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I have been spinning my wheels trying different things to find the vacuum leaks since I was getting P0171 and P0174 codes. (This truck is new to me.) Both banks 1 and 2 lean codes. I was thinking it was a manifold leak but didn't know for sure. I purchased a little smoke machine called Hypersmoke from Autoline Pro. Glad I did... I found 3 areas smoke was coming from. I totally missed the throttle body and plastic / rubber connection from the air filter / MAF tube was missing a hose clamp, major leak. I since I didn't have a large enough hose clamp I used some wire twisted up to stop that leak I found 2 more.
What are these parts? I think one is the EGR but the other I am not sure what it is. I need some help to figure out what these 2 parts are.
Suggestions and part names welcomed.
Thanks
small crack smoke was coming from. Is this the EGR?
very little smoke coming from this cap. this back hear close up of the the part at the back of the motor. tube connected to the part on the back of the motor.
What engine, what year? Where are you inserting the smoke?
Any air leak after the MAF sensor can cause those codes. A good smoke test will be done with the throttle blade open to make sure the smoke gets all the way to the MAF sensor.
Lean code causes
Low fuel pump pressure
Injectors getting plugged and need cleaning
Intake air leak past the throttle plate
Intake manifold itself warped or cracked
None of that stuff you have circled will cause lean codes
The EGR valve and the IAC are a no
You could spray that intake down with carb cleaner or Brakleen et al. to see if the idle changes
I would be checking the fuel trims to verify any possible intake leak or injector problem
Your fuel trims should be below 7 percent
I ran my Blue Driver OBDII scanner for the fuel trims and everything seemed to be in spec with what I was learning. If I was getting a lean code on 1 bank I would figure it was a sensors but both banks were having lean codes so it must be sucking unmetered air from somewhere. My first test was with 2.5 cans of brake cleaner and there was no change in RPM. Didn't seem like a manifold gasket leak since the brake cleaner didn't give me any RPM changes. I needed to get a smoke machine and look for vacuum leaks. I found 2 major areas where I was getting smoke coming out of the intake system after the MAF sensors. The big smoke leak was at the rubber intake where the throttle body connect. There was no clamp. The other area looks like it was leaking out the EGR valve. Looks like a small crack above one of the bolts. The idle air control had a very small amount of smoke coming from it.
I purchase an EGR and a hose clamp. I will be testing again after I replace fix these 2 issues. Clear the codes and test drive to see if the check engine light comes back.
( idle air control is the name of the part on the back of the intake. I didn't know what the name was and posted picture to ask )
You should look at Freeze Frame data. It tells you conditions when the code was set. Lean codes often set on cold engines (cold gaskets). Testing on a warm engine won't find those leaks.
That is a good suggestion. When I was trouble shooting I did just that. Got the codes when cold then cleared them and read the codes again after the motor was hot and the check engine light came back.
Got the codes when cold then cleared them and read the codes again after the motor was hot and the check engine light came back.
Not sure that you understand Freeze Frame. No offense. It stores the engine conditions in the computer at the time of the code setting. Doesn't matter when you read the codes, the info is stored. The parameters that the algorithm used to determine that something was off are the ones that are stored. Typically engine temperature, throttle position, engine load, RPM, etc.
It is a separate choice on most scanners. Here is a good explanation.
Example - a lean code that sets at low RPM is usually an intake system air leak. A lean code that sets at higher RPM under engine load is often a fuel pressure or injector issue. If you're testing for air leaks when you have a fuel pressure issue you'll be wasting your time. Freeze frame lets you focus on the right area.
Last edited by BareBonesXL; Oct 1, 2025 at 12:45 PM.
I took the truck to work today. 28 miles on the trip with no check engine light coming back on. I experienced the check engine light coming on after 10± miles from them being cleared before the repair.
I added a clamp at the throttle body to hold the rubber intake on better and replaced the EGR. There was a significant amount of smoke coming out of the EGR. Looks like it will be ready for smog out here in CA. once the system calibrates it self with no check engine lights.
The smoke machine was well worth the $75 I paid for it.
No offense taken. By no means I will say I know what I am talking about. I can work on cars and definitely am a novice with the my Blue Driver scan tool. Thanks for the link.
Lean code causes
Low fuel pump pressure
Injectors getting plugged and need cleaning
Intake air leak past the throttle plate
Intake manifold itself warped or cracked
None of that stuff you have circled will cause lean codes
The EGR valve and the IAC are a no
You could spray that intake down with carb cleaner or Brakleen et al. to see if the idle changes
I would be checking the fuel trims to verify any possible intake leak or injector problem
Your fuel trims should be below 7 percent
This is a gift truck with 280,000+ miles on it. I have sprayed down the manifold with brake cleaner and no noticeable change in RPM. My focus was the manifold with this test. I used 2.5 cans of spray. I need to research how to check fuel pressure. I posted a new post with more information.
Any suggestions?
This is a gift truck with 280,000+ miles on it. I have sprayed down the manifold with brake cleaner and no noticeable change in RPM. My focus was the manifold with this test. I used 2.5 cans of spray. I need to research how to check fuel pressure. I posted a new post with more information.
Any suggestions?
You have to watch fuel trims while spraying. The computer reacts too fast to let the RPM change.
And...Freeze Frame. The old school diagnostics don't work well. You have to let the computer do the work.
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