2000 chevrolet blazer 2 door 4.3L 4x4

Ok, so about 2 years ago i had to replace my spider assembly because of leaking fpr and age, then cat, then plugs,distributor, wires and cap, i noticed over time that the exhaust kept smelling richer and richer, well i checked the fpr its good, compression test good, plugs, wires,distributor, cap and checked the timing very thoroughly and found minimal play (about 3 degrees) but other than that and all was good. Oh yea and also a new coil and ignition module that conveniently took a huge sh** on me on the way home at 10:30 at night after working about 16 hours straight in 100 degree heat, luckily i had a old one with me in my toolbox that came off my wifes 2002 that still had a little life left in it, which i promptly replaced with a new one the next morning. So with all these new parts and tests i was pulling my hair out as to what was causing this rich exhaust smell, well i found out that with these engines that not only is the cam position sensor in the distributor(which most of us already have known that)but the strategy of the controller uses the cam position sensor for FUEL INJECTOR TIMING NOT IGNITION TIMING......anyways after researching all of this i pulled out my distributor and elongated the distributor hold down bolt hole and reinstalled the distributor and gave it a turn CLOCKWISE remember CLOCKWISE about 4 degrees and started my truck up let it run for about 30 seconds and walked around to the tail pipe and took a sniff and WALAAAA!!! no more richness, plus it obviously has more pep and power also, so the obvious thing is that my timing chain,gears,cam, and oil pump gears have some wear on them all added together over time, so anyways i hope this can help some people out there that have this same issue.

Good Luck!!!

 

im going to give this a shot today, ive got the same rich smell. so basically its the same as adjusting timing on an older setup, but its adjusting injector timing instead of spark timing? once again rifleman thanks for putting in the work to figure this out. ill post about how it goes.

 

The camshaft position sensor has absolutely nothing to do with injector timing. (Injector timing is calculated from the crankshaft position sensor.) The ECM uses data from the cam sensor along with data from crankshaft position sensor for misfire detection, cylinder identification and ignition timing. Turning the distributor on 96 and newer CSFI systems adjusts camshaft retard. It aligns the Hall effect switch in the distributor so the ECM "knows" when the camshaft is at TDC compression for #1 cylinder. When it is aligned correctly, it also keeps the air gap between the rotor segment and the distributor cap terminals to a minumum which keeps crossfire to a minimum. In a round about way, camshaft retard also sets base ignition timing. A timing light is not used on these engines, when cam retard is set correctly, timing advance is checked/monitored on the scan tool. To check/adjust camshaft retard, you need a scan tool capable of accessing the data in the ECM. Engine RPM must be above 2000 and the desired spec is zero degrees, plus or minus 2 degrees. Blindly adjusting the distributor is asking for trouble.

 

do you know if that works on 5.7 vortecs as well?

 

Sure does.

 

Document ID# 554327
2000 Chevrolet/Geo Blazer - 4WD


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DTC P0340 Camshaft Position (CMP) Sensor Circuit




Circuit Description
The camshaft position (CMP) sensor is a sensor designed to detect changes in a magnetic field. The control module supplies the CMP sensor with signal and ground circuits. Ignition voltage is supplied to the CMP sensor by an independent circuit. The CMP sensor produces a magnetic field whenever the ignition is ON. The CMP sensor is mounted near a reluctor wheel that is attached to the distributor shaft. When the distributor shaft rotates, or when the engine is cranking or running, the reluctor wheel changes the magnetic field. The CMP sensor converts each change in the magnetic field into a PULSE. The number of teeth on the reluctor wheel determines how many pulses the CMP sensor detects per camshaft rotation. The control module uses the CMP sensor signal in order to calculate the correct timing for sequential fuel injection.

If the VCM does not detect the CMP signal while the engine is running this DTC will be set.

Conditions for Running the DTC
The engine is running.

Conditions for Setting the DTC
The CMP sensor reference pulse is not detected once every crankshaft revolution.

Action Taken When the DTC Sets
The control module illuminates the malfunction indicator lamp (MIL) if a failure is detected during 2 consecutive key cycles.
The control module sets the DTC and records the operating conditions at the time the diagnostic failed. The failure information is stored in the scan tool Freeze Frame/Failure Records.
Conditions for Clearing the MIL or DTC
The control module turns OFF the MIL after 3 consecutive drive trips when the test has run and passed.
A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle.
Use a scan tool in order to clear the DTCs.
Diagnostic Aids
Electro-magnetic interference from the ignition coil or the spark plugs wire 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 the installation of aftermarket accessories and harnesses creating an electro-magnetic interference.

Refer to Symptoms .

An intermittent may be caused by any of the following conditions:

A poor connection
Rubbed through wire insulation
A broken wire inside the insulation
Thoroughly inspect any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Intermittent and Poor Connections in Wiring Systems.

If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Wiring Systems.

Test Description
The numbers below refer to the step numbers in the diagnostic table.

This step determines if the DTC P0340 is the result of a hard failure or an intermittent condition.

This step will check for a signal output from the CMP sensor. The signal can also read in AC voltage, approximately 5-7 volts AC.

If there are not any additional DTCs set, then refer to Diagnostic Aids for examples of conditions that could cause an intermittent loss of signal from the CMP sensor.

This step determines if there is an open in the ignition positive voltage circuit. If the fuse is the reason for the open, check for a short to ground on the circuit. The open fuse can be caused by a component that shares the same circuit.

