Well my car has been doing this for a few weeks now, and after taking a decent road trip last weekend it has gotten on my nerves a bit. In gears 1-3 the second turbo comes online like a charm, I can feel the transition just like normal.. and then the second one comes on. But for some reason, in the upper gears (4th and 5th) the transition is anything but smooth.. in fact sometimes there is no transition. For example, I drop into 4th to do a pass on someone, first turbo boost like normal up to about 4200RPM.. then the car just loses all power.. feels like someone pulled the plug. That only happens when I have the pedal to the floor though, if I am running say 1/2-3/4 throttle it will hesitate for a split second and then pick up again. Sometimes it even cuts in and out.. like turbo #2 can't decide if it wants to work that day or not. It is very hard to describe what is happening without riding in the car.. but in the lower gears it has full power to redline. I have not gotten to taking a look at the rat's nest yet, but I have a feeling the problem lies in there with a solenoid. Any ideas or guidance? TIA..

Matt
93 SSM

 

How many miles are on your vacume hoses, if they are old its more than likely the problem, i have had the same thing, do you have a boost guage? That will tell you a lot also. Check out: http://cyber.virtualrep.com/hosetech...g_products.tpl

for some new silicone hoses for the job.

 

Let me know if you resolve it. I have a similar problem, but it happens in all gears. The strange thing is that it doesn't allways happen. Sometimes everything works great. My first guess was that it may be related to an electrical problem I'm having (bad cable or connection between the alternator and battery giving me some headaches). I thought I may be losing spark.

Let me know if you make any progress. It pisses me off to have a fast car that sometimes is slower than my wife's diesel (maybe that's an exaggeration).

 

okay, I'll bite.

the fact that it only happens in high gears lends me to think it is a check valve designed to hold vacuum. as the boost comes on it starts to blled into vaccum system, longer and more boost makes it happen faster until the point where there is not enough vacuum to properly operate transition.

so, my guess for the day is the check-valves on the UIM that supply vaccum to the system, I think there is only one, maybe 2.

WHen it won't switch, try letting off the gas and going to vacauum, then try it again, if it switches over you know that is the problem.


good luck, let us know how it pans out.

 

Genuis.. that is precisely what happens, I have already tried that last weekend. If I back off the gas just a tad bit and then slowly get back on it.. BAM.. there's turbo #2. Sounds like I have some work ahead of me, I need to figure out where that check valve is.

Matt
93 SSM

 

if memmory serves me right they are on the back side. but check a vacuum diagram, they are all over the net.

 

I just recently had that problem fixed. It was a pooped off hose under the intake plenum. My second gues would be soleniods since my mechanic thought that would cause my problem also!!