LB7: Excessive blow by

blk smoke lb7

blk smoke lb7

<-----Lots of green $
Nov 8, 2010
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belvidere,ill
I've put the trans fluid in motors that I bought for cars I was flipping and sometimes it took motors that you would swear it had a rod out of it to being 1 of the quietest best running motors ever.You can't drive with it in there only bring it up to temp then shut it off and let it cool till cold and repeat.I had a 3.1 in a 95 grand prix that purred like a kitten after I did that.An old hot rodder taught me that.Only ever had to do it to that 1 motor but man was I impressed.
Yes I kept it sealed with some caps and plugs and there I didn't have plugs or caps I stuffed paper towels in every hole the thing had.

Upsets me because I don't sell bad stuff, and it ran so well for me.
 
Chevy1925

Chevy1925

don't know sh!t about IFS
Staff member
Oct 21, 2009
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I may try that on my 4.3 project if its makin noise when I fire it up.

Anyhow, I say leak down test the bad cylinder. Best way to do it without throwing things at it

If he gives the low cyl a couple squirts a oil in the glow plug hole and retest compression and sees an decent increase in pressure, that would also lead to saying its a stuck ring
 
Sandracer799

Sandracer799

LB7 Power
Mar 25, 2008
205
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Sandston,Va
blk smoke lb7 said:
Josh is it possible an injector didn't get seated tight enough and/or the injector body o ring got sliced and is allowing blow by????
Click to expand...

I got a new injector kit from my dealer before i re-installed my injectors. i soaked all the o-rings in oil before putting them on the injector and putting them in the motor, but I guess anything is possible.

I can hear a slight knock from the passenger side of the motor. I did a compression test on that side so far.

Cylinder's 1 to 5 are between 300 and 350. Cylinder 7 was right around 200.

I sprayed some WD-40 in the glow plug hole and am going to let it sit over night. I am praying that it might be a stuck ring and that this may solve the issue.
 
JoshH

JoshH

Daggum farm truck
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Feb 14, 2007
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Sandracer799 said:
I got a new injector kit from my dealer before i re-installed my injectors. i soaked all the o-rings in oil before putting them on the injector and putting them in the motor, but I guess anything is possible.

I can hear a slight knock from the passenger side of the motor. I did a compression test on that side so far.

Cylinder's 1 to 5 are between 300 and 350. Cylinder 7 was right around 200.

I sprayed some WD-40 in the glow plug hole and am going to let it sit over night. I am praying that it might be a stuck ring and that this may solve the issue.
Click to expand...
Those all sound a little low for a stock motor in good condition, but 200 is definitely a bad sign. What do the balance rates show? I would think you should be able to see something in the balance rates with a cylinder down on compression that much.
 
Sandracer799

Sandracer799

LB7 Power
Mar 25, 2008
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JoshH said:
Those all sound a little low for a stock motor in good condition, but 200 is definitely a bad sign. What do the balance rates show? I would think you should be able to see something in the balance rates with a cylinder down on compression that much.
Click to expand...

I haven't looked at them yet. My brother has my efi live at the moment a state away. I will hook it up this weekend if a leak down test doesn't show anything.
 
Chevy1925

Chevy1925

don't know sh!t about IFS
Staff member
Oct 21, 2009
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Sandracer799 said:
I haven't looked at them yet. My brother has my efi live at the moment a state away. I will hook it up this weekend if a leak down test doesn't show anything.
Click to expand...

i would suggest a wet compression test on the weak cylinder before all that. jsut simple and quick to do as well as tell you which way to start looking in your leak down test
 
Bonestock

Bonestock

Active member
Aug 9, 2010
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I believe GM has an additive also that you put in your oil and run the engine so long and then dump the oil and put in fresh. What oil are you running? Back in 2008 they had a recall on the 5.3 not seating the rings and were using this said additive. I would think it would work well for a possible stuck ring scenario.....
 
hondarider552

hondarider552

Getting faster
May 28, 2008
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Here's my engine, S475 was on for 3 weeks, blew passenger side front and driver rear headgasket, no pushed cups.


[YOUTUBE]hPOXsMAriNM[/YOUTUBE]
 
DURAMXD

DURAMXD

BOB SAGET!
Apr 24, 2012
348
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Wichita, KS
So are you able to feel the PCV tube pushing air out while it is running?

I have a very similar issue to this, where the truck will puff a bit of smoke coming to a stop, a lot of this seems to apply to my issue. So, I tried some of the things mentioned here. When I put my finger over the PCV tube at the bottom of the motor, I can't really feel any air pushing out, but it is hard to tell with the belt and the fan moving air around. I pulled my oil fill cap and it puffs out slightly (not as bad as the video posted by sandracer) but nothing out the dipstick tube. All my balance rates are fine.

Any advice here?
 
hondarider552

hondarider552

Getting faster
May 28, 2008
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Sandracer799 said:
When the oil cap is on and the dip stick in place all the smoke that was coming out of those 2 is blowing out of the PCV tube.
Click to expand...

Exactly what mine was doing. I only noticed this when I put on my electric fans so I could see the bottom oft he PCV box covered in smoke.
 
blk smoke lb7

blk smoke lb7

<-----Lots of green $
Nov 8, 2010
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belvidere,ill
#7 injector hold down backed out and compresion was pushing past the injector.Truck is out and running fine now.

Thanks to al the DD members for their input,much appreciated:thumb:
 
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