No boost at all on seq turbos
 

So, as the title says, i´m having trouble finding a way to get my car to boost again..

I have done the simplified sequential with full emissions removal, running a pfc ecu without wastegate and precontroll solenoids (running mbc´s instead). Tested every solenoid and replaced every vacuum hose about 2 months ago.

Car was boosting just fine, a little sluggish but hitting 9 - 8 - 9 in third gear without problems. In one run the car boosted until about 4500 rpm and suddenly boost dropped to 0 and never boosted again.

I´ve already checked:

Boos leaks (presurized the whole system and holds 20 psi)
Both vacuum and pressure chambers hold vacuum and pressure
Both wastegate rods are in place
Checked for loose hoses under the uim
Disconnected the wastegate lines to get full boost but is still getting 0
Plugged both abv and crv to see if they were leaking but no
No exhaust leaks
Primary turbo spins when i start the car and also by hand without effort.
Charge control valve stays closed until 4500rpm but still no boost after that rpm.

Could this be my primary turbo not building boost? I find it hard to believe since there is not much shaft play and turbo spins by hand without issues. Is there a way to see if wastegate flapper is closed without deassembling the turbos?

Car has 50k miles, it´s been rebuilt and running on stock twins with dp, cb, filters and fmic.

I'd suggest reading through the following link. Even if it doesn't solve your problem it's a great source for troubleshooting the twins. Some of it will not apply to you since you're non-sequential.

Troubleshooting

When you say you pressure tested the whole system....What does the whole system mean? The Y-pipe is a common source of failure. Are you running the 99 spec y-pipe or the 93 with a coupler? If you have the 93 Y-pipe check the coupler to make sure it hasn't either split or popped off.

-Dan

The only way you can get no boost is a boost leak. Period. Any of the sequential controls won't come into play, even with the sequential system jacked up you should still get 7-8 psi.

Dale

My setup is simplified sequential as I stated, I have the Pettit upgraded 93 y pipe with a silicone new coupler.

Anyway as instated, I put 2 caps on each turbo inlet, one with a air bleeder and applied compressed air and it holds 20 psi without any issues. So I am 100% sure I don't have a boost leak. I've had other turbo cars and turbo leaks with this same car and know how to recognize one. I've already seen that link and applied every step on it without any luck. Dale, if the wastegate would get stuck open I would still get some boost?

Start by diagnosing the following:

Turbo Control
Charge Control
Charge Relief

You can see how they operate here:

Turbocharger Overview

For instance, if the primary turbo isn't isolated during the initial part of the boost pattern, it will flow over to the secondary which is venting through the Charge Relief during the first 4200 or so RPM's. If the Charge Relief doesn't close, at 4200 or so RPM's, then it's still venting all your boost. Likely you messed something up doing the Simplified Sequential so you need to go back over your work.

Do you think I've messed something up in my simplified since the car was boosting ok for a while and suddenly stopped doing it? I've got a friends dyno 10 blocks away and got to test the car yesterday, until 4500 rpm air doesn't vent trough the secondary inlet or the charge relief. After 4500 air starts venting trough the secondary turbo inlet.

If the turbo control is not working, could it redirect all the exhaust gases so that my primary doesn't spool enough to build at least some pressure? Even though I've checked visually and manually that both turbo spins freely, I don't get any spool noise

there is no way that you can test if you have a boost leak unless you block off the intake ports at the engine some how. either one or the other rotor will have exhaust overlap and the air will just escape.. unless you have a really nice throttle body that doesnt leak a drop, in which case you arent testing the intake manifold and its maze..

either way.. its a boost leak or both turbos are completely seized.

That remind me of when my crossover pipe popped off due to a lose coupler, 0 boost after that.

I appreciate everyone triying to help me with this, but even tough i don`t have too many posts in the forum doesen`t mean i don`t know how to diagnose my own car. I`ve had some boost leaks before in this car and was able to diagnose them without any issues.

If i say im 100% sure my car has no boost leak, period. Primary turbo won`t spool enough to build pressure. I`ve removed the uim and checked solenoid connections and hoses and everything was in place.

I`m relating my boost issue to an exhaust problem. Turbo is not getting enough gases to build pressure. I`ve read other posts thinking it might be the wastegate stuck open, but i`ve tested both of them and they open and close ok. Both actuator rods are in place.

If anyone could help me and say if a faulty turbo control valve might cause this problem please let me know before i deassembly the turbos again, and in the case i won`t find anything wrong, convert them to non seq.

Thanks,

I know you say there is no boost leak, but what youre describing sounds like exactly that. Are you running a stock intercooler? If so, check the hot side pipe, but actually remove it and feel the rubber all around inside etc. This happened to me once and I made a post like yours, turned out everyone was right. boost leak...

So I'm not going to jump on the boost leak train because I had the same problem and it wasn't a boost leak. Check your electronics and make sure nothing is grounded out or cross wired. When I had my issues it was the boost control solenoids. Their wires had worn down and the coppers were crossing and shorting out. Once I fixed the electrics the car boosted just fine. Over-boosted actually to 13-11-13 to be exact because I had custom "pills" machined for my boost control.