99 grandprix gtp 3.8l sc gets 9/13 mpg!!!

[tiffany716]

hey guys been reading everything and i appreciate the input...now as far as parts go, i dont remember the exact part names of my parts but i can let u know that all were bought new from napa and advance auto and i didnt buy the "cheapest" model of any part, rather i spent the extra money for the quality. i mean this gas mileage was like this before ANYTHING was put on, this has all been very recent that im fixing this car up...btw i changed my ignition switch, that resolved all of the electrical problems my car was having, THANX AF!!!!!!...as far as rolling resistance i had 3 of 4 wheel bearings changed and besides for the 15" thats on my car, i have all brand new 16" winter "blizzak" tires..also had all brakes done and all calipers work correctly, no sticking......now the continous suggestion that keeps coming up is my cat. converter..i got my resonator replaced and my exhaust is very quiet..the only engine code ive ever had on this car was about the cat. converter...guy reset codes and it hasnt came back on since, but the only problem my car has now driving-wise is the gas and the little bit of hesitation there is on acceleration and startup idle....and it seems like all these problems are linked to the cat....the problem is that the guys at cole muffler cant actually "test" the converter output, only codes and visually looking for cracks or leaks, which checked out good..i dont wanna shell out the $350+ to get this repaired unless i kno its faulty, but then again i like knowing the majority of this car is brand new...but it seems like this is my biggest problem, and i gotta spend money on labor to save it on gas lol!

[blazeracer]

Tha cat is the airflow choke point on a GP. I put in a Random Technologies high flow cat I picked up Grandprixstore.com and it's been awesome. I took it to a little mom and pop muffler shop to get it put on. That costs about $140 for the cat and about $50 to put it on back in 01. Summit Racing sells the Magnaflow cats for under $100 now.

[tblake]

Or you can just hack the cat right out, weld a straight pipe in, and buy an O2 simulator for the O2 sensor behind the cat converter.

[Mickey#1]

Here's a couple free things to check.
1 - Make sure none of the spark plug wires are touching the O2 sensor. Try to position them at least one inch away.
2 - Turn the key to the run position a couple times then check for fuel in the vacuum line going to the fuel pressure regulator.

We need to know which spark plugs you installed. Pull one out if you don't know. I'd also check for vacuum leaks.

[tiffany716]

hey um i have ac delco plugs and wires...and as far as vacuum leaks, that check engine code said either cat. converter or vacuum leak somewhere, but i dont even kno how to check for one...

[blazeracer]

A great way to check for a vaccum leak is to take a spray can of starter fluid and spray it on and around the vaccum lines and connectors with the engine idling.. Just do little sections at a time, not the whole motor. When the the RPM's come up, you found the leak. Do this very carefully, started fluid is extremely flammable.

[richtazz]

If your CEL is currently on, take the car to a local Advance/Auto-Zone, and have it scanned for free and post the codes stored (don't believe them on what the codes mean). We could speculate all day, but cannot help further until you post the codes and check fuel pressure. I would also do a compression test to rule out a bad cylinder.

[tiffany716]

hey guys been awhile just wanted to end this post...my car finally had a check engine light come on that pointed to the cat. converter..i ordered one offline from the grand prix store, paid $75 to put it in and now my mileage is around 24 city/31 highway......i dont know if thats what this car should be at but i dont care because ive cut my gas costs pretty much in half..i love u guys, thanks AF!!!