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?

 

[nonickatall]

It is direkt behind the fuel tank, between axle and tank. You can reach it laying unter the car. 5 Minutes to disassemble. Cost 20$.

But i am not sure that this is your problem, because the so called EVAP system which is the vent valve, a purge valve direct on the intake, and a pressure sensor, plus the charcoal tank throws errors when one of this valves or sensor fail.

And if the vent valve stuck open, you have a leak, but so small that it should not lead into P0171 and P0174 if not something else is not ok.

I would check for intake leaks with smoke test, then check MAF sensor, and o2 sensors. Have you swapped the airfilter? And check for the correct fuel pressure. What is about coolant temperature? Is the coolant temperature normal when warm?

Something makes that you mixture is to lean, to lean to be adjusted by the ecm.

Because its on both banks i would suspect 1. air intake leak, 2. Fuel pressure, 3. MAF Sensor, 4. Two defekt O2 sensors.

 

[rod7515]

The reason I want to do a mole test at the intake is to see if the intake has any leaks. Does the vent valve need to be blocked off to do this? I. Not trying to check for EVAP leak. I am suspecting an intake leak.
Rod

 

[strutaeng]

The reason I want to do a mole test at the intake is to see if the intake has any leaks. Does the vent valve need to be blocked off to do this? I. Not trying to check for EVAP leak. I am suspecting an intake leak.
Rod

The EVAP vent valve under the truck? The smoke shouldn't make it that far...

The purge solenoid valve is normally closed, but if you want, unplug the line to see it leaks smoke out. There's a diaphragm inside the purge valve that can tear. However, in this case, the system will run rich because it's always sucking in fuel vapors.

Edit: lean on both banks (with fuel trims on both banks being the same, and percentage lean through the RPM range) is almost always a fuel delivery problem. If smoke test looks okay, hook up a fuel pressure gauge.

 

[nonickatall]

Thats true, that takes time, but I would not test the vent valve with a smoke tester.

Just start the car and blow pressure in the hose, which should be airtight while engine running.

And additionally as I wrote. Its not necessary to test the EVAP system with a smoke tester, because it should throw an error with a malfunction.

Just try this. Open your fuel cap and let the engine run. You should receive a Message: "Error: fuel cap open" or similar in the instrument cluster.

But attention. The EVAP self test only runs on certain conditions. I don't remember exactly, but something like: "fuel tank filled up to 3/4", or something.

The smoke test is more for intake, between MAF and trottle housing, intake itself, attached hoses, purge vent, throttle body, dipstick, oil cap and so on.

 

[Fless]

It will help your smoke test to have the system as closed as possible. You can apply 12v to the connector on it to close it, polarity doesn't matter as long as it's out of circuit. Here's a pic with the evap vent valve shown and circled in red (spare tire and fuel tank removed for clarity):

 

[rod7515]

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...

I didn't drove the vehicle over the winter since I use it only to tow my mowers 3 days a week from April thru November. So this spring I did a leak test and found no leak so I went and replaced the MAF because i was getting some weird numbers. That cured my CEL light for almost 2 weeks then this week I got a P300 random/multiple cylinder misfire. Later in the week probably about 25 more miles I got a P2135 throttle/pedal position sensor/ switch a/b voltage correlation code. I cleared them out and the my P300 came back on along with a P0420 catalyst system efficiency below threshold Bank 1.
The good thing is the lean on both sides seems to have been taken care of with the MAF. And yes these codes did come up a few times last year with the exception of the P420. This is the first time I remember seeing it.
The misfire seems to only set when going up a long incline hill but I never feel a miss. The coil packs were replaced before I bought it. Any help would be greatly appreciated.
Rod

 

[nonickatall]

First i would check, if all ignition cables sit tight...
Sounds like one is loose..

 

[rod7515]

First i would check, if all ignition cables sit tight...

Sounds like one is loose..

When you say ignition cables where are you talking about?
Rod

 

[nonickatall]

The cables from the ignition coil to the spark plug. I would especially look on the plug on the spark plug...

Excuse my bad English...

 

[strutaeng]

Spark plug wires?