1995 K1500 TBI 350 Running Rich

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[Schurkey]

79 kPa = ~11.5 psi = 18-ish inches of vacuum. Somewhat more reasonable than previously. But 450 rpm seems low.

 

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79 kPa = ~11.5 psi = 18-ish inches of vacuum. Somewhat more reasonable than previously. But 450 rpm seems low.

The last photo is when I blipped the throttle and the rpm dipped because it added excess fuel.

 

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This is after going for a 10 or so minute drive. Aside from the issue I’m having with over fueling when it’s cold (which appears to be because the ECM thinks it’s running lean.) I’m also trying to get some insight into how this truck is running in general. I have decent automotive knowledge when it comes to 1970’s era cars, but I don’t have much experience with looking at these data pids and determining if they are good or not and where to go from there. What should O2 cross counts be? It looks like long term is pulling fuel? The EGR system also isn’t functional and this truck burns oil (I think the valve guides are shot, because the compression test I did was within 10 percent variance from 170-180psi. Any help is appreciated.

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[IndexOf0]

Just switched to hg of vacuum. It’s a 9.5hg. That’s not very good. Shouldn’t it be around 18?

 

[Schurkey]

This is after going for a 10 or so minute drive.

Should be long enough to get to closed-loop and get everything up to temperature.

Aside from the issue I’m having with over fueling when it’s cold (which appears to be because the ECM thinks it’s running lean.)

It would get that info from the O2 sensor. How old is the O2 sensor? Does this engine have an AIR pump? Exhaust leaks? Misfire when cold?

What should O2 cross counts be?

Higher is better. Varies with engine RPM, less at idle, but probably not less than 7-ish at idle, not less than 18 at higher speed, and FAR more on newer vehicles, newer O2 sensors, etc.

It looks like long term is pulling fuel?

I see fuel trims within a few numbers of 128. 129--131. Computer is ADDING fuel. Nothing to worry about.

The EGR system also isn’t functional

That needs attention.

and this truck burns oil (I think the valve guides are shot, because the compression test I did was within 10 percent variance from 170-180psi.

Valve seals, valve guides, oil-control rings...wouldn't have to affect cranking compression pressures. More diagnosis needed.

Oil-burning is not doing the O2 sensor, or the catalyst any favors.

Just switched to hg of vacuum. It’s a 9.5hg. That’s not very good. Shouldn’t it be around 18?

First Guess: NOT "hg of vacuum". Hg of PRESSURE. The MAP sensor is a PRESSURE sensor, not a vacuum sensor.

If your barometric pressure is 30.00 in/hg, 9.5" of pressure = 20.5" hg of vacuum.

 

[IndexOf0]

Should be long enough to get to closed-loop and get everything up to temperature.


It would get that info from the O2 sensor. How old is the O2 sensor? Does this engine have an AIR pump? Exhaust leaks? Misfire when cold?


Higher is better. Varies with engine RPM, less at idle, but probably not less than 7-ish at idle, not less than 18 at higher speed, and FAR more on newer vehicles, newer O2 sensors, etc.


I see fuel trims within a few numbers of 128. 129--131. Computer is ADDING fuel. Nothing to worry about.


That needs attention.


Valve seals, valve guides, oil-control rings...wouldn't have to affect cranking compression pressures. More diagnosis needed.

Oil-burning is not doing the O2 sensor, or the catalyst any favors.


First Guess: NOT "hg of vacuum". Hg of PRESSURE. The MAP sensor is a PRESSURE sensor, not a vacuum sensor.

If your barometric pressure is 30.00 in/hg, 9.5" of pressure = 20.5" hg of vacuum.

The O2 sensor is only a couple of months old, but the cross counts are basically zero to 2 at idle. Even holding steady rpm at around 1500RPM it doesn’t go above at max. My oil burning problem has likely killed it.

Regarding the EGR system. I did clean out the crossover in the intake, but I think passages leading to the intake plenum are clogged somewhere along the way, because I can apply vacuum to the EGR valve, have it open and there is no idle change. Have any recommendations?

Valve stem seals were replaced a little while ago. Any recommendations for further diag? Leak down test? Cylinder 6 is the only spark plug that becomes oil coated regularly.

I did read what you are stating about the MAP sensor reading pressure. I don’t know why that was confusing to me, but I’m very much used to reading vacuum with a vacuum gauge so that threw me off I guess.

 

[Schurkey]

The O2 sensor is only a couple of months old, but the cross counts are basically zero to 2 at idle. Even holding steady rpm at around 1500RPM it doesn’t go above at max. My oil burning problem has likely killed it.

Oil burning can be a problem. MAYBE that's what's happening now.

I suspect something else.

Regarding the EGR system. I did clean out the crossover in the intake, but I think passages leading to the intake plenum are clogged somewhere along the way, because I can apply vacuum to the EGR valve, have it open and there is no idle change. Have any recommendations?

Remove manifold, clean thoroughly. Assure passages in cylinder head are clean, too.

Valve stem seals were replaced a little while ago. Any recommendations for further diag? Leak down test? Cylinder 6 is the only spark plug that becomes oil coated regularly.

You could try a leakdown test. But mostly, that's going to confirm the top ring, not the oil control rings. And it does nothing for the valve guides unless they're so wiped that the valve(s) don't seal--and you have good compression.

I did read what you are stating about the MAP sensor reading pressure. I don’t know why that was confusing to me, but I’m very much used to reading vacuum with a vacuum gauge so that threw me off I guess.

Common issue. Threw me for a long time, too.

 

[scott2093]

I see fuel trims within a few numbers of 128. 129--131. Computer is ADDING fuel. Nothing to worry about.

bottom pic of post 34 shows LT trim 108?

 

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Oil burning can be a problem. MAYBE that's what's happening now.

I suspect something else.


Remove manifold, clean thoroughly. Assure passages in cylinder head are clean, too.


You could try a leakdown test. But mostly, that's going to confirm the top ring, not the oil control rings. And it does nothing for the valve guides unless they're so wiped that the valve(s) don't seal--and you have good compression.


Common issue. Threw me for a long time, too.

So, what would you try to address first? I’ve obviously got compounded issues.