Turbo Precontrol Not Functioning
 

Hi everyone!

This is my first post on this forum, and I must say, it is a bit of a dream come true. I never thought I'd own a 3rd gen, but it finally happened about a year ago. I owned two 2nd gens years ago, because I couldn't afford a FD but had to have a rotary. Unfortunately, the one I ended up with is having secondary turbo issues. Hopefully some of the gurus here can help me out.

After a lot of testing, I've determined it is a precontrol issue. No matter what I do, I cannot get the precontrol actuator to open without the use a hand pump. If I use the hand pump to manually open the actuator on a test drive, the transition at 4500 feels seamless with a gentle increase in power. If I put a boost gauge on the side that runs to the solenoid, I get ~8 PSI. When I hand test the actuator, it doesn't move until 9 PSI, so I guess I'm 1 PSI of a good time. Anyone ever seen this? Also, I have checked primary boost in numerous places and get a 10-11 PSI.

Any input would be greatly appreciated.

Sounds like your turbo precontrol solenoid valve isn't working correctly.

Assuming that your car has a 1993 or 1994 stock twin setup, and that the hoses are connected correctly, the precontrol actuator has 2 hoses connected to it, one from the solenoid valve (which controls vacuum from the manifold) and the other from the primary turbo compressor housing (which supplies pressure). The relative balance of vacuum and pressure between the 2 determines the position of the actuator. Is the hose from the primary turbo compressor housing to the actuator OK? Does it have a stock restrictor (pill) in it? If it is OK, then your problem is with the other line, somewhere between the actuator upstream to the solenoid valve or beyond. Have you tested the solenoid valve?

The solenoid itself does not have a reputation for failure.

What is your boost pattern?

You are saying "precontrol' but I think you may be having problems with the turbo control door. Precontrol is to pre-spool the secondary turbo to get it up to speed, if something is funny with that you could have a drop in boost at transition then come up to full boost. If you don't have good boost up top it's usually the turbo control.

TC uses vacuum and boost and check valves, all things that can fail and make it not work.

Dale

Thanks everyone for the replies.

Retserf - This is an unmolested car with stock twins. I've traced the lines and referred to vacuum/boost diagrams. Everything seems correct. Someone correct me if I'm wrong but pressure to the actuator comes out of the primary housing into the actuator and then on to the solenoid which is vented into the primary turbo intake tube. The solenoid is cycled before 4500 to adjust the pre-spool and is then mostly open after secondary engagement so the pre-control valve is closed. With all that said, I would think I could plug the solenoid side on the pre-control actuator and the pre-control actuator would open with full primary boost? As for hoses and pills, they are all there.

arghx - you mean the solenoid combo with boost & pre-control doesn't have a rep for failure?

DaleClark - Hi Dale, boost pattern is 10-6-and a real slow rise in boost toward redline. Also, this link suggests that the rod should move during this test, but it doesn't. Here's the link: https://www.rx7club.com/3rd-generati...eutral-364327/

Based on your 10-6 pattern look at the turbo control solenoids (there are 2, one on top of the ACV and on on the solenoid rack).

this is also a good read to help teoubleshoot.
Turbo / Boost Problem Troubleshooting

Perhaps I misunderstood, but it sounded like the secondary turbo wasn't even pre-spooling, but when you operated it manually with a hand pump it almost worked correctly (8 lbs boost after transition vs. 9 or 10).

The Pre Control and Wastegate solenoids are 2 port duty cycle controlled solenoids that rarely fail. They are "boost control" solenoids.

The rest of the solenoids in the vacuum rack are much more prone to failure (turbo control vacuum and pressure, charge control, charge relief) and there are things like check valves and vacuum/pressure tanks. They are much more like the emissions control solenoids used for things like EGR and the air injection pump.

See this thread on how the system works

https://www.rx7club.com/3rd-generati...tified-841821/