i just bought a 91 350 trans am. im used to having pretty bad gas milege being that i used to own 3 different fox body mustangs, but this thing is kinda riduclus. its completly stock accept for a drop in k&n, and the thing seems to get like 10mpg. is it just because its a 350, or because somethings wrong, i dont get it. i work at grease monkey, so i did a full fuel system cleaning on it, and then i recharged the k&n filter today, but it still seems to get ****ty gas mileage. this thing is worse than my 93 mustang with heads cam and intake, i just dont know wat it is... is this just how f-bodies are?ive driven it like an old grandma since i bought the damn thing.

and one more issue... when its idle-ing (no matter the engine temp) the car will idle fine in park and then about every thrity seconds, it kinda stumbles, recovers, then idles fine again.

i dunno, mabye im just being picky (i never had any problems with any of my 5.0's like this)
so any help would be greatly appreciated. thanks a lot, mike

 

Did you clean the K&N before you recharged it? A dirty and fouled up K&N will make any motor run like crap. Also what is running that 350? TPI, TBI? 02sensor can give crappy gas mileage.

 

i had the same issue with my o2 sensor.

 

well, to start off, yes its a TPI, and yes, i cleaned the filter using the recharge kit, and before hand washed it from the inside out with hot water. the guy said he had replaced the o2 censor, so i'll ask him when exactly he did it.

 

it could be a couple of things. bad fuel pressure, stuffed cat, O2, garbage gas, low air pressure in tires, etc. it's best to take a day and go over everything on the car and fix whatever might be wrong or is wrong.

 

yeah, i was wondering how i could find out my fuel pressure. also, when i do find it out... how do i kick it up? but yeah, the cat thing really got me thinking. that woulld really suck. is that pretty common to have the cat get all clogged up like that? if so, what brand should i replace the cats with?

 

To check the fuel pressure you'll need a fuel pressure tester with the zerk fitting. The zerk nipple will be located on the fuel rail under the MAP sensor. Take the MAP sensor off the upper plenum and then the FP tester will screw onto the zerk nipple. Then turn the key on to the run position and charge the fuel pump. Watch the FP tester to see where the guage stops and then let it sit for a few minutes to see if the pressure bleeds off. The only way to adjust the FP is with an adjustable FPR. If you already have one installed then I think the adjuster is on the top of the AFPR. Is there a heat shield installed under the K&N to keep the hot air from the radiator and engine from being sucked through the filter?

 

lol

hehehehehe :-)

Alos of note, only use Delco 02's in GM products as the commonly available Bosch sensors(one wire) have a known grounding problem and arent quite the same as a GM 02.

Get a scanner and make sure all the readings are good. Check the coolant temp sensor reading and see if any codes are stored.

Manually check it with the car hot and cold and use an ohm meter.

If that proves okay and no obvious things are found like vacuum leaks or missing parts, ohm the fuel injectors :-)

should be near 17 ohm if stock injectors or factory replacment. they should all be over 12ohm(believe the limit in the manual)

If u find some that are 5, 10 etc, u need a new set of injectors as the factory ones in your car are garbage for lack of a better word.

If they ohm out okay, lift the fuel rail up and pressurize it and place paper towels under it to see if u have leaking injectors.

Something I rambled here should help u out.

later
Jeremy

 

unfortunately w/ efi there are so many things that can throw off an engine's performance, but anything anyone comes up with is a helpful idea. little things add up, it sux i know. as for cats, it depends on what you really want to do with your exhaust in general. i like catco's hi flow cats, but i don't have a cat on my iroc, so that doesn't say too much.

 

well i got it in a bay at work today, and the heat sheilds on the cats looked clean, along with a few other things which lead me to belive that these cats have alreay been replaced. i'll have to take some time out of my schedule to check the f/p. but for now, i will start with the simpler things like a fuel filter. mabey pick one up tomorrow or thursday, but anyway, keep the ideas coming (if there is any more lol). is there any place like a parts stroe or something who will scan the car for free. the only scanner we have at work is obd2, so im kinda sol.but thanks for the ideas guys.

 

hey also just thinking, because it died on me today just out of the blue once... will finding out the fuel pressuse tell me if my fuel pump is going out?if not, then how can i? is that a feasible problem? it just got me wondering because for the second time in a week (coincidentally in the exact same place) it didn't want to start. after getting mean with it a little, and giving it some gas, it started, but not without a little stumbling. so im guessing it's between the fuel pump and the fuel pressure...would that make sence im new to the whole f-body thing so i wouldt know.

 

Wo Wo Wo! did I just hear you right when you said the cat convertor looked clean because on the rack the heat shield was clean.

Spend 20 min out of your day and take the car to an exaust shop.
They drill a hole in your exaust and take measurements on how the exsaust is flowing.

You also mentioned that the last guy changed the O2 sensor. THEY ARE 20 BUCKS. Change It

No one has mentioned tune up. before you go pulling the fuel rail up to check for leaky injectors. PULL OUT THE PLUGS.

If only one or two are in bad shape then check the injector leak by.

Dont take how I am saying these things the wrong way but you compared a F-body to a Stang and that is not very smart on a F-body web site.

all you have to do is get acqinted with the car and you will love it. TRUST ME!!!

 

Oh yeah exsaust shops check you catalitic convertor for free!!

