FD RX-7 Sequential Turbos Explained

In this video I will go over the function and diagnosis of the sequential twin turbos in the 3rd generation Mazda RX-7. I'll also talk about twin vs single turbo and common problems with the sequential system.\
Vacuum Diagram Link
www.rx7bruh.com/how-tos
00:00 Video Purpose
00:42 Basic Operation/Overview
01:37 Deeper look at opertion of events
03:48 Solenoid Operations
06:37 Charge Control, Charge Relief, Y-Pipe
10:03 Waste Gate and Pre-Control Operation
13:59 Turbo Control Actuator Function
17:56 Boost Leak locations
21:58 Testing Solenoids
24:48 Single Turbo vs Sequential Twin Discussion
27:09 Sequential vs Non-Sequential Discussion
31:21 "Simplified Sequential"
32:32 Check Valves
35:19 Double Throttle Control
36:23 Wastegate and Pre-Control Operation
37:29 Vacuum Lines

[@bowenyu4088]

This is the best RX-7 vacuum/pressure control system info on KZbin Universe. Hat off to you Sir!

[@rx7bruh]

Thank you! Glad you liked it!

[@sarchavius1111]

This is a perfect example of what makes youtube and the rx7 community special. Thank you so much for this valuable info! I will definetly be referencing this video a lot while diagnosing my turbo issue! Thank you sir!

[@defekticon]

Great video! The third gen Rx7 coffee table book from Jack Yamaguchi explains how mazda arrived at the push/pull operation on the turbo control actuator. Initially they only had one solenoid controlling the actuator, then added a second one in late development. Really fascinating read. If it were made today the actuators would be electronically controlled instead of needing pressure/vacuum reservoirs. Would be drastically more reliable.

[@rx7bruh]

Yes I have read that about the solenoids! I always assumed that’s why the extra solenoid is mounted to the ACV and not the rats nest. I was researching electronic actuators a while back, I found one with the right throw but I think the amperage may be too high for extended use. The biggest problem is the amount of heat generated at the exhaust manifold

[@defekticon]

@@rx7bruh Very few people have taken the time to understand how this works, so I appreciate the in depth explanation. When the Sequential system works, it really makes a single turbo unnecessary unless you're going for drag applications or max power numbers. Of course they make great power, and the EFR 8374 will spool nearly like stock, but it only took 30 years to get there. I prefer the sequential operation though as it retains the quirky mazda engineering that sets the car apart (aside from the rotary engine). It seems like the market agrees because the more stock sequential cars sell for more money now!

[@alialhosani8899]

great explanation and you make it easier good job

[@terrencethorsen]

Fantastic! Big thanks for putting this together. It demystifies the turbo system. The movie version of Dale's book.

[@TonyWestDIY]

Great video. I never understood the system and never had to learn it anyway since the car was already single. However, it blew my mind that this was made in the early 90s.

[@rx7bruh]

Yea it’s actually a pretty genius system! Took a lot of engineering to figure out.

[@klmelj]

Good Stuff!!!!!

[@drivewithwill7]

Great video!

[@rx7bruh]

Thanks buddy! Your car still working good?

[@drivewithwill7]

@@rx7bruh yeah works better than ever thanks to your knowledge!

[@billyverduzco2337]

Thank you for this! I downloaded this for more review

[@rx7bruh]

My pleasure! Hope it will help you

[@billyverduzco2337]

@rx7bruh me too, I have the issue with the second turbo not boosting, so I'm going to be reviewing this a lot thank you again!

[@rx-heaven]

efr 7670 best of both worlds plus more tq

[@rx7bruh]

If you watched the video you can see that I explained advantage of modern single turbo

[@5455jm]

........... amazingly enlightening. Rexy will go to Mag &Turbo over in Auckland (Glenfield) ............ I will not attempt a reset of my turbos after watching you. You are not the typical rag-it-and-drag-it fd owner and to this end, you actually know what you are doing. My fd is too precious for me to stuff it up. I can build you a home, design you the most fecking brilliant interiors but I am challenged with metal and mechanics; I do know what looks good, I know better what is the most fun to drive .... However, I will be asking the boyz' over at Mag and Turbo to watch you first before they stick a ham fist under the bonnet of my boy.

[@Mrderlinkinparkfan]

nothing to say but awesome.

[@rx7bruh]

Thanks glad you liked it!

