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Discussion Starter · #1 ·
Hello,
New to the forums so my apologies if this thread is in the wrong location but here’s my issue. Recently bought an 2004.5 lly Sierra with 180k miles, completely stock. Under medium/hard acceleration the truck will cough/sneeze and cut power for a second blowing more than normal black smoke. Doesn’t happen everytime but I feel this issue is beginning to occur more and more. I’ve recently replaced air filter and fuel filter, and injectors were done about 30k miles ago so we can rule that out. I’ve been reading and only found two possible reasons. One forum said this issue is EGR related and the intake pressure is exceeding exhaust pressure. The other said the issue was fuel related so I will do the bottle test before anything else. I have a video of this noise/ power loss I will attach if I can find out how. (Not sure if you can attach videos) If anyone has any input or advice/knowledge on this issue your help would be greatly appreciated. I will update shortly.
Thanks
 

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Best way to share a video would be to upload to YouTube and put the link here.
 

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Check for chaffed wires in the harness going over alternator.
 

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Google ice pick repair on the injector plugs.
 

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Do you have anything to monitor with? It almost sounds like maybe the turbo is doing something, like the vanes are opening up when they shouldn't be. Might watch vane position and see if it moves a bunch when that happens or something
 

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If not the turbo vanes doing something crazy maybe a boost leak that is opening up under pressure? Google Duramax boost leak check. The boot on the inlet of the intercooler gets a lot of oil from the PCV.
 

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Discussion Starter · #8 ·
@05 3500 2wd @DMAXfirefighter
My first thought was a boost leak and I did a quick over of the hoses but I’ll check again. What threw me off though was the fact that after this power cut and “blowoff” I can continue to build pressure and boost. It cuts mid acceleration then afterwards it’s back to normal. If it was a boost leak would I be able to build more boost after this point of blowoff?
 

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Boost leak would open under pressure, not do what your video sounds like. To me, its the vanes allowing it to work properly-but intermittently opening then returning to where they are supposed to be, effectively just dropping boost then coming back
 

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Discussion Starter · #10 ·
@DMAXfirefighter
Would you recommend just going right ahead and replacing the vane position sensor? Or maybe the sensors not the problem and I’m having a separate issue which is giving my sensor wrong AR ratios? Any common troubleshooting ? Any tests I can do to further diagnose the exact issue?
Thanks again
 

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Without first knowing what it is doing for sure, I wouldn't recommend just throwing parts at it. Need to get something that will show you data and you can see what the vane position is doing, what the fueling is doing, what the map/maf/baro sensors are reading. Using a CTS2 or something like that you can easily watch the vane position and see if it is dropping out when this is happening
 

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Discussion Starter · #12 ·
@DMAXfirefighter
Little update: I have pulled the EGR valve plug and drove about 30 miles with no issues, not sure if I’m speaking to soon but this has seemed to fix my problem. Going to try to get something to read my gauges but trying some things along the way.
Could the EGR have been my issue, telling the turbo vanes to act incorrectly?
 

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Probably could, if the valve isn't operating properly and allowing a huge dose of exhaust gasses to flow into the engine it could make it do strange things. If that seems to have alleviated the problem, maybe its time for a delete?
 
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Discussion Starter · #14 ·
@DMAXfirefighter
Put another 30/40 miles on it with no issues or engine light. I had ordered one last week and it came in this morning so I think so. I will keep send updates soon when the delete kit is in.
 

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Discussion Starter · #15 ·
Ok so EGR delete went in on Thursday 10/8. Immediately after I noticed a similar power loss like the problem had come back. Seemed to come and go no worse than before. Yesterday I was out for lunch and noticed a new noise and inability to build any pressure. Returning home my engine light came on and it read p0234 I believe, overboost code. Digging around the engine bay I noticed that my delete tube had pushed the elbow of my Ybridge completely out. Maybe this y bridge elbow was loose the whole time and this was my issue? Or maybe this is something new and my delete wiggled it out. I’m not sure but to my understanding this is now where I’m loosing all pressure. My next step I think will be ordering a welded one peice y bridge since I read these elbows are a pain to get back in and never really stop in even with the aftermarket strap. What does one do in the meantime ? Can you drive safely with a loose ybridge elbow? Or is that a terrible idea?
 

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Likely it popped out after the delete. The egr system holds that elbow in very solid and wouldn't let it move out in factory form. Depending who/where your delete pipe came from, some of them don't have the support to keep the elbow from popping out. Yes they can be a pain to get wiggled back in, but the strap has worked from my experiences. Not a good idea to keep driving with the elbow popped out since it won't build any boost pressure
 

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Discussion Starter · #18 ·
@CalebGmax @DMAXfirefighter my welded y bridge came in today. I have been driving the truck here and there, my engine light went off and stayed off for the most part. It came on once after hard acceleration and went back off. As long as I didn’t build much boost I had no issues. Hoping this leak will cause an overboost and this fixes the issue
 

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I don't think a loose bridge will cause an overboost code. Only time I have run into the overboost code was a couple times several years ago. I was in the throttle hard, then let off abruptly, then back in it hard. Something about that combination in my truck it what would do it. But, its an LB7 and that was with a canned tuner, not EFILive tuned, so hard to say if there was a parameter set different that triggered it or what
 
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