Ok Ive read on like 100 different forums about differect cars with similar problems, but now i want to narrow it to my car.

HERES THE PROBLEM. when the car shifts into overdrive, usually around 45mph the car begins to hesitate, i push the gas harder it goes no faster, RPMS dont change and even my girlfriend says it seems like my car is struggling. it struggles up to about 55 or so. If i put it into the "D" thats not circled AKA take overdrive off, the rpms jump up and the problem goes away. On a 3.4 V6 camaro with normal around town conditions i get 160 miles to a full tank. the car seems to run and drive great aside from those few MPH. i have replaced the following

plugs
wires
fuel filter
air filter
belt
did a professional fuel injector service "motorvac"
trans fluid changed

HERES WHAT IM THINKING
02 sensors
weak fuel pump
bad wire
TPS- doubtful but maybe

 

The engine is struggling under load, and you have done the basic stuff. Check the fuel pressure before changing fuel pump. You can also check the TPS with a multimeter. New O2 sensors is a good idea if they are old, and they can be checked with a scanner, a code reader won't do the job. Could also be that the transmission fails to shift out of overdrive (really 4th gear) and the small engine has to work really hard to make the car pick up speed. It is also possible that the EGR is hanging open when you step on the gas.
Is the check engine lite lit or flashing??

 

No cel and no misfires or anything. I did check fuel pressure the pressure seems to take a little to long to reach normal probably why the car cranks to long before starting. But wouldn't there be more of a load when the car shifts out of overdrive and the engine revs to 3k. Vs in overdrive at 1500. I can't see how a weak fuel pump would only affect 10mph throughout the whole range.

 

My first thought was that the trans may not be shifting out of overdrive on it's own, like Pete also said. Can you feel it downshifting with the gas pedal down? And everybody has their own idea of what "goes no faster" means, based on what your expectations are compared to what the engine is actually capable of delivering. For starters, when driving around town, don't even bother putting the shifter into O/D. Engine rpm's will be way too low, well below the 3.4's torque band, for O/D to even be needed or wanted. Watch your tachometer, it's not there for decoration.

 

I've had my share of cars and I work in a shop as an ase certified mechanic. I know what's to be expected of a car what feels right and what doesn't. I also know wjat a tac is used for lol. I had a 4 banger grand am that was dog slow and a low 12 second gtp. I'm familiar with how a car works and what it takes to fix certain things but it seems to weird the car runs and drives perfect. Except for 45mph to about 55. IMO. It should take more load to get a 3500lb car moving then to keep it cruising at 50 over drive on or off somethings wrong. When I push the gas even with a decent amount of force the rpms don't change and neither does my speed I have to go almost 3/4 throttle then the car will automatiy down shift and will regain power.

Ps sorry for any spelling or punctuation errors I'm trying to do this in my cell haha

 

OK, wasn't trying to purposely dumb it down. On these forums it's hard to know a persons qualifications with just some questions. I'll have to put that in my diary now. Let's see...Blackwidow95, ASE certified, got it!
By your user name I assume your car is a 95? I used to have a 94, 3.4 with an automatic. Mid-range performance on that car was less than desirable, by what I'm used to expecting anyway. And if it isn't going to downshift between 45-55 mph, the car isn't going to get out of it's own way in a hurry while in O/D. But it doesn't sound right that it doesn't accelerate at all with giving it throttle, even in O/D. Have you checked to see whether the cat converter might be restricted? Is it turning red on you?

 

As Z28pete said EGR valve. But I will add Map Sensor. The diaphrames can get stiff with age and they can cause this. BUT 10 MPG sounds like your in LHM or your O2 sensor are shot.

 

well now that you mention it, right after i bought the car, the CEL came on for an EGR code. i cleared the code and havent had the light come on for anything since i cleared it. that was about 6 months ago.

i cant just scan my car with any scanner though because i have an OBD1 system with a OBD connector and OBD1 is pretty lame for diagnosis.

see im kinda getting the same results here that i was getting googling. this problem could be 101 different things. i wish someone had this exact same issue in the past lol but dont take it wrong guys, your helping me out alot!!!!

 

same as mine and all i did was change the spark plugs and its acting up.

I use to have this spark plugs

http://www.autozone.com/autozone/cat...&parentId=62-0

but i was thinking its a waste of money and i bought the cheaper ones

http://www.autozone.com/autozone/cat...-Platinum-Plus

Lol im gonna change them again next week

 

well I did some tests, my O2 sensors seem to be switching just fine, I did another motorvac( FI cleaning) the problem is still there. Im starting to wonder if its a trans issue