1995 K1500 TBI 350 Running Rich

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Intake passage for the EGR is cleared out finally. The last time I did this job I assumed getting the carbon out of ports was good enough, but I didn’t realize there was a passage leading to the intake plenum that I needed to clean. It was full of carbon. I’ll provide an update after I get the intake back on.

 

[IndexOf0]

i was able to take the truck out on the highway. No code 32, but my O2 cross counts are very low even at cruise so I’ll be replacing the O2 sensor next and hopefully that will wrap this saga up.

 

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02 cross counts are much better with the Delphi O2 sensor. I have anywhere from zero to as high as 17 at idle. Now onto the oil burning problem. How is it determined an oil control ring is the problem? Cylinder 6 is the only one that’s coated in oil deposits. It burns oil if you rev it to 3000rpm and you hold it there but not at 2,000. It doesn’t smoke right away either it just seems like it builds up. Could it be a bad valve guide? Could it be the valve stem seals I just replaced? Please point me in the right direction.

 

[Schurkey]

02 cross counts are much better with the Delphi O2 sensor. I have anywhere from zero to as high as 17 at idle.

Anything under ~6--7 is cause for concern. More is better.

Now onto the oil burning problem. How is it determined an oil control ring is the problem?

Diagnosing rings is a "when everything else is ruled-out, it's rings" sort of issue. Compression rings can "pump" oil into the chamber even with acceptable compression pressures. There's no definitive diagnosis; although burning more oil with increased RPM and increased load is a sign of ring problems--but also a potential sign of wiped valve guides, and perhaps oil consumption via the PCV system if there's insufficient oil-baffling at the PCV valve or the fresh-air hose.

Cylinder 6 is the only one that’s coated in oil deposits. It burns oil if you rev it to 3000rpm and you hold it there but not at 2,000. It doesn’t smoke right away either it just seems like it builds up. Could it be a bad valve guide? Could it be the valve stem seals I just replaced? Please point me in the right direction.

Given the huge amount of deposits, and the fact that the valve stem seals are fresh...I'm guessing you're looking at "exploratory surgery". PCV-related oil consumption wouldn't be confined to Cylinder 6 although it's worth looking at the the PCV hose to see if there's oil inside. It's unlikely but possible that the valve guides for #6 would be toast while the guides for the other seven cylinders are "ok".

It's also unlikely--but possible--that the rings on #6 are the problem while the other seven cylinders are OK. Detonation? Broken rings? Ring(s) installed improperly?

Maybe a failed or out-of-position intake gasket, allowing oil into the intake port from the lifter valley?

That kinda leaves a cracked casting--perhaps a crack between the intake port and a rocker stud hole, with oil going down the rocker stud and into the air/fuel stream. There was a guy on the Pontiac forum that had numerous oil-leaks into the intake port of his engine--mostly but not entirely the result of excess grinding during a D-I-Y porting job.

 

[Road Trip]

02 cross counts are much better with the Delphi O2 sensor. I have anywhere from zero to as high as 17 at idle. Now onto the oil burning problem. How is it determined an oil control ring is the problem? Cylinder 6 is the only one that’s coated in oil deposits. It burns oil if you rev it to 3000rpm and you hold it there but not at 2,000. It doesn’t smoke right away either it just seems like it builds up. Could it be a bad valve guide? Could it be the valve stem seals I just replaced? Please point me in the right direction.

EDIT: Reply collision with Mr. Shurkey. But it looks like we are in agreement, so I'll leave this as-is.

Excess oil consumption diagnosis can be tightened up by varying the load on the engine while watching the exhaust carefully.
(Either helper or rear view mirror)

* The intake valve guide is exposed to a significant intake manifold vacuum when the engine is revved under
no load conditions. (Or during long closed throttle engine braking with a standard transmission.)

With loose guides or damaged valve stem seals, a sustained deceleration/throttle closed engine braking down a hill will
be clear behind you (think fuel shut off) ...followed by a blue cloud once you get back on the gas. Seen this firsthand.
NOTE: A puff of blue smoke on start up after sitting overnight is from the same loose valve guide and/or bad intake valve stem seals.

