Big Hesitation!!!

[AlfaJack]

Was driving tonight, engine more or less warm.

Put but foot down off a min roudabout, hit second gear and got what felt like a bigger than usual surge of boost and then at around the 5K rpm mark there was a massive hesitation at which point I imediately came off the throttle.

I put my foot down again later and it did the same. :(

Dont want to try again becasue it felt like the sort of thing thats going to snap or bend something internal, as well as nealy hitting my face on the steering wheel.

The last time I drove it (sunday) I felt there was more boost too but I didnt take the revs as high as today.

Any ideas what about to brake??? :cry: :cry:

Its fine driving generally and idles nicely.

Symptons: More boost, and big hesitation at 5K

EDIT for more info:

Its virtually doubled the boost and is now reaching 1.6 and I dont think it was going to stop!!

I do not have a bleed valve

Standard intercooler.

I had a good look at things a couple of weeks ago, all seemed well, no close up inspection though.

The extra boost is lovely (up to the hesitation) but not at the cost of a non reinforced engine.

Brul suggested to me it could be a vacuum pipe, anyone else had this experience too?

Cheers
Jack

[Steve Webb]

Could be a sticking wastegate thats allowing boost to get to high, which in turn trips one of the ECU's safety cutouts. Or the higher than normal boost causing problems with the spark plugs.
Did you manage do see what boost the engine was producing before it hesitated?

Steve

[wrinx]

Ok...not a clue really, but...on my old JTD saloon I had several big hesitations which have been put down to the turbo over boosting....? Unfortunately it's supposed to be an early sign of impending failure.....but, I repeat, not a clue really!

wrinx

[AlfaJack]

Could be a sticking wastegate thats allowing boost to get to high, which in turn trips one of the ECU's safety cutouts. Or the higher than normal boost causing problems with the spark plugs.
Did you manage do see what boost the engine was producing before it hesitated?

Steve

Just edited my first post to include more info.

@wrinx: :cry: :cry: Hope not - 100K (95K actually) miles could be its life though :?

[Steve Webb]

If you are tripping the safety features of the ECU then you will be exceeding 1.5bar, which is not good. Had you been sat in traffic before hand? Was the car very hot? I've suffered hesitation before when the charge temp got too high.

[AlfaJack]

If you are tripping the safety features of the ECU then you will be exceeding 1.5bar, which is not good. Had you been sat in traffic before hand? Was the car very hot? I've suffered hesitation before when the charge temp got too high.

Nope, had driven a couple of miles at about 30-40mph, its about 1C outside, engine was about 70-75C

[pitucas]

Same problem some months ago (or similar...).

My turbo had broken.

I've noticed that the car runs fine until 5000 rpm (+/-500) and then power seems to drop.

But no more power boost like you...

Until the day I've push the car to is limits and turbo "RIP".

Take a look to the turbo ...

[AlfaJack]

I think the turbo is ok-ish.

This is a power-cut rather than a drop, Im sure its the ECU from what Steve said about it cutting the fuel at 1.5Bar.

I will look at the weekend

Thanks all

[Steve Webb]

Jack, do you still have the standard MAP sensor, because if you do remember it can only cope with 2.5bar max. So if you saw 1.6bar boost pressure you were definately into dangerous territory as the ECU could no longer calculate how much fuel was needed.
I still think a jammed wastegate is the root of your problems. It is allowing the turbo to make far too much boost.

One other thing that has occured to me, and this is as much a question as anything else, has anyone had a problem before with the pierburg valve failing and allowing far too much pressure back to the wastegate? This could cause the symptoms as well.
The pierburg valve allows boost pressure back to the NA side of the wastegate so that the pressure drop across the wastegate is less than the actual boost being produced, fooling the turbo into producing more boost than the wastegate is set to. If the Pierburg valve is faulty and is letting all the boost back to the wastegate all of the time, it look the same as if the wastegate was jammed.

Jack, you might want to disconnect the small bore hoses from the pierburg valve and see if that makes any difference.

Steve

[AlfaJack]

Yup, standard map sensor.

Hopefully something has just fallen off or gone brittle.

The wastegate is a TAS re-circulating one - looks pretty solid but I will check it.

The pierburg valve is still squeaking away like a mouse as normal after boosting ect

Will let you know.

p.s - now I know how the higher boost feels, I think I want it permanently! Time to get more serious on the mods maybe! :D

[Steve Webb]

Not the recirc valve Jack, the wastegate on the turbo. Its a cylinder about inch long/inch diameter with a rod going into it. I'll see if I can dig out a pic for you.

[Steve Webb]

Here you go Jack,

http://www.lotusespritturbo.com/Garrett_AiResearch_T3_Turbocharger.jpg

Your problem might be due to the 'pressure sensing hose' coming lose, or being split. With this hose gone, the wastegate wouldn't open and would let the turbo boost up to the 1.6bar you saw.

Steve

[AlfaJack]

Ah cheers Steve,

I always though wastegate was another word for dump valve - a lot to learn here :? :?

[Jarkko]

and to all you. that might be the Alfajacks problem, but remember that if you are using squadra chip, that cuts the fuel earlier in high revs ( about 1.35bar and +5800rpm or something like that ) . if the hole hose is gone, it should rise the boost very quickly to the 1.5bar level, and cut the fuel.( pressure sensing hose) :wink:

[AlfaJack]

and to all you. that might be the Alfajacks problem, but remember that if you are using squadra chip, that cuts the fuel earlier in high revs ( about 1.35bar and +5800rpm or something like that ) . if the hole hose is gone, it should rise the boost very quickly to the 1.5bar level, and cut the fuel.( pressure sensing hose) :wink:

I have a squadra chip installed, hope its just this hose. I have a Spesso had gasket to the extra boost i made a few times I hope has not done any damage.

Also, someone told me that the fuel cut can potentially cause a piston to run very lean and melt? What are the chances?

[cuore_sportivo_155]

If it's really a fuel cut, there will not be any fuel injected, ergo no combustion. Impossible to run lean. But if your boost is too high maybe the injectors aren't up to the task, and you run lean before the fuel cut off?

[Juan AR155Q4]

I agree with Steve.
All symptoms shows you hace some problem with your wastegate, thats why you have overboost, and that overboost makes ECU fuel cut.

Check the hose that goes from the pierburg to the turbo. Also you could check that the capsule of the wastegate hasn´t got a leakage.

Just for 2 runs you won´t break anything of the engine, don´t worry about that. When you melt a piston, it´s instanteanusly. You will see a BIG cloud behind you... I assure on that :oops:

[AlfaJack]

I assure on that :oops:

lol, cheers Juan.

Solved, pipe had just dropped off the pier-burg valve! :roll: :roll:

[wrinx]

:lol: ...glad it was an easy fix :D

wrinx

[Steve Webb]

I'm doing well on solving hose related problems at the moment, sorted Pavs out a couple of weeks back, now you Jack.