Second turbo intermittently comes online

[TonyBlair]

Advice and help if you can please guys...

Recently I have noticed loss of power out of the Rex where the second turbo should come online. I\'m fairly certain it is the case that the second turbo isn\'t coming online rather than something else.

It\'s much more noticeable in 2nd and 3rd gear. It pulls very nicely up to about 4500rpm (first turbo doing it\'s job well   ) then at around 5000rpm I usually expect to get pushed back into my seat whilst the second turbo does the business... this doesn\'t seem to be happening.

The intriging fact about this problem is that sometimes the second turbo does come online! 4 out of 5 times, it appears not to, then once in a while... whehey! the power is back again!?

It\'s a 92 FD with stock twins (recently rebuilt with 360 degrees thrust bearings - if that makes any difference?). I\'ve got a HKS boost controller currently set to 0.9 bar as the max limit of boost - was told by GHB Motorsport who rebuilt the turbo\'s that\'s a safe level. The guy there Bob set-up the boost controller for me so I assume he\'s done it right.

I have an aftermarket boost gauge which seems to show the boost going up to 0.2-0.3, this is where I feel the loss of power. On the rare occasion that the power re-appears I\'ve noticed the boost go up to around the 0.5 mark.

I was considering taking the Rex up to TDI this weekend to get my Apexi installed and mapped... I\'m not sure what to do now, it could be a wasted journey since there\'s no point mapping a car that isn\'t running properly?! Or perhaps the mapping will reveal the problem?

Any thoughts, comment will be most appreciated.

Thanks,
Jon

[nikp]

Well, if i understand your problem correctly, firstly it sounds very very similar to the problem i\'m having at the moment. I\'m in fact taking my Rex to pip at WGT tomorrow, cos i\'m fed up of trying to diagnose it!

So, if i understand your problem correctly, your boost is not very often peaking past 0.2-0.3 bar - this is very low. But where abouts on the rev range is this boost occurring? Is it consistent boost at this level, or is it higher and then drops off? For the second turbo to come on line it requires 7psi of boost or more, and this equates to approx 0.5 bar - therefore chances are, your second turbo is not coming on at all - not even when you hit 0.5 bar.

Firstly, i would say check all your hoses for splits and potential boost leaks and replace if necassary. Also if you still have the original plastic intake and intercooler pipes, it might be worth replacing those with more reliable hard pipe kits. Then it might be worth consulting this web page: //www.rx7city.com as there\'s some useful stuff on there about troubleshooting the twin turbo setup. However, i couldn\'t figure out what my problem was, so as i said before, i\'m off to pips!

[jonrx7uk]

Pull off the pipe that connects to the front of the Charge Control Actuator.  This will tell you if the Vac chamber is doing its job.  You should hear a strong hissing if everything is okay.  If not, you need to trace the problem as the vac chamber is necessary for controlling the 2nd turbo coming online.  I traced my problem to a kink in one of the vac pipes on the Charge Relief solenoid after replacing all the hoses.

Cheers
Jon

[TonyBlair]

Thanks mate! I\'ll check it out when I get home tonight.

Much appreciated your input.

All the best,
Jon

[TonyBlair]

Originally posted by nikp
So, if i understand your problem correctly, your boost is not very often peaking past 0.2-0.3 bar - this is very low. But where abouts on the rev range is this boost occurring? Is it consistent boost at this level, or is it higher and then drops off? For the second turbo to come on line it requires 7psi of boost or more, and this equates to approx 0.5 bar - therefore chances are, your second turbo is not coming on at all - not even when you hit 0.5 bar.

Hi Nik,

Correct - the boost more often than not peaks at around 0.2-0.3 and goes no higher. This boost occurs at around 3k rpm. The boost is consistent (stays at 0.25\'ish) up to 7k rpm.

I think I understand what you are saying; for whatever reason (boost leak perhaps) the first turbo is not achieving 0.5 bar of boost, therefore the 2nd turbo is not coming online.

I initially thought that the revs determined when each turbo came online, however you are suggesting that a combination of factors (including current boost level) determines when the second turbo comes online - this actually makes sense to me  

I think my best bet is to start searching for baked/cracked/kinked pipes etc.

Thanks for your comments Nik and Jon.

All the best,
Jon

[nikp]

Yup, that\'s right. Basically, some of the actuators will only start to move once there\'s enough boost. And if those actuators don\'t move, then other parts of the system won\'t operate. It could well be something simple, but currently your Rex aint performing half as well as it should be!

[nikp]

First place i would check is the Y pipe connector hose. Could be partially split, venting boost. However, the fact that sometimes you get better boost is interesting - which makes me think it\'s not a split hose. However, sometimes hoses can get more pliable when more heat has been applied to them, so if your \'good\' boost is predictable, say, when the engine is a bit colder, it could still be a hose.

However, i would guess not. But it\'s basically got to be a system of elimination - eliminate all possibilities until you can corner the problem down.

[TonyBlair]

I guess I\'ll just have to don my over-all\'s this evening and start eliminating the elements that could cause the issue, starting with checking the Y-pipe and the other relevant pipes/hoses...

It is interesting that the problem is intermittent. You could be right with your suggestiong that heat plays a factor in whether a pipe/hose/"something else" is effected at different temperatures.

I\'ll have a look tonight and report back.

Cheers
Jon

[nikp]

I shall also report back after tomorrow, cos as i said, I\'m off to WGT to try and get mine sorted. I\'ve given up trying to figure out what my problem is, but it\'s very similar.

Basically, mine boosts fine first time (0.7 bar), then afterwards only boosts to 0.5 bar (Meaing the second turbo is not online). Occasionaly the boost will be back up to 0.7 again, but not often. So, it\'s a similar problem, and may be a similar cause! But i have checked all hoses, and replaced all the old rubber (Now plastic!) hoses with silicone ones.

[deanflowers]

mine was doing this and was down to a faulty solenoid which pip found almost straight away,

but my turbos have now died so back to the drawing board for me

[TonyBlair]

Originally posted by deanflowers
but my turbos have now died so back to the drawing board for me

That\'s bad news mate  

My twin\'s were fduk\'d when I got the car, cost me £1300 to get them rebuilt. I\'m fortunate in the sense that my dad had the tools and experience to take them out and put them back in (sounds like such a simple task put like that). Adding the cost of the labour to do that would have pushed the bill up a lot higher.

I feel for you mate. Do you think you can get the sorted soon?

Cheers
Jon

[nikp]

There\'s only one option left: Go Single!

Nah, bad luck dude! Maybe worth trying second hand? Bit of a risk when you\'re talking turbos, but if it saves money, maybe worth taking.

[deanflowers]

ivemanaged to source a set of secondhand ones, but as you say the labour is awesome, so will probably have a go myself i have the engine removal vids so i can see what is involved in taking the turbos off,

at present i am painting out the garage a nice bright white so i can see what iam doing when i start.

ive noticed some cracking on the one flange which may cause me problems so may not fit them yet will see the state of mine when i take them off.

single would be nice though

[TonyBlair]

Dean, any chance you remember which solenoid it was which was causing your turbo problem? I think I\'ve got a diagram somewhere of the solenoids and hoses etc. I don\'t know whether the solenoids are named/labelled?

Cheers
Jon

[jonrx7uk]

Try this