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2003 Chevy pickup 5.3L engine. Misfires during
Misfires must be diagnosed. As you can see, randomly changing parts in an attempt to diagnose the problem can be vert COSTLY. Besides all the parts that you have allready replaced, there could be a problem with the fuel injectors, there could be cylinder compression problems caused by a number of possible causes including bent/burnt valves, broken valve springs, or a head gasket blown between cylinders. There could be timing problems due to erratic knock sensor input. Fuel shutoff due to throttle position sensor "dropout". "Random" misfires (which is what a code P0300 code is) can even be caused by something as crazy as a vacuum brake booster leaking and creating a large vacuum leak....the list goes on and on....
It is easiest and most cost effective way to diagnose this type of problem is by using a scan tool and looking at all of the engine data and/or taking a "snap-shot" of the data when the problem is occuring. This way, you can tell which parts of the engine control system are being affected so those areas can be inspected for possible failures. The first step is to isolate the causing SYSTEM. So far, you have replaced parts for the fuel system, the ignition system and the EGR system....
on Nov 12, 2011
1999 chevy won't come out of 4 low, tried
Your problem shows as a problem with a 1999 Chevrolet C1500. Then you describe the problem as not coming out of 4-wheel Low. If your Truch HAS 4 wheel drive, it is a "K" series truck, not a "C" series truck. K1500? (Minor detail, but some people don't know the difference and can give you some really goofy advise if they try to look it up the way it is listed.)
Anyway, I have to ask this: Did you actually scan your transfer case module or did you scan with a generic OBD code reader? It should be noted here that MOST OBD code readers CANNOT access information from the transfer case or body control modules. They can only access the "GENERIC" side of the engine control computer (or PCM). They also cannot access "vehicle specific" information from ANY modules including the PCM.
With this type of problem, you really need a full access scanner that can read data from all of the modules. That is the only way to check and see if the computer is getting the signals from the control switches to change your drive mode. If the computer is not receiving the signals, then there is a problem with your selector switch or the wiring between the switch and the computer. If the computer IS getting the signal, then there is a problem either with your shift actuator motor assembly or the wiring between the computer and the shift actuator.
Reading the data will also verify the range that the actuator is reporting to the computer. Just because the motor runs, does not mean the actuator is functioning properly. It COULD be reporting to the computer that it is in 2-wheel High when it is actually stuck in 4-wheel Low. This is where comparing computer data to functional testing comes in.
on Sep 17, 2011
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