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wstefan20

Mystery Leak? Lean condition

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Alright, so I'm getting to the point where I might have to break my rule and take my beauty in to the shop.... hopefully someone can help and save me the hassle!

To preface, the car runs "ok" and has since I got everything rebuilt. However, I've always noticed that it struggles going up hills and doesn't have much "get up and go" which has bothered me. 

I finally had enough time to hook up my scan tool and check things out in detail this weekend. There are NO check engine lights, but after bringing everything up to temperature, I get around 15% lean long term fuel trim at idle and when my foot is off the accelerator, which immediately makes me think vacuum leak. 

The bad is that there is no auditory leak either vacuum or exhaust. The MAP pressure is normal vacuum and responds with throttle accordingly. The fuel pressure is around 55-60 psi and increases to 70 when regulator vacuum is removed or throttle is snapped. MAF sensor is in range and responds as it should (and I just cleaned it). IAT sensor is at correct readings. EGR seems to be functioning correctly. O2 sensors are operating normally. Idle rpm is around 750-800 (I think that's normal).

I used the propane test EVERYWHERE and no leaks detected. Unfortunately, I don't have access to a smoke machine.

There isn't excessive crankcase pressure, and no detectable blow-by by removing the oil fill cap.

Basically, I'm lost... help! lol

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A misfire will show lean, because the oxygen didn’t get consumed. Bet a nickel you have an ignition issue, most likely a flaky coil.

That's what I thought for a moment too. I've been driving it for weeks and had a scanner on for several periods of 10 minutes or more. There is absolutely zero kr and no historical or current misfires on any cylinders. Engine idles smooth as butter too. This issue is killing me!

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A misfire will show lean, because the oxygen didn’t get consumed. Bet a nickel you have an ignition issue, most likely a flaky coil.

I second this. When the coils fail the car still runs but it does weird things.

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A misfire will show lean, because the oxygen didn’t get consumed. Bet a nickel you have an ignition issue, most likely a flaky coil.

I second this. When the coils fail the car still runs but it does weird things.

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If you're absolutely sure that the issue is not electronic related then start looking for mechanical issues.

 

You mention that you *rebuilt* the engine? Are you positively certain that the cam timing is correct?

 

Judging by your sig I take it that the engine is the 3.8L N/A or is it blown........

 

You didn't mention what engine you're dealing with here....

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If you're absolutely sure that the issue is not electronic related then start looking for mechanical issues.

 

You mention that you *rebuilt* the engine? Are you positively certain that the cam timing is correct?

 

Judging by your sig I take it that the engine is the 3.8L N/A or is it blown........

 

You didn't mention what engine you're dealing with here?

Sorry. Forgot to mention that. Thanks for pointing that out! It's a L36 with L26 upper intake swap (aluminum intake so it's basically a L26).

 

I think I might have just answered my own question here. I did change the vacuum for the pcv valve which is a "metered vacuum leak". So if I increased the amount of vacuum it was able to flow, then that would also increase the leak and boost the airflow and cause it to run lean. However, this would also explain why it changes when I accelerate since it only marginally affects the total airflow at wot.

 

Not sure if it's ok, but I think one way of "tuning" for this would be to put a ball valve in line and therefore I could restrict the amount of vacuum and just adjust this manually until my fuel trims are correct. Anyone see anything wrong with doing this?

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 I've always noticed that it struggles going up hills and doesn't have much "get up and go" which has bothered me. 

 

I finally had enough time to hook up my scan tool and check things out in detail this weekend. There are NO check engine lights, but after bringing everything up to temperature, I get around 15% lean long term fuel trim at idle and when my foot is off the accelerator, which immediately makes me think vacuum leak.

This doesn't sound like a PCV problem.

 

Define "15% lean".  Is this the ECM commanding the injectors to supply 15% extra fuel, or 15% less fuel?

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It's a L36 with L26 upper intake swap (aluminum intake so it's basically a L26).

 

I did change the vacuum for the pcv valve which is a "metered vacuum leak".

