Smoke testing Procedure help needed

[rod7515]

I have a 2003 Yukon with a 6.0. I bought it in May with 249k miles on it. It runs great but has had the CEL on since i got it. Ive checked and cleared the codes many times during the summer but I needed it everyday to tow my mowers so I didnt have time to get to involved. Now I am done mowing for the season and want to take care of these codes. Both banks are lean so I lean towards an intake gasket. The previous owner had replaced the plugs, injectors and coil packs plus new wires. He said the light was on all 4 years he owned it but he never replaced the intake gasket. Oh, he also replaced the the throttle body as well. I was wondering if this engine has a port to hpok up the smoke machine or if i need to block of just behnd the MAF and push thru the intake? I have a smoke machine of my own that I used to use 15 years ago when I was a mechanic. I just dont remember what all needed blocked off and if this engine would have a port to hook into. Ive also heard that after market MAF sensors can cause issues as well but i have no way of checking that without just replacing. I prefer to test not guess. LOL Dad beat that into my head many years ago.
The Yukon runs great and does a fantastic job of towing my 2 standup mowers so Id like to get it free of these lights.
Appreciate what ever information you can pass on to complete a good smoke test. Also any other suggestions would be appreciated.
Thanks Rod

 

[strutaeng]

If you had a scanner that gave live data, you can see the sensor data as you give throttle and see if reported values jive.

You can also monitor fuel trims to determine if you have a vacuum leak or possibly something else.

But anyway, to smoke test it, just unplug any vacuum hose and power your machine. A nitrile glove over the intake tube serves as a simple plug. You should probably do it on a cold engine because sometimes intake manifold gaskets swell up when they get hot and the leak only occurs on a cold engine.

Since both banks are lean, you should also test the fuel pressure. Fuel delivery problems always affect both banks equally.

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

You are already receiving sage advice from the knowledgeable folks on this Forum.

Also, consider purchasing a Chinese knock-off Tech 2 bi-directional scanner (~$350) for your truck, and it will save you both time and money to diagnose and resolve issues that arise with your truck.

 

[nonickatall]

The most interesting question is, what codes did you have exactly?

Lean on both banks can be, MAF, airleak, evap, fuel pressure, but as well o2 sensors...

Please post the exact codes...

 

[DBacon]

Don't forget, the smoke can escape through a leak in the brake booster's vacuum circuit.

 

[Fless]

This is (was) a hit-n-run.

 

[nonickatall]

This is (was) a hit-n-run.

As we say in Germany: ingratitude is the world's reward

 

[rod7515]

Nope Nope Nope it was not a hit and run. lol. I was waiting for sometime in the winter to check this engine out. Codes are 171 and 174.
This vehicle is only used for towing my mowers from job to job during grass growing season. SO its been sitting most of the time since the first week of November. Well now its time to see if I can fix the Check engine lights before I start using it again. SO this week I plan on doing my smoke test. I see that there is a breather tube going into the intake on the rivers side which comes up from the back of the valve cover. I will push into there. I will use a rubber glove to seal off the front of the air intake between the MAF sensor and front of intake. Ive already cleaned the MAF sensor and it was just put on before I purchased this vehicle. Lets be clear about this engine, It has 255k on it. Runs fantastic but the Check engine light is always on. If I clear the codes the light is back on in less then 5 minutes of run time. doesnt matter if its highway or in town driving. It doesnt need inspected until June so thats not a problem.
Anyway thats my story and Im sticking to it. I do have a code reader but it doesnt give me live data however I can borrow one if needed.
Rod

 

[Fless]

With the ignition off the vent valve in the rear will be open, so you'll want to plug that somehow.

 

[rod7515]

Exactly where is this vent valve? Is it solenoid control and if so can I jumper it with a 12v signal?