Leakdown results - one cylinder weak? How to test PCV/blowby

1353 Views 40 Replies 6 Participants Last post by paul93VR4, 13 d ago

mydecember1985

Discussion Starter · 2 mo ago

So I did the whole leakdown test today. Although my crappy compressor was set to 120psi regulated, I could only get the tool to about 85psi. Holding my thumb over the test side of the hose, it would peg about 85psi. If I let it free-flow, it would show about 8-10 psi, but it should be at 0, so I'm not sure how accurate this tool is.

The only cylinder that seemed odd was cylinder 6. All cylinders lost a little bit of pressure to ring blowby. Every one of them had a very minor hiss from the oil cap. 2 of them (including cylinder 6) had a very, very faint hiss in the exhaust. I mean I could barely hear it at all over the birds and breeze. The wife said she couldn't hear anything. The imgur video gives an example of the background noise level. Cylinder 6 would peg the regulator side at only 69-70 compared to the other cylinders pegging 75-80

Cylinder 1

Cylinder 2

Cylinder 3

Cylinder 4

Cylinder 5

Cylinder 6

Cylinder6 closeup (wife's nails, not mine lol )

Ratios: PERCENT LOST COMPRESSION TEST FROM LAST MONTH
Cyl1 81.5 to 79 = 3.1% 191
Cyl2 80 to 78 = 2.5% 180
Cyl3 76 to 75 = <1% 183
Cyl4 74 to 72 = 2.7% 186
Cyl5 76 to 74 = 2.6% 187
Cyl6 69 to 64 = 7.25% retest was 69 to 65 = 5.8% 181

I tried throwing a glove over the oil filler to see if it would inflate, but I forgot to cap off the PCV and breather. But it barely made the glove even move, so it's not much.

What do you think I should do to verify the test results? The weird thing is that the rear fuel trims are ADDING fuel in the rear bank. So if the rear exhaust valve is a little tweaked, it would be blowing unburnt fuel and poorly burnt exhaust gases past the o2 sensor, so I would think it would be reading rich and PULLING fuel trims....

No hiss in intake from any of the valves. Looks like rings and exhaust on minor scale. This makes me wonder where my 1/2"Hg shaky needle was coming from since there is no pressure blowing back into the intake plenum. The only pressure making its way to the intake manifold would be the PCV because there is some blow-by. Is there an easy way to test the PCV system? What do I block off and use to test?

It is back together now, though.

Here's the imgur video of trying to inflate the glove and gives you an idea of background noise. 95% of the hiss you hear is the regulator on my compressor leaking in the garage.

http://imgur.com/a/TaXaxwv

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box

· #2 · 1 mo ago

What's actually wrong with your car? Engine miss? Oil consumption? Or just looking for a problem to fix?

Get another leakdown tester, it shouldn't have two identical gauges like that. One should be pressure, one should be % leakage. Read the instructions and set it up accordingly.

The PCV valve test procedure is in the workshop manual.

mydecember1985

Discussion Starter · #3 · 1 mo ago

box said:
What's actually wrong with your car? Engine miss? Oil consumption? Or just looking for a problem to fix?

Random misfire at idle. Not a complete cylinder drop, but slightly poor contribution. Replaced near everything ignition/air/fuel related and it hasn't gone away. Rarely, the car idles great, but it mostly stumbles around 620-650RPM trying to find a steady rhythm. It just feels like it's choking a bit at idle. Nowhere near enough to stall, but it's a concerning amount. Vibration is never good on an engine. I have replaced all vacuum lines and intake gasket, but it looks like the next steps is a smoke test or better vacuum gauge. Just really dreading taking it apart again. You guys have several inches of room behind the rear head. I have next to none. Lots of dropped tools and scraped hands.

EGR diaphragm holds vacuum and pintle doesn't leak. PCV seems to work as intended, but I plan on testing it legitimately tomorrow. I also want to retry the glove trick with the PCV breather and valve blocked off to see how much blowby is coming from all cylinders. Blowing into it towards the valve cover does let some air by, but not much. No matter how hard I suck on it (🌈), it never seems to reduce flow like it should as vacuum increases at idle, but I also can't instantly create 20" of Hg.

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box

· #4 · 1 mo ago

If I was a betting man, I'd put a reasonable amount of money on the line and say it's not an internal engine issue. Not with those numbers. Put it back together again and keep investigating.

Make a video of it playing up and post it, might help shed some light on the situation.

