Tech Tip No. 5

Ned Ritchie

Originally published in the quattro quarterly

Copyright 1997

LOSS OF BOOST PRESSURE, Part I

My Audi Turbo engine has lost it's power, and no longer has the boost pressure it had before.

The reason for this problem can be divided into two categories: Physical & Electrical. In this Tech -Tip I will discuss the physical aspects and save the electrical reasons for Tech-Tip 6.

The most common reason is that all the compressed charge air is not getting to the engine. It is leaking out somewhere and will cause a fuel rich condition . The engine will run rough and misfire under boost and you may see smoke from the tail pipe. Check the following places for leaks or split hoses:

1. The hose between the intercooler and the intake manifold. On the 5000/200 models the hose is accordian shaped, about 7 inches long, and 3 inches in diameter and rapped by steel rings. The insidious thing about this hose is that most splits occur on the under side while the top side looks new. The charge air path is coated in oil from the crankcase oil breather system and some oil pools in the bottom of the accordian pleats. In time the oil softens and weakens the rubber and one day it just gives way under boost. Note: Under idle conditions the split may close and the engine will run normally!

2. The hose between the turbo and the intercooler.

3. The seal between the intercooler core and the plastic end tanks. (5000/200 models only)

If the area where the end tanks join the core is oil soaked suspect a leak. If this has happened the engine will also idle slower and stall and be hard to start. I'll cover this in another tech-tip.

Low boost pressure can also mean a wastegate problem. The wastgate's normal job is to keep the boost pressure from becoming excessive; however, the following could happen:

1. The valve can stick open.

2. The seal for the valve can crack.

3. The spring can break.

4. A bad turbo. It may not be spinning. A good excuse to upgrade to a better turbo.

5. A plugged catalitic converter.

6. The wastegate is not receiving the correct pulsed pressure from the computer.

             (This topic is discussed in Low Boost Pressure - Part Two)

INTENDED ACCELERATION ^®

© Copyright 1997-2000 by Ned Ritchie