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Zac88GT
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FEB 15, 03:27 PM
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I checked all the O2 sensor wires and everything looks fine. Watching the ALDL stream the sensor status is always "not ready". There is power for the heater and the heater ground is good. The signal ground and signal wires go right to the ecm and theres no breaks or bad connections there. I tried grounding the sensor signal wire and the ecm read 0mV so i'm pretty sure the ecm is fine. Also I got a code 13 for Oxygen sensor so i'm thinking that I need to buy a new one. I've never heard of one failing this fast though. It probably has less than 100 hours of run time on it. It's an expensive bugger too, I guess I'll order one today though. As for the oil i'm still not sure. All the valve seals are new, and i didn't knick any when i put them in, so i dont think it's them, i'm gonna take a look inside the intake and see what i can see. I still think the fact that it's the back 2 cylinders (7&8) is not a coincidence, it must be some indication of whats causing it.
EDIT: I took the throttle body off and you can already see little puddles of oil that have formed infront of the #7 and #8 intake runners. There might be oil infront of the other runners but I can't see that far back. I'll outline the conditions and possible causes and let me know what you think.
Conditions:
-Burns oil during high vacuum, low load like long deceleration, high rpm decel, and sometimes idle
-Oil burning has become worse since initial startup at which time there was little to none
-Compression is decent ~195-205 with one cylinder at a little over 180
-Idle vacuum is good, 21KPa absolute
-Oil puddles now present in bottom of intake manifold infront of runners
-Burned oil in the same manner prior to rebuilding
-#7 & #8 plugs have oil on them
Causes:
-Rings
-Valve stem seals
-PCV
-I don't think it's the rings because the compression numbers and idle vacuum are quite good. The rich condition 10:1 while driveing (due to the O2 sensor) could be contributing to the oil burning as it might be washing the cylinder walls.
-I don't think it's the valve stem seals simply because they are all brand new and the engine burned oil before I rebuilt it too.
-The PCV system makes the most sense to me. The reason it didn't burn oil on initial start up was because I had cleaned the intake manifold out during the rebuild. I think the oil is traveling through the PCV system into the intake manifold where some of it falls out of the air and to the bottom of the manifold. Cylinders 8 and 7 are the first to see the PCV air so that would make sense why they're burning the most oil and why there are puddles infront of the runners. As i said the engine burned oil like this before i rebuilt it too, and back then the intake had a substantial amount of oil inside of it. I guess what I'll try is to disconnect the PCV system for a while and just run breathers to atmosphere. I might have to run it like that for a while to eliminate any residual oil left in the intake. If that doesn't clear it up after a few hundred kilometers or so it's gotta be something else.[This message has been edited by Zac88GT (edited 02-15-2008).]
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AJxtcman
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FEB 15, 07:32 PM
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ryan.hess
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FEB 15, 08:51 PM
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| quote | Originally posted by Zac88GT:
I checked all the O2 sensor wires and everything looks fine. Watching the ALDL stream the sensor status is always "not ready". There is power for the heater and the heater ground is good. The signal ground and signal wires go right to the ecm and theres no breaks or bad connections there. I tried grounding the sensor signal wire and the ecm read 0mV so i'm pretty sure the ecm is fine. Also I got a code 13 for Oxygen sensor so i'm thinking that I need to buy a new one. I've never heard of one failing this fast though. It probably has less than 100 hours of run time on it. It's an expensive bugger too, I guess I'll order one today though. As for the oil i'm still not sure. All the valve seals are new, and i didn't knick any when i put them in, so i dont think it's them, i'm gonna take a look inside the intake and see what i can see. I still think the fact that it's the back 2 cylinders (7&8) is not a coincidence, it must be some indication of whats causing it.
EDIT: I took the throttle body off and you can already see little puddles of oil that have formed infront of the #7 and #8 intake runners. There might be oil infront of the other runners but I can't see that far back. I'll outline the conditions and possible causes and let me know what you think.
Conditions:
-Burns oil during high vacuum, low load like long deceleration, high rpm decel, and sometimes idle
...
Causes:
-Rings
-Valve stem seals
-PCV
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Couple things... first, a lot of things can kill an O2 sensor. Coolant and silicone sealant come to mind immediately.
Second, oil in the intake is normal. You get unburned hydrocarbons from shutting the engine off, PCV condensate, etc.
I think will ran into a problem like this on his rebuild and it turned out to be a bad hone job leaving rough patches in the cylinder finish. He has a thread somewhere, but I'm too lazy to search for it. It's a million pages long, so it's hard to miss.
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Erik
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FEB 15, 10:34 PM
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| quote | Originally posted by ryan.hess:
I think will ran into a problem like this on his rebuild and it turned out to be a bad hone job leaving rough patches in the cylinder finish. He has a thread somewhere, but I'm too lazy to search for it. It's a million pages long, so it's hard to miss. |
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Iwas thinking the same thing
here is the link
http://www.fiero.nl/forum/Forum2/HTML/044924.html
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Will
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FEB 15, 11:38 PM
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| quote | Originally posted by Zac88GT:
I used a ball hone on it, but it smokes exactly the same as it did when i first got it. So that leads me to believe it's not the rings. |
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What material was the abrasive on the ball hone?