[@Mrderlinkinparkfan]

​@@rx7bruh I'm new to the Rotary Universe in general, but my FD is teaching me every time that things can be done complicated (...well i mean complicated looking), but after you understand whats going on, you understand why mazda did things exactly this way. Except the location of the Rats nest ...why on earth would you put it direclty on top of the engine where it will be baked to death. Hoping to get my registration soon so i can drive it finally😁

[@5455jm]

came from Instagram, sub'd here now. mny thks

[@rx7bruh]

Thanks for following!

[@coodie1988]

IMy FD currently dumps boost as soon as the secondary turbo kicks in I’ve been trying to diagnose. Bookmarked this vid to hopefully finally stop pulling my air out🤞

[@rx7bruh]

I’m going to bet your 90 degree hose for the charge relief valve is broken.

[@coodie1988]

@@rx7bruh vac line off the turbo elbow was capped that provides vacuum to the pre control and wastegate solenoid. Fixed that today but weather didn't permit a drive to see if that fixed it. If that doesn't fix it I'll check that 90. You are a life saver with this vid man👍🏻

[@scotty305]

Thanks for making this. It's long enough that some chapters or timestamps would be helpful. I'm interested in testing the Turbo Control Actuator today, it's at 13:56 .

[@rx7bruh]

Great idea, I’ll see what I can do.

[@rx7bruh]

I have added Chapters for ease of navigation. Thanks for the suggestion!

[@SinfidelityMusic]

Hey bro. Thanks for the helpful explanations. I’m hoping this video will help me figure my issue. I’m having symptoms similar to LIMP mode. But I don’t have any error codes except air pump relay. I have stock ecu with emissions delete. I can rev to around 5k before it falls flat. If I hold throttle in flat spot, it cuts and on cuts and on continuous. Like limp Ive triple checked solenoids, vacs and electrical. Omp etc.

[@rx7bruh]

Have you checked your TPS voltages?

[@SinfidelityMusic]

@@rx7bruh it is within spec. 👌

[@SinfidelityMusic]

@@rx7bruh initially I thought ecu was the cause, cos it also wasn’t sending ground signal to fuel pump relay. When I bought the car, it had a jumper in diagnostic to ground the pump relay. Anyway, the new ecu fixed that issue, but not the weird limp kinda symptoms. Wondering if I have a vac reversed down at the actuators. The vac routing I followed the online pics. It maybe the lower ones connected to actuators are backward. They seem to logically only go or reach to one location really tho

[@SinfidelityMusic]

What could possibly cause Limp Mode, but not throw a code? This thing driving me nuts. Definitely won’t make Boost, as soon as it tries to go above zero, it cuts.

[@panikosrxristodoulouxristo1733]

Hi,just watched your video and lm glad you are supporting the sequential turbo.💯👍 A question please, l own my self an rx7fd3s and i have some oil leak from the secondary turbo and i was wondering can you remove the turbo pack without taking the engine off. Thanks

[@rx7bruh]

Yes you can

[@edgardoarroyo7418]

I just bought an FD with stock twins and once it reach 8psi engine cut

[@ChErRyaVe20pK]

How can i check my wastegate actuators by teeing into them? What numbers should i expect to see? Also, where can i tee into to find the absolute raw pressure of the primary turbo, i.e before it gets to any sort of piping where there could be leaks, etc?

[@rx7bruh]

Hi please review the information at the time stamp 10:05 To test it you apply vacuum to one side while blocking off the other side (the side with the pill in it) There is technically no place to check primary turbo pressure without potential for leaks. The closest place would be on the y pipe

[@trracing582]

Great video mate, I have recently lost boost pressure on my front Turbo, makes all the woshing sounds but produces no boost. At around 4000rpm the second turbo produces boost. Any idea what's going on?

[@rx7bruh]

That’s an interesting problem to have. Anything that causes pressure loss for the primary would also cause pressure loss for the secondary turbo. What does your boost gauge say? How much pressure are you getting under and over 4000rpms?

[@RONIN_RX7]

Is it possible to run an aftermarket blow off valve with the stock twin setup?

[@rx7bruh]

Yes however you need the proper adapter for the hose.

