intermittent boost problem
 

First of all, hello to everyone as this is my first post here. I recently bought a 93 Touring with many mods and still running the sequential turbo setup. Unfortunately, I'm already having problems with the second turbo coming on. The problem seems to occur mainly in first gear, but it doesn't happen all the time. Sometimes in higher gears, the second turbo will seem to come on, but then I get a surging as if the boost pressure is quickly rising and falling.

I have started troubleshooting and found a split hose at the air bypass valve, which I replaced. The check valve in the pressure chamber feed line also appeared to be bad, so I replaced it. Niether of these seem to make any difference, so here are some details that might help:

Vacuum at 750 rpm (warm engine) is ~11in.
Revving in neutral produces no boost at all
Primary turbo reaches 10 psi, but it takes it until 4000 rpm to do so
If secondary comes on, I get 13 psi to redline
If secondary doesn't come on, I get 10 psi to redline

I'm really worried about the fact that I get no boost at all if I rev the engine in neutral. All the troubleshooting guides point out in the early steps that you should see 4 psi. However, I have not found any information regarding what to do in the case that you don't get any boost in neutral.

The vacuum seems low, but the engine is a PFS streetported engine. So, I'd expect it to be a little low. Is 11 in. too low?

If anybody has any thoughts on this, I'd appreciate it.

Gary

You should not get any boost in neutral. When yuo gas it in neutral your boost guage should go from -14Hg to about -9Hg and thats it. This is b/c you have no resistence on the system. YOu will never get boost if it is not moving under power. I hope this helps a little.

Actually, you should get about 4 lbs of boost in neutral at around 4k rpms. If not, you have a boost leak.

true

So, if I have the symptoms of a boost leak, but no leak, are there any other possibilities? I checked all the hoses and only found one of the 1" hoses split. After replacing it, I still get no boost in neutral. I have driven around a bit since then, and so far I haven't seen the problem again, other than slightly low boost on the primary.

Welcome to the wonderful world of sequential turbocharging. There is a big rats nest of tubes under the intake manifold. Did you check all of those? Aside from that there are a number of solenoids and one way valves, also the pressure and vacuum chambers. Get it? Find someone in your area that is good with rx-7's and introduce yourself. You'll be seeing them often.

I have checked all the vacuum lines and one way valves. I somehow forgot to check the air bypass valve itself, which I plan to do in the morning. I wouldn't be surprised if its leaking, based on what the car is doing. We'll see...