Date: Wed, 01 Dec 1999 17:49:13 GMT From: supersambanopsameja.com Subject: Re: classic 900T early waste gate dump
In article <uGGwv8tN$GA.348nopsamnbbsa02>, "RWS_1" <RWS_1nopsamail.com> wrote: > 88' 900Turbo spg - Garrett > > When I step on it, I think the waste gate seem to be opening prematurely. > The turbo gauge only comes up half way in the yellow zone instead of to the > top of the yellow. The engine runs smooth except for full throttle or mid > boost range. It occasionally runs perfect when full throttle is applied, > full boost is indicated at this time. Occasionlly at ideal, the (three > vacuum line and two wire) solenoid valve mounted next to the coil has > chattered (opened and closed rapidly like it's confused). The solenoid > valve passed the "Haynes" shop manual test. > I believe the APC could be sending a bad signal, maybe a bad knock sensor. > Does anyone have any ideas or experiece with this? > Thanks > Yes lots of ideas and experience of this problem. The first step is to verify if the problem is with the APC system or the wastegate actuator(the round can with a rod going into it on the bottom front of the turbo). This is easy to do; 1) Pull of the hose going from the solenoid into the wastegate actuator. It doesn't matter what you do with it so just secure it somewhere or take the whole hose of. 2) Go for a drive and gently feed in the throttle around 3000 rev's. You should see the boost gauge fly up into the red. If it doesn't the first time try a little more throttle but be carefull. If the needle goes past about 1/2 way through red you will hit the overboost switch which shuts down fuel supply i.e. a sudden and drastic loss of power. If these things happen then the wastegate actuator is mostly OK and the problem is with the APC system. If the actuator is screwed you may get awfull rattling noises from the wastegate on full throttle and only get decent boost at full throttle and loads of revs. Remmember you should see big boost from 3000 revs and it should really kick you in the back. If you suspect the wastegate check that the actuator rod is actually securely connected to the actual wastegate of the turbo (The big dirty bit connected to the exhast manifold). The split pin that holds things in place may have broken off. You can pull the rod towards the turbo i.e. away from the can part of the actuator, to verify that the spring is actually doing something. You should get a lot of resistance. If you find it easy to pull the rod several mm then the spring may well have failed or be worn. If it feels a bit slack then having past the first driving test you can verify if the actuator spring is weak. This may require several drives. What you need to do is too adjust the length of the rod (i.e. make it longer) so that when driving you don't hit the overboost switch. In doing this I found that the standard actuator I had couldn't hold in 1 bar boost (about 1/3 way into red). What happens is that the back pressure in the wastegate pulls on the spring and hence opens the wastegate letting out the boost above 4000 revs. If you suspect a weak spring you will see the same effect even if you set it around the end of the yellow. Remmember of course that with the hose reconnected the actuator spring is then being loaded from the air pressure in the hose as well. A good actuator should either stay at a constant boost or always give rising boost levels(i.e. if the spring is strong enough back pressure in the wastegate will never open it) as the revs rise (it should actually really give the latter case as long as the rod isn't so long that the wastegate is always open). With the hose reconnected the air pressure feeding into the actuator should of course give a constant boost level except when the APC system has decided to start letting off. A lot of people don't realise it but the APC system is actually feeding some boost down to the actuator all the time. It does this to smooth the on slaught of boost and torque you get if you ditch the APC system. In my own car I don't have the APC and I get 1 bar of boost at 2500 revs with no turbo lag at all (as long as I am above about 2300 revs when I hit the throttle). If after all this you find that the actuator is OK, then your problem resides with the APC system. I will save you alot of trouble by saying that it is 99% certain that the pressure transducer is faulty. Before ditching the piece of crap that is the APC I went through 3 of emm. BTW if you do decide to ditch APC you will have alot of work installing a decent intercooling system, but that is another story. Happy Saabing. Neil Sent via Deja.com http://www.deja.com/ Before you buy.
 |
 |
 |
 |
 |