 

i have never seen a cat cause bad fuel mileage, poor performance yes.
if you had a clogged cat the first thing you would notice is your car wouldn't have the high RPM performance it should, if the exhaust can't get out, the fresh mixture can't get in. if the cat is real bad the car would be hard to get up to speed, the farther you press the accelerator the less it wants to go.

the quickest things to check as mentioned above are fuel pressure & the regulator, to check if the fuel pressure regulator is leaking fuel into the motor, pull the vacuum line off of it & look for fuel, if it looks dry start the motor up with the line still off & check the vacuum hose fitting on the regulator again.

a way to scan it is really needed. the nice thing about the older GMs is live data, something the older fords don't have. if you have a lap top, all you really need is a cable to get data as there are several programs you can download for free that will let you see just what is going on. if you don't have a lap top, there are a few people on here that have taken their desk top pc out to the car to scan it. the cables are pretty cheap. around $30.00 or so, or you can build one yourself.

you can find the cable here,
http://www.moates.net/

you can find TunerPro here,
http://tunerpro.markmansur.com/

there are other places to get the cables & other programs out there, a search for "ALDL cable" here should get you some good hits & a search for "scan programs" may get some hits for software.

 

hey jamon, no offense but a tune up to me isn't just pulling the plugs. it's like i said earlier, going over the car and finding out what is wrong or what could be wrong and fixing it, that's a tune up. tuning is more than just ignition, it's the whole aspect of making an engine run efficiently with as much power as possible, i.e. TUNING.

carbed, turn your car to the on position, don't start it, and listen for the hum of the fuel pump priming. if you're not hearing that when you're having the problem starting it, you could have a pump problem. if you do and its still buggin out on you, check your electronic ignition control module, seen these screw people a hundred times over. and as jamon said with a tune up, check your coil, plugs, wires. while your at it, check your tps signal, your egr, map, maf, O2, all of them. if you're getting an ses light, run down to a local parts store and pic up a scan tool. you can pick up an actron for your car for around $30. as for your fuel pressure, pick one up through jeg's or summit. my hypertech cost me somewhere around $50 and you don't have to remove the map to hook it up. hope this helps.

 

You could also clean the Throttle Body and IAC (Idle air control).

O2 sensor and coolant temperature sensor if replaced should be with ACDelco ones.

Fuel Filter could help your stalling problem and if it was really clogged up, you could save some fuel because you won't need to press the pedal as further down as before to make the car go.

Check the timing and basic stuff...

 

ok, well, as far as ignition stuff. the guy (and this is in the past few months) has already replaced:
plugs (bosch platinum, i heard those are crap though...you tell me)
cap
rotor
wires
o2 sencor (i'll call him and find out which brand)
fuel injectors
coil

things i've done
FULL fuel system cleaning (courtesy of grease monkey where i work)
oil change (duh)
and thats about it.


so, according to you guys, the following should be checked and/or replaced:

fuel filter (picking one up tomorrow)
test cats at any good exaust shop
coolant temp sencor (sounds dumb, but where is it?)
check that fuel pump is working
elect. ignition control modual (again, where might that be...lol sorry)
im pretty sure im not getting any lights, but i will definetlay check
and fuel pressure.
timing

if i missed anything...correct me, but as far as you guys helping me out in a time of stress...THANK YOU! you gus couldn't be any more helpful. thanks againg, and i am curious as to where the coolant temp sencor and the ignition control modual might be. thanks again, mike

 

I was not talking about a tune up, I was talking about the condition of the plugs. if they are lean he knows that he has a fuel delivery problem and if they are rich or fouled he knows to check injectors or reg and he also knows which hole to check.

As far as the convertor, a partial plug could cause some of the problems he has.

Did you hear me once down the ideas that you have. This is the type of attitude that does not work for these forums. If I had a problem and needed advise I would be happy to have any good advise.

pulling the fuel rail before checking the plugs is retarded. Read your helms manual or do you have one. I think GM knew what to do with the product they were building.

 

no, i know that i shoudn't hate on gm cars on a gm forum. i was just kinda getting fustrated, but you guys are being a huge help, so im definetly cooling off a little bit. you guys kick ***!

 

That is true about the Bosh O2 sensor causing horrible gas mileage. It must be very common because I've seen it happen twice.
Use a GM/delco O2 sensor.

 

carbed- you will learn a new respect for gm once your car is running right, lol. it's the same as any other car, little things add up, whether bad or good, they all make a difference. btw, your ignition controle module is in your distributor under the cap.

jamon, no one downed your ideas. a simple misunderstanding, it seemed very clear that you were talking about a tune up since you were using the same paragraph, and the fact that you said "tune up". learn your grammar if you want to get pissy about something you wrote and some responded to it.

 

oh, ok, yeah, i remember my friend replacing his ignition control modual on his suburban. but i was looking at that o2 censor, and i was wondering what would be the best way to get to it. im guessing up top, but you guys tell me. well, its looking like it's pretty much narrowed down to the 02 censor, so i will pick one up when i grab a fuel filter.

thanks again guys, mike

 

if your car has the stock exhaust manifolds you should be able to reach the O2 from the topside. if you have headers then it would probably be easier getting at from the bottom.

 

thats what it looked like i m gonna have to do. i took a look at it when i replaced my fuel filter today