Reactions: 1

Chang oil

· #5 · 1 mo ago

Instead of doing the glove trick
If you crank it up with the oil fill cap off
You should be able to put your hand over the oil fill hole of valve cover or use the fill cap to open and shut off any air coming out

With good rings you shouldn't have any compressed air coming out at all

If your rings are heavily worn this will be blowing smoke and oil out all over the place when open
Slightly worn rings will give a slight bit of pressure outwards but not much
Which shouldn't be that big of a issue

But for your idle stumble issue
the base rpm idle needs to come up a bit like to 700 or fairly close to it

Should fix your ghosts

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mydecember1985

Discussion Starter · #6 · 1 mo ago

So I put it all together last weekend. It sat Sunday. Drove to work Monday and it was acting a bit more strange than usual. Actually idled better (albeit up around 900), but was just weird at light throttle. I didn't drive far until I plugged in for some data and see this:

Found out the EGR gasket had shifted when reinstalling. Vacuum was down to 15-16. Fixed that issue and let the trims normalize for the last 3 days. I'm back down to my normal low trim of 90ish in the front and 120 in the rear now. Vacuum is back to around 19.3ish via the PCV>lower manifold tube and at the brake booster.

Here's it idling yesterday. RPM bounces around 620-650. Sometimes 650-680. I have tried several 1/4 turn adjustments of the BISS, but it always seems to settle back into this low RPM state after a short drive. Any more than 1-1/2 turns back from fully seated, I can hear the BISS hissing, so I don't go beyond that.

http://imgur.com/a/ksOxKLv

I plan to smoke test it next, but need to find a shop.

I always thought adjusting the SAS was a no-no. Should I hold off til a shop can check it out?

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mydecember1985

Discussion Starter · #7 · 1 mo ago

Chang oil said:
Instead of doing the glove trick
If you crank it up with the oil fill cap off
You should be able to put your hand over the oil fill hole of valve cover or use the fill cap to open and shut off any air coming out
With good rings you shouldn't have any compressed air coming out at all
If your rings are heavily worn this will be blowing smoke and oil out all over the place when open
Slightly worn rings will give a slight bit of pressure outwards but not much
Which shouldn't be that big of a issue

Meant to come back to this. I need the wife out there as an extra pair of hands, but I did disconnect the breather tube and the PCV to intake tube yesterday. I then removed the oil cap and there was a faint bit of smoke wafting out very slowly, but definitely not under pressure. With her assistance, I can probably cap the whole PCV system and try the glove trick again to be sure.

Chang oil

· #8 · 1 mo ago

mydecember1985 said:
So I put it all together last weekend. It sat Sunday. Drove to work Monday and it was acting a bit more strange than usual. Actually idled better (albeit up around 900), but was just weird at light throttle. I didn't drive far until I plugged in for some data and see this:
View attachment 311136
Found out the EGR gasket had shifted when reinstalling. Vacuum was down to 15-16. Fixed that issue and let the trims normalize for the last 3 days. I'm back down to my normal low trim of 90ish in the front and 120 in the rear now. Vacuum is back to around 19.3ish via the PCV>lower manifold tube and at the brake booster.

Here's it idling yesterday. RPM bounces around 620-650. Sometimes 650-680. I have tried several 1/4 turn adjustments of the BISS, but it always seems to settle back into this low RPM state after a short drive. Any more than 1-1/2 turns back from fully seated, I can hear the BISS hissing, so I don't go beyond that.

http://imgur.com/a/ksOxKLv

I plan to smoke test it next, but need to find a shop.

I always thought adjusting the SAS was a no-no. Should I hold off til a shop can check it out?

Wonder if you have a brown test lead in behind the passenger front strut tower as well for calibrating TPS - CAS in order model 6g72 and "setting base timing with timing light"
Setting idle with biss screw as well
Have to do it this way or your not telling your ECU the corrections of what base idle needs to be
Just moving your BISS screw in and out is confusing your ECU

Engine: Adjust Idle Speed - 3000GT/Stealth Wiki

www.3swiki.org

Chang oil

· #9 · 1 mo ago

mydecember1985 said:
Meant to come back to this. I need the wife out there as an extra pair of hands, but I did disconnect the breather tube and the PCV to intake tube yesterday. I then removed the oil cap and there was a faint bit of smoke wafting out very slowly, but definitely not under pressure. With her assistance, I can probably cap the whole PCV system and try the glove trick again to be sure.

Would suspect if your compression per cylinder is below 150 to 140 the rings would definitely be concerning
Not quite sure were your compression should be if its NA should sit quite higher then 150

But if you crank it up taking the oil cap off if its blowing exhaust smoke and oil out all over the place then you would definitely need to do something about the rings
If it is doing this the pressure from compression slipping past your rings has to go some where
Either PCV side or breather blowing the oil and kicked up trash back thru the intake and thru the heads to try to burn this nasty stuff off again
Normally fouling plugs first and then causing performance in horse power and drivability issues
Mostly getting carbon deposits stacked up on your exhaust valves decreasing air flow
Killings catalytic converters not long after if driven like this over time

With what specs you have and you doing the glove trick I don't see any horrible issues with rings

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white93gt

· #10 · 1 mo ago

mydecember1985 said:
Meant to come back to this. I need the wife out there as an extra pair of hands, but I did disconnect the breather tube and the PCV to intake tube yesterday. I then removed the oil cap and there was a faint bit of smoke wafting out very slowly, but definitely not under pressure. With her assistance, I can probably cap the whole PCV system and try the glove trick again to be sure.

