Thread: 1998 grand prix gtp 0-100 km in 9.5 seconds diagnosis

clean the throttle body.
replace the fuel filter.
clean the maf sensor
replace the pcv valve
replace the upstream O2 sensor
check and see what kinda plugs were actually put in the car. these cars don't like platinum.
put the 195 tstat back in if the pcm isn't programmed for a 180
get headers or get a 3 inch downpipe with a high flow cat and a plog from zzp
buy a new gas cap and look for vacuum leaks.

here is a vacuum diagram...inspect all those hoses for cracks.

I hope you are running 91+ octane fuel like the owners manual says too.

Running either 91 or 94 is fine, it really doesnt matter. As long as it's 91+.

Throttle body removal is very simple. Just take the throttle cables off and unplug the IAC, TPS and MAF sensor, remove air intake tube, then remove the 3 bolts holding the TB to the supercharger. Then you can clean it off the car and make sure not to damage the honey comb MAF screen on the front of the TB, that is needed to smooth the air flow acrosss the MAF sensor.

Also, make sure you have a spare TB gasket handy as it's likely to be ruined when you remove it as it's a paper gasket.

that screen is held in with a spring clip around the outer lip ot the tb.

but thats not the side that needs cleaning. you need to take the TB off the engine and clean the back side. thats what gets carbon coated.

remove the maf sensor too, dont let any cleaner touch it unless its maf cleaner. any thing else can kill the maf.

hold up fella. if you still have the stock 3.8 pulley on there , you don't want the AL104 plugs. these cars come stock with iridium plugs. never heard of titanium plugs...lol. if your gonna run copper plugs use the AL606's or 605's . you want the hottest spark you can get that doesn't cause knock. since you still have the stock pulley on there's no reason to run a plug as cold as a 104. platinums are the plug you don't want.

if you have an aftermarket pcm such as zzp's , the fans are programmed to come on at 185 degrees , so you run 180 tstat. if your pcm is stock the fans come on at about 210 degrees. the fans are supposed to cool the coolant in the radiator before it circulates. if you run a 180 tstat and the fans don't kick in till 210 , the coolant will constantly circulate and never be cooled by the fan , which can actually cause you to run even hotter.

Eh, I'd slap the 104's in there if he already has them. Are they ideal for his car, no but it can't do any harm either.

Oops sorry I did mean to say platinum and not Titanium, my mind was still on school mode. I have yet to install the 104's, I was planning on waiting for everything else for the 3.4 pulley to get here before I put them in as the current ones don't look very worn and are gapped to .06. Since they are platinum would it be better to pu in the 104's? I also have been quite busy so I haven't had time to clean the TB yet. But GOOD NEWS! I found the culprit. I was curious about the units for each of the LED bars on the boost gauge as I usually get 4 or 5 bars at WOT, turns out It should reach max! So I followed a tutorial on YouTube to bypass the SC bypass selenoid (took it out, plugged both vacuum lines) and it felt like a completely different car. The boost gauge would go all the way max and I timed my 0-60 to be 7.5 seconds! Hell yeah! Now the problem is I have no clue where to find a replacement one, I can't find anything online or in local part stores. Might go to GM and ask them but I'm not sure about an item number or the actual name for the part. Any ideas?