On the other hand, weak rings that have lost their tension (think bad overheat) or suffer from a poor ring seal are not that
affected during a light load/high vacuum conditions. Instead, if you (or the spotter) see blue smoke during heavy acceleration
(think pulling a grade) then 2 things happen. First, the intake manifold is near atmospheric, so there's not nearly the
pressure differential across the intake valve stem seal. Second, with heavy throttle and maximum combustion pressure against
weak rings you end up pressuring the crankcase w/blowby. This ends up piped into the intake & burned, with blue-tinged results.

NOTE: I have not mentioned the exhaust valve guide/seals up 'til now, because with normal exhaust backpressure the pressure
differential causes the airflow to be up the stem. However, on a couple of rare occasions we replaced the stock exhaust manifolds
with tuned long tube headers, and instead of just adding performance, we suddenly had a marked increase in oil consumption.

And after looking everywhere else, we would finally drop the headers and see obvious signs of oil in the exhaust ports? But nothing
on the spark plugs? As it turns out, tuned headers can actually develop a vacuum at the exhaust ports when they hit resonance
at certain engine speeds & loads. (Think highway cruise.) And this a special case where you are burning oil, but with no signs
of this insde the combustion chamber. Rare, not seen in a stock engine bay, but is possible after header installation, and also
features a unique failure footprint.

It wasn't the fault of the headers, for they were working as advertised. The fault was ours, for we were putting headers on
a tired engine, and the previously 'no problemo' worn/loose exhaust valve guides with the stock iron exhaust manifolds now
s*cked oil into the exhaust worthy of the reed valves in a 2-stroke motor. :0)

****

The point of all of the above is that dynamic pressure differentials actually move around inside the engine depending upon how we are
driving it. So by paying close attention to when the blue smoke does and does not appear while you are driving it will help you
figure out where the problem is occurring. By the way, having 1 cylinder as an outlier is an important clue. If these are factory
rings then the probability shifts to towards the guides. But if this is a rebuilt motor, it's possible that there was an assembly
assembly error during ring installation. (Or even this cylinder was driven into detonation and the piston is wounded.)

Apologies for the length, but your comment regarding the 2000 vs 3000 rpm caught my eye. Again, it would be interesting
if you could see if the problem is during light loads/high vacuum vs pulling a grade/low vacuum. And also when the visible
smoke is at a minimum.

For what it's worth --

 

[studigggs]

I don’t have much experience with looking at these data pids and determining if they are good or not and where to go

The snap on reference books give pretty good descriptions of the PIDs and sometimes list nominal values. Starting on page 390 for GM

https://www.snapon.com/Files/Diagnostics/UserManuals/USDomesticVehicleCommunicationSoftwareManual_EAZ0025B01H.pdf

 

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Anything under ~6--7 is cause for concern. More is better.


Diagnosing rings is a "when everything else is ruled-out, it's rings" sort of issue. Compression rings can "pump" oil into the chamber even with acceptable compression pressures. There's no definitive diagnosis; although burning more oil with increased RPM and increased load is a sign of ring problems--but also a potential sign of wiped valve guides, and perhaps oil consumption via the PCV system if there's insufficient oil-baffling at the PCV valve or the fresh-air hose.


Given the huge amount of deposits, and the fact that the valve stem seals are fresh...I'm guessing you're looking at "exploratory surgery". PCV-related oil consumption wouldn't be confined to Cylinder 6 although it's worth looking at the the PCV hose to see if there's oil inside. It's unlikely but possible that the valve guides for #6 would be toast while the guides for the other seven cylinders are "ok".

It's also unlikely--but possible--that the rings on #6 are the problem while the other seven cylinders are OK. Detonation? Broken rings? Ring(s) installed improperly?

Maybe a failed or out-of-position intake gasket, allowing oil into the intake port from the lifter valley?

That kinda leaves a cracked casting--perhaps a crack between the intake port and a rocker stud hole, with oil going down the rocker stud and into the air/fuel stream. There was a guy on the Pontiac forum that had numerous oil-leaks into the intake port of his engine--mostly but not entirely the result of excess grinding during a D-I-Y porting job.