 

I think one way of "tuning" for this would be to put a ball valve in line and therefore I could restrict the amount of vacuum and just adjust this manually until my fuel trims are correct. Anyone see anything wrong with doing this?

1.  WHAT CAR???

2.  What does "change the vacuum for the pcv valve" mean?

3.  Why not just progressively clamp the hose with a pinch-off pliers and see what happens to the fuel trim?

 

 

 

I'm suspicious of the PCV system causing a "15%" fuel trim change.

What is the cranking compression pressure?

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from gpf post, hes got a catch can hooked up  and what i from what i can tell the evap port is connected to a vac port, instead of being capped off at the tb for one, the rest could all be done wrong too. theres no need for any of it, i suggest tearing it all off and hooking things up the right way. 

 

20171202_161451.jpg

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What's that happening with the MAP sensor? Yeah it may be better to start over and put it closer to factory. Still don't understand the catch can, or the breather.

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This doesn't sound like a PCV problem.

 

Define "15% lean".  Is this the ECM commanding the injectors to supply 15% extra fuel, or 15% less fuel?

+15% ltft is defined as increasing the injector pulsewidth by 15% therefore increasing fuel. Negative numbers decrease the injector pulsewidth thereby decreasing fuel

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1.  WHAT CAR???

2.  What does "change the vacuum for the pcv valve" mean?

3.  Why not just progressively clamp the hose with a pinch-off pliers and see what happens to the fuel trim?

 

 

 

I'm suspicious of the PCV system causing a "15%" fuel trim change.

What is the cranking compression pressure?

1. 2002 Pontiac grand Prix GT with L26 upper

2. I re-routed the PCV system to incorporate a catch can. Long story short, I routed the pcv vacuum externally through a catch can. You can check out the process at my thread here: http://www.grandprixforums.com/threads/107064-L26-swap-PCM-question

3. I actually did just that and will post the results in a few minutes once all my tests are complete.

 

Cranking compression on all 6 is around 150-160psi (crappy harbor freight gauge so those numbers could be way off)

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What's that happening with the MAP sensor? Yeah it may be better to start over and put it closer to factory. Still don't understand the catch can, or the breather.

I actually did reset it to factory, and no change. It looks like the ceiling for stft is 20% and ltft is 15%. The short term fuel trim should oscillate, but it's not, which is strange.

 

The MAP sensor is reading normal vacuum pressure for the pressure here which is around 30kPa (not inHg) and decreases as the throttle is opened (which indicates vacuum is decreasing which is normal)

 

I'm going to try bypassing the catch can to see if that improves the numbers or not. The problem is when I pinched off the hose (actually used a ball valve), I could only go so far before the MAP sensor stopped reading anything correctly (vacuum too weak because valve is basically shut and reading pressure backing up from pcv). If it improves, I know the catch can is leaking.

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The "catch can" could decrease vacuum to the PCV valve, but not increase it.  If the vacuum is decreased, it could be because of a leak which could add additional, un-metered air to the intake manifold.  If it's decreasing vacuum because it's plugged, there'd be less air going to the intake manifold.

 

If it's leaking enough to screw-up the fuel trim by 15%, I suspect you'd hear it.  I am not inclined to blame the PCV system for this.

 

I'm used to seeing LT and ST fuel trim numbers, not percents.  (i.e., 128, which would be no fuel added, no fuel subtracted.)

 

The last time I dicked with unreasonable fuel trim numbers with no obvious air leaks or fuel system problems, I had a faulty O2 sensor sending incorrect data at highway speed.  The O2 sensor "tested" good, including reasonable cross-counts at lower speed--but fell on it's ass as speed went up.  OTOH, this reliably set a code, which you aren't getting.

 

Do you have an AIR system?  Any chance it's blowing upstream when it should be downstream?

 

If vacuum hoses are routed incorrectly as others have implied, that's gotta be corrected or you're just chasing your tail.

