Low boost reading

[jebadiah04]

Im on a trip across a couple states and for some reason i cant push over 13.3lbs of boost. Cruising at 70mpg im holding 6.5 lbs and vgt reading says 44, no movement.

If i crush the gas boost reads 11.3 and vgt goes to 14.

This appears to be true every time i try it.

I should see at least 20 lbs under wot.

Any ideas?

Truck is running good.



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[jebadiah04]

I should also note that the rubber line off the manifold to tge sensor is intact. I cant see any leaks either

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[blacksnapon]

You'll get max boost under a load at WOT. If you're already at 70 mph, you wont have as much load when you go wot as you do at say, 10-15 mph.

 

[jebadiah04]

Tried it at all speeds. Most i get at wot from any speed is 11ish. Im thinking vgt is stuck or i got a small hole in my intercooler or something weird. Like i said. Truck is running ok. Seems to have power. So im a bit confused

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[blacksnapon]

If you can get a scanner that can read data, look at MGP (manifold guage pressure). From what you describe, good running and power, looks like something isn't reading actual boost.

 

[jebadiah04]

Will the scangauge read it?

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[blacksnapon]

Dont know on the scangauge but the PID is MGP on the IDS.

 

[m-chan68]

Where are you getting those readings from? What is your VGT duty cycle while idling?

 

[jebadiah04]

From my scangauge. Its at 44 while idling

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[jebadiah04]

Im thinking the vgt has gotton stuck/worn out. Turbo has been whining for a while now. I have the chance to pick up a brand new stock for 300 bucks, so ill grab it. And even if i dont NEED it. Ill swap anyways. The issue is, im 2 time zones away from home. So ill have to swap it on my next rotation, so ill probably just tune my truck back to stock to be safe and take it easy home.

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[blacksnapon]

generally, you look for 75 low idle, 43 at hot or high idle.

 

[jebadiah04]

What things can cause low boost reading. Theres a sensor coming up from the manifold, i would imagine theres a good chance that could do it. Theres also a sensor that comes off the exhaust manifold that i assume checks for back pressure. Is that potentially going bad?

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[blacksnapon]

the exhaust backpressure sensor is mounted to a tube coming off the driver exhaust manifold (a major contributor to boost calculations). Make sure the tube isn't plugged up.

 

[jebadiah04]

Just pull the sensor off and fire the truck up? Lol

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[blacksnapon]

Just pull the sensor off and fire the truck up? Lol

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Remove the sensor and run a coathanger through it.

 

[jebadiah04]

No change...other ideas. Can scan gauge test these sensors?

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[blacksnapon]

egr valve, sticking vanes on the turbo, map sensor and/or hose, map port plugged on manifold. Any chance its overheating, or "thinks" its overheating?

 

[jebadiah04]

No, it never reads over 200. Im starting to think the turbo veins are stuck.

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[jebadiah04]

Finally figured it out, the rubber hose that runs from the manifold to the MAP sensor had a cut in it. Looks like wear from the clamp. Cut about 1/2" off the hose and reinstalled. Now its fine.