 

I realize your information is straight from the GM shop manual, however, the information ranges anywhere from misleading to incorrect, bare with me...

"The number of teeth on the reluctor wheel determines how many pulses the CMP sensor detects per camshaft rotation."

There is only one window in the reluctor wheel, one pulse per camshaft revolution.

"The control module uses the CMP sensor signal in order to calculate the correct timing for sequential fuel injection."

The very next line prooves the CMP does not determine injector timing:

"If the VCM does not detect the CMP signal while the engine is running this DTC will be set."

The problem is that the engine will still run with the CMP totally disconnected which prooves that injector timing is not calculated by the CMP.

Injector timing and ignition timing are both calculated by data from the crankshaft position sensor. The ECM uses data from the cam sensor along with data from the crankshaft position sensor to determine which cylinders are misfiring.

 

As far as the number of teeth on the reluctor wheel is irrelevant, i'm sure it's just generic terminology as far as GM is concerned, an i am totally aware that it has only one window as GM is also.

Also its says only that a dtc will be set if no signal is received from the cmp sensor and that is all, that would explain if you would change out your distributor or crank position sensor it will need a case relearn but the engine would still run,only setting off the code and/or performance issues or both, so that tells me there is a default program to at least let the engine run regardless of condition of the cmp sensor.

"The control module uses the CMP sensor signal in order to calculate the CORRECT timing for sequential fuel injection."

The word CORRECT in this sentence straight from the GM manual is telling me that it uses the cmp sensor for injector timing at a specific engine position AND also for fine adjustment throughout rpm range.

This worked absolutely perfect for me, not trying to argue with you captain I simply have no time or interest in that, but what i researched and tried did work for me, if there is some other info that says otherwise about injector timing please post it and do not waste time arguing and post it up, like info of some kind that you may have, because what i've read in the GM service manual is exactly opposite of what you are saying.

Maybe what you are saying works for engines with marine applications?

 

I have had that "Rich" smell for yrs. It doesn't appear to cause any problems in the operation of the vechile. So, if it isn't broke, don't try to fix it. I do have a small hole in the bottom of my muffer and the junk that leaks out of it is unreal and very hard to clean off my garage floor, again the vechile runs fine..I know someday, I will have to "Fix" it. But until that day...well I'll just wait until then. It still gets the gas mileage for a 2000 blazer Lt 4x4 with 105K on it...15 in the city and 20 sometimes 23 on the open road, but I have notice a difference in noise of the motor at 80 mph, sounds like the muffer. I know that day is coming...but until then, its wait and see.

 

After reading the P0340 diagnostics again, there are more discrepancies that could very well be, as you referred to them as, "generic terminology".

"The number of teeth on the reluctor wheel determines how many pulses the CMP sensor detects per camshaft rotation."

There is one window, which means there is one pulse for each camshaft rotation, (two crankshaft rotations). The important thing to remember here is that the CMP only pulses when the camshaft is at TDC for #1 cylinder on the compression stroke. The ignition module fires every 60 degrees of crankshaft rotation so when camshaft retard is adjusted correctly, every cylinder fires at the correct time. Camshaft retard adjustment puts the camshaft, distributor cap, and rotor terminals, in sync with each other.

"The control module uses the CMP sensor signal in order to calculate the correct timing for sequential fuel injection." If this statement were to read: "The control module uses the CMP sensor signal in order to calculate the correct ignition timing." It would then be a true and correct statement. My thoughts are this is merely a misprint in the manual that is causing a misunderstanding and confusion.

Quote:

Originally Posted by RIFLEMAN 308

….Also its says only that a dtc will be set if no signal is received from the cmp sensor and that is all,….

It actually does elaborate on that: “If the VCM does not detect the CMP signal while the engine is running this DTC will be set.” If the CMP signal is not received, it has the same basic effect as disconnecting the EST wire from the ECM to the ignition module on the OBDI engines and the engine will still run. The crankshaft position sensor relearn must be performed if the CKP sensor is disturbed in any way that changes its orientation with the reluctor wheel. The relearn does not affect camshaft retard. Camshaft retard adjusts the CMP sensor. If the relearn is not performed, the ECM uses the data from the position that the original CKP was oriented, and yes, the engine will run with that data, however, ignition timing and injector timing will not be correct. They would most likely be within a few degrees, but not perfect.

This is from the diagnostics for P0336 CKP Sensor Circuit Performance:

“The CKP sensor is mounted near a reluctor wheel that is attached to the crankshaft. When the crankshaft rotates, when the engine is cranking or running, the toothed reluctor wheel changes the magnetic field. The CKP sensor converts each change in the magnetic field into a PULSE. The number of teeth on the reluctor wheel determines how many pulses the CKP sensor detects per crankshaft rotation.”

The reluctor wheel on the 4.3L has 3 “teeth”. After each cylinder completes one cycle, the crankshaft has completed two revolutions, 6 pulses. These pulses are used by the ECM to determine engine speed, crankshaft position, and to detect misfire. (The ECM must receive a signal from the CMP sensor to detect misfire.) The ECM also uses the data for ignition and injector timing. If the CKP sensor fails, there is no spark and no injector pulse. You can verify this very easily by disconnecting the CKP and try to start the engine… No spark, no injector pulse.

This is an interesting topic that I’m sure several other members are watching. I’m not looking to get into an argument either; I don’t have time for it. I’m attempting to clear up the confusion.