I think you’re too worried about a mere 5.8% leakage; I’ve leaked many engines over the years including high horsepower racing engines. I never paid any attention to any leakage below 10% and have seen several that ran fine at up to 20% leakage.

I’d say pay more attention to what @Chang oil is saying or look in other areas.

white93gt

· #11 · 1 mo ago

Chang oil said:
Would suspect if your compression per cylinder is below 150 to 140 the rings would definitely be concerning
Not quite sure were your compression should be if its NA should sit quite higher then 150

@Chang oil, if you missed it his compression numbers are from 181psi to 191psi, listed at end of each leakage in his first post.

Reactions: 1

mydecember1985

Discussion Starter · #12 · 1 mo ago

Chang oil said:
Wonder if you have a brown test lead in behind the passenger front strut tower as well for calibrating TPS - CAS in order model 6g72 and "setting base timing with timing light"
Setting idle with biss screw as well
Have to do it this way or your not telling your ECU the corrections of what base idle needs to be
Just moving your BISS screw in and out is confusing your ECU

Engine: Adjust Idle Speed - 3000GT/Stealth Wiki

www.3swiki.org

I do have that brown, round wire by the black fuel pump hotwire and the blue connector (can't remember purpose). I do not have the CAS on the passenger side of the head, though. My harness is on the middle section of the firewall near the emission controls and closer to the brake booster.
Quite sure I don't need a timing light, but I'll double-check my service manual.

Crappy crop from previous photo

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Chang oil

· #13 · 1 mo ago

Engine: Adjust Idle Speed - 3000GT/Stealth Wiki

www.3swiki.org

^^^^^^^^
To set your base idle correctly
Moving your BISS screw round without telling the ECU that you moved it
Is not gonna get you where you wanna be

Getting the engine up to operating temp idling
Turn the car off
Ground your brown connector to a ground regardless of where just ground it
(Battery / firewall - good ground and leave it grounded
Crank the car back up the check engine light should turn on this is normal
Should run a little boggy again normal

Now with the BISS screw turn it while watching your rpms in your scan tool set it as close as possible to 700 rpm .... with all the loads turned off ..... AC / blower motor / lights etc..... OFF.....

When that is completed.....
Turn the car back off .....
Disconnect the brown test lead from ground install the brown cap back onto the connectors and tuck back against firewall

Crank the car back up and let it idle for 30 mins without touching the throttle
Leave the throttle alone
And let it learn again .... ( fuel trim )
After that this should take care of your stumbling issue your having

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Chang oil

· #14 · 1 mo ago

The same goes for the SAS screw which should never be messed with
Unless moved prior
Needing a feeler gauge to set this up correctly as well with the TPS being recalibrated again as well

You have to ground the Brown test lead in doing this as well
What this is doing is grabbing the attention of the ECU and tells it to pay attention to what you are changing ( calibration mode )

mydecember1985

Discussion Starter · #15 · 1 mo ago (Edited)

Chang oil said:
The same goes for the SAS screw which should never be messed with
Unless moved prior
Needing a feeler gauge to set this up correctly as well with the TPS being recalibrated again as well

You have to ground the Brown test lead in doing this as well
What this is doing is grabbing the attention of the ECU and tells it to pay attention to what you are changing ( calibration mode )

Although idling in gear is a little bit low, it looks like in Neutral/Park, it's pretty spot-on

BUT WAIT!
So I sit in the car watching idle and take a glance at what the idle RPM is reporting. This scan tool only refreshes maybe 2x a second, but that signal plate at the crank sensor is going +5V to 0 700RPM/60secX3plates = 35 signal plate passes per second.
I got the edit backwards but you get the idea. A total of 5 times in 4 minutes, I saw the RPM signal randomly go from 700 to instantly over 2,000.

Is this suggestive that my crank sensor is bad or signaling wrong? Or just the tool acting up?

Also, here's a video of the blowby test. The glove inflates, but I'm not sure how much is "bad" and it seemed to be only on startup for a few seconds. I can't feel anything blowing out and the paper barely moves. The only smoke that started coming out was when the wife let go of the PCV>manifold tube and it nearly stalled. You can see some coming out as the video cuts.
The blowby popped the glove, but even reattaching it with a small hole should've made it flutter a tiny bit if it was a concerning amount, right? I leaned down to put my cheek next to it since our faces are pretty sensitive to wind/pressure. I felt nothing coming out. Let me know if you want me to repeat the test with a better glove.

