Hi All, I own a 1987 GTS Turbo with intercooler, and hopefully someone can give me a bit of insight here. I have been having problems with the turbo lately. When the pressure reaches 0.7 - 0.8 the turbo starts "coughing". It seems to be blowing intermittently at that pressure level, which makes the engine lose power and the whole car vibrates as a result. It feels like the turbo is turning on/off with a 0.5 seconds interval. It may be that the turbo blows intermittently all the way to 0.8 pressure, but that the pressure differential between on/off only becomes apparent above 0.6, and not only at high pressures. And it does happen consistently either (i.e. some days it happens and some other days it doesn't), though it happens most of the days. All this smells like an electric problem, but any help is appreciated. I'm pretty lost here Thanks
The turbo cannot blow intermittently or turn on and off. It is just a shaft with two impellers that spin at a very high rate of speed. It sounds like you are having a problem with the overboost protection system. The maximum boost for the turbo system is 1.05 Bar. If the boost pressure exceeds that, the ignition is cut until the boost drops down, and then it is restored. This can be very abrupt, it feels like someone has turned off the ignition and then turned it back on again. If you keep your foot on the gas, it will happen at specific interval (.5 sec in your case) as the boost builds, the ignition is shut off, boost drops and ignition is restored. There are a couple of things that can cause this: The boost is actually too high due to a malfunctioning waste-gate and the system is functioning as it should, but your gauge on the dash is inaccurate. To check this, you can plumb a known good mechanical pressure gauge into the system and check the actual boost. If it exceeds 1.05 Bar, then you need to look into the wastegate function. The other cause of the malfunction is the boost pressure input to the ignition system. This may be telling the ignition that the boost is too high even though it is below 1.05 bar. There may also be another fail-safe boost pressure switch that cuts fuel pressure. Other turbo cars of that era (Saab for example) used a secondary switch that interrupted power to the fuel pump as a safety precaution. Do you have a factory shop manual and wiring diagram specific to your car? If so, that should show all of the boost sensors and switches
