Pontiac Repair: 98 pontiac grand prix sc 3.8l, throttle position sensor, upper intake manifold

Question
QUESTION: I replaced head and intake gaskets, Won't start, I have good spark and good fuel presure at the rail. I also have power to the injectors bot no fuel past the injectors. Conections are all good.


ANSWER: Hey Tom:

Do you have injector pulse? What I mean is is the computer grounding the injectors to turn them on? If you have spark and fuel the only thing your missing is compression. if you have all three of them it should start and run. there is a possibility that the cylinder were washed down when you did the head gaskets and you have weak compression... It's a real long shot. Are the aprak plugs fouled? That will do it as well. all of the obvious things are reconneced and hooked back up. If you had the upper intake off and the pcv valve out did you put it back in with the o-ring under it? Are all the lower intake manifold bolts tight including the ones under the upper intake manifold? just throwing stuff out there with out seeing this It's hard to say exactly what's up with it. Good luck :)


---------- FOLLOW-UP ----------

QUESTION: How do I check injector pulse? do I need to remove the rail and check for spray? and if I don't have injector pulse where do I look to fix it. Plugs are dry and clean.

Thanks Again

Answer
You need waht is called a noid light it plugs into the injector connecor in place of the injector. You can use a computer friendly test light that has led's in it also. if you do not have injector pulse but you do have spark it is more than likely an issue with the computer. The ignition module runs the spark at time of cranking the engine once it fires and runs the computer controls the sprk timing. You may have a blown fues or one of the sensors is skewed high or low making the computer not fire the injectors. The Throttle position sensor "TP" is the most sensitive to this and turning off the injectors if the computer sees a high TP sensor voltage then it goes into a clear flood mode and basically turns off the injectors. try unplugging that and crank it over and see what happens. The other possibility is there is a large connector on the front of the engine it's right by the #1 and #3 injectors it has maybe 8 or 10 wires in it that is the link between the ignition module and the engine computer make sure none of the pins are bent over in it from when you re connected it. Like I said I'm only guessing here! good luck.