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vwcorvette
vwcorvette SuperDork
4/11/18 3:33 p.m.

What I don't understand is the AFR reading.  It appears to be fine.  It wobbles just a little around stoich. Only going lean under closed throttle decel.

Streetwiseguy
Streetwiseguy UltimaDork
4/11/18 3:52 p.m.

In reply to vwcorvette :

It is reading correctly because the fuel trims have made it so.  If it is running lean, and you were to clear the memory and unplug the front sensor, it would show lean.  If you then plug the sensor in, it should start adding fuel (trimming) until the sensor is reading correctly.  Or, in the case of an out of range O2 sensor, it will add fuel until the sensor is happy, but the mixture is wrong.

alfadriver
alfadriver MegaDork
4/11/18 3:59 p.m.
vwcorvette said:

What I don't understand is the AFR reading.  It appears to be fine.  It wobbles just a little around stoich. Only going lean under closed throttle decel.

It is fine- doing what a WB O2 sensor is supposed to do.  But for some reason, it's at the limit of where it can compensate for whatever is causing it to be lean.  Cycling around stoich is best for emissions.  

And fuel generally turns off during decels.  

Does the intake have the PCV system fully connected?  I'd bet you have the connection in the intake manifold, but what about the fresh air supply into the engine?  Or is there an issue with the vapor system that is leaking?  Perhaps the valve is stuck open?

Streetwiseguy
Streetwiseguy UltimaDork
4/11/18 4:07 p.m.
Streetwiseguy said:

In reply to vwcorvette :

It is reading correctly because the fuel trims have made it so.  If it is running lean, and you were to clear the memory and unplug the front sensor, it would show lean.  If you then plug the sensor in, it should start adding fuel (trimming) until the sensor is reading correctly.  Or, in the case of an out of range O2 sensor, it will add fuel until the sensor is happy, but the mixture is wrong.

I lied in the middle of that.  It wouldn't show lean because the sensor is un plugged, but as soon as you plug it in, it should show lean.  Then, as it is trimmed, the AFR would come up to normal.

vwcorvette
vwcorvette SuperDork
4/11/18 5:04 p.m.
alfadriver said:
vwcorvette said:

What I don't understand is the AFR reading.  It appears to be fine.  It wobbles just a little around stoich. Only going lean under closed throttle decel.

It is fine- doing what a WB O2 sensor is supposed to do.  But for some reason, it's at the limit of where it can compensate for whatever is causing it to be lean.  Cycling around stoich is best for emissions.  

And fuel generally turns off during decels.  

Does the intake have the PCV system fully connected?  I'd bet you have the connection in the intake manifold, but what about the fresh air supply into the engine?  Or is there an issue with the vapor system that is leaking?  Perhaps the valve is stuck open?

I've pinched the pcv closed with no apparent change. It goes right into the intake. I've disabled the vent from the valve cover,  it's separate from the pcv. Running a road tube for now. 

I drove it just now. Under light load at pedal tip in it goes lean momentarily. The rear o2 however is bouncing all over the place. Excess fuel is definitely  getting through.

alfadriver
alfadriver MegaDork
4/11/18 5:23 p.m.

In reply to vwcorvette :

So that the intake system can be eliminated, can you put the complete OEM intake back in?

And it that does not solve it- is there a way to rig up the fuel pressure sensor so that you can see it while driving?   Then you are down to a bad fuel system or a bad O2 sensor.  Unless there's a misfire...

vwcorvette
vwcorvette SuperDork
4/11/18 5:42 p.m.

In reply to alfadriver :

No returning to oe without buying parts. 

Putting the fuel gauges on for driving might be possible, but not a lot of room with the ecm part ofbthe intake housing. 

There is a misfire. At light load,  2500-3000 rpm any gear. 

underpowered
underpowered New Reader
4/11/18 10:07 p.m.

Fix the misfire first.  Misfire could be letting unburnt fuel/air mix through...giving false readings.

Stanger2000
Stanger2000 New Reader
4/12/18 2:20 p.m.

Does this intake reuse the OEM MAF housing?

Have you checked for vac leaks everywhere?  

vwcorvette
vwcorvette SuperDork
4/12/18 7:56 p.m.
Stanger2000 said:

Does this intake reuse the OEM MAF housing?

Have you checked for vac leaks everywhere?  

No. 

Yes. 

vwcorvette
vwcorvette SuperDork
4/12/18 7:58 p.m.

In reply to underpowered :

Going to do compression and leak down test this weekend. 

 

Starting to pull my hair out over this thing. Shouldn't be this hard. 