[@seran2316]

can we substitute some of these solenoids to modern 3-port MAC solenoids? especially for the exhaust control valve, instead of having 2 solenoids for vacuum and pressure, have a 3 port solenoid plumbed similar to a 2-port external wastegate

[@rx7bruh]

I upgraded all of my solenoids to Fabco solenoids. There is a write up on my website. www.rx7bruh.com I’m sure there is other ways it can be done. But you’d have to figure that out for yourself!

[@seran2316]

@@rx7bruh gotcha, thanks!

[@blackice1231000]

Any idea what could could cause no secondary turbo boost after 20 minutes of driving? But before it gets heat soaked it's drive perfect. Full power. New engine from Mazda turbos rebuilt. Every vacuum line replaced and gaskets. Any help or idea would be awesome. Thanks

[@rx7bruh]

Most likely in that case is a stuck turbo control solenoid, either the vacuum or more likely the pressure operated one. Read through this and give it a try it takes very little work and will help unstick a solenoid. Easy test. www.rx7club.com/3rd-generation-specific-1993-2002-16/fix-sticking-sequential-turbos-tca-solenoid-e-cheap-easy-fast-effective-1120259/

[@Mrderlinkinparkfan]

21:24 does the actuator move with IGNITON on an off or engine on/off? If its ignition -> how does it operate if the engine isnt creating pressure/vacuum to move the diaphragm? 🤷‍♂ Or is it rest of pressure/vakuum in the chambers?

[@rx7bruh]

It’s operated by the remaining vacuum in the vacuum tank. Hence why it only works a few times before the vacuum runs out.

[@Mrderlinkinparkfan]

​@@rx7bruh ah thank you for clarifying

[@johndoe-yi6pn]

Im having a similar problem to the other guy here in the comments. I have a series 8 FD and my problem is as follows. Rev in nuetral: Cant get to +4psi Boost pattern 7-0-0 KOKO Test: CCV rod moves in like normal 6+ times KOKO Test: TCA doesnt necesarily stay in on the Key-on position. Kinda pulses in if you get what I mean. But it reverts back to its normal position though. Is the rod supposed to stay in on the key on position or is it just supposed to pulse? I can get a video up of it if you'd like. It moves in when revving in nuetral though. Check valves are all upgraded to the Viton ones that Dale Clark mentioned. Pressure tank holds pressure Vacuum tank holds vacuum (hissing sound on both) All lines good. All couplers good No signs of smoke on smoke test. All solenoids have been tested and function like they should. (I managed to get the "black box" apart and put in new check valves and test the solenoids lol) CRV and ABV both pop open when tested under a vacuum guage. No hoses are collapsing as i took off the turbo inlet hose temporarily to test for that. My only suspect is the Wastegate and Precontrol Actuators as i havent looked at these yet. The TCA would be the other suspect as something seems off about it as i mentioned earlier. Unless my explanation of it seems normal to you, in that case, i can rule it out. What do you suggest? Would the wastegate and Precontrol actuators cause these issues?

[@rx7bruh]

You don’t build much boost revving in neutral, you need load. Sounds like you have a massive boost leak if you have 0 psi after transition. But I know you said couplers and such are good. The TCA doesn’t move at all until 4500 rpm which is when it pulls in and opens the flap to send exhaust to the secondary turbo. Possibly wastegate and/or precontrol issue, stuck open likely.

[@johndoe-yi6pn]

Okay, ill take a look again. Perhaps i crossed a vacuum line or left unhooked when putting the uim back together. Thanks. And yes im aware the car doesnt build boost while not under load, however, it should build upto 4psi in nuetral past 5000ish but that doesnt even happen.

[@rx7bruh]

@@johndoe-yi6pn you will not build more than 1-2 psi revvin in neutral

[@thomas54321blastoff]

Hey, I've watched this video a couple times now and still can't work out where I've gone wrong. Would really appreciate any input you might have. Essentially I had to pull the motor for rebuild and have since put it back. Prior to rebuild the seq twins worked exactly as they should. Now with the engine back, it starts, runs and idles fine but I make 0 boost. Not 0 PSI, but actually no boost as when I rev in neutral the boost gauge goes from -0.4bar to -0.6...0.8 and so on. I have triple checked all of my vacuum fittings and connections but can't for the life of me see what could be causing it. For such a dramatic loss of boost it surely has to be a massive leak somewhere right? Also went under the car and confirmed wastegate actuator arm is still attached. Any ideas would be amazing. Cheers

[@rx7bruh]

Sounds like there’s a leak. I’d check the rubber hoses to the BOV and Charge Relief valve, the o ring in the y pipe, and the y pipe to crossover tube connection (coupler on 93-95 or gasket on 99 y pipe) and check all intercooler couplers as well.

