Failed smog..need advice please

[Lance Hohimer]

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[Lance Hohimer]

These are my results. 1994 Yukon 5.7. I have tested MAP, replaced CTS, my EGR solenoid checks out. EGR valve may be bad(i know the NOx are good) but at the time of this test I had the EGR valve off my 93 k3500 on it not realizing it was wrong for my Yukon. So I put the original on and it failed NOx miserably.
A little history, I got this Yukon with a blown up 5.7. My 93 K3500 had a 5.7 in it, I swapped that into the Yukon. Runs great!. But had some issues and I have been addressing them.
What I have done so far, NEW fpr, replaced the filters on the injectors, new spark plugs...035" gap, fresh oil/filter, new air filter, new fuel filter, new CTS. I just bought a new Denso O2 sensor today. I have no codes.

 

[Schurkey]

High HC is generally misfire.
High CO is generally rich mixture.

Misfire causes the O2 sensor to report a false lean condition, the computer adds fuel to compensate not knowing that O2 is reporting false information. Fix the misfire, I bet the CO fixes itself once the computer straightens itself out.

In my driveway, I'd be doing a power balance test to find the misfiring cylinder(s); AFTER checking all the usual suspects--plug wires, cap 'n' rotor, fuel pressure. Make sure the coil can fire a spark tester calibrated for HEI. One clue is that the only O2 sensor is on the left bank of the engine, so it's extremely likely that at least one cylinder on the left bank is guilty of misfire. There may be one or more on the right bank.

"Codes" does not mean what most folks think it means. Connect a REAL scan tool, look at the data stream. Codes can be helpful. Data stream is essential.

 

[PlayingWithTBI]

plug wires, cap 'n' rotor, fuel pressure. Make sure the coil can fire a spark tester calibrated for HEI

This and, check your base timing too.

 

[Knuckle Dragger]

It's been almost 15 years since I did smog in Cali but it looks kind of like a lean misfire to me. O2 is a little high, CO is low and HC is high. The low NOx numbers give me pause because if it's too lean the chamber will heat up and drive NOx up. Are these numbers after the spark plug change? What is your fuel pressure at?

 

[Lance Hohimer]

The results posted are with old plugs, old FPR(blown), EGR valve off my 93 k3500, old CTS, dirty K&N air filter.
I changed the plugs, FPR, put the Yukon's original EGR valve back on, new air filter and took for a retest...NOx went up to 900! CO came down to around 20 and HC was still around 200.
So I ordered a Denso O2 sensor, tested my MAP, EGR solenoid, both tested good. I do not know my fuel pressure. I also rigged up a vacuum tester for my 'tests' above and for the egr valve. The egr valve bleeds down slowly. So I am ordering a new Delphi from rockauto.

 

[Schurkey]

It looks kind of like a lean misfire to me. O2 is a little high, CO is low and HC is high. The low NOx numbers give me pause because if it's too lean the chamber will heat up and drive NOx up.

CO is not low. It's near the limit, way above "average". This indicates rich mixture.
NOx is low because the engine is running rich, and the EGR is functional--therefore the burn is of moderate temperature, not enough to create oxides of nitrogen.

The results posted are with old plugs, old FPR(blown), EGR valve off my 93 k3500, old CTS, dirty K&N air filter.

I'm not sure there's a difference in the EGR valves. Maybe yes...maybe no. But at least it "worked", even if it might be incorrect.

Practically everyone cleans their K&N filter too often--which is the worst thing you can do to them. They filter BETTER when they're "dirty"; and worse when they're "clean". K&N used to say that you should leave them alone unless they've got an eighth-inch of buildup on them--the pleats would be nearly full. Now they say to use an air cleaner restriction indicator, and don't clean until there's a restriction.

I changed the plugs, FPR, put the Yukon's original EGR valve back on, new air filter and took for a retest...NOx went up to 900! CO came down to around 20 and HC was still around 200.
So I ordered a Denso O2 sensor, tested my MAP, EGR solenoid, both tested good. I do not know my fuel pressure. I also rigged up a vacuum tester for my 'tests' above and for the egr valve. The egr valve bleeds down slowly. So I am ordering a new Delphi from rockauto.

Installing a failed EGR valve increased the peak combustion chamber temperature; and it may be that the fresh plugs and repaired fuel pressure regulator have made some or all of the cylinders run better. NOx increases, CO reduces...but I still think there's a misfire (or the catalyst has failed.)

Get the rest of the engine running right, assure that there's no misfire. MAYBE the catalyst will clean itself. Possible, not likely.

This engine is crying out for someone to put a scan tool and fuel pressure gauge on it, and an IR thermometer on the inlet and outlet of the catalyst(s).

 

[Knuckle Dragger]

CO is not low. It's near the limit, way above "average". This indicates rich mixture.
NOx is low because the engine is running rich, and the EGR is functional--therefore the burn is of moderate temperature, not enough to create oxides of nitrogen.

Yeah upon review I was looking at the average CO numbers, not the actual. Hard to read sideways I guess. I agree he is rich.

 

[Lance Hohimer]

Sorry about the sideways picture, my camera SUCKS and that was the only way I could get a 'clear' pic.
I am getting a new cap/rotor/ wires today. May even put my spare distributor in. The one that is in there is from the 93 k3500. Timing is dead on '0' and does not bounce around. I did hook up a vacuum gauge and it read steady at 16"..no bouncing or fluctuations. When I revved it up, it shot straight to 20/21 and right back to 16.
Also sending my injectors to Mr Injector to be cleaned and inspected. For 18 ea I cant complain.

 

[Knuckle Dragger]

Sorry about the sideways picture, my camera SUCKS and that was the only way I could get a 'clear' pic.
I am getting a new cap/rotor/ wires today. May even put my spare distributor in. The one that is in there is from the 93 k3500. Timing is dead on '0' and does not bounce around. I did hook up a vacuum gauge and it read steady at 16"..no bouncing or fluctuations. When I revved it up, it shot straight to 20/21 and right back to 16.
Also sending my injectors to Mr Injector to be cleaned and inspected. For 18 ea I cant complain.

Misreading the picture is on me.