Ok here is my 1st question. When 1st start up my 99 Bravada(cold) and start to drive, when you push down on the gas pedal, the engine reacts like your not giving it gas at all. It will do this for about 20-30 seconds. After 20-30 seconds, the runs normal. I have no check engine lights and the only one I had cleared with my scanner as of late was a fuel evaporative(small leak) code. both right and left O2 sensors have been replaced and the dealer I bought it from said he replaced the fuel pump. I have had this Bravada for about a month. Any ideas?

 

If you're not getting an SES light, the problem is not anything that the PCM monitors. Check fuel pressure and leakdown. It's quick, easy, and free. Most auto parts stores rent/loan/sell pressure testers. You'll need to check it under the same conditions that it acts up. Before you start it for the first time in the day, connect the pressure tester and check the pressure. Ignition ON, (don't start the engine) fuel pump will activate for ~2 seconds and deactivate. Pressure must be checked while the pump is activated. Pressure must be 60psi to 66psi and must remain above 55psi for at least 10 minutes after the pump deactivates. Post your results.

 

I think my scanner reads fuel pressure via OBD. However, my scanner is out being updated so I may not see it for a week. Is it possible that the fuel evaporative(small leak) or commonly known as "the gas cap" error code causing this. Thank you for your response. When I get my scanner back I will post the results.

 

The fuel delivery system, (fuel pump, pressure regulator etc) and fuel pressure, are not monitored by OBDII on your vehicle. The EVAP DTC P0442 will not affect engine performance. Any number of issues in the fuel delivery system will affect performance. That's why it's the first thing to check.

 

*Moved to '2nd Gen Tech'*

 

Ok, I finally got my scanner back and found out my scanner does monitor the fuel system as well as run a test for the fuel. It doesn't give me at read out of what the fuel pressure is at. It just tells me that it has passed the test and that everything is running fine. With that being said, my Bravada didn't act up though either! Magic right? LOL! I also tested the O2 sensors and heaters again and all passed.

 

Correct, that's the fuel delivery system, which is not monitored. Some scan tools will allow you to view fuel trims, oxygen sensors, injector pulse width, etc etc. Your vehicle does not have provisions for monitoring fuel delivery system data: regulated fuel pressure, leakdown rate, fuel pump operation, and the fuel pressure regulator. Some vehicles monitor fuel pressure, (mainly Ford) but not S & T body GM vehicles.

It's not surprising that it didn't act up. Very common for fuel pumps to be intermittent before they completely fail. You'll need to check fuel pressure and leakdown when it's acting up to determine if the problem is in fact fuel delivery related.