Possible head gasket and turbo problem

[jamie9048]

Right my car s2 aby boost great has loads of pull... then all of a suden in all types of conditions it decides to hick and hesitate on the gas it strugles up past 4 -5k then pulls again.

after a little cool down it seams back to normal then happens agian at random intervals

it runs about 90-100 but when I take the top off it pushes loads of water out nearly emptying it Ive blead the system to see if that solves it but what effect could a head gasket have on the turbo?

and the other night after being driven in anger and sitting waiting to turn in to my drive it started boiling up it went from 100 all the way to the warning indicator...

[JP]

First of all the reason the water system normally doesn't boil even when over a 100degrees is because it is sealed and under pressure. You'll find water can go in excess of a 120 celsius without boiling when in a sealed pressurized environment. So automatically if you take the cap of it will boil over right and proper and practically empty out your water system.

Now obviously you need ot look at the reason why your temperatures are going over 90 celsius especially if the car has been driven hard. Old school paper headgasket = headgasket failure. Faulty waterpump, blades have perished and not circulating water properly at low rpm, air pocket in the water system due to not being previously bled properly, faulty cooling system i.e. fans not kicking in at the right time etc...

Now if you have a headgasket issue the easiest tell tale sign is froth in the expansion tank and loss of water inbetween outings. Everything else is just a process of elimination through trial and error.

[Ian Simmonds]

possibly water vapor condensation around the spark plugs, take the cover off and have a look around the plugs... If there's any damp or condensation showing, it'll vapourise to steam as the engine warms up, this dissipates the spark to earth and gives a full boost misfire.

Dry it out completely and run it up to temperature, then try full boost....

This might not be the answer, but our ABY has pulled the stunt twice in 8 years and has now been sealed down, as water migrates under the bonnet and under the cover on long wet motorway runs or after steam/pressure cleaning.

[jamie9048]

Right Ive done a sniff test and it`s clear no head problems that just leaves my intermitant turbo clich full service next week and go from there

[chezz]

Thermostat jamming or fitted incorrectly?

[jamie9048]

I`m at a total loss this morning the car was very little boost then 5k and woosh shes away.

Parked it at work today with the o/s on the kerb and no problems at all from leaving work loads of power and boost got 8 miles of steady driving and the lack of mid boost re-appers but if I stick with it and get her up over 5k it comes back...

any ideas

I wonder with the car being parked off the level could there be water in the tank?

[A80Avant]

your lamda may be at fault as well. Do you have any way of looking fault codes? if not, i have a vag reader and we can read it that way if you like

[prj]

Lambda will NEVER ever cause such issues on stock Motronic ECU. You can unplug it and Motronic will NOT go into limp mode. Furthermore, lambda in Motronic is only used on cruise, the moment you give it even a BIT of throttle, it is ignored completely.

If any sensor is to blame, then having a dead range with no power between 2500 and 4500 rpm points to broken MAF or bad contact within the MAF plug.

Have you read codes? If not, stop guessing and read them.
Somehow I doubt any sensors are to blame. Even if you disconnect almost all sensors, your temp will not go over 90 degrees.

As for boost getting pulled - boost gets pulled on heavy knock. Thrashing the car when there is an obvious and possibly serious problem, will just lead to an engine rebuild.
In fact pressure test your system and make sure, that there is no leakage betwen the MAF and turbo, where unmetered air can enter. Lean mixture due to MAF-Turbo hose failure + detonation is a pretty common fault.

Easiest way to test - unplug the MAF and see how the car drives. If it's better, then you have an issue with unmetered air (read: leak).

[jamie9048]

right I`ll check it tomorrow where is the plug located on the s2?

[A80Avant]

Dimtri, when you go part throttle, is your lamda out of the loop?

i say this, that on my engine i had this problem twice with the lamda sensor when i was using motronic. Maf was the same, or replaced with a new unit, car behaved the same, and once i changed lamda, everything went back to normal. Also the car was reaching full boost and ran nicely only on WOT. So perhaps Jamie is having a different problem, i dont know. But im sure on part throttle my lamda was causing problems up to 1-1.4bar if i remember correctly.

[prj]

Dimtri, when you go part throttle, is your lamda out of the loop?

i say this, that on my engine i had this problem twice with the lamda sensor when i was using motronic. Maf was the same, or replaced with a new unit, car behaved the same, and once i changed lamda, everything went back to normal. Also the car was reaching full boost and ran nicely only on WOT. So perhaps Jamie is having a different problem, i dont know. But im sure on part throttle my lamda was causing problems up to 1-1.4bar if i remember correctly.

It depends heavily on the software you run in ECU.
But in stock ECU and in sensible mapping, the load threshold where the engine goes open-loop is very low.
Of course I have seen some funny chips which mapped the lambda threshold way too high...

Lambda is basically only active when you are "holding" it at a speed. The moment you start to accelerate, even a bit, it gets ignored.
The only way you get issues with lambda, is if your fuel trims are way off. But I don't think it uses fuel trims when it runs open loop either.
But all this is very, very easy to test. Just disconnect the lambda sensor and reset the ECU

[aelred]

Why a lot of cars run hot is because the auxillary rad has been removed and if they have air con they will tend to overheat due to the AC rad being in front of the main water rad, also you find air diflectors to channel the air to the rad are missing on a few cars.
I dont know if this is the case in your car.

[A80Avant]

you are right Dmitri, it could be just the map i had. I believe jamie's car is stock tuned, so may well be the maf then

[neebover]

Just to add a brand new maf and lambda sensor were replaced when I had the car as I had a few running problems. Receipts for these in the history Jamie. Not sure what the issue is then?

Chris.

[prj]

Check for boost leaks - as first issue.