My car is an S4 Turbo II, engine is stock, turbo is OEM. Here is a list of modifications done to the car by the previous owner regarding the performance, with "spec" from manufacturer:


1-) CC replacement straight pipe & pre-silencer
Racing Beat #16207
Turbo boost climbs from 5.5 to 7.5 psi.
14% / 25 horsepower increase:
(SAE) 185 to 210 bhp @ 6500 rpm.
Torque 183 to 196 lb-ft @ 3500 rpm.


2-) HKS #7 Power-Flow air filter (3333EC-58182K)
Greater response & peak power. Turbo lag is virtually eliminated. Twin-scroll turbocharger boost is increased to 9 psi.
15 horsepower increase:
(SAE) 210 to 225 bhp @ 6500 rpm
Torque 196 to 210 lb-ft @ 3500 rpm


3-) Borla T-304 stainless steel performance exhaust
Flow-through design bumps power up by 15%. Turbo boost climbs from 9 to 12 psi. 30 horsepower increase.
(SAE) 225 to 255 bhp @ 6500 rpm
Torque 210 to 245 lb-ft @ 5000 rpm
Curb weight is reduced from 2875 to 2800 lbs.


3-) HKS PFC F-CON & FCD fuel management system
Programmed Fuel Computer monitors data originating from the absolute pressure transducer and OE ECU which allows for a longer injector pulse width to ensure proper air/fuel rate during high air flow conditions. Fuel Cut Defencer raises fuel cutoff beyond attainable specified boost levels.
Tri-Point Engineering


4-) Down pipe high-flow converter
Pre-silencer high-flow converter
Tri-Point Engineering

I know some of these modifications are old school like the Hks PFC F-Con and FCD, so I bought almost everything to put a Power FC in the car. I haven't done it yet, but will do soon. I don't have a boost controller btw.

What I would like to know is why I don't boost more than 6-7 psi with that actual set-up. It's my second modified TII, and the first one was boosting 10 psi easily with similar mods.

I also got a low idle that I am desperately trying to fix. I've done this as advised by scrip 7: ( on that thread )

1) A visual inspection of the throttle lever to insure that it contacts the stop screw (by using a mirror and flashlight or temporary removal of the intercooler)

(2) If a gap is found between the throttle lever and stop screw, inspect thermowax and fast idle cam position adjustment, dashpot function and adjustment, and throttle cable slack.

(3) With the throttle lever against the stop screw, perform vacuum leak test using the propane method.

(4) ...

(5) ...

(6) Adjust BAC screw (if equipped) to obtain 750 rpm idle (or your preferred speed at 1000 rpm or less) and re-adjust A/F mixture screw if required.

(7) Adjust TPS per FSM and re-adjust idle speed if necessary.

I wasn't able to adjust the idle more than 5-600 rpm and it want to die. It was first at 1400 rpm and bouncing so its better now but far from perfect. Engine stops each time I'm at a traffic light with A/C on, it was like that before I lowered the rpm to 5-600.

I will buy a timing light tomorrow to adjust timing (#4) as I am unable to do it without proper tools. I haven't tried adjusting the A/F mixture screw (#5) on the PFC F-CON, as I wanted to make sure the timing was good first.

Propane test haven't done any results, there is no leaks that I could find with that technique, but I will buy the necessary hardware tomorrow to do the compressed air method, as I think a leak could lead to low boosting, even tho I don't hear anything abnormal.

If my Exhaust is too restrictive, I will remove it, but I would like to boost properly with it, as I think they will force us to do emission test in a near future.

So advises are welcome.

 

how many miles on the turbo?

 

Turbo has about 39 000miles.

 

Perhaps the previous owner modified the car correctly and ported the wastegate? That should keep boost in check. Only way to tell will be to pull the downpipe and get in there with a mirror and light.

 

+1

Fixed. If an aftermarket manufacturer claims that adding an exhaust part increases peak boost, it's due to boost creep. The S4 wastegate port is really tiny (13mm), so it doesn't take much. The normal way to increase boost is with a boost controller and a properly sized wastegate.

 

Yes, you are right, my last RX-7 was creeping badly and this one isn't. I'll be quite surprised if the wastegate was ported tho, because every single modifications that was made to the car was carefully documented by the previous owner, and nowhere it is stated that the wastegate was ported. I got all the bills. But I will definitely check later as soon as I can lift the car and remove the downpipe.

Maybe it was a well kept secret at the time that you can port the wastegate and they havent mentioned that anywhere... We'll see.

 

Enjoy the fact that your boost is in check.

You may seek more boost with a boost controller. You can build a ghetto manual boost controller with hardware store components.

 

No, unfortunately... I am pretty sure the wastegate is not ported, but I will do that as soon as I can and buy boost controller, to at least control that properly. This was my problem:



It's probably the main reason of my erratic idle as well...

