Car Not running Smooth! Where to start?

[Andrew7DG]

Ok I just got my first GSX not that long ago! Very happy about this purchase and I love the car!!!!

I did make a mistake when I bought the car though. I bought it with a problem. I know I shoul have found one problem free but I though the car was for a great deal

The car is a 90GSX

There are no mods to the car.
The transmission was replaced 20,000 miles ago

Things that have been changed on the engine
switch to synthetic Mobil 1
New Plug wires
new spark plugs
new coolent new O2 sensor
New fuel filter
last owner said he did a boost leak and everything checked out
basicly I tried to change everything that needed matenince

The problem is when it is running. When I bought the car i drove it home from wisconson and took note of the gas milage because when I bought the car I didn't know how good of gas milage I would get. I got 25mpg. Lately though when I have been driving it I can't get more then 17mpg. I don't think it is my driving becuase i just came back from a road trip and was doing mostly 60 on the back roads trying not to boost. I don't know if this has anything to do with this but it seemed the bad gas milage got bad when i replaced the fuel filter. After my long trip though (thinking that it was leaking or something) I put my hand around it and checked for gas leaks on the side... nothing

When I first bought this car it has a studdering problem or it would hesitate in the upper RPM and at full boost. I took out the plugs and they had lots of carbon deposits on them so I replaced them and that helped for a while and when the car is under full throttle. However what is really anoying is when the cruise is on, the car is going up a hill, boost starts to creep up and it starts loosing power again or hesitateds/studders.
I do smell rich gas. I am thinking it is the O2 sensor however it just got replaced!!!

I do have an O2 sensor from my GS laying around, would that work in the turbo model just to test?

If the cat was backed up what symptoms would I be seeing?
The other one was it might be the timing and i am going to try to check that later
This could be a boost leak also

the car looks (from the spark plugs) and smells (at a stop light at idle) like it is rich! just i don't know where to check. Is there anything common that goes out on these cars? THANKS!!!

 

[reeper]

if the cat was clogged the car would run like crap

 

[gurmanator]

vacuum leak...take a can of starting fluid and mist the vacuum hoses you will hear a change in rpm's if you have a leak.

 

[prostreetdsmx1]

does sound like you may have some kind of leak bud. Do a pressure test yourself and make sure that everything is cool. Make sure your plugs are properly gapped and give you car a little BG fuel treatment too. Something to help clean up your fuel system to help make sure there isn't anything blocking or limiting flow.

 

[Andrew7DG]

vacuum leak...take a can of starting fluid and mist the vacuum hoses you will hear a change in rpm's if you have a leak.

Um... I hate to sound like a newbie but which vacuum hose or do you mean the intake hoses? It idles well right now. Spraying starting fluid on a running engine sounds like i am going to start the car on fire.

If you can explain it a bit more that would be great!

 

[Andrew7DG]

does sound like you may have some kind of leak bud. Do a pressure test yourself and make sure that everything is cool. Make sure your plugs are properly gapped and give you car a little BG fuel treatment too. Something to help clean up your fuel system to help make sure there isn't anything blocking or limiting flow.

Yeah I think that is the next step i am going to try. I did the fuel treatment with some sea foam didn't help much though. Something happen to it since I bought it and now which was only less then two weeks.

 

[reeper]

If you decide to do leak down test here is a link
http://www.dsmgrrrl.com/FAQs/leakdown.htm

 

[gurmanator]

Um... I hate to sound like a newbie but which vacuum hose or do you mean the intake hoses? It idles well right now. Spraying starting fluid on a running engine sounds like i am going to start the car on fire.

If you can explain it a bit more that would be great!

carb cleaner works just as good...with your carb cleaner and the little hose that comes with the can,take and spray each and every rubber hose.example=the vacuum hose that comes from your intake to your power brake booster,spray each connection(just a shot).if you have a leak there the engine rpm will rise just a tad,do that to every vacuum hose connection and spray your tb also.after time thoes hoses will dry rot and crack with out you knowing it.

 

[Andrew7DG]

did a boost leak test. Pumped air into the system and found it was an intercooler problem. I do have a small leak by the fuel injectors but it isn't that bad compaired to the intercooler one. I am thinking the rubber seals are just dried up around the injectors. runs great now! However I don't know about the gas milage yet.

 

[GVR4592]

Any type of boost leak can affect performance, driveability and mileage. The injector seals are an easy fix and pretty inexpensive.

 

[oldman]

Never ever trust anybody but yourself when it comes to boost leak test. Also, which plug and what gap?