Boost Issues
 

I had an FC years ago and recently I bought an FD with 99k on the original motor and have been trying to troubleshoot some issues since day one. It's a simplified sequential setup that was done by the previous owner's "rotary mechanic", at the same time a silicone hose job was done. Originally the car idled fine but didn't have primary boost, I hooked up a boost gauge and found that my boost pattern was 0-0-5.

To start my trouble shooting I found that there was a crack in the plastic crossover pipe. I replaced the whole Y-Pipe and crossover with a new Efini Y-Pipe, after that my boost pattern was 0-0-7.

Next I took off the UIM and found that the turbo control solenoid (the one originally attached to the ACV) was missing. The vacuum lines that would normally go to the turbo control solenoid were just connected to each other essentially bypassing the solenoid. I bought a new solenoid and installed it. At that time I also replaced a faulty purge control check valve (the metal one) with Dale Clark's check valves, the other check valves were replaced by the prior owner with Dale's check valves. I tested the rack solenoids that are still in use with a Mityvac and all seemed ok, I also tested the pressure and vacuum chambers and those were OK as well.

After reassembling everything the idle is very poor, I get a bunch of white smoke (did not have this before), and my boost gauge only reads 10hg , it doesn't move from that position regardless of what I do with the throttle, prior to the installation of the turbo control solenoid I was pulling 18-20hg at idle. I can hear the primary turbo spooling which I didn't hear before the installation of the turbo control solenoid but there is no boost being measured or felt. The car drives very poor a significant hesitation around 3,000rpm and no secondary boost.

I took the UIM off again and realized that I installed the purge control check valve in backwards, I fixed this and again checked everything over and it looked ok. After putting everything back together again I still get the same results as before, only measuring about 10hg and no boost.

I have researched for many hours to try to find out what the cause could be but I have come up empty, any advice as to what the cause of the issue is?

You could have a multitude of problems that may not be solved simply by assessing your symptoms. Suggest you go through the simplified sequential hose diagram and check all the hoses and valves

https://www.rx7club.com/3rd-generati...-turbo-749702/

The solenoids should be checked warm as well as cold. Also check your actuators and CCV. This is all laid out in the FSM, Chap F and also more simply explained....

www.rx7club.com/3rd-generation-specific-1993-2002-16/how-test-your-solenoids-actuators-other-turbo-stuff-802060/

Good luck

Thanks I have the vacuum diagrams printed up and laminated, I have taken off the UIM again and will recheck everything. When the previous owner did the simplified sequential they left all the vacuum lines along with the unused solenoids, I think I'm at the point where I will actually remove the unused lines and solenoids.

I followed degessaman's guide but I didn't check the solenoids when they were warm, only at ambient temp. however the problem is as soon as the car starts where there is not enough time to allow them to be heat soaked. I checked the CCV and it seems to work properly, I checked to see if any of the C clips came off the arms and those are ok as well.

First off, you need to see what changed that is making the car run rough. That's similar to having the MAP sensor unplugged. Also, the MAP sensor stock has a filter in-line with it - I hope you didn't try and put a check valve there, as it will then act like it's unplugged. The MAP sensor needs to see vacuum and boost.

Could possibly be a spark issue as well, like a plug wire that's off or something.

You'll have to look at everything that was touched to find what's acting up for the running rough problem. If you REALLY start running out of ideas, do a compression test and make sure the motor is happy. Hopefully something didn't fall down the intake manifold while you were working on it and break and apex seal! Good reason to tape up those holes or get a SakeBomb Garage "nut blocker", I have one and it's fantastic.

On the boost problem, the only way you're getting boost that low is a substantial boost leak or the wastegate actuators aren't attached at all. I would do a pressure test on the system and look for leaks.

Good luck!

Dale

I'm having the same problem. Car boosted perfectly, then it developed a fuel leak (line connecting primary and secondary fuel rails).

While it was apart, I replaced:
vacuum lines
fuel hoses
check valves
fuel pressure regulator
pressure damper
tested the fuel pump
had RC flow the injectors
installed new injector grommets

So either I plumbed the rats nest incorrectly, replacement solenoids may be bad, or?
ps did a compression test it's good.
I will be following this post

There were a couple of issues that I found, the first was the charge control solenoid did not have the connector plugged in. The second is that it was running in limp mode. I pulled the codes and reset the ECU, it has significantly improved but not perfect yet. I am now boosting 8-5-8. I think I may have a solenoid issue, but haven't had a chance to test them again.

https://www.rx7club.com/group-buy-pr...d-rack-968956/

Use these and will solve your issues!

This makes me think you may be missing the pill in the wastegate line (and maybe prespool line).

I found that the wires in the harness near the solenoids were frayed and intermittently shorting the wastegate and turbo (2) control solenoids.
See attached. This caused the 0 psi boost problem on the primary turbo (wastegate was open due to wiring issue).

Found this by removing the solenoid rack, with ignition key on, checked for 12 volts on each solenoid electrical connector + terminal, and with dvm - terminal attached to chassis ground. (should be 12volts, if less there is a short in the harness wiring).

Lesson learned #1, always check these signals after moving the harness for the vacuum hose job, and before bolting the intake back on. (Note: removing the baked on harness protective sheath to trace the short and repair wires was a pita)..

Lesson 2, I inadvertently swapped the wastegate connector and turbo (2) control connectors during one of my 3 attempts at removing the rats nest to solve the original problem (easy to do unless you check the wiring color in the fsm since the turbo (2) control, wastegate, and precontrol solenoids all have the same connector).

i would replace that harness, looks to be at the end of its serviceable life. You could end up making a career out of running down electrical faults and gremlins. The worst are the intermittent ones you are finding. The system is complicated enough as is.

Have you resolved your issue with the white smoke coming from the exhaust? If not unbolt your down pipe, if you have oil in your down pipe you may have a vacuum line crossed and creating pressure in your crank case