Pontiac Repair: 1992 , Pontiac Grand prix 3.1L Misfires , slugish, poor vacuum, pontiac grand prix

Question
1992 Pontiac Grand Prix with 3.1L engine
It has begun to misfire, run sluggish and auto transmission seems to shift hard or wrong, A/C only floor,  what can it be ?


I've replaced all plugs and wires, verified that all coils were firing "with a grounded spark plug"  new air/fuel filter and checked/ replaced all Vacuum lines in engine bay, I don't know where to look for the HVAC vacuum lines inside car would these affect performance so much?

Exhaust smells like fuel, NO smoke and there is NO oil/coolant mixture nor is there any exhaust in coolant, car worked great 2 days ago!

are there any "hidden" vac lines I've missed ?

Answer
Hi Fred:
Well there is a vacuum line diagram under the hood on that car it is the white emission label it's either on the radiator support or on the strut tower it shows where all the vacuum lines are and where they go. You more than likely have a vacuum leak of some sort or just the engine is running that poorly. if it were a bad enough vacuum leak the engine would "race" when it's in park and have a high idle. weak or poor vacuum will have an effect on the transmission if this is a 4 speed automatic. I would also check your fuel pressure on this engine. When the car is off the pressure should hold at or near what it was when it was running for a while say 20 minutes if the pressure drops you could have a leaking injector causing it to run bad and the "gas" smell you referred to. Without a diagnostic scanner it's really hard to tell you what's going on with the engine it's all pretty much guess work without one But it sound like you covered the basics. As for the HVAC some of those cars had a big vacuum solenoid block under the dash on the right side under the glove box and some of them all the HVAC modes are electric motors and no vacuum at all. Hope this helps you some more :)