Where did all my boost go? - sequential troubleshooting
 

In my efforts to track down my boost issues, I've performed the following:

Brand new solenoids (all of them)
Four new check valves (thanks Dale!)

My problem has remained largely unchanged, however. I figured based on search results that I should replace the solenoids and check valves anyway, just for good measure.

Primary boost is excellent down low, however, as the RPMs climb, my boost will drop suddenly and drastically, and struggle to climb back up (but never reach) where it was. The engine noise also seems to change pitch.

However, if I accel off and give it time to let the RPMs drop, I will have immediate boost again.

Cruising and going into the throttle I have no issues building boost either, it seems to be related to high rpm and the changeover process?

The shop that did the work is familiar with FDs, and you can see the picture below the check valves replaced, and the one that was left alone. I'm assuming this was done correctly as far as the check valves go, as Dale mentioned to only change the green/white and Green/Black.

Anyone have any suggestions on where to pursue this problem further in terms of troubleshooting?
https://cimg6.ibsrv.net/gimg/www.rx7...a6128d9245.jpg

I had a similar issue when I first got my car on the road. It would intermittently have no boost at the transition and make a Ric Flair "whoo" noise.

Turned out to be the actuator on the front part of the manifold with 2 Hoses hooked to it. It would hold one way but not the other due to a failed diaphragm. Pretty easy to test with the car on ramps.

Vince

If you can, maybe double check the crossover tube connection from the y-pipe turbo going to the intercooler, make sure nothing is torn. In my case I had a similar issue that you had described, however it turned out the connection between the y-pipe and the intercooler had a huge hole in it causing a massive boost leak, may be worth looking into.

That said however, also take a look at the vacuum chamber, you could potentially have either a faulty one way check valve going to the vacuum chamber, Or the vacuum chamber itself is no longer holding vacuum?

So I would first check the check-valves if you haven't already as it might be a good place to start.

I'm sure other members with more experience than I have can probably chime in with their thoughts and wisdom on this issue.

Take your time, don't rush anything and good luck with finding the issue!!

Glad you got the check valves!

There's one that is typically under that pressure tank there, did they get that one swapped out?

Do you have a boost gauge?

Most likely the problem with be the turbo control actuator. As stated above, some have blown diaphragms and if so the turbo control door either won't open or will open slowly or partly. This is a large can mounted to the exhaust manifold, you can get to it under the car (kinda). It has 2 ports, one pressure, one vacuum.

Probably worth doing a simple test on it to make sure it's good before diving into the solenoids. disconnect the 2 hoses going to it, push the rod in, put your finger over one port, and the rod shouldn't go all the way home until you take your finger off. This should be true on both ports.

Dale

I do indeed have a boost gauge, but it's in kpa. Not that it is an issue being in that measurement. I believe it reads about .7-.8 kpa max boost before the issue starts. When the issue happens it will snap below .5 (how low I'm not sure, but its not zero.) and then will struggle to slowly build back up (but never reach) .7-.8.

That engine sound change is noticeable, too. It's almost like the motor made a change to an N/A exhaust note (even though I have boost. Boost struggling to build when this happens, but boost nonetheless.

The Rotary tech (I wish I could work on my own cars here) did all the solenoids and the check valves, except what I'm assuming in the picture is the one Dale mentioned to not change, as the tech told me there were four check vales I dropped off (that Dale sent) and five that were on the car, so he left the odd ball one (in the picture) unchanged, and did the others.

I'll look into the turbo control actuator this weekend, How much play is considered too much? I know you mentioned it shouldn't go all the way back home with my finger over one of the two holes, and to test them both, but I was making sure there wasn't an allowable margin.

Edit: I will double check under the pressure tank to make sure it was changed.

I did some verification later today to confirm when exactly this happens. The whole thing starts right about 4500 RPMs

4500 RPM is the normal transition point.

Stock boost is .7 kpa. Stock boost pattern will be .7 to .55 or so at transition then back to .7. You could also have a minor boost leak as well.

On the TCA, it's not as much play as just verifying the diaphragm isn't torn. WIth your finger over one port it shouldn't be able to go all the way back home.

Are you in an apartment or something that forbids working on cars? Sounds like you need to make an off-site buddy with a driveway you can do some work at :).

Dale

Basically. Rather annoying not being able to work on my own car.

Definitely not the normal 10-8-10 boost pattern (or .7 - .55 - .7 since I'm talking Kpa here.) Boost will plummet to a few kpa. Not zero, but low, and will struggle to build back up and not reach .7.

I've considered the possibility of a boost leak, but it boosts absolutely fine on the primary. I can't think of any issues as long as I stay below 4500. Theoretically, that would mean I shouldn't have a boost leak, because the entire system is charged when it's just the primary operating, and I'm not having any issues there, correct?

I've tried searching for a TCA (should I need a new one) and I can't find anything. "Turbo Control Actuator" hasn't gotten me anywhere as far as search queries go, is there something I'm missing?


Thank you guys for the insight so far.

You could have a boost leak on the secondary side - the small hoses that go to the charge relief valve are prone to leaking/cracking/getting hard.

I wouldn't just buy a TCA unless you KNOW it's bad. It's not a hard test to do and it's a pretty solid "this is good/this is bad" answer. Just stinks getting TO it to test, it has to be done under the car.

