Cruz with no performance low VE and codes for MAF, Lean and Cat

Clinton Owner/Technician New Hampshire Posted   Latest  
Unsolved
Driveability
2014 Chevrolet Cruze LT 1.4L (B LUV) 6-spd (6T40) — 1G1PC5SB9E7182077
No Performance
Lack of Power

I have a 2014 Chevy Cruze that has multiple issues. Customer bought from a used car lot and came in originally with a massive oil leak. I diagnosed the oil leak as originating from the failed intake manifold that was allowing boost pressure into the crankcase. It also had a CEL and I told them most likely related to the failed intake but would need to diagnose. They ended up negotiating with the used car lot for repairs. 

Now it is back with CEL no performance oil and coolant leaks. The oil and coolant leaks are from the hack job they did installing a dorman intake and valve cover which they screwed up the seal on valve cover. They also managed to crack the coolant outlet fitting.

Main thing I want to know is it looks like they have an exhaust cam out of phase but I cant locate any known waveforms for this year vehicle. I had originally thought that the cat was plugged from earlier poor running. But I also know on some of these engines they do have unusual camshaft phasing as well so I may be barking up the wrong tree. Snap throttle did seem to show the exhaust back-pressure ramping up a bit before the exhaust valve closed as well.

Thanks for any input.

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Greg Technician
Colorado
Greg Default
 

Hi Clinton, apologies - I am unable to open the ATS files, but the picture shows valve overlap that I would be testing another cylinder to compare for similar characteristics. Should the hump tame-down, I would be thinking sunken exh. valve/worn intake cam. (note, I cannot see the Intake close point to comment on Intake cam timing) Any chance you've got one to compare?

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Clinton Owner/Technician
New Hampshire
Clinton Default
 

Yes, I can share other captures. I do not have any cylinder that is performing any worse or better than another one. Just a general lack of performance and very low VE for a turbocharged engine. Also can see at idle intake vacuum is low and when power braked or snap throttle intake pressure barely goes positive. Basically almost no boost. Thanks

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Dmitriy Analyst
Ontario
Dmitriy Default
 

Clinton, would you mind me asking a question about the cranking compression graph: -5psi during the induction stroke, is it because you blocked the intake for the test, or is it what happens with the engine as is?

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Clinton Owner/Technician
New Hampshire
Clinton Default
 

That was my mistake, I had earlier done a smoke test of the intake system for leaks. Got distracted and later went to do the in cylinder and still had the intake blocked. Actually learned a lot on these little turbo engines. Most of my results were normal for this engine and the main issue was a bad PCV breather hose between the intake and turbo causing lean condition and bad MAF readings that…

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Geoff Diagnostician
Hawaii
Geoff Default
 

CJ, So the PCM disables turbo function when some DTC (like lean) set? That is great strategy info right there. Haven't dealt with any of the new-age small turbo engines out here yet. Thanks.

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Dmitriy Analyst
Ontario
Dmitriy Default
 

Oh OK, that explains it, thanks! Glad you found the issue.

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Clinton Owner/Technician
New Hampshire
Clinton Default
   

I was essentially checking a cylinder since easy to do for back pressure as I thought I may have had a restricted exhaust. Was not expecting camshaft looking shifted as does not have any cam codes. Here is the cam crank signals for reference.

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Steven Mechanic
Washington
Steven Default
 

Hey Clinton, I'm not familiar with that engine, but in general, engines with VVT do not have overlap at idle speeds, and that is why you will see that hump at the end of the exhaust stroke. The piston is still going up and the exhaust valve closes (and the intake valve hasn't opened yet) so the piston compresses a small amount of pressure there. It's normal to see that on a lot of VVT…

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Clinton Owner/Technician
New Hampshire
Clinton Default
 

Thanks for the info, I was wondering if I was going down a rabbit hole with this. Up to this point most of my pressure testing has been in light trucks that do not have VVT or if do not as extreme as the small turbo engines. My test drive VE calculations basically confirmed no boost on a drive. However my Snap on scanner wasn't showing any disabled boost data. Guess I need to pull out my GDS2…

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Bill Owner/Technician
Michigan
Bill Default
 

Visually inspect the turbo hoses and tubes for leaks, pressure check the intercooler ( I have seen a few of them cracked due to people hitting parking curbs) check the waste gate linkage for excessive looseness where it connects to turbo pivot. Manually activate the waste gate make sure it is working. Turbo failure is not uncommon on this engine.

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