Intermittent no boost - why ?

[hobieboy]

It happened a few times on my way back from the track earlier this week...

Driving on the highway, step on it. And nothing. Zero boost even if I floored the car. RPM doesn't rise and of course no sound (i.e. action) from the BOV when I lift. Then, everything back to normal after, say, 15 sec. (this is also the random part).

I suspect it must be a stuck open WG?

My set up is... Tial 46mm WG with Tial 50mm BOV & Profec B boost controller. The controller can up the boost but minimum pressure is set by the WG (it has a 0.4 bar spring).

So 2 questions....

1) Anyone has any tips about testing Tial WG? And any parts that could need replacement?

2) Any other guess?

thanks!

[wjfk32]

Greetings:

Same problem here...It was a nightmare...Checked everything I could think of/ (INTERMITTENT BOOST-CUTOFF/HESITATION)..

Finally found it was the fuel head inside...The piston was getting stuck..Plus plunger...

Easiest solution if it works..Techron or if anybody knows any other secret solution..If not start taking things apart...

Hopefully this is your problem...It could be so many things...

Good luck

Walt

[hobieboy]

Originally Posted by wjfk32

Greetings:
Finally found it was the fuel head inside...The piston was getting stuck..Plus plunger...

A little slow... how could the fuel head affect boost?

In my case, my car is EFI-ed so no fuel head

[wjfk32]

0k--
No fuel head.......

I would chk for air/leaks and vacum hoses. Electrical/fuses and relays...
There are guys on the board here with EFI--who would be a great help.

Hopefully they will chime in...or do a search.


Walt

[WERK I]

I would check the wiring and the sensors, MAF, MAP, TPS, etc. A wastegate is not a fail-safe device. In other words, if it fails, it remains shut and boost rises beyond the set threshold, over boosting the engine. I have never seen one fail in the open position. Besides, your exhaust noise would be higher unless it's muffled, in that case.

[hobieboy]

I datalogged the engine parms when this happened...

TPS is accurate in reflecting my right foot. Fueling follows RPM/MAP. Other parms - CLT, MAT, ... are all normal. And there's no sign/sound of misfires. That's why I thought - could it be that the WG is stuck open?

If my turbo starting to fail, will this be the symptom?

[RarlyL8]

What about your BOV?

[mark houghton]

Wastegate is most likely stuck open, or the BOV.
You can do a quick and dirty WG check by applying pressure to the diaphram. Disconnect the air line from the intercooler and plug the port at the IC, then with a suitable air source put pressure to the line leading to the wastegate. If you've only got a .4bar spring, then you shouldn't need much more than 6 pounds of pressure to open the gate. Do this with the engine running and you should hear the exhaust exiting the WG pipe.

Wastegates usually fail in the opposite direction....failing to open under boost due to a ruptured diaphram. But if the valve guide or valve stem is corroded or carboned-up, it's possible that it's sticking in the open position.

[hobieboy]

Originally Posted by mark houghton

Wastegate is most likely stuck open, or the BOV.
You can do a quick and dirty WG check by applying pressure to the diaphram. Disconnect the air line from the intercooler and plug the port at the IC, then with a suitable air source put pressure to the line leading to the wastegate. If you've only got a .4bar spring, then you shouldn't need much more than 6 pounds of pressure to open the gate. Do this with the engine running and you should hear the exhaust exiting the WG pipe.

Wastegates usually fail in the opposite direction....failing to open under boost due to a ruptured diaphram. But if the valve guide or valve stem is corroded or carboned-up, it's possible that it's sticking in the open position.

Good suggestion to test it on the car with the engine running ! That way I can also determine if the exhaust sound changes, if any, was similar to what I heard while driving when this happened.

Somehow I kept thinking I need to take it apart to examine/test

[hobieboy]

Originally Posted by RarlyL8

What about your BOV?

Yep - guess I should test that as well... though mine tends to produce very loud noise when it opens (Tial 50mm ones) but when I had no boost, there was no big change in sound nor the "violent vroom" when the BOV normally opens.