First off hello everyone, my first post

I have a 1994 Type R2 which I bought with a boost problem (after reading a lot about the rx7's boost habbits I was sure I could sort it). The car has a full Kakimoto twin tail system (inc de-cat), HKS panel filter, Blitz ss bov, standard ECU.

The problem originally was..

The first turbo would spool on WOT at low revs to 0.7bar no problem, as you kept it WOT the boost would drop off (as it hit around 3,500 - 4,000 rpm) to 0.2 bar. It would stay at this to redline. If you floored the accelerator above 3,500 - 4,000 rpm it would only hit 0.2bar and not make 0.7bar, it would only make 0.7bar if you were WOT at low revs. I'd read about the hoses coming off and thought I could sort it.

I did some looking around and found a vacum hose off under the inlet manifold. I placed the hose back on and cable tied it on. Set my Defi boost gauge to warn if it got to 0.95bar (as a helper to back off if something was wrong).

I took the car out and WOT at low revs gave 0.7bar (as before) but as it revved it stayed around 0.7bar (wahoo I thought) but as soon as it got to around 4,500 - 5,000 rpm the boost came in real hard I saw the defi warn flash up and backed off. I tried some gentle runs to see where the boost would end up (with caution) and even part throttle was seeing nearly 1.2bar. It almost feels as though there is no wastegate control when the 2nd turbo comes in, it feels that if you WOT when the turbo hits at those revs it'd go as high as it could. I've had around 16 turbo'd cars and have come accross similar feeling wastegate (or non) control when messing with Pinto turbo setups on SU carb many years ago). What I'm getting at is that I know what it feels like when the boost would go as far as it could.

What I'm trying to find out is if anyone knows of any causes of the 2nd turbo hitting real hard like this?.

I've so far removed the inlet manifold and checked all hose connections, checked the one way valves (they work 1 way ok but seem a bit restrictive when blowing through them, should they be slightly restricted?). I've checked all the hoses are connected to the actuators on the turbo's, MAP sensor feed on etc. I've just removed all the intake pipework and removed both hoses from the front turbo inlet compressor housing feed to the actuators. They both have the pills in line and the pills are straight (understand they can turn and block pipes) and flow air nicely.

I was a bit dissapointed the pills were straight in the actuator hoses and I'm now at a bit stuck for things to look for


I've just replaced the 2 hoses to the actuators with normal hose (without pills) and I've reset the ECU. I can't get out for a while as it's snowing and the roads are like an ice rink here but I'm not confident the no pills hoses will work as the car would still pull the boost on partial throttle (ie not just a restriction quick spike).


Only other things I can think of is maybe an actuator seized up (from when the 1st hose was off and no pressure signal was being sent to it). Or the ECU has something to do with the problem (as the car wasn't used a lot and the battery was disconnected when not used and would have been reset with the 1st hose off causing some sort of ECU learn with the hose off and the 0.2bar, then I've replaced the hose and the ECU isn't aware as it learnt when the hose was off??, nonsences probably)


Any help/advice appreciated

 

You need a boost controller
Return the original prespool hose (with the restrictor) to its original location, and put in a manual boost controller in the wastegate line.

http://www.robrobinette.com/boost_controller.htm

 

And a damn ECU upgrade.

 

Make sure the pre-control and boost control solenoids are working properly. You can pressure and test them if you have a 12 volt powere source you can hook up. Some people have posted that some solenoids react differently cold vs. heated up.

 

Your symptoms sound like the WG is not operating. Here is a site w/ some troubleshooting info:

http://www.autosportracetech.com/RX-7/rx7stuff.htm

 

Thanks for the replies

Really does seem like the wastegate is not operating (as DaveW says), like I say even if you slowly accelerate the boost feels like it will just keep going as far as the turbos will flow. It's not just a spike.

I'd like to think the MBC would sort it but I haven't even had it WOT at high revs and it's gone to 1.2bar, I'm too scared to keep my foot planted to see if it stops at 1.3bar or something lol. It just feels like it'll go to 2bar or so.


Yep Power FC waiting until I've sorted this out. The engine has recently been rebuilt and I'm not using it, I'm only troubleshooting until I can sort this problem and then it's going for the power FC and mapping

 

From the link posted..


This is all it says about too much boost, which I've obviously checked.



One thing that did catch my eye was this quote from the same link..