There is currently an exhaust leak before the cat that I’m going to seal up. May that be the cause for the lower than ideal cross counts?

My intake gaskets are fresh as I had to pull the intake to clean out the EGR passages do I don’t think that’s it. I will check the PCV tube as well. I know there is always oil on the PCV valve when I take it out, but my valve covers are stock. The reason why I’m leaning toward either a stuck oil control ring or guides is because there was a lot of sludge inside of the engine when I changed the intake gaskets the first time and the valve springs have a lot of build up on them so long intervals between oil changes was definitely occurring. I probably need to take it apart to figure it out honestly.

 

[IndexOf0]

EDIT: Reply collision with Mr. Shurkey. But it looks like we are in agreement, so I'll leave this as-is.

Excess oil consumption diagnosis can be tightened up by varying the load on the engine while watching the exhaust carefully.
(Either helper or rear view mirror)

* With valve guides and stock exhaust, the intake valve guide is exposed to a significant intake manifold vacuum
when the engine is revved under no load conditions. (Or during long engine braking with a standard transmission.)

With loose guides or damaged valve stem seals, a sustained deceleration/throttle closed engine braking down a hill will
be clear behind you (think fuel shut off) ...followed by a blue cloud once you get back on the gas. Seen this firsthand.
NOTE: A puff of blue smoke on start up after sitting overnight is from the same loose valve guide and/or bad intake valve stem seals.

On the other hand, weak rings that have lost their tension (think bad overheat) or suffer from a poor ring seal are not that
affected during a light load/high vacuum conditions. Instead, if you (or the spotter) see blue smoke during heavy acceleration
(think pulling a grade) then 2 things happen. First, the intake manifold is near atmospheric, so there's not nearly the
pressure differential across the intake valve stem seal. Second, with heavy throttle and maximum combustion pressure against
weak rings you end up pressuring the crankcase w/blowby. This ends up being recycled into the intake & burned, with
blue-tinged results.

NOTE: I have not mentioned the exhaust valve guide/seals up 'til now, because with normal exhaust backpressure the pressure
differential causes the airflow to be up the stem. However, on a couple of rare occasions we replaced the stock exhaust manifolds
with tuned long tube headers, and instead of just adding performance, we suddenly had a marked increase in oil consumption.

And after looking everywhere else, we would finally drop the headers and see obvious signs of oil in the exhaust ports? But nothing
on the spark plugs? As it turns out, tuned headers can actually develop a vacuum at the exhaust ports when they hit resonance
at certain engine speeds & loads. (Think highway cruise.)

It wasn't the fault of the headers, for they were working as advertised. The fault was ours, for we were putting headers on
a tired engine, and the previously 'no problemo' worn/loose exhaust valve guides with the stock iron exhaust manifolds now
s*cked oil into the exhaust worthy of the reed valves in a 2-stroke motor. :0)

****

The point of all of the above is that dynamic pressure differentials actually move around inside the engine depending upon how we are
driving it. So by paying close attention to when the blue smoke does and does not appear while you are driving it will help you
figure out where the problem is occurring. By the way, having 1 cylinder as an outlier is an important clue. If these are factory
rings then the probability shifts to towards the guides. But if this is a rebuilt motor, it's possible that there was an assembly
assembly error during ring installation. (Or even this cylinder was driven into detonation and the piston is wounded.)

Apologies for the length, but your comment regarding the 2000 vs 3000 rpm caught my eye. Again, it would be interesting
if you could see if the problem is during light loads/high vacuum vs pulling a grade/low vacuum. And also when the visible
smoke is at a minimum.

For what it's worth --

Thank you. This gives me some insight. So, in the morning when I leave for work it smokes a lot when I first get on it for my acceleration up to 50 but it does clear even while I’m still on the throttle. I’ve also tested having the engine in first gear while I’m driving holding 3,000rpm but the load isn’t huge and it smokes. If I floor it and the transmission downshifts, it doesn’t really smoke. It does smoke worse on hard decel though. There is no smoke at idle and cylinder compression is within 10 percent variance from 170-180 for all cylinders with no outliers. Having this information, what do you think? I also have videos.

