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Discussion Starter #1
04 lb7 190k
Just got this truck a month ago, mostly stock, bigger down pipe and 5in exhaust. Not getting any smoke, pressure tested the intercooler, watched desired rail vs actual (no difference), waste gate works good, changed fuel filter, air filter, balance rates good, return rates good, maf reads around 390-400 wot. Only problem I have is a slight surge or lope at idle, presumably the fpr, could this cause the low boost? Or could collapsing fuel lines cause this? But I figured I would see a drop in the rail pressure. I have a video of a wot run showing my edge insight if anyone wants to help out I can send it to them somehow.
 

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A few more details, please.

You said you recently bought the truck but didn't say if the low boost issue came with it or was a new situation.

How confident are you the boost numbers you are reading are accurate?

Where is the boost sensor line plumbed into the system?

What does the PO tell you?

Best
 

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Discussion Starter #4
You said you recently bought the truck but didn't say if the low boost issue came with it or was a new situation.

How confident are you the boost numbers you are reading are accurate?

Where is the boost sensor line plumbed into the system?

What does the PO tell you?

Best
It came with the truck I figured it was as simple as a worn out fuel or air filter.

It's an edge CTS 2, I assume these are pretty accurate, it was always accurate on my lbz.

I haven't changed the plumbing for the boost sensor Its going from the factory location on an lb7.

PO?
 

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Po

PO is previous owner. You know, that guy we always blame for messing up our trucks:wink2:.

Regarding boost plumbing, I completely forgot the engine has its own sensor providing 411 to the ECM. I have an aftermarket gauge and understand readings are different, depending upon if the sample point for the gauge is before or after the turbo.

For my information, where is the OEM boost sensor located?

Although your Edge CTS 2 should be solid gold, could you use a MightyVac to pull vacuum on the OEM boost sensor and check for agreement with the Edge reading?

Often, when situations (like yours) turn into real head scratchers, it's a good idea to assume nothing and recheck all "known" aspects of the issue.

I believe it was Mark Twain who observed: "It's not what you don't know that gets you into trouble. It's what you think you know that just ain't so."

Finally, what performance issues are you experiencing that might be a result of lower than expected boost?

Best.
 

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You said the waste gate works, does that mean that you know that it opens, or that you know that it stays closed until it is supposed to open? a common low boost issue on the LB7's is the waste gate opening early and bypassing perfectly good energetic exhaust gas around the turbo reducing your boost pressure by preventing the turbo from spooling to full speed.
 

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Discussion Starter #7 (Edited)
PO is previous owner. You know, that guy we always blame for messing up our trucks[img= class=inlineimg]/forum/images/DuramaxForum_2016/smilies/tango_face_wink.png[/img].

Regarding boost plumbing, I completely forgot the engine has its own sensor providing 411 to the ECM. I have an aftermarket gauge and understand readings are different, depending upon if the sample point for the gauge is before or after the turbo.

For my information, where is the OEM boost sensor located?

Although your Edge CTS 2 should be solid gold, could you use a MightyVac to pull vacuum on the OEM boost sensor and check for agreement with the Edge reading?

Often, when situations (like yours) turn into real head scratchers, it's a good idea to assume nothing and recheck all "known" aspects of the issue.

I believe it was Mark Twain who observed: "It's not what you don't know that gets you into trouble. It's what you think you know that just ain't so."

Finally, what performance issues are you experiencing that might be a result of lower than expected boost?

Best.
I bought this truck from the stealership so the PO remains a mystery lol not knowing who owned it is a blessing and a curse.🙈

As far as the boost I believe the ecm takes the difference between the map sensor and baro to determine boost.
You said the waste gate works, does that mean that you know that it opens, or that you know that it stays closed until it is supposed to open? a common low boost issue on the LB7's is the waste gate opening early and bypassing perfectly good energetic exhaust gas around the turbo reducing your boost pressure by preventing the turbo from spooling to full speed.
Thanks for your comment figured out the issue. Wastegate opens at 15 psi. I figured it would partially open at a lower psi and then fully at its capacity. I plugged the line to the wastegate temporarily and was able to build 20+ boost. I stopped there because I was scared to over boost. As far as the wategate, I'd rather not buy a banks aftermarket replacement and I dont see any OEM wastegates online. Would it work if I put a manual boost controller between the wastegate and set it so it let air thru at let's say 23 psi?
 

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I bought this truck from the stealership so the PO remains a mystery lol not knowing who owned it is a blessing and a curse.🙈

As far as the boost I believe the ecm takes the difference between the map sensor and baro to determine boost.

Thanks for your comment figured out the issue. Wastegate opens at 15 psi. I figured it would partially open at a lower psi and then fully at its capacity. I plugged the line to the wastegate temporarily and was able to build 20+ boost. I stopped there because I was scared to over boost. As far as the wategate, I'd rather not buy a banks aftermarket replacement and I dont see any OEM wastegates online. Would it work if I put a manual boost controller between the wastegate and set it so it let air thru at let's say 23 psi?


so long as you set it so that there's no condition where you would over spool the turbo it should be safe. You might even find that something like the PPE boost valve would give you a little more boost for only 20 bucks or so, its basically just a regulator to the waste gate. I saw maybe 3 pounds of boost out of it over stock on my LB7, might do more for you since your popping the waste gate so early.

Keep in mind that there is a lot of energy stored in the intake system and turbo at high boost. the force against the compressor and turbine wheels is very large, as is the torque on the shaft connecting them. and the whole thing is spinning very.... very fast. the LB7's are pretty basic trucks, that waste gate is literally the only thing protecting that turbo from coming apart. So long as you have the ability to monitor boost, and can keep it around stock levels you should be safe, but that is a very risky component to gamble on.


Also, i got my truck from a dealer, they were nice enough to leave the PO personal information programmed into the navigation system, so we could have a chat one day about some of the weird shit he did to this truck >:)
 

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2003 lb7 230k 1 owner 🙂 with PPE wastegate valve, fass filtwrs/lift, edge tuner, afe intake, 4" exhaust, max boost at WOT seems to be barley barely hitting 18 psi. smoke at about 15psi.. Shouldn't I be seeing more boost? Edge tuner @ 3 drive mode. I feel it should be better, any theories on what my problem might be?
 
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