If you DO need one, PM one of the guys that sells parts like FritzFlynn or Tomsn16 they will possibly have a good one.

Dale

Do you happen to know what size & Length hose I need for the charge relief valve?

Minor update - I looked at the charge relief valve today, and while I didn't pull every hose off and look into it, they all looked cosmetically fine. No obvious signs of cracking or missing clamps.

+1 to checking turbo control actuator. Mine has been acting up since the 99 spec turbos were installed. Frickin annoying.

The various ~1" diameter hoses on the Y-pipe for the charge control and blowoff can't really be diagnosed by looking. With the clamp on a crack can easily hide and many times they are so hard that they simply don't seal even clamped down.

I found silicone replacements for those hoses a while back, search around on my old posts. They were reasonably priced, fit great, and have stood the test of time on my car.

Dale

I'll have to look into that.

As a minor update, I did look at the couplers to make sure there wasn't a boost leak, the crossover pipe actually has a new-ish looking Greddy coupler there. I've ordered a new TCA (mine looked pretty grungy, but thats besides the point) and I'll look into the hoses as well. Eventually I'll run out of things to inspect/replace. At this point I'm considering it all preventative maintenance.

Edit: Dale, I tried searching by your username specifically, but my terms might not have been close enough, any suggestions on what I should tailor my query to?

I just ordered replacement silicone hoses for my CRV & ABV (BOV) based on Dale's recommendation... the link in his old post on Amazon was out of stock so I sourced them through Pegasus:

https://www.pegasusautoracing.com/pr...sp?RecID=11046
https://www.pegasusautoracing.com/pr...sp?RecID=12998

Just cut them down to size with a razer blade however you want and you're good. Working great and they seem to seal well even without tightening clamps on them (still put them on but had some loose when I did some boost leak testing and they didn't leak)..

Yep, here's the 90 degree hose -

https://hpsperformanceproducts.com/p...lack-blue-19mm

HPS is who makes the one I bought, I got a black version. The 3/4" ID is what you want, that fits great.

I would also get some Norma-Torro hose clamps as well. They tighten up on that hose great and won't cut the silicone.

FYI here's the original post I'm referring to -

https://www.rx7club.com/3rd-generati...valve-1060209/

I Googled "90 degree silicone hose daleclark site:rx7club.com" and it was the first hit. Use Google to search, the forum's search sucks most times.

Dale

Awesome, thanks Dale! That should do the CRV hose nicely. I know you mentioned the charge control and blow off hoses as well, but I'm curious as to how much approximately I would need length wise, as their site offers a few different variants.

Just measure with measuring tape and see how much you need. It is going to be different if you have a stock intake or aftermarket intake.

That 90 degree hose I ordered had long legs on each side, I cut those off and was able to use those as well.

Dale

My car is completely stock, I suppose I can just measure the BOV/CRV hoses. Those should be the only other ones I'd need in that size, correct?

Yeah, that's the only hoses to worry about. The air pump hoses I think are the same size but they typically don't crack and get crappy.

Dale

Well, the TCA was replaced, and the problem persists (at this point, like I mentioned above, I'm considering this preventative maintenance. What I fix now is less issues to crop up later. The car's 26 years old, so I don't see an issue with overhauling all these components anyway.) I think all I have left are the hoses on the secondary side, like the one going from the CCV and the ones from the BOV/CRV.

Edit:

Just to recap (for the sake of possibly helping someone else down the line)

Work that has been done:

Replaced all solenoids w/new OEM
Replaced all check vales w/DaleClark specials
Replaced Turbo Control Actuator with known good actuator.

What's left to do:

Replace Hoses on Charge Relief Valve (CRV), Charge Control Valve (CCV), and factory BOV.

The hose was mostly out of stock online, unfortunately, but I did find a local hose supplier that had what I needed.

Thanks to DaleClark pointing me in the right direction, I sourced two pieces of silicone hose with the 3/4" inner diameter and a 90 degree bend.

The other hose (rather than risk getting not enough) I just grabbed six foot of 3/4" inner diameter straight silicone hose.

It will likely be tomorrow by the time I get to replacing the hoses, as its stupid hot right now and I'm not keen on burning myself.

We sure it's not like an old thread where the guy had clogged his catalytic converter??? I'm getting Deja vu.

I have had my BOV/CRV hoses leak they usually pop them straight off and make the rick flair wooooo or whistle/screams at you. If your on stock intake box it might hide the noise.
I tightened down some hose clamps and it went away. Roll your windows down and boost away you can't miss it.

The only real audible difference is at the changeover at 4500, the engine exhaust note sounds louder, and almost Non turbo at that point (though it is still attempting to and building a small amount of boost) if that makes sense.

So I did some testing today after the TCA was replaced, it looks like it's become slightly more consistent. I did a few pulls, and I'm seeing 10 psi on the primary turbo. When transition happens it drops down to about 2 psi, then builds up to and holds at 7~ psi, though the buildup is slow.

Anyone have any ideas?

Thought I would post an update here until I have a chance to get to the CRV & CCV, as well as their hoses for inspection.

Do you still have a catalytic converter? Maybe it's clogged.

Vince