FD with occasional low boost/no secondary turbo
 

Hi everyone, I'm Evan. I live in the Bay Area and picked up my first rotary car about a month ago. It's a 1994 Touring. It was all stock except for a racing beat exhaust. All I've done to it is put some koni yellows/ground controls and some 17x9F/17x9.5R Volk SL's on her. I intend to keep this car as my street car/dd so I plan to keep the car mostly stock other than some minor reliability/cooling mods. I have been toying with cars for 15 years, mainly with honda's. I have a k20 powered EK civic that I love and use for track days. So far, I love my FD but just want to make it run right

Here's my problem, I have 3 symptoms:

1) random times where I get low boost (barely any whatsoever) all the way through the power band
2) random times where primary spools up fine but no secondary kicks on
3) random times where the primary and secondary operate as they should and the car is quick as hell

Car has 73k miles, no mods other than a racing beat exhaust. I'm gaging the amount of boost from the sound the stock ABV (removed stock rubber pipe to airbox). I have a boost gage on order though.

I've done alot of reading but I have yet to find a situation where sometimes the car is perfect and sometimes when it's either got full primary only, and sometimes where the car has low boost.

I do plan on going through the Troubleshooting list, but wanted to ask the pro's on this site if they can at least guide me in the right direction rather than pulling everything apart.

Any help? Thanks!!

Here's my car:
Attachment 653126

You may want to check the piping to the secondary turbo.

I'm not an FD guy but I keep seeing that the piping can pop off or be loose and effect boost.

my friend had a similar problem with his dsm and it turned out to be his o2 sensor.

Thanks guys. I'll check out the piping this weekend. I think it may be the y-pipe connector or the pipe leading to the primary turbo. At least that's what I gather from reading on here. O2 sensor provides info to the ECU, but since the wastegate is operated by the spring in the primary, I don't know if that would affect having little boost. But i'm pretty new to FD's so please correct me if so.

Thanks again!

my car was doing the same but its once and a while I can go a month without it doing it and boost drop real bad

mine does it consistently. I gotta dig into the car and check all the rubber hoses. I think one of my 1" hoses off the Y-pipe is leaking cause it's SUPER hard like plastic and can rotate a bit. It's the one that goes to my charge relief valve.

First suspect is a major boost leak, but usually you can hear those. If it is a leak, it's most likely from the OEM rubber 'y' pipe to cross-over coupler just above the turbos. Replace with a good silicone coupler or consider an efini 'y' pipe. PnP bolt-up eliminates the coupler completely and flows a bit better to boot.

Since it's intermittent, I'd also be looking for a sticky boost control actuator or a failed vac/pressure hose going to it.

I'd suspect your Charge Control Valve first, since the coupler would result on low boost under ALL conditions, not just secondary turbo.

When the CCV fails, the secondary turbo's output gets forced back out through the air filter. Hence, no secondary boost.

Mazdatrix spells it out a bit better here: Turbo

Thank you for that mazdatrix link! I don't have an update to my problem yet as I'm waiting for the new rubber hose that goes to the CRV to come in. It should be here tomorrow so I can try that out. After that, I'll be investigating the CCV and Y-pipe coupler, like you guys suggested.

Thanks for the info. I'm gonna keep trying!

---Evan

I'd also inspect/replace your check valves.

So replacing the hose didn't help at all. Must be the charge control valve or check valves. Not sure if it's the big coupler on the y pipe collapsing. It feel ok by touch. I guess I'll just keep replacing parts till I get to it.

Anyone know a good Mazda tech in SF Bay area? I don't know if it's more cost effective to buy all this stuff or just take it to a shop who can figure it out quick.

Thanks guys

You're the man. I just found a broken in half check valve off the vacuum tank. Gonna order a new one and swap it out. Where do you guys order your check valves from btw?

Thanks!

Forgive me if I'm a little in the dark on the FD and its specific component locations, but if accessing the vacuum chamber and check valve in question means pulling the UIM, it seems like a wise idea to redo all of your vacuum lines in silicone. I would suspect that if one of your check valves split in half, the lines have been equally affected by the heat.

Dale Clark has an excellent FAQ on this, and I believe he offers Viton check valves as well. I know they can be found on ebay too. Just search for "RX7 Viton Check Valve" and you'll find them sooner or later. As for silicone vacuum hose, the correct thick wall stuff can be found for ~$1/foot if you know where to look. Sizes and amounts you'll need are on Mazdatrix's site.

Most of the time you don't have to pull the UIM for a check valve. IF that solves the OP's problem, then personally I'd change it and leave things alone. True that if he's dealing with OEM rubber vacuum lines, they're probably harder than a whore's heart. But if left undisturbed they usually don't present a lot of issues in my experience.
That opinion would change if he has to move or otherwise jack with the rat's nest at all...say for fuel issues or a rebuild. In that case DC's check valves are the best choice, but I'd also have silicone hose and spare solenoids at the ready and do it all.

I also have this problem mainly in lower gears 2nd the most but 2nd turbo always comes on if I shift up a gear very annoying problem good luck with it I will update you with what I find also

Thanks guys. So i replaced the bad check valve and in doing so, the rubber hose snapped in half. Went to kragens to get some rubber hose and put it all back together. Second turbo works now but only in higher gears (3rd, 4th, 5th). So I'm going to order silicone hoses and DC's check valves and just re-do it all. I may replace the CCV too and y-pipe coupler since it'll all be off... I'll keep you guys posted. Tough to make this car run right!

Update,

I'm going to remove the UIM and redo all the vacuum hose with silicone and DC's check valves. I think that since it's all apart, I'm going to replace the CCV since it's $150 from Pettit racing which is pretty reasonable. I'm debating order the pre-control solenoids and turbo control solenoid as that's another $200+$80... I'll also replace the y-pipe coupler with silicone. Spark plugs and boost gage while I'm at it. It's getting there...

Was there ever a resolution to this issue?

Wow glad I'm still subscribed to this because I would have totally forgotten about this post.

Welp I did all those things I said and it didn't work. Regrettably I ended up pulling the motor and swapping in a ls1. I actually didn't like it though so sold the car. Looking back, going single turbo would have been what I should have done or a newer set of twins. Oh if we can only go back....and now I live in Japan.

What was it about the LS1 that you didn't like?

I'm not trying to throw shade here, but I wouldn't go LS1 in the FD. I would rather figure out how to keep some rotary in it.

I've got a '94 touring and while it sure is a thing to keep on the road it is like a mission in life. A higher purpose. With the FD numbers small to start with and falling all the time, it is nice to be part of community of "the crazy ones".
Ok. maybe a beer too many.