 

get the corksport TID

 

The stock TIDs always crack. It'll definitely cause idle problems, but having an opening like that won't keep the turbo from building boost. The mixture will get a little bit leaner due to unmetered air, but it wouldn't be any kind of restriction.

 

Does anyone know where can I find a TID without paying 200,00$ ? Corksport doesn't have that on their website. They just have air intake for n/a...

I'll buy a cheap one on ebay if I cannot find any better solutions, but I'll have to wait for shipping and for solderig the bungs that I need. So something already made to fit there would be awesome.

 

corksport does have it under the turbo system parts section instead of the intake section

http://www.corksport.com/mazda-rx7/1...-system-parts/

 

My idle is still shitty, I don't have a camera at the moment to record it but i'll try to find one this week. Its below 1000rpm. Each I put it in gear it goes down to about 600rpm and if I put the A/C on it dies. I'd really like to use the A/C but I was never able, as each time I stop at a traffic light engine dies.

I adjusted the fast idle cam and there is no gap between the throttle lever and the stop screw,

My thermowax is not stuck open and is functionning properly. My throttle cable is a bit loose, I adjusted it as tight as I could. Should I change it? Even if I keep it tight with my finger holding it, my idle is not consistent tho.

I did a vaccum test, changed the TID, readjusted the TPS, nothing but the same...

When I am adjusting the bac valve it doesn't change anything, except when the screw is completely deep inside the bac valve the engine dies. I took the resistance and it is at 13.7 so should I change it as the FSM says? I tried to adjust the fuel mixture screw inn the HKS pfc-F-con, but it does not affect the idle.



I don't know what to do...

Any help would be greatly appreciated.

 

So: "low" boost (lower than expected) and low, rough idle? Have you thought about getting a compression check?
You might also try removing the F-con just to make sure it's not causing any issues.

 

Just make your own! It's super simple and cheap...

 

Throttle cable should be loose, if it is too tight it will actually cause irratic idle!

 

i just had a shitty idle problem. turns out when i did my FMIC i did not reattach my trailing coil pack to the fender, so it was randomly grounding and sometimes not grounded at all. noticed it the other day, ran a wire directly from the bolt holes in the pack to the negative battery terminal, idles flawlessly now. id say check grounds?

 

mine stock setup used to spike not creep.


I had full exhaust w. offrd pipe/720ccx2/fcd/filter on stock TID. 3rd+ gears used to hit 9 psi and drop to 7 by redline. on really cold night it would almost hit 11 psi dropping to 7.

When i did a BNR it also spiked on ^^ that setup and no boost controller. THEn i installed a bad *** 3" mandrel TID and it started creeping to 14 psi at readline. Creep was never fixed. so i put stock TID back on to control boost.

 

did you get around the checking the waste gate?

also:
are you jumping off the connector by the battery to put the computer into a "learning mode"

 

I did something amazingly stupid today, just to be sure that I don't succeed. I've adjusted pretty much everything I could today, and my idle was getting a bit better. So I told myself, why not go for a ride and warm up that engine! I bolted the intercooler, and put back every vacuum I removed previously (in a hurry as I wanted it done).

So I went to the highway. While on my way the idle seemed pretty good at 850-900rpm so I floored the gaz while entering the highway on 1st, 2nd and 3rd gear. As soon as I boosted in 3rd car started to run incredibly shitty with no power. I took the next exit (about half a mile away from the highway entrance), and stopped on the street side. My intercooler wasn't bolted properly so the piping went off. I bolted everything back (happily I was carrying my tools). I ended with a 2000rpm with everything bolted back together. I cam back home, and started to redo every adjustment. For now Idle sits at 1600 rpm warm, 3200 cold.

I hope everything is OK.


I am sure my compression is (was) ok. As I've read on the forum erratic idle is a common problem, and my car sound like a lot of videos posted here.

I guess I should try to remove the PFC-F-CON. It's not a bad idea.

I bought one custom made by a nice guy in my area. So this is already taken care of.

Thank you, it is really good to know. I won't buy a new one then!

Checking grounds is my nightmare. Each time I think about an electrical problem I got nausea. Still it is my 5th RX-7 so far, so nausea isn't that bad after all. Everything like the coils packs are on the OEM spot so I doubt it is a bad ground but I don't know for sure.

I don't have a garage, I am working in the street for now (currently shopping for a house) so I haven't had the time/space to lift the car and to remove the downpipe, etc.

I didn't know I could do that. I've unplugged the BAC and my Idle was the same so I try to fix everything around it for now. But I'll try that tomorrow.

Thank you all for your contribution, I will continue my quest for a nicely idling RX-7. Hopping I haven't toasted my engine.