Streetwiseguy
Streetwiseguy UltimaDork
4/12/18 8:29 p.m.

Have you driven it with the front O2 sensor disconnected yet?

vwcorvette
vwcorvette SuperDork
4/12/18 8:54 p.m.
Streetwiseguy said:

Have you driven it with the front O2 sensor disconnected yet?

Sorry,  just realized I didn't provide that info. Yes,  after work yesterday. Only I drove it connected about 15 miles before unplugging. Last 10 miles was worse.  

alfadriver
alfadriver MegaDork
4/12/18 9:05 p.m.

Lets back up a little here- you have a Corksport intake on your 2...

For how long until you started to have this issue?  

When did this first happen?  Was it right after a fill up?  Was it something slowly breaking?

Need more info that lead to this situation.

hhaase
hhaase HalfDork
4/13/18 5:48 a.m.

Do all the plugs look equal?  Don’t have one that stands out as excessively clean or burned?  Just looking to rule out a clogged or non-firing injector.  

 

Stanger2000
Stanger2000 New Reader
4/13/18 11:46 a.m.
alfadriver said:

Lets back up a little here- you have a Corksport intake on your 2...

For how long until you started to have this issue?  

When did this first happen?  Was it right after a fill up?  Was it something slowly breaking?

Need more info that lead to this situation.

Just a thought on this.  Sometimes these intakes that incorporate the MAF sensor into their own tubing can throw a code or cause issues on newer cars due to how they're calibrated from the factory and some are more sensitive than others.  Some cars require a tune to compensate for this.  You should be able to read MAF live data readings on TQ Pro app, although I haven't used mine in a while since I got an actual OBD II scanner that features this.  

Again, if it were me I'd resort to go back to the stock intake set up, unplug the battery/clear out the code(s) and start over to completely eliminate that from the equation.  

alfadriver
alfadriver MegaDork
4/13/18 2:45 p.m.

In reply to Stanger2000 :

It's also important to note that hot wire sensors require a decent cross section of airflow to work well, and if the intake changed the flow to bias one side of the meter, it will be off.  

But before more guessing what is going on, I'd like to know some more background info.

Streetwiseguy
Streetwiseguy UltimaDork
4/13/18 3:05 p.m.

I brought up the intake, but its been on the car for 2 years, and the problem is fresh, IIRC.

vwcorvette
vwcorvette SuperDork
4/13/18 7:13 p.m.
Streetwiseguy said:

I brought up the intake, but its been on the car for 2 years, and the problem is fresh, IIRC.

Yes,  it's been on the car for much longer than I've had the problem.  Unfortunately  I don't recall having random misfire before getting the MIL the p0171 code. 

Today I cleared the KAM again,  unplugged the AFR,  cleared any codes and started the car up. Right away it ran poorly. Enough that I didn't feel comfortable  driving out of the parking lot. I reconnected the AFR. STFT goes to 25%, rear O2 goes rich. 

Let the car idle for a bit. 

Drive home: at @ 2000 rpm accelerate and LTFT drops to 0 and STFT climbs to 20% while rear O2 swings to 800mv. AFR holds steady about 14.6 with lambda command dropping to about .85.

 

Other times with acceleration the LTFT swings to zero while the STFT goes the other way to plus about 23%.

At 2500-3000 rpm random misfire unless I accelerate harder than half throttle. Occasionally I catch a glimpse of the AFR going above 16 or 17 to 1.

No misfire code when I get home.  And the readiness codes have set for the first time in a long while with no MIL illuminated.

Going to a friend's house tomorrow to check compression and leak down and get a closer look at the exhaust and EGR. 

frown

alfadriver
alfadriver MegaDork
4/13/18 7:20 p.m.

Please post more details of when and how it failed.  

It at least sounds as if something broke, and not the intake.  Which is at least something.

BTW, the long term fuel trim takes a while to set- and it's not one value- it will depend on mostly airflow.  So at areas that you rarely run, it will have not learned.

vwcorvette
vwcorvette SuperDork
4/13/18 7:59 p.m.

In reply to alfadriver :

I'm hoping nothing is broke. Just trying to rule out everything. 

I'm wondering if valve timing is off too. The engine uses a chain. It's got 99,500 miles on it. Could it stretch? I've never checked valve lash. It is adjustable. 

vwcorvette
vwcorvette SuperDork
4/14/18 11:46 a.m.

compression fine.  no issues. 

Ignition timing all over the place. Should it retard from plus 40 to about fifteen degrees under load and acceleration? 

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