Boost issue question?

1989 GTA Turbo boost builds nicely on half to three quarter throttle but tends to back off boost a bit if throttle is hard down. I am currently looking for leaks but any other ideas?

Trevor.

Is your dump valve fitted the correct way around ?. Ive seen some on backwards !.
Also the bosch dump valve can get weak as it gets older, so boost maybe overcomming the spring and pushing it open.

Do you have a good boost gauge on yours ?.
According to the D501 Renault manual, the Boost should be a maximum of 0.8 bar.

That or actuator is weak .

I assume that if the dump valve was the wrong way round it just wouldn't work as the boost would be pushing the valve onto its seat? Does sound a little like a weak actuator. Think I may have a Forge one around somewhere. Is it ecu controlled or rely purely on spring pressure?

Trevor.

Purely spring rate .You could fit a dawes device type adjuster but be sure to fit a good quality boost gauge and keep it within std boost limits .

Paul,

I havent looked yet but are you sure it's .8 bar? that's nearly 12psi. More than I am used to with the Esprt's which are more like 8psi.

Clee,

Had a look at the Dawes device type and wonder if in this case it is a band aid rather than a cure?

Trevor.

I use them for adjusting boost for tuning more than anything else ,far better than a bleed valve and it saves no end of time and burnt fingers .They do stay very stable but yes better to set boost on the actuator arm .

Std boost is 10 psi but if you want to up it a bit
http://www.renaultalpinetuningservices. ... +Upgrade+/

Paul,

I havent looked yet but are you sure it's .8 bar? that's nearly 12psi. More than I am used to with the Esprt's which are more like 8psi.

Clee,

Had a look at the Dawes device type and wonder if in this case it is a band aid rather than a cure?

Trevor.

Just checked back over my old threads.
Its actually 0.85 BAR MAX on a GTA Turbo. As per the renault workshop manual.

See here.
http://www.renaultalpineownersclub.com/ ... e&start=15
Halfway down page 2.

Trevor - it could also be fuel mixture ratio, just another possibility if it is directly related to throttle position - the ecu does not have a throttle angle input, and hence sets fuel ratio on manifold pressure. You can maintain the same manifold pressure, and back off the throttle slightly... this restricts the engine airflow slightly, but on the flat not enough to affect things (boost - under normal conditions), but this does then enriched the fuel mixture directly (AFR). You can test this easily on the road by backing the throttle off very slightly, and see if the boost picks back up immediately. So if the actuator doesn't help, have a look at your pressure reg, reg control lines, and injector cleaning.

Thanks all,

I have tested the wastegate actuator with a Mityvac and this appear to be working as it should so will not replace that at this stage.

Martin,

What you describe is exactly what is happening, backing off the throttle slightly improves boost. I have bought a Dawes type device off Ebay today and will fit that and see what happens also. Can you tell me how to check the components and where they are located?

Trevor.

I

Trevor, check the small hoses that go into the plenum (the one with V6 on it) at the end near the turbo.

There's two small hoses - if you have a slight split you can potentially bleed off the boost and when you come on and off the throttle it can open and close the split. (Split the other one and it'll overboost)

Worth checking as I had it on mine years ago and I was losing about quarter of the boost for a while before it split more and I could spot where it was.

20 year old rubber hose, so always worth checking the obvious before you start digging deeper.

Martin,

What you describe is exactly what is happening, backing off the throttle slightly improves boost. I have bought a Dawes type device off Ebay today and will fit that and see what happens also. Can you tell me how to check the components and where they are locate?I

Hi Trevor... could have chatted about it earlier, I was going to try and pull you over M1 / M25... I waved to you on the M1 in the black Audi A4 that followed you! Laugh

Just replied to your spotted thread . Would have been nice to have had a chat too.

Trevor.

Having picked up the manual boost controler last night I'm not sure its the one I need as it's a bleed type? Also when I got the car the boost gauge wasnt working but the car definately boosting so on looking at other turbo GTA's at the Ace I see that a casule in the engine bay was not plumbed in. I assumed this was a boost sender unit and sure enough when I T'd it into the boost line for the Recirculating dump valve, the gause worked. Is this correct? Pic below. The yellow Tygon tubing is temporary to test it and I now have black silicon.



Also what is the smaller capsule below the one I have plumbed the yellow Tygon into?

Trevor.

Yep ,that is the gauge sender .
You can feed it from the inlet plenum or from the inlet manifold ..If you fit an aftermarket gauge then plumb in to the manifold so you will see vac as well as boost .This helps as it will show up leaks if and when they occur + you get true pressure at the pots .

The one below is not used .It has a vac size barb and is tapped in the rear to accept some sort of pressure sensor/overboost etc .There are no wires for it in the loom .I expect that whole assembly it is a generic Renault item .