Detail your build for me.
Buring oil and smoking on high RPM coast down is normal for a high mileage Northstar.
My first attempt at rebuilding one resulted in an engine that burned 2 quarts of oil in its first hundred miles. It had puddles of oil on the backs of the intake valves (pull your intake and see if you get this).
The problem was that the shop had used silicon carbide stones to hone the bores. SiC works fine on a production Chevy because the iron is cheap and relatively soft. The Northstar bore liners are very good high nickel iron and are much harder. The SiC stones just polish them, and as you ought to know, a polished bore does not result in a good ring seal. Aluminum Oxide is the correct abrasive to use to hone Northstar bores. I have the Sunnen part number that Total Seal recommends around here somewhere...
You'll see good compression because your rings are slathered in oil, which is sealing the gaps and grooves during a compression check. ...of course it also gets pulled into the chambers while the engine's running...
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Zac88GT
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FEB 16, 06:40 PM
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| quote | Originally posted by Will:
What material was the abrasive on the ball hone?
Detail your build for me.
Buring oil and smoking on high RPM coast down is normal for a high mileage Northstar.
My first attempt at rebuilding one resulted in an engine that burned 2 quarts of oil in its first hundred miles. It had puddles of oil on the backs of the intake valves (pull your intake and see if you get this).
The problem was that the shop had used silicon carbide stones to hone the bores. SiC works fine on a production Chevy because the iron is cheap and relatively soft. The Northstar bore liners are very good high nickel iron and are much harder. The SiC stones just polish them, and as you ought to know, a polished bore does not result in a good ring seal. Aluminum Oxide is the correct abrasive to use to hone Northstar bores. I have the Sunnen part number that Total Seal recommends around here somewhere...
You'll see good compression because your rings are slathered in oil, which is sealing the gaps and grooves during a compression check. ...of course it also gets pulled into the chambers while the engine's running... |
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I can't find any information on what material the abbrasive was but it was 120 grit ball hone from KD tools. Using standard replacment rings, and stock pistons. There was nothing special about the rebuild. Pretty well just freshening the bottom end up with new rings, bearings and seals. The top end got all new valve stem seals. The only preformance stuff was porting and polishing, backcutting the valves, CHRF springs and retainers, and cometic steel shim head gaskets. I'll pull the intake tonight and check for oil on the backs of the valves. I really hope i dont have to pull it out and tear it apart again.
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Zac88GT
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FEB 16, 07:56 PM
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I pulled the intake and there is a film of oil in all the runners in the head. There was some visible liquid oil on the backs of the valves. How much would it take to be considered pooling? I put about 150 kilometers on it thursday and it's burned between 0.5-0.75 liters. Decelerating on the highway to a stop would result in a blue cloud passing my car when i came to a stop.
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AJxtcman
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FEB 16, 08:44 PM
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| quote | Originally posted by Zac88GT:
I pulled the intake and there is a film of oil in all the runners in the head. There was some visible liquid oil on the backs of the valves. How much would it take to be considered pooling? I put about 150 kilometers on it thursday and it's burned between 0.5-0.75 liters. Decelerating on the highway to a stop would result in a blue cloud passing my car when i came to a stop. |
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OK you did not read the thread I posted above.
Pull the PCV valve out of the valve cover. Look inside of the hole and run the engine up to 2500. You should never see any oil running in the hole.
If you have oil in this area the PCV valve will suck it up. I have drain almost a cup of oil from an intake once. I usually get about a 1/2 cup if the baffle in the valve cover is not sealed. The baffle was sealed with RTV at the factory.[This message has been edited by AJxtcman (edited 02-16-2008).]
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Zac88GT
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FEB 16, 09:04 PM
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| quote | Originally posted by AJxtcman:
OK you did not read the thread I posted above.
Pull the PCV valve out of the valve cover. Look inside of the hole and run the engine up to 2500. You should never see any oil running in the hole.
If you have oil in this area the PCV valve will suck it up. I have drain almost a cup of oil from an intake once. I usually get about a 1/2 cup if the baffle in the valve cover is not sealed. The baffle was sealed with RTV at the factory.
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I read the link. I already had removed the baffles and re-sealed them with the engine sealant when i put the motor back together. I ran the engine at about 3000 rpm and looked in the hole, there was no river of oil directly below the PCV valve hole. I could see some oil if i looked at an angle and looked way down though. I just read through some of your thread WIll. When i said there was visible liquid oil, there was only like a drop, not half a teaspoon like you posted in your thread. How can I check to see if the hone job was ok without ripping the engine apart. Will a leak down test provide any kind of relevant data? If i use a boreascope do you think i'll be able to see any indication of the rings not being seated? Should i try putting the manifold back on and run the engine again, then shut it off and check for oil again?
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AJxtcman
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FEB 16, 10:25 PM
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After you drain the intake drive the car and see if it builds up again. See if it is just on the valves or in the bottom of the intake and on the valves.
What kind of work did you have done to the heads?
I have seen a large amount of failures in the 3.6L engine. The valve guides have .015 clearance. The spec is .0007. When I pull the intake off of them they have puddles of oil on the intake valves.[This message has been edited by AJxtcman (edited 02-16-2008).]
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