Tach acts very jumpy too. Steady some then bounces from 800 to 2k sometimes

 

I looked in pending codes and it also has the P0327 knock sensor

 

Now my idle stays near 2k which I assume is limp mode. If I hit clear codes the blazer idle goes back down to normal then it fluctuates near stall out and slowly goes back to 2k. So I cleared again and it did same thing. I go to pending codes and crankshaft position sensor keeps popping up first so I clear it and same thing idle goes back down then goes back up and the pending code p0335 is back again.

 

After clearing codes and waiting awhile I get the p0101 and the P0335 in the pending codes.

 

After clearing codes last time now the first and only code that comes up is p0101

 

Now there all three back lol

 

I used to say the OBD diagnosis in some cases can be more confusing than helpful. An input (feedback) parameters for the engine process are inaccurate, so the engine controller gets over regulated and switching into a limp mode.

If You have nearby any electronic engineer You may ask him to probe with an oscilloscope the feedback information on the sensors appearing on a fault list. For me it seems You are facing a problem with one of them. It could be within a sensor or a grounded or broken wiring. Unless the sensors are cheap and accurate troubleshooting is not worth the efforts...

 

I did test ground on the sensor and that is good. I guess I can try to plug my meter into the power of camshaft sensor wire and look for 12volt with key on? And I think u can test other wire for 12v by having someone manually turn the crank? Is it the same for crank sensor too?

 

Typically, on a RPM pickup You have three wires:
- a common wire
- power wire
- return signal wire
Common wire should be grounded to a chassis - a simple, continuity test with a multimeter

Power wire provides the power for the sensor. You may use a multimeter to measure the voltage in between the common one.
- on a 20V DC range (or so) You should have a steady reading when engine runs
- change over to an AC range (5V AC or so). If the power line is in a good condition Your readings shall be close to zero. If You get something around a volt or so it would mean the power line is broken somewhere (I assume for a shorted one You would end up with a permanently blown fuse).

Feedback wire is most tricky to be tested. It should send the feedback pulses whenever ametal extrusion of a rotating part crosses a front of the sensor mounted on the origin point. A multimeter has a limited capabilities so You cannot observe the shape of a signal like You would with an oscilloscope. The feedback signal could be wrong with an amplitude, could have a dead spots while transmission, etc.). A thing You can do is to:
- set a multimeter for AC voltage (range 20 or so),
- attach a probe between common wire and a feedback wire at the sensor (otherwise You will not know whether the problem is within wiring or a dead sensor)
- observe the feedback signal that should be steady
If You're lucky You could see there is no signal at all or it disappears for some period of time. But like i said - this is a limited method as You cannot see the signal shape and highly depends on Your multimeter quality. Yet another side note from my side - a grounded feedback line will not likely blow any fuse. In general, depending on a type of sensor, separating the wire from feedback line may not give 100% accurate results. Quite often, the sensors require pull-up or pull-down resistors, depending on their output circuit (PNP/NPN). Disconnecting a wire with external load resistor (located usually in ECU) will disable the sensor output. That may lead to a wrong conclusion after all.

Oh, and as we speak of a quality multimeter - some of a good ones have a frequency measure capability. That would count the output pulses and display in [Hz] how many of them comes out per second. In that case You could wait till the engine gets into a limp mode (open loop, steady rpms) and check out if the data from sensor is steady as well.

I haven't been digging into the Chevy sensors much, but I do have some background in the subject of engines. Crossing my fingers for Your accurate troubleshooting. Keep us updated.

 

Well I just picked up a camshaft sensor and a crankshaft sensor. Now should I try camshaft sensor first to see if anything changes? Or should I try the crankshaft sensor first to see if any changes? I don’t know which one reads to the other but I would assume/hope that maybe one not working could cause other to throw code?