Owned my 2004 Z06 for a few weeks and absolutely love the car - Has CAI, Headers and hi-flow cats - not sure of other mods. Car threw a P0172 and a P0175 -started to dig a bit and noticed I dont see a PCV anywhere? Have been reading a bunch of things online and got confused - I see that the LS6 does not have hose to the left (driver) side valve cover- its capped but I thought there should be an inline PCV. where is the PCV Valve? Thanks in advance.

 

your car has the correct pcv configuration. the metering orifice is a plastic box attached to the valley cover and can only be seen by removing the intake and valley cover. Very unlikely to be associated with the p0172,0175 codes.

These codes indicate a rich condition. You can throw hundreds of $ worth of parts at the car , or try some simple fixes. First if you have a blocked air intake path like a clogged filter, that is your first check. If you have, say an aftermarket K&N filter, people very often over oil them and F U the MAF sensor. The first thing I would do is CAREFULLY clean the MAF filaments. (search this forum) . The MAF is right behind the filter air box in the air intake path. If a dirty MAF is not the cause, then you will need a scan tool to look at MAF and MAP performance, O2 sensor performance. Then you will need to have a fuel rail pressure gauge to make sure you don’t have too much fuel pressure (unlikely). Bad wiring to the MAF or IAT is a possibility, but you would have additional circuit high or circuit low codes as well. When you take out the MAF for cleaning, just be careful with the electrical connector.

 

thanks for the reply - tthat explains wy I could not locate the PCV - the CAI intake is the Vararam - I will check the filter and MAF

- I already started scanning to get a baseline.

 

So you have a scan tool. GREAT!!! use that first before taking anything apart.
1.Check to see if you are in open or closed loop.
2. With the engine at idle, check the MAF reading in grams/sec. The number should be close to 5.7, the displacement of the engine. If it is much higher, then you may be in for replacing theMAF. A dirty MAF may under report air delivery. so if high it is usually an electronic failure of theMAF. A dirty throttle body could be sticking open, but this would show up as a high idle. Idle speeds are different auto vs 6sp.

The PCM sets injector pulse width initially based on air flow measured by the MAF. (unless you have had a “tune”). The O2 sensors then sense the amount of oxygen after combustion and correct fuel delivery based on trying to achieve 14.7 to one air to fuel ratio. So,
3. is to look at fuel trims If everything is hunky-dory, short terms will be oscilllating around 0 long terms 5 or less. For your codes, the 02 sensors are telling the system to pull fuel delivery.
4. O2 sensors could be wonky, but since you have both banks rich, this is not likely. One bank failing, for sure, but 2 independent components failing at the same time not likely. So you’re quest is probably going to be on the air intake side.
5. Since you aren’t reporting misfires, we can rule out ignition, spark plugs, wires etc. for the time being.
6. for a short time, take out the air filter and see if the MAF number changes at idle.

I’m on my second glass of Jameson, so I’m running a bit rich at the moment. My mode is to first try to fix no parts needed.

 

haha.... Not sure how deep you are in the Jameson by now but.....
The MAF is registering low... . 02. When I removed the Map, it was dirty. I cleaned it and reinstalled. Will scan again later. I myself started on some Johnnie Walker and need to stop wrenching 🤪. Anyway, thanks for the reply... Will post my findings tomorrow. Cheers

 

When you get back to your scanner, see if it will data-log. If so, you can test the MAF by capturing the MAF reading as a function of RPM. Record the MAF at 1000, 1500,2000,2500 and 3000 RPM. Then plot it on graph paper or EXCEL. If the MAF is working correctly, the plot should be a straight line.

See if you can change the MAF units to g/s, grams/second on your scan tool

 

ok... Clear head... So I can not change the maf units. I did notice the maf is showing similar readings as before the cleaning. The short fuel trim is oscillating between 0.8 and 6. There is no misfires and car pulls nicely.

 

In post 3 your scan tool reports .02lb/s. I googled a conversion and got 9.07 g/s. your TPS (throttle position) is 7%, basically fully closed, so your g/s for your engine should be approx 5.7 So I think your MAF may be reading way high, which would explain the rich conditions setting the rich codes. However today’s fuel trims, while not perfect, should not be tossing 0172,0175. Also, independent of me do a conversion from lb/s to g/s to see if my google agrees with your google (internet trust issue w/me)

Time to clear these codes drive a bit and see if they come back

Can your scan tool report readiness monitors? if so, see if they all report ready. This may be called a mode 6 report on your tool. The readiness monitors replaced the tail pipe sniffers for inspections. Here in NC you can have 1 DTC code with all readiness monitors saying OK provided no check engine light.

