Bad MPG after top end rebuild and y pipe mod!!
 

alright ,ive cleaned my injectors very good,ive changed ;plugs,wires ,dist cap,rotor,ThrotlePositioningSensor(and yes this thing cost me alot) and i did a y pipe mod known as (chief pipe mod) alot of dudes did it before me,and im runing no cat,and my fuel filter is new and my air filter is cleaned (k&n).

the only thing i did not changed is the O2 sensor,witch i think is as old as the truck itself,could it only be only that little sensor thats doing all this??

i meen its really bad its even worst than before i did the rebuild,and i had a damn hole in exaust valve numb 6 and i had one driping injector and everything was dirty ,i meen wut the hell.i think i get around 10 or 11 miles per gallon in town.makes me nuts :con:

any sugestions?

I would certainly change the o2 sensor. A bad o2 sensor can have a major effect on your mileage (5-8 mpg). Definitely go with an OEM sensor.

:eeek: wow that much.. thats insane, i can get one for 112 can dollars,so it should be worth trying right.

try www.sparkplugs.com

Hmmmm new free flowing exhaust = less bottom end torque more top end hp due to lack of back pressure. Perhaps your problem is in your foot to get the truck going as fast as before but with 10 less torque.

I don't know, but this might say something about the problem. :)


Not trying to start a flame war, just a thought.

Katie
:)

These are 4 stroke engines, They dont need back pressure, They need velocity and scaveging affects.
2 stroke engines do.

I would say O2 sensor, Check the wires too, possibly may have pinched or burnt.
The O2 sensor is after the Y pipe right ?

yep the the O2 sensor is after the y pipe,as for my spark plugs ,. i got one of the best for my kind of vehicule ,heres the picture:
NGK IRIDIUM TIP,superiror to platinum. around 25 bux for two;

http://img227.imageshack.us/img227/6858/p1010019mw9.jpg
http://img211.imageshack.us/img211/1980/p1010020mk9.jpg

i havent changed my O2 sensor yet ,but i noticed something when checking my timming with a timming light, my TPS is NEW but i havent adjust it yet ,i just bolt it and leaved it like that,im trying to do it right now ,i hope its the cause .if not ill try to change 02 sensor.

*edit*
Im an idiot

Since he is from canada he would be hit with border charges..
would be cheaper just to pay more localy.

yea ive checked the prize and its 112 can bux for OEM sensor

Where from?

I was going to hit up lordco and get a NGK plug.

local savaria auto part, just like napa but less expensive.

sparkplugs.com has NGK for less than $100.

what is so horrible with bosch?
im running a bosh O2 on a 98 camry.

$200 sensor....

You dont need back pressure, is correct, what you need is hot enough exhaust for it to move fast. Hot air flows faster than cold air. Too much free flow at low RPM prevents your exhaust pipes from heating up sufficiently. This is one reason people that have headers wrap them.

Now, put a cat on your truck. :spank: Poisoning the air is not acceptable just because it makes you think you can go faster. Plenty of people drive with converters and don't have the problems you are having and they aren't contributing as much to lung disease. Driving without a cat is like driving a 2 stroke, and you should save that for riding your old motorcycles. :devil:

good point there buddy,but first i dont have no cat cause i want more power,haha,its cause i dont have 150 bux to spend on it.now I FOUND THE PROBLEM LADIES!! it was the tps i adjust it carefully this morning and rechecked my timming wit a timming light gun,10 btdc advance,cause i run high octane gas,and voila! it takes me almost half of what it took me before to get from one point to the other. and im thinking to replace that O2 sensor soon too and see if its even better.

:bang: .....

Plus currency conversion
Plus shipping (minimal)
Plus border fee's

Its just cheaper overall if you buy one in canada if you live in canada.

That is the stock set timing and is suitable for 85 octane. Only get enough octane to prevent pinging, and use only Teir 1 gas. ;)

I run 17*btdc and run 93 octane.

I use nothing but 87 octane!! Never had any pinging :D

You can check the O2 sensor with a meter. When O2 sensors stop sending a signal, the ECU interprets that as a lean condition and enriches the mixture accordingly.

Back pressure affects the frequency of an exhaust system's scavenging and very much affects the performance of a 4 stroke engine. Unless the engine is built to rev extremely high, back pressure is necessary to scavenge within the engines mechanical operating limits.

More pressure will lower the frequency and you will experience low RPM scavenging and corresponding torque. Pressure will build quickly and typically sap higher RPM torque and thus power. (power = torque * RPM)

Less back pressure conversely increases the frequency thus scavenging at higher RPM's. As you have guessed this means more power.

All things equal, pumping and friction losses are higher at higher RPM's so producing power at a lower RPM is better for fuel economy because those losses make up a smaller fraction of the total engine power at the point. This will make your truck slower.

All that said, it is highly unlikely your Y pipe mod and lack of catalytic converter have reduced back pressure to a point the engine is scavenging at an RPM it cannot reach.

When my cat was stolen, I was very curious to see the effect on engine performance. The effect was pronounced, the engine had very little torque; acceleration was terrible. This lack of torque was evident throughout the RPM range. Not only is scavenging affected but EGR is as well increasing the likelihood of knocking and resulting retarding of the timing. The addition of the high flow cat and more free flowing cat-back exhaust increased engine performance over stock and yielded a 1.5MPG increase in economy.

Frank

I never said the engine needed backpressure. A properly setup system with the correct backpressure will allow for a better low end torque range. A fully free flowing exhaust will knock that low end torque down and up high end horse power. I know that for a fact cause I did it to my camaro when I put headers and 3" tubing all the way back on my 305. It had an exhaust to handle 500hp on a 250hp car.