History:
’94 touring with 77k miles. The turbos were replaced around 7k ago, and the engine about 4k ago. Prior to the engine replacement the turbos ran fine.

Symptoms:
For one gear I get both turbos online just fine pushing 10-8-10. However, all subsequent gears give me 2.5 to 3 across both turbos. Sometimes, the secondary turbo will go into a fit and start stuttering down to 5 before I lose boost. If I keep off of the secondary turbo and just boost the primary, I can get a full 10, but as soon as I hit the secondary its gone. Now, if I stay at vacuum for a minute or two, the turbos go back to normal.

Guess:
A collapsing solenoid, but which one?

Any ideas or suggestions? Money is VERY limited, so anything that could be done without taking the car in would be wonderful.

 

it's probably a TCA solenoid. It's the one bolted on the ACV. You need to remove upper intake manifold. You will see it as soon as you remove it. It has some kind of metal shield over it. It's the one that usually goes bad and gives those sympthoms because of all the heat.

 

Could you be more specific? Part number, picture, or a page from the workshop manual? Sorry. It's been awhile since I've worked on this car.

 

http://www.autosportracetech.com/RX-...leshooting.htm

 

Going through that URL, it sounds like the vacuum chamber:
I'll try the test they describe, but I think that describes the problem pretty accurately. Anyone else concur?

 

I've been having somewhat similar boost problems. Primary turbo boosts fine, secondary boosts very little if at all. I'm confident its the turbo control actuator (TCA) but I've seen no point in testing it since I dont have the cash to replace it right now. Blew my AST last night so I'm going with the ASI Racing AST which is the best one and still have to checkout the rest of the cooling system to make sure nothing else is wrong.

 

Does anyone know where I can find info on testing the various parts of the turbo system? For example, how to test the TCA, pressure chamber and vacuum chamber?

I still need to pick up a good vac/pressure pump. What's a good cheap one?

 

Well, I removed the check valve that was suggested at the URL above and still no go. Now I get a sound when the turbos are ready to work again. I have to be at vacuum for a few seconds and then it'll return to normal.

I plan on checking the TCA next. What's the easiest way to get to it? How about the TCA solenoid?

 

I've been playing with this problem some more and have more information.

First, the problem only occurs if I hit the secondary turbo. If I keep below 4,500 RPMs then I can choose which gear I want to go all the way through. However, if I do it in 4th or 5th, the pressure from the secondary tapers down to 3psi.

Second, if I lose the turbos and it sits at 3psi at WOT, all I have to do is get the RPMs until 3k to restore them. I can do this either by slowing down, up shifting, or just disengaging the clutch long enough to have the RPMs drop.

Does this sound familiar to anyone?

 

James,
I am willing to bet money that it is the TCA vacuum solenoid, and or some of the supporting hoses. If you would like to test this, disconnect your boost gauge and plug the manifold. Then place a tee in between the TCA vacuum line bridging the rat's nest to the TCA hard pipes going down front face (under air pump) of the motor and plug in your boost gauge there. There are two hoses, and without looking at a diagram I cannot tell you wich one it is, but that both will be usefull to tap into. You will have to loosen the pressure chamber to get to them, and you may need some long needle nose pliers to pull them off.
You will see either boost or vacuum, but if you see both or none, then you know you have a problem. Most of this will take place at or before 4500. Also, to answer you below 3k thing, the car stays in dual mode until you dip below 3K. You will see this.

 

For the TCA solenoid, is the part number N390-18-741? I'm trying to put together the vacuum diagram and the parts diagram and I'm not sure if it's the right one. If it isn't, does anyone have the part number?

 

Okay. So I searched out the turbo control solenoid part # (N3A7-18-741) and installed it. I broke the double throttle solenoid along the way (1480-13-240A) and had to replace that along with the obligatory broken hoses. I still have the same problem.

I'm about to give up on this problem and just deal with it. Anyone know what the issue could be or could come by Irvine, CA to take a ride? Except for the TCA itself, I'm at a loss.

 

A good tool to use is http://www.mityvac.com just about any automotive parts place will sell this or know where to get one.
A good explanation of the TCA is at http://www.autosportracetech.com/RX-...aryExplanation down a couple paragraphs to "Turbo Control Solenoid(s) / Actuator". The important thing is that there are two solenoids, one vacuum and one pressure to move the TCA.

 

richel,

Does your exhaust note change during this period of instability?

 

I here a relationship between low and high vacuum conductions within the thread. I would just make sure the pressure tank and the vacuum tank are doing their jobs. I would think there is a difference in WOT time. You could just be running out of vacuum.

 

wel richelesro guess what brother I have the exact answer to your problem.Check your charge control solenoid.and all of the vacuum lines that go to it.The turbo control solenoid is controlled by two solenoids.Therefore if one goes out you will be able to boost but more sulggishly.Its not your problem.Your problem kicks in at 4500 rpms at the transition point and thats when you lose all of your boost or a majority correct?
You should also hear a weird noise like a valve of some sort shuts and then your turbos sound differently as well as getting a weird boooo sound once you let go f the gas instead of hearing the pssst sound of the blow off valve.Your boost will also return to normal if you let the car slow down to below 3000 rpms.
You know how I know all of this? Becuase I had the same exact symptoms.Check your solenoid as I had a split in a vacuum hose going to the charge control solenoid which is located underneath the Upper intake manifold.