 

[Road Trip]

Thank you. This gives me some insight. So, in the morning when I leave for work it smokes a lot when I first get on it for my acceleration up to 50 but it does clear even while I’m still on the throttle. I’ve also tested having the engine in first gear while I’m driving holding 3,000rpm but the load isn’t huge and it smokes. If I floor it and the transmission downshifts, it doesn’t really smoke. It does smoke worse on hard decel though. There is no smoke at idle and cylinder compression is within 10 percent variance from 170-180 for all cylinders with no outliers. Having this information, what do you think? I also have videos.

Greetings IndexOof0,

When you read the following keep in mind that we aren't dealing with a scenario where the valves are 100% responsible
while the rings are 0% responsible, or vice versa. And we've all been around engines where the valves were 50% and
the rings were 50% -- in other words, everything is equally worn out. :-(

In English, there may be some overlap between failure modes. For example, let's say that wear in the valve area is causing
80% of the blue smoke, while the rings are contributing 20%. So we have to factor in that in the real world interpreting
the symptoms will be a matter of degree.

****

EDIT: High compression is an indicator that the rings are in good condition, as well as the valve face to valve seat sealing.
And since oil is running down the valve stems, this excess oiling is on the other side of the valve that's seeing pressure
during the compression test.

So it's possible to have good valve to valve seat sealing, and if you add good rings to the mix then you have good compression
readings -- while at the same time also having poor oil control in the valve seal/valve stem/valve guide area. (!)

After reading the above I'm going to say that the majority of your oil burning is during periods of high intake manifold
vacuum. And the highest probability of where oil is being pulled into the intake stream would be down the intake
valve guides. Either the valve stems are so loose inside the valve guides that the seals can't perform their job while
the stems are jumping around -or- the guides aren't worn but the seals were damaged during installation. (A third
possibility is a higher lift aftermarket cam creating an interference situation at max lift while the valve spring is fully
depressed.)

NOTE: Any way that excess oil can be sucked into the intake manifold during periods of high vacuum
is a possibility. Usually if the intake manifold is leaking between the lifter valley and the bottoms of the
intake ports, one or more affected cylinders are running rough at high vacuum (low MAP) readings. On
the other hand, I've seen heads with bad intake seals run smoothly while metering oil onto the backside
of the intake valves. (BTW, these are general statements and not absolute rules.)

Anyway, when you drive your truck tomorrow, watch for:

* Puffs of blue smoke on initial start up. Definitely points to a valve guide/valve stem seal problem.
Why it occurs: Oil drains down valve stems from valve spring retainer and pools onto backside of
intake valves. When the engine is first started, this oil is washed off by the air/fuel mixture, goes
into the cylinder, is burned, and puffs of blue smoke are visible. NOTE: You may want to stand
behind the truck and have a helper turn the key for you. BTW, this is not a rare sight on a high
mileage SBC, especially the older ones where the umbrella seals would harden, crack, and fall away.

* Wait until the exhaust clears up, and then take off. In order to give yourself the clearest picture
of what's going on, try to drive as smoothly as possible. That is, watch the exhaust while doing
a long, steady acceleration. I would expect that the longer you accelerate (for example climbing a
steady grade on a highway) the cleaner the exhaust will look.

Conversely, if you were to slow down via engine braking (downshifting, automatic or standard) I
would expect more blue smoke than if you were to put the transmission in neutral and use only
your brakes to slow the vehicle. And remember, during engine braking with a closed throttle
a fuel cutoff may occur, so there won't be any smoke initially, followed by billowing smoke when
the fueling restarts.

Q: You mentioned recent replacement of the valve stem seals? If you have already described
how it went, could you point me to where you wrote this? And if you haven't, please describe
how you went about it, and what snags, if any, did you run into? Is all the associated
valvetrain factory original, or are you running a higher lift aftermarket cam?

At any rate, with careful observation we should be able to figure out where the oil consumption
is coming from, giving you enough data in order to make an informed decision of what
it's going to take to keep your GMT400 on the road...where it belongs. :0)

Safe travels --