I got a 2000 pontiac grand prix gtp the car runs well but the boost level will not go more than 1/4 on the gauge, one mecanic said to change the spark plugs because they are 4 or 5 years old (iridim...
The spark plugs have absolutely nothing at all whatsoever to do with boost levels.
However; change them anyway because new plugs are always better. In the GTP, don't use the iridium plugs, use copper core. I highly recommend Autolite 605's, gap them to .055"
In the GTP, spark knock is a common, performance robbing issue because of the supercharging. You'll lose 5-6 horsepower for every degree of timing ****** that the engine computer will employ to prevent the spark knock. If you use copper core plugs though, this problem will be less likely because copper dissipates the residual heat much faster than iridium, so that only the electrode spark alone can be hot enough to ignite the fuel. The only other difference between the plug types is how long they last. Iridium plugs were the originals only because they last longer...they offer no performance benefit to the GTP.
Now on to your actual question.
There only a few causes for loss of boost pressure in the GTP, all of which are an easy fix.
Supercharger belt slip, disconnected or damaged boost bypass valve hoses, or maladjusted boost bypass valve linkage.
The easiest thing to do first is the boost bypass valve adjustment. This will produce results even if you DO still have belt slip or a leaking hose.
Locate your boost bypass valve. You will find it mounted directly in front of where the throttle body bolts into the intake plenum.
You will see that it is held in place by three bolts. Loosen them in this order; left, right and rear. You will find that you'll need a 4" extension socket to reach the rear one. Hold your socket on that one while you push down on the valve body. As you may notice the mounting bolt holes are elliptical, allowing for the height adjustment. You can use this as a visual reference for how far to push the valve down. You shouldn't push it down all the way, only about a half an inch will suffice.
What the adjustment does is reduces the amount of throttle opening needed to produce boost, by shortening the travel length of the valve lever that is attached to the throttle. When properly set, it will allow about 11 to 11.5 PSI at wide open throttle, or just short of wide open throttle. In any circumstance you may also notice that your GTP is a little quicker from a standing start after the adjustment.
Jun 26, 2011 |
2000 Pontiac Grand Prix