Judder on boost

[FLAT-SIXY]

I was coming back home the other day after our trip away, and noticed when accelerating hard aproaching full boost, my turbo began to develop a judder and its acceleration Seemed to back off. My first thought was to check the pressure hoses at the inter cooler ends, but they are still attached. The cars running great apart from this, I have not yet had the chance to get it up on a ramp, but I thought I’d see if anyone else out there has had this experience, thx Neil.

 

[IndischRot]

I presume no check engine light came on? My advice would be to see if the ECU is storing any error codes. After that it's difficult to diagnose unless the fault is repeatable. It might be a stuck or stiff wastegate. It could be a fuel delivery issue. A sticky wastegate frequency valve. Or a number of other things.

If the ECU senses too much air going through the airflow meter for the operating circumstances (engine speed and throttle position) it will attempt to reduce the airflow by opening the wastegates via the frequency valve. If this fails it will reduce timing advance in big steps to achieve the same result. It will also do the same if the intake air temperature is too high or knock is sensed. All this is to protect the engine.

Can you advise as to engine speed, what gear you were in and the ambient temps. And using fresh 98 or greater octane fuel?

 

[FLAT-SIXY]

I presume no check engine light came on?

Can you advise as to engine speed, what gear you were in and the ambient temps. And using fresh 98 or greater octane fuel?

I must confess that there is a check engine light, sorry i left out this information. The check engine light has been coming on intermittently over the last year. OPC Cambridge have investigated once with no fault codes apparent, another time the check engine light came on and then turned off again after a long run.
During my recent trip to Italy in the car the light came on again but I shrugged it off as it’s been the story of my life in the last few months. The judder only became apparent after some substantial millage had been acumelated on the trip, i.e 1500 miles or so. I hope the light is connected this time as the OBD2 will hopefully tell me what’s up.
With regards to what gear/speed etc,
yesterday i was doing,
30-60 mph in 3rd gear
oil up to temperature ie 3rd marker
then it juddered with power backing off under load.
Going through Europe I always used what ever super unleaded was on offer 97 to 100 octane,
Kind regards, Neil.

 

[IndischRot]

Dealers often just clear the codes first and then test drive the car to see what codes "stick". Understandable in some ways but not always helpful for intermittent faults.
Please do post back with any stored codes.
When were the pre-cat O2 sensors last replaced?

 

[FLAT-SIXY]

When were the pre-cat O2 sensors last replaced?

In the 14 years I’ve owned the car, never to my knowledge.
I will post more info when I get it.

 

[T911UK]

The ECU on these cars are very basic in logging info, Im sure you wont have any codes in it.

Mine did a similar thing very occasionally for over 3 years. I then had a real problem when driving for 90 minutes or so of power going and engine cutting out, all dash lights on, not much fun on the outside lane of the motorway!

The DME relay was nearly too hot to touch, I replaced it and car fired up straight away and was good for another hour or so then same thing, changed the relay back to the other one, which was nice a cool now and all good again.

I replaced it with a solid state version 2 years ago and have not had any problems since

 

[IndischRot]

Mine did it once years ago after I started the car from cold and let it idle for 10 minutes before driving off. It was a bit recalcitrant but then never did it again.

As T911 says error code logging is quite basic and the ECU "sheds" error codes over time if the fault is no longer found. If you're at all interested in what your car's doing it can be money well spent to get a basic OBD dongle that connects to a smart phone via wifi or bluetooth so that you can read the error codes, particularly at the time that there's a check engine light.

If the O2 sensors are at least 14 years old it's not a bad idea to replace them. They get "lazy" over time.

 

[FLAT-SIXY]

Many thanks, I will take both your advise onboard.
Neil

 

[FLAT-SIXY]

Just a little update, I purchased a Bluedriver obd 2 scanner that connects to my iPhone, very impressed with it so far, lots of toys to play with, and just happy that it talked to my car.
I scanned the car and it threw up fault code (PO430 Catalyst system efficiency below threshold Bank 2)
I'm going to delve into the app a bit more to see if it can tell me anything more specific, but my hunch is the O2 sensor.

 

[FLAT-SIXY]

A bit late but It turned out that the pre cat sensor was to blame, I took some Advise from the forum and purchased left & right Bosch pre cat sensors. Nick at Auto 2000 near Bedford kindly fited them for me today. The car seems to be running a hell of a lot better, with a smoother power delivery and no hesitation or juddering on boost, oh & no check engine light, problem solved. ??