Red Rotary Rocket

I've been having trouble with low boost at transition lately. My boost pattern is 12-6-slowly climbing to 11. Today, I hooked up a garden hose (really!) to the output of my CRV and ran it into the cabin so I could see if there is anything coming out of it. Sure enough, nothing came out. I know the CRV is opening and closing because I teed a vac/pressure gauge into the control line and I tested the valve as well. The CRV control system and the CRV itself are working fine.

Does anybody know why my second turbo is not prespooling? Thanks in advance for any suggestions.

spooledUP7

Get your self some T adapters and lets start doing some test.

Tee your boost gauge into the nipple that is on the back of the Y-pipe just behind the Charge Relief Valve's (CRV) hose connected to the Y-pipe.

Go for a drive.

This is what I saw on my car (My car is 11-8-11 boosting)

3rd gear - WOT

2000 RPM - 0PSI
3000 RPM - 0PSI
3500 RPM - 0PSI
4000 - 4500 RPM - Rolled up to 8 PSI +-1PSI
4500 + RPM 12PSI

What is happening: Page F-84 in the manual

0-4000 RPM - Precontrol controlled by ECU, CRV off (Venting) Charge Control Valve on (closed). Turbo Control off

4000-4499 RPM - Precontrol Optimized by ECU, CRV off Charge Control Valve on (closed). Turbo Control off

4500 RPM - Precontrol fixed (5% open) CRV on (closed) and Charge control valve off (open)
Turbo Control on

If you are getting anything close to what I saw with my test, then you can rule out that your precontrol is not working. This means that you should see a build up of boost just before 4500 RPM on the secondary turbo.

If you don't see any boost before 4500 then you may be right, the precontrol is not working.

If you notice, the turbo control is off before 4500 RPM. The Turbo control is the flood gate to the secondary turbo and if shut, you will only have the fixed 5% open of the precontroller pushing the secondary turbo. Does this seem like enough to move 10 PSI? No.

ech

you need two things (at least) to work correctly - your CRV and your pre-controll actuator/solenoid.

The precontrol solenoidis pretty easy to get to - just pull the pressure tank on the top of your engine, and you will see two solenoids that attach w/ 2 10mm bolts. you can test the impedence on each when the car is shut down - I don't remember exactly, but they read > 50 ohms then they may be the problem. You can also pull them off and test their ability to function as valve.

But also slide under your car (easier said than done) and loot to make sure your pre-control actuator is still connected to the gate arm.

those are two other good starting points. There

Red Rotary Rocket

Ech and SpooledUP7,

Thanks for the replies guys. Here are some comments with respect to your suggestions:

The Pre-Control actuator is attached and functioning. I've already checked that. I'm sure that the pre-control door is opening.

Something I didn't mention before...I have completely removed the pre-control pill, so this thing should be pre-spooling like crazy but it's not.

I've measured the resistance of the pre-control solenoid. It is within spec.

I tried completely bypassing the pre-control solenoid by installing a dawes boost controller on only the pre-control side. So the configuration was intake manifold->dawes device->pre-control actuator. The other side of the actuator was capped off. The wastegate control was left entirely stock. I was able to change my primary boost from 7 to 14psi by adjusting the dawes device, but no matter what I set it to, the transition is still about 6 psi. This is without a pre-control pill. This is more confirmation that the pre-control actuator/door are working, but somehow the 2nd turbo is not spooling.

I will probably try to tap into the nipple behind the CRV hose next, but I wonder if that will get me any new info. The CRV is open until 4500 rpms, and it never blows....not even a little bit, so I'm pretty sure that I will see 0 psi until 4500, then a quick build up after the turbo control opens up.

Any other ideas?

spooledUP7

Red ..Rocket

If you took the precontrol pill out you will not see a significant build up of prespool. It works the opposite of what you were thinking.
The more pressurized air you allow into precontrol actuator, the more the precontrol door is going to deflect the exahust gas away from the optimum posistion for prespool.

Put the pill back in, and hook the precontrol solenoid back up. If you want to control your prespool, you can pipe your boost controller in line where the pill would go.

Don't forget to include that kind of information next time when you are asking for help. That is a biggy.

Red Rotary Rocket

SpooledUp7,

I get a low transition regardless of how I have it hooked up. Even with the pill in and everything hooked up like stock, the transition is still low.

I offered the dawes device example to simply illustrate that I can control boost with the pre-control door, hence, the pre-control door is working.

