# 740d No Boost - Turbocharger issues



## walkernight88 (Jun 3, 2018)

Hello there.

Lately I got some issues with boost/air intake. After rebuilding the 740d (N57 with 2 turbos) I got a SH pair of complete turbos with manifold. The problem is that the car never pulled as I tought it had an issue with the transfer box. Yesterday trying to diagnose it I found that the small turbo had the axle broken. Replaced the turbo with another one, still no boost. At idle ISTA reads 35 kgh and required is 50 kgh. Revving it up I don't hear any turbo, and boost pressure in ISTA remains at 1.000 mbar (drops to 950, raises to 1050), but required on map goes up to 2000mbar. I've check all the vacuum lines, found a broken one, I've replaced it. No changes. Replaced the two pressure converters, no changes. Took off the big inlet from the big turbo, I see it spinning. Checked for boost leaks, none. I don't understand why it doesn't make even 200mbars of boost. Visually, when somebody revs the engine, I can see the small turbo actuator moving up and down.

Going on the highway, the car accelerates like pulsating (revs in steps) and pulls like a tractor. I don't think it makes more than 100HP.

ISTA faults are obvious (3 faults: Glow plugs missmatch, Charging pressure too low, Air mass too low).









Any ideas would be super appreciated...


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## walkernight88 (Jun 3, 2018)

Update: Solved. The big turbo exhaust bypass flap was not closing completely, so small turbo was not spooling as required on low revs. Changed everything (Exhaust manifold, big turbo, actuators...) now works as expected.


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