Ive got a 1998 tahoe with a 350 and ive been chasing a electrical problem or what i think is a electrical problem anyway Ive checked most of the wires from all the sensors and they all seem good. But my question on the mass air flow sensor is should I be getting volts on the yellow sensor signal wire that goes from the sensor the the red # 28 pin on the comp. Ive got volts on the 12 volt supply pink wire. On all the other sensor signal wires ive checked there where no volts. Thanks for any help.

What kind of electrical problem due you think you have?

Thats a tough one to answer without a diagram in front of me. Depending on the sensor you are checking the voltage could be a/c or d/c. In the case of the MAF sensor it (if memory serves me correctly and somebody please correct me if I am wrong) it is sending a/c voltage. The PCM looks for the frequency and interprets it into measure of volume. The crank sensor will aslo be an A/c voltage since it is sending square wave signals to the PCM. The coolant temp sensor for example is recieving a reference voltage which is dropped through a resistor. The PCM recieves the left over d/c voltage and determines the coolant temp.

Well long story short Alot of misfiring, backfiring and spitting and sputtering. Its idles real rough. Ive had it in two different shops and over 2000 dollars later it still does the same thing. Every electical thing under the hood has been changed, all sensors, computer, distribator, fuel injectors . . . well pretty much everything. Both places told me its not in the motor, its something causing it to throw a camshaft position sensor code. So now Im chasing wires and so far there all checking out ok. that maf sensor threw me for a loop though when it had volts in the sensor signal and none of the others did. Also does any one know anything about the fuel pump/oil pressure switch. its in my wiring diagram Im following and what will happen if oil pressure is low. Its showing that the fuel pump and oil gauge is tied in to one another by a switch. Would this cause the motor to run bad if my oil gauge isnt showing pressure. Thanks

I would think it would. If you turn the key on, the relay should kick in or not kick in being now that the fuel pump let the car light up, it better show pressure or that oil needle/light is the analog showing all systems go. So yeah, if say you expose that oil sensor dry or low level to trigger the oil sensor, then yes, no fuel to injectors.

The oil pressure sending unit (it is a sending unit which supplies data to a guage, a switch only turn off or turns on a light) is a backup for the fuel system. When there is adequate oil pressure it will supply voltage to the fuel pump if the primary system (PCM, fuel pump relay, ignition switch) has failed. It is nothing more than a backup. If you unplug it the vehicle will continue to run even though you theoretically have no oil pressure and an open cicuit for the fuel pump side of the sending unit.

Well long story short Alot of misfiring, backfiring and spitting and sputtering. Its idles real rough. Ive had it in two different shops and over 2000 dollars later it still does the same thing. Every electical thing under the hood has been changed, all sensors, computer, distribator, fuel injectors . . . well pretty much everything. Both places told me its not in the motor, its something causing it to throw a camshaft position sensor code. So now Im chasing wires and so far there all checking out ok. that maf sensor threw me for a loop though when it had volts in the sensor signal and none of the others did. Also does any one know anything about the fuel pump/oil pressure switch. its in my wiring diagram Im following and what will happen if oil pressure is low. Its showing that the fuel pump and oil gauge is tied in to one another by a switch. Would this cause the motor to run bad if my oil gauge isnt showing pressure. Thanks

General code descriptions really don't work well here. What we need to help you are actual code numbers, such as P01345, etc. Todays cars & motors set these codes, DTC's (Diagnostic Trouble Codes). There are trouble shooting trees for each and every code.

With that in mind some codes may have something in common that can point to a particular unit (part) that may be causing your troubles.

Well long story short Alot of misfiring, backfiring and spitting and sputtering. Its idles real rough. Ive had it in two different shops and over 2000 dollars later it still does the same thing. Every electical thing under the hood has been changed, all sensors, computer, distribator, fuel injectors . . . well pretty much everything. Both places told me its not in the motor, its something causing it to throw a camshaft position sensor code. So now Im chasing wires and so far there all checking out ok. that maf sensor threw me for a loop though when it had volts in the sensor signal and none of the others did. Also does any one know anything about the fuel pump/oil pressure switch. its in my wiring diagram Im following and what will happen if oil pressure is low. Its showing that the fuel pump and oil gauge is tied in to one another by a switch. Would this cause the motor to run bad if my oil gauge isnt showing pressure. Thanks

did you /they remove plugs and compare ....? did they measure the plug wire resistance and is this OEM spec..?..how about the ground wires and the distributor being grounded....auto mechanics and electricity is like water and electricity ....$2000.oo for zero effect ouch!

The code its throwing is PO341 camshaft position sensor circuit, range or performance problem. All the plugs come out looking the same, Black carbon colored.Dont know about the wires except for that they are new. I checked the fuel pressure earlier and it was good at 60psi.

Check the value against the book or take a good known cam sensor and check that way if you do not have a manual.

Here is the deal. Cam sensor takes the last good known signal upon final start-up. Meaning, once you turn the key off, the last good known signal was saved in the RAM. Now you turn the car over and she just cranks is the cam sensor has not the correct voltage value reading to register to fire off.
You have spark and fuel but the spark will fire like once and stop is the base signal needs the sensors or she is a boat anchor.

I agree you need to focus on that problem first. Once that is repaired you can focus on the other things if need be. 9 times out of ten the hardest problems have the easiest fix. I am guilty myself of making things more complicated than there are. When I'm really stumped I take a little break, do something else, and come back to it. Heck my boss would be the first one to tell you I do my best diagnostic work when I'm sleeping! :biggrin: More often than not when I come back to it the problem reveals itself.

P0341=CMP Sensor Performance. Here's an over view out of my '98 C/K service manual.

Electromagnetic interference (EMI) from the ign coil or the spark plug wires could cause a poor signal condition in the CMP signal circuit to the VCM. Ensure the routing of the CMP sensor circuitry is correct. Also check for any aftermarket accessories and harnesses creating EMI.

Are there any other codes present? If so they need to be addressed 1st.

With the motor running move/wiggle the engine harness at various locations all the way to the VCM. If the motor rpm's surge while doing this you have either wiring problems or EMI.

Would that EMI cause the motor to run so bad. Meaning the motor runs rough. The tach bounces up and down as its spitting and sputtering and backfiring. the other code I was getting has been cleared. It was a crankshft position sensor PO336 but by changing it it cleared it. But the PO341 will not go away.

Would that EMI cause the motor to run so bad. Meaning the motor runs rough. The tach bounces up and down as its spitting and sputtering and backfiring. the other code I was getting has been cleared. It was a crankshft position sensor PO336 but by changing it it cleared it. But the PO341 will not go away.

my take on this is the plugs are all carboned and I bet not getting the correct spark/timing... the tach jumping is indicative of a CPS/wiring problem, the tach jumping is what the computer sees and this is why your spark is messed up....CPs simply supplies the computer pulses ,, which indicte the position of the crankshaft or on other engines camshaft as well...noise as mentioned can and will cause the CPS signal to get interference and threrefore cause a confusing signal the the computer for plug firing ...