Paying attention in this instance to the part that says 'the one with the pill in it'

This is suggesting that only the wastegate control line has a restrictor pill in it. Now, I have both hoses from the compressor housing off and they both have pills in them is there not supposed to be a pill in the turbo precontrol hose?.

 

Both hoses have restrictor pills. Don't believe everything you read........ except for me

 

There should be a pill in both of those lines - that statement is a tad misleading.

Yes, the stock check valves should offer some resistance to blowing through them - that's totally normal.

Considering the primary turbo is doing its job properly, I'm guessing something is funny with the secondary system - like the wastegate for the second turbo isn't opening or isn't opening enough.

Dale

 

yeah, just read the whole of that boost control link and it says about the restrictor in the pre control hose.

Also it says that the bigger the hole in the restrictor the bigger the spike on change over, so better be putting that original pre control line with it's pill back on before I test drive

 

Thanks Dale

 

So, you basically have a "FULL EXHAUST" w/o any sort of boost controller, aftermarket fuel management, nor wastegate porting? Aside from a boost controller, having a straight-through exhaust will likely cause the boost spikes and/or boost creep that you are experiencing. Like the guys said before, you really need some sort of boost management and a PFC.

 

I believe that on some newer versions of the turbus the pre-control had a pill built into the hose nipple and therefore no pill. The pre-control you definately do not want to run without that pill in it. The pre-control controls when the secondary comes online. If you have the line wide-open with no restriction the secondary comes on earlier and you will get a huge boost spike at around 4k or whenever the transition is. If you have the line completely blocked you will conversely have a huge boost dip at the transition. The proper size nipple is vital to get a good boost pattern.
Leaving off the other line will pretty much just limit you to about 7psi, no real danger there.

 

Right, put the wastegate pre control hose (with restrictor) back in and changed the actuator control hose with my own (without restrictor) and put a ball and spring boost controller inline in the same hose. Also reset the ECU (just in case).

Finally taken her out for a spin (in some scary ice, especially scary when I've been driving a 1.8 mercedes for 2 weeks)

It seems like it's ok on transition now, I don't have any preload on the boost controller (but they run a very tiny bit of preload but literally enough to seat the ball bearing) and boost is coming in at 0.6bar on 1st turbo and you can feel the transition but it's only spiking a tiny amount up to 0.7bar!.

I'm a little bit cautious about being elated (as it's freckin dangerous out there) because I haven't done any long WOT at high revs runs to make sure it's 100% ok. Before it was coming in way too hard though on transition and it's not doing that now I managed to floor it briefly at 5,800rpm and it didn't spike beyond what I said.

If it is ok, it seems I've been a bit over cautious (if the ecu reset hasn't done anything) as the last time I drove the car when it was seriously overboosting I would sware blind that a restrictor inline in the wastegate control would not have any effect (as I tried easy throttle runs and it still went mad when transition came in). It just seems the setup these cars run and the way they prespool is so different to anything I've experienced (turbo'wise) that the restrictor in the wastegate line was enough to make the prespool and 2nd turbo action behave like it did. Normally a restrictor in a single turbo watsegate line would have an overboost effect at WOT but on a slow build of revs it doesn't spike like it would on WOT. The setup these cars runs seems to spike however you throttle up because of the complexity. Feel a bit stoopid not trying this before but was blinded by previous experience

Oh well I've learnt a lot about my car (as I've had it in bits a few times now lol) and I'm pleased.


Thankyou to everyone who's offered help, really apprecite it

 

Do a full test on the turbo system the next time you get out. Put it in 3rd gear and rev it from 2,800rpm to at least ~6,000rpm. This way, you can see what the primary hits (3,000rpm), what it hits at transition (~4,500rpm), and what you get after transition.

 

Glad to hear that it's working right ............... You're very welcome

 

Hi again

Right, been out for a long play today..

Highest spike of the day was 0.85bar (which was recorded on my defi boost gauge), this is literally the highest and most spikes on WOT would only see 0.80bar. I think this is pretty good control considering what I had before?.

Normal boost is 0.75 bar on 1st turbo and an increse to 0.80bar or rarely 0.85bar when 2nd turbo comes in, then it backs off slightly at the high end of the revs.

Is it worth running another ball and spring boost controller in the pre control line to lower the transition spike or am I being over cautious at 0.80bar?

Also it's worth notuing the temperature here is about 0*c which may mean it's boosting more than normal

I'm quite pleased and it seems to go quite nicely