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Old 07-16-2017, 05:13 PM   #1
Hwyknight
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Default WTF? Engine light

So I take out the air cleaner do a little detailing, and put it back........now the check engine light is on? Everything else is plugged in etc.

I also have one of those small tube or jar like pcv catch cans. When I removed the air cleaner I noticed a small tube with nothing connected to it on the passenger side of the rubber intake. Is this for the regular pcv valve? Should there be anything connected to it? Should I plug it?



Any help is appreciated
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Old 07-16-2017, 05:17 PM   #2
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Pictures would help .... I am sure you did not hook up a hose which triggered the CEL
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Old 07-16-2017, 05:33 PM   #3
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Collecting the code would give you a definite answer, but in the world of guessing games, the only two faults I know of related to the air filter are
Failure to plug the connector back on the MAF, If you happened to have it unplugged

If you left the air filter element out of the housing that could set a CEL because even though airflow is calibrated, there will be a discrepancy out of range in the TPS position the ECM sees and the frequency the MAF is delivering.

So, given those two might not be the problem, the "tube" on the passenger's side. Is this the plastic preformed tube that inserts into the rubber accordion air intake tube? That is a vent bypass from the valve cover, I'm pretty sure. If it is unplugged and vented to outside air, then that is changing the metered air too and possibly setting a CEL. That's all the guessing I can give without a code.

Best,

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Old 07-16-2017, 05:35 PM   #4
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go to the auto parts store and check the code.
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Old 07-16-2017, 05:47 PM   #5
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Quote:
Originally Posted by LowRyter View Post
go to the auto parts store and check the code.
Or.....buy yourself a scanner so you can do it yourself. Just so happens this morning I got my first CEL because my Vette had an engine miss. I hooked up my scanner (Actron CP9550) for the first time and it said "#5 Cyl misfire". I pulled off the fuel rail cover which revealed the #5 cylinder coil pack wire had worked its way loose. Hooked it back and and all is well. Scanner paid for itself!
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Old 07-16-2017, 05:51 PM   #6
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Let me add to post #3. I had to think it through BC I am supercharged and don't have an actual example any more, but if you have an LS3 (don't know if LS2s are the same), and you're talking about the hard plastic tube connected to the accordion air intake, That bypass CC vent comes in AFTER the MAF on an LS3. So, if you were just hanging in the breeze on one end, then you were drawing in lots of unmetered air likely causing a lean condition. I'll guess some more - your CELs are P0171 and P0174 and/or the tps/MAF airflow mismatch.

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Old 07-16-2017, 06:07 PM   #7
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Let me add to post #3. I had to think it through BC I am supercharged and don't have an actual example any more, but if you have an LS3 (don't know if LS2s are the same), and you're talking about the hard plastic tube connected to the accordion air intake, That bypass CC vent comes in AFTER the MAF on an LS3. So, if you were just hanging in the breeze on one end, then you were drawing in lots of unmetered air likely causing a lean condition. I'll guess some more - your CELs are P0171 and P0174 and/or the tps/MAF airflow mismatch.

Yep
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Old 07-16-2017, 08:43 PM   #8
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Here are a couple of pics. Does that catch can bypas whatever was connected to that tube? Should the tube be plugged? I'll pic up a code reader tomorrow. Anyone recommend one in particular?
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Old 07-16-2017, 09:03 PM   #9
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That tube before the throttle body should have a hose on it, or it should be plugged .. I agree with Blindspot, It's pulling in unmetered air which is setting a lean code...WW

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Old 07-16-2017, 09:20 PM   #10
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That tube before the throttle body should have a hose on it, or it should be plugged .. I agree with Blindspot, It's pulling in unmetered air which is setting a lean code...WW
I agree also but ... you need to fix that

there is something that attaches to that even with a catch can as I just installed mine

he is missing a plastic hose with an end on it that clips on to that

My car is in the garage otherwise I would go look, lift up the passenger side plastic valve cover and see if its under there

Dave
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Old 07-16-2017, 09:22 PM   #11
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you can see it in this picture

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Old 07-16-2017, 09:57 PM   #12
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you can see it in this picture

I can see that something is connected to yours, but on mine I don't know what's missing. I didn't see any detached hoses, etc. I'll have to see if I can find a golf tee or something to plug it with and see if that kills the code.
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Old 07-16-2017, 10:14 PM   #13
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Take the passenger side cover off , that hose and connector has to be there as the car did not run without it otherwise you would have had a code way before this .... if it was not so late I would pull my cover off and take a picture ...and I am traveling tomorrow
Maybe someone can take a picture of theirs and post it
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Old 07-16-2017, 10:47 PM   #14
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The MAF electrical connector appears to be disconnected also - the purple electrical connector in the first pic. That would be my first guess. I accidentally left the air hose you are describing loose once after changing my air filter. It did not throw a code or cause the CEL light to come on.
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Old 07-16-2017, 10:52 PM   #15
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The MAF electrical connector appears to be disconnected also - the purple electrical connector in the first pic. That would be my first guess. I accidentally left the air hose you are describing loose once after changing my air filter. It did not throw a code or cause the CEL light to come on.
It's disconnected because he had it apart when he took the picture .... I also left mine disconnected one time and it idles high and surged, I am sure it would have eventually thrown a lean code
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Old 07-17-2017, 07:25 AM   #16
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This is the missing line, and as I posted above, it is a CC bypass vent from the passenger valve cover on an LS3. I believe it is piped differently on LS2s and possibly LS7s.