PS sorry about filming vertically

Thanks guys

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Chang oil

· #16 · 1 mo ago

For the blip in the 2100 or so rpm reading very well could be a sensor misread or fault

Now with the blow by i see very minimal blow by but you shouldn't have to cap things off
Should be able to just let it idle and take the oil fill cap off with no issues at idle
From what I see with the glove this is very minimal in blow by

Need to see If you can possibly get a hold of a camera scope to feed down into the cylinder from the spark plug holes in the heads
And check the lowest spots in the cylinders walls / V block left bank or rear head would be the closest spot in the cylinders towards firewall
For the right bank or front head the lowest spots in the cylinders would be closest to the radiator
Of course were gravity would tend leave
heavier deposits other the fuel vapor and 02

as over time carbon deposits / poor air filter changes etc.....and dirt getting sucked up very well could've scratched grooves in the cylinder walls thus letting compressed air blow by the rings in the scratch lines on cylinder walls
But for the glove this is still minimal for the blow by you have
its nothing serious

Now if I was seeing a chew chew train effect with smoke and oil blowing out everywhere this would be in the extreme case of some serious blow by

And this would need to be addressed asap
Causes : running low on oil / Fuel in oil from poor combustion / over presurized block pressure / fouling plugs & everything I said previously

I don't see your engine having any serious issues in this situation

Slap a new crank and a new cam sensor on

go from there

While tapping the gas are you still getting the boggy lag you had previously

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Chang oil

· #17 · 1 mo ago

This is just a random video I snatch off youtube which will put it better perspective for you in terrible blow by
These ecotec engines are complete trash anyways
No better then the GDI's that are in Hyundai / kia etc.....

But in this ecotec which these cylinders just tend to turn and twist ther own paths ....
Random warpage and cause some serious blow by issues ....
Doesn't help to have a very poor design in the pcv placement and pressure to vacuum ports on these guys are terrible and horribly designed

Example video ...

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mydecember1985

Discussion Starter · #18 · 1 mo ago

Chang oil said:
Need to see If you can possibly get a hold of a camera scope to feed down into the cylinder from the spark plug holes in the heads

I don't see your engine having any serious issues in this situation

Slap a new crank and a new cam sensor on

go from there

While tapping the gas are you still getting the boggy lag you had previously

Thanks for all the info. I would've spotted serious blowby like that a mile away. I've seen that on an old spitfire. With the PCV hooked up and the oil pan removed, I would say there is little to no pressure. Almost a suction. I can try that tomorrow.

I do have a camera, but the focal range is trash. I've done shots of the pistons before, but not the sidewalls. Hard to get the camera to angle toward wall once through the spark plug hole. I can try to pull #5 cylinder tomorrow and get a better shot. Easy to get to.

I did message BlackStealth to see if he has ever seen the tool do that RPM blip before. Waiting to hear back. Would love to find a cheap oscilloscope somewhere to see the crank's Hall effect signal before I have to rip it all apart. $70 ain't bad for the 2 from RockAuto, though.

If I go 60%+ on throttle, it does get up and move pretty much like it should, but simple things like a 40mph hill climb is painful. Having to go into the throttle like 40-50% to maintain speed. Casual changing lanes to get around a slow person feels like a bunch of dead weight.
I am using premium now, so it's not detecting detonation. It's not pulling timing anymore. Better, but not great.

My coworker has a 1.8 Chevy Cruze and he is clueless. Motor was 3quarts low on oil and I hear tap-tap-tap as he's pulling in. Rod bearing for sure, but light. Give him the 1qt out of my trunk. Stick is still bone dry. Told him go to WalMart right now and don't wait lol

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mydecember1985

Discussion Starter · #19 · 1 mo ago

Taking it apart now. I can flex the lower cover enough to get it out without having to remove that pesky upper left bolt behind the engine mount bolts.

Does this look off-center to you guys?

Perspective plays a good role here, but it looks like the tooth lines up with the left side of the divot, but is to the left of the right side straightening out. I count 25 teeth divided by 360 degrees is 15 degrees peak to peak.

Should i be concerned that this may be about 2 to at most 3 degrees advanced?

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white93gt

· #20 · 1 mo ago

mydecember1985 said:
Does this look off-center to you guys?
Should i be concerned that this may be about 2 to at most 3 degrees advanced?

Looks dead-on to me if that raised line on oil pump housing is correct one, not familiar with Diamante engines. I certainly wouldn't worry about 2 to 3 degrees advance there (if you're correct

), because that would only be 1 degree or so at cams and since one whole tooth up there is 7 degrees, you couldn't make it better anyway. Hell cams might run that much off when running just from belt flop.

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