I disagree with your interpretation of the operation of the pre-control system. A bigger pill (or no pill at all) in the pre-control line will increase the pre-spool. The secondary turbo only prespools when the pre-control door is open. If the door is open more, then more exhaust gas goes through the secondary turbine to spool it up. The pre-control actuator operates with boost, so more boost will open the pre-control door a larger amount. The pill restricts the boost that the PC actuator sees, thus reducing the amount that the door opens. Removing the pill increases boost to the actuator, which opens the door further, which spools the secondary turbo.

Pressurized

Umm.....you might wanna check your vacuum lines? I have a low transition and I didn't have any pre-spool then I saw the vacuum hose right by the stock crossover pipe was disconnected......

Now my boost response is much better and the secondary pre-spools like crazy.....but I still have a low transition.....

I'm not very mechanically inclined with the FD yet.....

Red Rotary Rocket

Pressurized,

Thanks for the suggestion. All my vacuum lines are ziptied and silicone, so they should be in good shape. I've been looking for loose ones just in case, but I haven't found any so far. I've teed a vac/press gauge into the CRV line, the precontrol line, both sides of the turbo control, the pressure chamber, and the vacuum chamber....all seem to be doing what they should, so I probably would have seen something wrong if one of the lines was disconnected....

This problem is really frustrating me.

bond007

<grin>

Everyone forgets the obvious.....
Tap a voltmeter into the PC line from the ECU :-)
The voltage specifications are in section F, look for the section on troubleshooting with the ECU harness tapping board or the DTS-1000 service tool. That will give you the specs.

How much do you want to bet your old/brittle wiring harness is experiencing technical difficulties?

I'm helping TWO other people with exactly the same problem.
The PC solenoid isn't getting the signal for the PC from the ECU.

It inducts the signal from the WG.
They have both run an auxillary wire from the ECU to the PC.

Even more obvious - you said you ran the system without a pill. What does that tell you? It should have a large amount of prespool (the lack of pill will "tune" for that). You don't.

You need to check if the PC solenoid is HOLDING boost when it is turned off and not leaking it. Apply pressure to the nipple that is attached to the PCA vent line, and see if it will hold pressure. If it doesn't, you won't be able to have the ECU control the pressure in the PC actuator.

For reference:
WG with large orifice = lower boost
WG with small orfice = higher boost
PC with large orifice = big spike/more prespool
PC with small orifice = normal transition/less prespool
(to put it grossly exaggerated....)
Look at robrobinette's article on boost control. There seems to be some confusion here. You set them up opposite, so to be close to normal (if you used a variable orifice) you would open up WG all the way, and close down PC all the way, and tune them closed and open respectively.

Yes, go to all original equipment when testing. You can't do it any other way, otherwise, you have another variable to muck things up.

Last point, you need to tap into the hose behind CRV and use that to determine if you are prespooling :-)

Tapped in there, you should see nothing until 3000, buildup before transition, and hold max boost until redline...

What you see at the manifold/normal boost gauge location is another story...

a.f.

Red Rotary Rocket

Bond007,

Ah, now there's an angle I haven't looked at yet, or even thought of for that matter. That's exactly what I was looking for...something I haven't tried. You say the PC can induct the signal from the WG....interesting. I'll have to try to run a separate wire and see what happens.

Am I completely off base to make the assumption that the opposite can happen as well, i.e. the WG can induct signal from the PC? If the signal swapping goes both ways, then I could see how complicated problems can arise.

Thanks for the tip.

Oh, yeah...I have already verified that the PC (solenoid and actuator) holds boost, so that is not the issue.

Mach2

RRR,
Did you check both sides of the TCA? For vacuum and boost at the transition? If that's fine then I think you should diconnect the hoses going into the PC solenoid and the WG solenoid and cap them off. Then you should install the stock pills and see if that speeds up the transition. You'll probably see a little less overall boost and a slower initial rise of pressure, but the transition should be quick. Also you might have a bigger problem then you think. I had a similar problem and when I rebuilt my engine I disassembled the turbos and found them to have "huge" cracks around both valves(PC,WG). This is very possible if you've never replaced your turbos. Keep us posted.

Red Rotary Rocket

Mach2,

Yeah, I checked both sides of the TCA. In fact, I discovered that the vacuum side was a little slow. I was so happy, I thought that I had solved my problem, so I tested the lines for leaks...no leaks so I bought a new solenoid. It didn't solve my problem of low boost at transition, but it sure sped up the recovery after the transition.