[@rx7bruh]

I’d also verify your gauge is functioning properly

[@rx7bruh]

Also make sure the turbo control actuator arm hasn’t come off as well

[@thomas54321blastoff]

@@rx7bruh thanks mate, I'm in the process of replacing couplers and rubber pieces so will pull put the y pipe and inspect today. I did replace the oring during the rebuild, however I will double check its not pinched etc. Thanks for the fast response, will report back with findings

[@thomas54321blastoff]

@@rx7bruh Hey okay so uponn further inspection, there's a definite ticking noise coming from the turbo area. It's metallic sounding and confirmed to be from the turbo/manifold via a stethescope. Is it possible to incorrectly install turbos in such a way that the wastegate or manifold flap door thing are 'stuck' open letting all boost out? Will upload a video I took shortly with the sound - it's pretty bad but doesn't really increase with RPM too much from what I can gather. Also no smoke from turbos and they were working 100% fine before engine rebuild.

[@mariosandreou7441]

Hello, i need your opinion and your help if you can please. I have recently rebuild my engine on my 1996 jdm rhd rx7 fd3s . Im running a stock engine with the sequential turbo but my engine don't have the rat nest but it has the black box the more simplified vacuum system . On the first turbo i get 0.7 bar when i accelerate, But when the second turbo kicks in my boost jump to 1.1 to 1.2 bar of boost and not 0.7 bar like it is from the factory. But is not only this problem. When my rpm reach 5000-6000 the engine cut of from it's power. The car slow down like i get a fuel cut from the ecu. Below 5000 rpm the car drives beautifully but above this the car won't accelerate. The only modifications i have on my car is this:exhaust from HKS. Catalytic converted from SARD. Air intake from A.R.C and intercooler little bigger and thicker from Knight Sports performance. I don't know what is the problem. If you have any idea i would like to hear it. Thank you for your time friend, i wish you all the best!

[@rx7bruh]

During primary turbo operation boost pressure is controlled via pre-control (pre-spool) actuator. During secondary turbo operation the wastegate comes in to help regulate boost pressure. So if your boost is spiking during secondary turbo operation I’d be looking at your wastegate solenoid and actuator. I think the stock ECU will fuel cut because it doesn’t have the capacity to increase fuel above the set boost levels. So you’ll just be leaning out which is bad. You need to figure out why your wastegate isn’t keeping your boost levels down. Even with your modifications I wouldn’t expect to get more than 12psi /.8 bar

[@mariosandreou7441]

Thanks for the reply friend! I appreciate it! Im going to check what you told me.

[@maniacallyhappy]

What do you think of running a simplified rats nest for a sequential turbo set up?

[@rx7bruh]

I talked about that in the video.

[@rx7bruh]

Starts at 31:16 if you’re interested

[@maniacallyhappy]

@@rx7bruh My bad! I saw this video at like 2 am and got half way through, way before getting to that point of the video. Yeah, emissions delete, thermal pellet delete, double throttle delete sound familiar lol. Not gonna lie, "Simplified" rats nest may be the reason why my FD won't stop idle hunting, I was thinking I might have a vacuum leak at the lower intake manifold, seeing this, I think I may as well just pull out the engine and redo the vacuum system as I have zero faith in the mechanic who helped me put it all back together after my engine rebuild. Have an annoying oil leak and have to check my power steering and steering rack because I think he busted the shit out of everything trying to get the engine back in the car... oh well, learned my lesson to be weary of who I let touch my car

[@efrainhuerta1585]

In minute 7:51 witch way its the actuator open. With vacuum open ?

[@rx7bruh]

When Vacuum is applied it closes the charge control actuator

[@efrainhuerta1585]

@@rx7bruh Thank you for info that would save me time. Question again in minute 11:30 you talk about prespool and wastegate selenoids. How do you know witch plug goes in to each selenoid. They both look same and they can be plug left or right. Any advise and how to identified the electrical plugs?? Once again thanks for info

[@rx7bruh]

@@efrainhuerta1585 you can’t really switch them, one has a white marking on it which goes to the right one if I am remembering correctly. Otherwise you can check the wire colors and consult the wiring diagram for which one goes where.