My 2002 Z has always reported high MAF flow at idle. The Z06’s don’t have the honeycomb screen, so this could be normal. At idle, mine reads about 6.8 g/s and fuel trims spot on. Be careful if you decide to replace your MAF. There are a lot of knock-offs and both ebay and the big A sell “genuine” AC Delco that are frauds.

 

thanks again for the info.... So I cleared the code but the light came back. My scan tool does have readiness monitors and all are reading OK except the evap. It's says "Inc". Anyway, the MAF was replaced at some point, it's a Delphi unit. Anyway, I'm gonna order a new MAF and see if that helps.... Not sure where else to go. Car is running good but I can smell it's running rich at times. One question though, is there anyway to tell if the car had a tune using the scanner? Thanks again. Mark

 

so the DTC codes are like using a thermometer to find out you have a fever. Not much of a clue why you have a fever.

The fact the evap system is giving you an incomplete says you have a fault in the evap system, but no code. The evap system keeps fuel vapors from entering the atmosphere. Consists of the ability to seal the tank, test the seal, and provide a path to send the residual fuel vapor through the combustion process. Becides the fuel tank, there is the charcoal canister that collects the excess vapors, a vent valve that seals the system for the testing sequence, and the purge solenoid, that when turned on allows engine vacuum to sucs the accumulated fuel vapors from the charcoal canister into the combustion process.

There are lots of Youtube vids about the GM EVAP system. If the purge solenoid is allowing flow all the time, this could be a cause of the rich condition, and cause the CEL and the readiness test to be incomplete. If the charcoal canister gets saturated with liquid state fuel, then when the purge valve opens is sucks a lot of fuel into the intake. Sometimes a little check valve on the fuel pump can fail, and if you try to fill the tank beyond the first click you end up ruining the charcoal canister.

The purge solenoid valve is on the driver side of the intake and there is a ribbed plastic hose that connects the purge solenoid to the charcoal canister. You can push the gray lock to release that ribbed hose, and the electrical connector from the purge solenoid. Start the engine, and if you feel vacuum on the exposed nipple with the connector unplugged, the solenoid is probably bad.

After testing the purge solenoid and finding it is OK, things get a little tougher. Now you need a scan tool with bidirectional control to test the EVAP system. Tell us what you find from testing the purge solenoid.

As far as driving the car, the fuel trim you have is manageable and should not hurt the engine. Lots of folks run for months with EVAP faults and get away with it until annual inspection time. I personally don’t, just sayin’ this is reality.

 

. Ok.. So there is vacuum at the exposed nipple when disconnected. Going to replace that solenoid and see if the problem goes away. Thanks again for the help. Will post results when it comes in.

 

You found vacuum with the solenoid disconnected electrically, right?

 

Yes

 

just makin’ sure. I like to bench test purge valves, and found OEM parts better. Also, it will take a drive cycle to get all the readiness monitors. Sometimes EVAP ones will take more than one drive cycle. Also, if your fuel trims get to close to zero, you will be there. You may have to clear DTC codes a couple times until all readiness monitors are good. It is kind of a back and forth deal sometimes.

 

thanks again - will post results

 

Typically, the unscreened Z06 MAF sensor does not work well with a Vararam unless it's tuned. Where is the MAF sensor installed, near the throttle body or near the filter housing?

The readiness monitors reset every time you clear the DTC codes so that'd be why you have an incomplete monitor. Not a big deal unless you drive it a few times and it never sets. Typically though, they will either set or stay incomplete and eventually throw a code.

That scan tool is only showing 2 decimal places for the flow so that could possibly represent a number between 0.011 to 0.02 or 0.015 to 0.0249 depending on how it handles rounding. Point is that I wouldn't read too much into that number. The required resolution is simply not there.

 

The MAF is installed closer to the filter housing -

 

so new purge valve Installed and have done about 300 miles... No check engine light. Knocks on wood. Thank for all your help!!

 

how are the readiness monitors and fuel trims? If it was the purge solenoid, and all is good, AWESOME! Although patience is needed for trouble shooting, much cheaper than firing the parts cannon at the car.

 

I still have to scan just have not had time - will this weekend. Gonna try to get a better scanner as well! Much appreciated!