I had my turbos out of the car last September (rebuilt by turbo city). There was one crack on the gasket face where it attaches to the exhaust manifold, but none near either the wastegate or the pre-control. The Turbo City guys said that the one crack I did have was typical of the RX-7 turbos they see, and that it was still useable. After I installed my turbos, the boost pattern was fine. I guess that it is possible, though, that I have gained some extra cracks since that time. I hope not, I have only pulled my turbos once, but I hated that job.

There's only one job I hate more than pulling the turbos...and that's changing the fuel filter (believe it or not)!

KZ1

I am batlting with a similar problem I was getting 10-7-10 stock, and 11 7-11 with exhaust and intake (no mp) slapped in IC and PFC got 12 8 12, adn 10 8 10. I put a midpipe on and get 12 10 12. WEll I am suppose to get 12-12-12. go figure, no boost spike at transition with midpipe, nothing. anyway. It seems as if my transition is slow as well. I tested all selenoids tpc, wg for leakeage and venting operation, activated them by grounding appropriate connections at ECU. I have new TCA, pills are stock, pressure and vacuum to TCA are good to. I have no primary leaks because I push like 13.5 lbs on it sometimes.

I was told that I may just haev some lazy actuators. I am interest in how you said the vacuum build was slow. how did you know that? what is slow?. Also, when I monitor the pressure on the TCA I see an immediate jump to 4psi, just for a sec before it hits >7. Coudl this have somthing to do with it, whouldn't it immediatly jump to >7??

spooledUP7

Regarding the TCA, I have been playing with the idea that aftermarket hoses may cause a slower reaction time for the TCA.

I am not certain, but if the aftermarket hoses are even slightly smaller in ID, wouldn't it make sense that there would be less volume of PSI and Vacuum. Small straw big straw theory.

Also, if you look at the TCA vacuum solenoid and the way it forces the hoses to do a strict 90 degree turn it could be easy to see a flow restriction. I personally used a longer hose to lessen the bend, but what about yours?

I would think that if you could maintain the same ID of the hard lines throughout the sytem, that you would increase the spead, or at least optimize the reaction timing of the TCA.

Red Rotary Rocket

SpooledUP7,

Yeah, I think you are probably right. The size, length, and bend radius of the hoses probably play a key role in the reaction time of the system. If somebody uses hoses that are much longer, larger in diameter, or have tighter bends, then there may be a consequence as far as the reaction time of the system. When I did my hose job, I cut all my hoses just a bit longer than the stock hose it was replacing, mainly for bend radius reasons since my silicone hose is not preformed like the stock ones. I can't say that I really noticed much of a difference in the boost pattern when I did it (it was about 2 years ago) but I did gain ~2 in Hg of vacuum after the hose job

KZ1,

I teed a vac/pressure gauge into the vacuum line right before the TCA. At transition, the line went from atmospheric to ~10 in Hg, very quickly, then slowly climbed to ~22 in Hg after that. Since this was during the transition (on boost) the vacuum is coming from the vacuum chamber, so there is no reason for the vacuum to jump and then slowly climb unless the solenoid was sticking. That was what I meant by a "slow" solenoid. What you are seeing on your pressure side sounds a lot like what I saw on the vacuum side. Lucky you, the pressure TCA solenoid is a lot easier to get to than the vacuum one

ATPRX7

which solenoid is the pressure TCA and which one is the Vaccuum? Like where in the rats nest?

Thanks,

Ravi

spooledUP7

pressure: Third one from front, bottom row.
Vacuum: Under the upper intake manifold, on top of the ACV behind the WG & PS solenoids.

To T into the TCA, there are two hoses just south and to the left of the altenator. They shoot straight down. This is easiest place to tap into.

Red Rotary Rocket

SpooledUp7,

Are you sure? I don't have my manual handy (at work now), but isn't it the other way around? The TC vacuum solenoid in the bottom row and the TC pressure solenoid on top of the ACV?

Just from memory, if I'm incorrect, my bad.

spooledUP7

Positive on this one for sure. I tested it, and for good measures I checked it out in the manual. I'm a little gun shy from getting the prespool pill backwards, but I am pretty confident on this one.

Red Rotary Rocket

SpooledUp7,

Yup, I'm home now, with my manual, and I'm the one who's got the vac/press locations backwards.

No need to be gun shy. We all make mistakes, myself included

I hope I didn't come across like a ***** with the pre-spool pills, because I didn't mean to.