3.1 firebird, severe gas mileage/power problems

[no_doz]

ok guys, a long time ago i got a 92 firebird 3.1 fuel injected with 4 speed auto trans, but noticed that it is awful on gas (the second worse gas mileage vehicle that ive owned, second only to an extremely low geared nissan pathfinder 3.0 with a JUNK motor...) & that it doesnt have half of the power that it should. i have a pretty good reference point considering ive had several chevy luminas with the same motor (the plenum & shit looked different & they had coil packs, but otherwise were the same), & they had a decent amount of power (not the fastest cars, but were able to beat a lot of my friends shit without any kind of modifications) & got pretty good gas mileage (around 26 hwy and 23-24 town). the firebird has just as much if not less power than my friend's older 4 cylinders, & averages 15 mpg hwy running it EXTREMELY nice. im preparing to get rid of the car because i simply cant use it when its getting worse mileage than a lot of my friends 350's & having 1/10th of the performance, but if i can find a way to correct this then i would gladly keep it & drive it every day. anyone have any idea of things that would cause this & how i would go about diangosing such problems?

thanks guys!

[no_doz]

by the way its got fresh plugs, fresh oil change, & the cat/regular muffler have been removed & replaced with a straightpipe & a thrush magnum in the middle (with virtually no extra noise added, its not loud at anything but WOT).

[Doubt_Incarnate]

timing chain may have skipped a few teeth, that would make everything suck. if you havent eliminated old/bad wires, cap, and rotor thats a good place to start. check the fuel pressure, change the fuel filter. try seafoam top end cleaner, clean the injectors. or you can skip all the small things and do a compression check to see if everything is good inside, that will at least tell you if its worth trying all the other stuff. if it isnt in the motor somewhere then its the tranny slipping or binding.

[no_doz]

thanks for the advice man, i really appreciate it! im going in to the shop to begin working on it monday, but how would i go about telling if it has skipped a tooth? also how would i check the fuel pressure & cylinder pressure (i assume i have to buy specific things to check em because ive done it on other cars, but with other ppls equipment), & is the fuel filter in the tank or is it inline? aslo, is there anywhere on the net that i could find the cap & rotor specifically (i dunno if it is universal between the smallblock chevy/pontiac v6s or what lol)?

thanks!
js


would this work? http://cgi.ebay.com/ebaymotors/PONTI...QQcmdZViewItem

[tractorman]

I see on a couple of your other posts that you're talkin' about takin' this motor apart because of your bad gas mileage. My semi-unsolicited advice is this: Don't jump the gun.

Doubt's suggestion about the timing chain isn't a bad idea- although it's highly unlikely that it has skipped a tooth. A timing chain has to get REALLY loose to skip a tooth- I"ve never seen it happen. I HAVE seen timing chains get loose enought to make an engine run poorly just 'cause of the slack. How many miles does this engine have on it?

I'd be looking for more external and simpler solutions before tearing down that engine. Have you done a compression test? Have you checked to see if your fuel pressure regulator is leaking (I"m told it's common on your engine)? Does you check engine light come on? Have you checked the timing? Is it advancing properly?

There are lots of things you ought to be checking before taking heads off and that sort of thing. Even that timing chain would be a long ways down on my list.

[Doubt_Incarnate]

just go to the local store for parts. unless its a major part your going spend more to ship it than you'd pay down the road.compressiuon tests are easy, especialy with 2 people. diconect the coil, pull the plgs. install the compression check tool line into one of the plug holes and crank the motor so it turns a few times. do that for every cylinder and if they are way out from each other, or below norm. something ir wrong inside.
fuel pressure ichecked at the test fitting on the rail.
there is a filter in both the tank on the end of the pump, and in the line coming from it.

i had a plymouth 318 and the chain was so slack it skipped enough teeth to bend 9 of 16 valves and all the push rods. still ran enough to get around, but not real good.

eliminate small things first before you start taking stuff apart. make sure the distributor (if it has one) is timed correctly too. you do this with a timing gun/light. if its off check that the distributor is tight. if it is tight, then you do a have a timing chain problem.

[no_doz]

thanks for the advice guys, but heres what i -plan- on doing. 1st off, goin up to autozone & getting a cap & rotor kit & wires, along with the compression tester, then doing all of that (i know how to check comp & all of that, but i dunno how im going to go about re-timing it once i get the new cap & rotor on it, although i do know that we have a timing light in the shop) if that doesnt work, then im gonna try the injector cleaner stuff (also, i dunno how to check fuel pressure on em, i assume i have to buy a checker & hook it up to the little valve thats made for it haha). oh & about takin the motor apart, that would be mainly for performance -if- i can bring the mileage up first (right now its like the power of an old 2.2, & mileage like a 350 lol). also, it has just over 160k, which is a lot if its not toyota, i know this (its not a lot to me until it reaches about 180 lol). thanks guys

[IsaacHayes]

Oxygen sensor? I'm going to replace my 180,000 one since my gas sucks allthough my motor is extremly peppy for beign stock and old. I do have lots of raw gas out the back though......

[no_doz]

that's another thing i've considered. if i get one though, im gettin a wideband so i can use that for my future Forced ind. setup (if i can get around to one!).

[bszopi]

You think 160k is alot? For a 92? I have a 98 Blazer that is about to roll 150k, and almost 50k of that has been done in the last 2 years.

Since you have a lack of power, the timing is most likely off. Get a timing light and time it. Hell, just loosen the distributor and turn it to see if it starts to idle better.

[no_doz]

haha, personally -i- dont think 160k is alot, like i said, i dont think its even gettin high until 180k, & even then it isnt real high until atleast 190k.

[no_doz]

also, could the o2 sensor being junk have a dramatic effect on the gas mileage? (im getting ready to go to autozone, get the rotor, cap, wires, plugs, & o2 sensor, because im starting to think that it might be everything just building up to kill the mileage/power).

[tractorman]

What about the fuel pressure regulator? I know lots of the older 3.1's have problems with it leaking into the intake- I don't know what setup yours has though.

[no_doz]

how would i check that?

[Doubt_Incarnate]

if you disconnect the vacuum line and smell fuel, its bad.