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Ron, ASE Certified Technician
Category: Pontiac
Satisfied Customers: 33093
Experience:  34 years as a Tech
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I just sent you messages on my 99 grand prix gt, 1999, I am

Customer Question

I just sent you messages on my 99 grand prix gt
JA: What year is your Grand Prix?
Customer: 1999
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: I am trying to do it myself but this one has me stumped.
JA: Anything else you think the mechanic should know?
Customer: I have replaced the upper plenum and tidy gasket. The tstat and plugs and wires are new. Coil pack are all good car is running hotter than normal but I just moved to texas from wisconsin. Any other info just ask
JA: Have you checked the coolant? Have you noticed any leaking?
Customer: No coolant mixed fluids
Submitted: 3 months ago.
Category: Pontiac
Expert:  Ron replied 3 months ago.

Hello, my name is ***** ***** I am a professional here at Just Answer. I have noticed that your question was not getting a response and thought I would see if you still need help with this.I apologize for the delay and I hope I can still assist you with this here. If you can explain what type of problem you are having and post back with complete details I will see if I can help you with this. Your cooling fan is designed to turn on right at 215 degrees. Can you monitor the coolant temp on your scan tool and see if that is the case?

Customer: replied 3 months ago.
Cooling fans are working as designed. I am just out of my realm because I recently moved from wisconsin to texas. My car originally was just running hot...I hit an armadillo and it crushed the oil pan. Long story short..I got an engine from a yard down in houston. I installed it and it ran great but I had to change the thermostat the next day because it was running warmer than I am use to but the thermostat was bad. I also changed the upper plenum gasket. Afterwards I took it for a ride and it tripped a low/high voltage mass air sensor code and a random multiple misfire. I am stumped
Expert:  Ron replied 3 months ago.

If you not loosing coolant and the fans are running as they should you may not have a heating problem. If you give me the actual fault codes your getting I will have a look at that for you.

Customer: replied 3 months ago.
Po300 and po102
Expert:  Ron replied 3 months ago.

The P0300 indicates the PCM has detected a random misfire and if you have access to a scan tool that can read the data stream you can look at the misfire count and determine which cylinder it is. The common cause for the P0102 to set in most cases is usually a failing MAF . Start with making sure its clean and the air intake hose is sealing and tight. If so then run the test steps in the link below to check it before you consider replacing it.

Customer: replied 3 months ago.
Let me get back with you in a bit..I will go run some tests.just a quick question..if I have for some dumb reason had a bad seal on the upper plenum would that cause this misfire and the running warmer?
Expert:  Ron replied 3 months ago.

It could cause the misfire and could affect engine temp if you somehow have a vacuum leak causing the engine to run to lean. In most cases if that is the case you would also see a lean code.

Customer: replied 3 months ago. lean air fuel guage registers lean at highway speeds
Expert:  Ron replied 3 months ago.

The fuel gauge should have no affect no engine performance as long as you have fuel in the tank.

Customer: replied 3 months ago.
Noo...not the actual fuel guage...I have an air/fuel guage that sweeps while the car is running to monitor the o2 sensors..
Expert:  Ron replied 3 months ago.

Well if its reading the Air/fuel mixture then you may be lean but like I said, the computer will usually pick it up and set a lean code.

Customer: replied 3 months ago.
Ok..I am gonna go run a slew of tests and check the mass air flow
Expert:  Ron replied 3 months ago.

Okay, Im here all day if needed.