the stumble won't go away, fuel would be the next method of tuning, but should not be the first. Adding fuel and keeping ignition timing will just result in the flame moving faster. Advancing timing does the same damn thing.

Cars will get the best gas milage at the leanest AFR that allows stable combustion. The only problem with that statement is the human element. As the AFR gets leaner, you make less power. With less power one requires more load on the engine to move at the same speed. If you have the ability to cruise under high vaccum conditions and deal with the HP loss, a difference between 15.5:1 and 16.0:1 will result in different fuel consumption. The leaner one obviously resulting in better mpgs.

numbnuts22715

I only get 180 miles per tank if i take it easy...

Atleast I have to drive all the way back to my tuner. ahh