Ok so I have a 97 sierra ext cab 4X4. Couple of days ago check engine light came on and it started running really rough. Took it to autozone to have codes pulled. it is throwing o2 sensor, cam-crank timing, MAF sensor and cylinder 3 misfire. Not sure if 1 causing the others or what. Would love any help you can give me here! oh it has 350 as well.
There is a good chance that your poppet nozzle is dirty and gummed up with carbon. It's a common issue with the Vortec engines and the only way to clean the poppet nozzle is to have it cleaned professionally with a injector cleaner machine.
The machine injects nitrogen in to the fuel line at the shredder valve to clean out the poppet nozzles. At worst your going to have to replace the SCFI system, but there is good new. The good news is that there is a conversion kit for the SCFI to convert it to a MPFI system like the ones used in the 2002 and up Vortecs.
The 1996 to 2002 4.3-liter, 5.0-liter and 5.7-liter Vortec engines are sensitive to fuel deposits in the fuel injectors because of the intermittent firing of the fuel injectors. So cross your fingers that it's just a dirty poppet nozzle that may need cleaning.
The other thing that comes to mind is a bad fuel pressure regulator leaking fuel in to your upper intake platinum which is causing your miss fire and the rest of the faulty codes.
Here is a few test for you to do.
1. Test the fuel flow. The fuel pressure should not be less than the "Key On-Engine Off" (KOEO) specification. If it is less, test the fuel pump and voltage supply circuit. Pressure from the fuel pump should be 70 to 80 psi or higher. The pump should also output a quart of fuel in 30 seconds.
2. Check the fuel pressure regulator. After the key is turned off, the fuel line pressure should hold for at least five minutes. This can be done at the shredder valve with a fuel pressure gauge.
3. Monitor the airflow sensor with a scan tool, and the Fuel pressure in the CSFI system is 60 to 66 psi with KOEO; the operating pressure maintains at 55 to 57 psi. The poppet valves in the spray nozzles should open at about 40 psi. Clean the MAF sensors by spraying the sensor element with electronics cleaner (use only electronics cleaner; any other type of cleaner or solvent can damage the sensor).
Good luck and keep us posted.
Here is a link for you to read to get more information about your SCFI system.
http://www.underhoodservice.com/Art...k__central_port_fuel_injection_diagnosis.aspx
http://www.theautoshop.net/VortecMPFI.htm