There is an anti-siphon filter on the underside of the valve cover. If pressure builds it will push out to the air inlet, but doesn't allow it to be pulled like it will fresh air if the tube is not connected. If the tube doesn't exist, then cap off the air fitting on the accordion at least, or, just purchase a piece of rubber tubing and reconnect the valve cover, better.

BTW, if the MAF is left disconnected on a startup it should immediately set at least a P0102, and or a P0106, unless some tune intervention has a speed density only setup with the MAF and associated P-Codes disabled.


Mine can barely be seen in this pic, the valve cover outlet line is capped, but I have a more sophisticated catch can that picks up this bypass directly through the oil filler cap.


Last edited by BlindSpot; 07-17-2017 at 07:39 AM.
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Old 07-17-2017, 08:20 AM   #17
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Quote:
Originally Posted by cstapp99 View Post
The MAF electrical connector appears to be disconnected also - the purple electrical connector in the first pic. That would be my first guess. I accidentally left the air hose you are describing loose once after changing my air filter. It did not throw a code or cause the CEL light to come on.
It takes a while to set lean codes. They are not instantaneous upon startup. Fuel trims continue to adjust for lean conditions (such as vacuum leaks) until it maxes out at a 25% fuel correction. That could take as many as 50-100 miles of driving, or, it just might not be enough unmetered air to reach 25% correction. If LTFTs stabilize at 22%, no codes would be set.

On the other hand, and especially at idle, because MAF frequencies are so low, unmetered air after the MAF could cause a correlation error between the MAF frequency and the TPS position, something like a P-2135 or other P-Codes.

But here again, reading the actual code is SO valuable in diagnosis. We STILL might be off track as we're all proposing hypotheticals that might not apply.
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Old 07-17-2017, 08:49 AM   #18
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But we all can agree .... he needs to either hook up the hose or block it off .....
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Old 07-17-2017, 03:19 PM   #19
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Got a code reader, haven't checked the code yet......but there is more. The pics might be a little hard to follow but I'll do my best.


This photo shows the red line coming from a metal fitting going to the catch cup, then blue returning to a plastic fitting on the intake just below an electrical connector. Is this a correct install?



Same as other photo, just a little closer.



This tube comes off the passenger side of the valve cover near the oil fill. It runs up to and hangs alongside the radiator and terminates in an open brass fitting shown in the next photo. The brass fitting isn't connected to anything, the tube and fitting were just hanging alongside the radiator. I believe this is what you are saying should be connected to that tube on the rubber part of the intake. If I make that connection there will now be vacuum in that line. Is that correct?

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Old 07-17-2017, 03:55 PM   #20
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So a couple of things.

Whoever set up the catch can ended up jerry rigging the bypass CC vent. Having routed all the way over to the radiator and opened to the atmosphere isn't hurting anything, but if a tech type did an emissions inspection in, lets say, California, and he/she was sharp, they would fail the car. But again, venting to atmosphere is better than plugged. The harm is coming in letting the other side, the rubber inlet tube, open to the atmosphere. With a "hole" in your intake tube, when intake air volume is present, it will create a low pressure point at that opening (like a vacuum) drawing unmetered air into the air inlet stream. That is NOT good. You'd be better just blocking this off while the tube is vented to the atmosphere. Better - is to hook the tube (at the radiator) up to the air inlet opening. That would mimmick the original bypass. But, there is NO vacuum at this line. CC pressures will naturally exit the valve cover making its way into the air inlet stream, but nowhere near the volume of an open port. And. because of the way the valve cover tube is baffled under the valve cover, vapors from thee crankcase will only release in that tube if there is CC pressure. This is not possible if the two lines on the catch can are clear and the CC is functioning.

On to the catch can. I don't know this particular catch can or how it's plumbed. At least, if it is a two port can, those two places, the crankcase outlet and the intake manifold inlet are the two ports connected to a typical two port can. Hopefully they're connected correctly, they could be on backwards. There are so many cans on the market. Some designs are not that good, and again, I don't recognize this one at all. But, at least you have the correct lines terminating at the can.

BTW, check that little plastic "ell" fitting in the rubber inlet. Maybe the previous guy blocked it.

Anxious to hear what the codes are!

Last edited by BlindSpot; 07-17-2017 at 04:03 PM.
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