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from gpf post, hes got a catch can hooked up  and what i from what i can tell the evap port is connected to a vac port, instead of being capped off at the tb for one, the rest could all be done wrong too. theres no need for any of it, i suggest tearing it all off and hooking things up the right

 

Thanks scotty! lol That's actually my old setup! :) Here's a picture of what it looks like now: 

 

20180103_145303.jpg

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The "catch can" could decrease vacuum to the PCV valve, but not increase it.  If the vacuum is decreased, it could be because of a leak which could add additional, un-metered air to the intake manifold.  If it's decreasing vacuum because it's plugged, there'd be less air going to the intake manifold.

 

If it's leaking enough to screw-up the fuel trim by 15%, I suspect you'd hear it.  I am not inclined to blame the PCV system for this.

 

I'm used to seeing LT and ST fuel trim numbers, not percents.  (i.e., 128, which would be no fuel added, no fuel subtracted.)

 

The last time I dicked with unreasonable fuel trim numbers with no obvious air leaks or fuel system problems, I had a faulty O2 sensor sending incorrect data at highway speed.  The O2 sensor "tested" good, including reasonable cross-counts at lower speed--but fell on it's ass as speed went up.  OTOH, this reliably set a code, which you aren't getting.

 

Do you have an AIR system?  Any chance it's blowing upstream when it should be downstream?

 

If vacuum hoses are routed incorrectly as others have implied, that's gotta be corrected or you're just chasing your tail.

Thanks for the input!

 

Well, it isn't much, but you are correct about a restriction to the map sensor. The readings I got with the catch can hooked up was 50kPa idle up to 100kPa with throttle (14.7inHg-30inHg) and 30kPa-90kPa (8.9-26inHg) with no catch can. While this is a restriction, I think it shouldn't affect the pcv operation, however, that means it would mess with the MAP sensor readings, so if I want to run a catch can, I need to relocate my map sensor either after the catch can, or to another vacuum source (I plan on moving it to tee off of the evap to read pressure).

 

The stranger thing though is that there was no change in this is that there was no change in pressure or fuel trims when closing the pcv valve unless I closed it all the way, then the engine stumbled and it dipped.

 

Funny thing though is that with the pcv completely shut off, the short term fuel trims went to between +-3% and the long term fuel trims dipped to between 5-10%. 

 

Short term fuel trims without the catch can is now around zero, but strangely enough, long term is still up near 16%, and both with and without go near 0 when the throttle is opened. 

 

I'm attributing the short term fuel trims being restored to the fact that the MAP sensor readings were off due to a restriction caused by the catch can.

 

However, since the vacuum readings are now normal along with the MAP sensor readings and the ltft is still off, I'm thinking that vacuum leaks couldn't cause the issue because restricting the pcv vacuum didn't cause any change in trims, it was only when I completely shut it off that they went near zero. I suppose this theoretically could be caused by a vacuum leak, but then why would my vacuum pressure read normal, and why can't I detect it with sound or with propane???

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I'd like to see a picture of the engine bay.

 

Is the L26 manifold vented from the top right or is it capped?

 

Are you still running EGR or no?

Just posted a picture in the post above.

 

The L26 pcv intake is running to the adapter plate and to the original L36 pcv inlet which is metered through the throttle body.

 

Yes, I am still running EGR. As far as I can tell, it's working normally, and there's absolutely no codes.

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at least the breather is gone, did that make anything change when you plugged that hole up? 

Well, you never want to plug that hole actually. It is the intake for the pcv system, so everyone drilling through the side so it intakes from vacuum and then capping this is literally shorting the pcv system entirely and just equalizing the pressure (not good).

 

The stock pcv air intake on the L36/L67 is actually through the throttle body and is metered air. I used the hole tapped for this in the adapter to hook these up because the pcv air intake on the L26/L32 uses this nipple connected before the throttle plate but after the maf sensor.

 

Basically, while it's good to have the pcv intake metered, it's actually better to have a breather here rather than capping it or drilling it to vacuum.

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