Boost problems....

[bigdan]

My ABY coupe has been playing up more or less since i bought it 6 or 7 months ago. It has no mods.

I can only achieve max boost pressure and overboost when the engine is cold. As soon as the engine reaches operating temperature, it cuts down to 0.4 bar mechanical boost. Sometimes when i hit WOT (at running temp) it will start to boost, then it dumps, then it boosts and dumps. Almost like switching a switch on and off!

I have disconnected the MFTS as it packed up and i thought i had found my problem - it wasnt.

I have a cone filter fitted and thought that maybe she was sucking hot air, so i made and fitted a stainless steel heat sheild. still the same.

I can drive less than a mile down the road to tesco, pop in to fetch a pint of milk, and by the time i jump back in the car, i've lost boost.
If i continue to drive, then boost lasts a bit longer.

I hope this sounds familiar to someone and maybe there are some suggestions out there?

Dan.

[s2_bo]

What happens if once the car has cut boost you switch the engine off and then back on. Does it give you full boost back for a few seconds?

If yes then it may well be the knock sensors, they went on my s2 and that was cutting boost to about .5bar after a few miles of driving.

[bigdan]

No, once boost cuts, thats it for the rest of the day more or less.
Won't be untill the next morning that i get it back.

[Tonks4x4]

Do a leak test first or have a flick through other threads on the same issue. The answer will be on here somewhere.

[AUDIS2avant]

It also be the inlet temp or water temp sensors that are playing up.
If they misread and tell the engine is to hot it will cut the boost of

[gedu]

Temp sensors would be my first quess also.

Does ABY use multifunction thing for overheat signal? but that should also light overheat reaction from dash I think... Is there water temp sensor in back of the cyl head in ABY, maybe that is malfunctioning?

[bigdan]

well, the MFTS has been disconnected because it was playing up and cutting boost from cold(and showing the warning light), and yes i believe that there is one in the back of the cyl head. will that one also cut boost if it plays up?

as for inlet temp sender, where can i find this?

[AUDIS2avant]

Inlet temp, isent that the one on the top of IM right near the throttle body?

[bigdan]

Inlet temp, isent that the one on the top of IM right near the throttle body?

Ok i know the one you're talking about, i wondered if it was that one
Does anyone know the resistance values at ambient temp?

[AUDIS2avant]

Im not sure it effekts anything other then if it reads to high it shuts down the boost.
But if it´s broken then it woulden give boost when engine is cold, so i deffo think watertemp sensor

[Jamo]

No, once boost cuts, thats it for the rest of the day more or less.
Won't be untill the next morning that i get it back.

Sounds like a classic case of duff knock sensors to me.

[S2central.net]

Quick skim here... could be knock sensors, or an air leak, or bad MAF, or bad temp sensors...

http://www.s2central.net/ds_G62.html

http://www.s2central.net/ds_G42.html

http://www.s2central.net/ds_G61_G66.html

http://www.s2central.net/ds_G70.html

or longer shot is faulty MAP or ECU - much less common.


Its BAD to disconnect the MFTS (F76) - you can't see water temp on the gauge for one thing... Measure the voltage on the 'R' pin at F76 - cold and hot if possible then let me know your findings. That will determine whether the ECU is being told about an overheat situation or not.

[vonbeck]

i have a problem very similar to this when the car is cold it runs fine but once the temp gauge gets to the first mark it runs like poo! as though it needs to clear its throat! i`ve changed the thermostat when i put a new rad on 4 months ago ,could it be the coolant temp sender or air temp sender as far as i know these have never been changed,what sort of money are they got the part numbers of s2 central, cheers paul, what kind of job are they to change and are they a main stealer part thanks
simon

oh yeh boost seems fine

[quattrodude]

I also have dissconected my MFTS sender as it stopped boosting with no warning or anything, i checked every poss. problem i could think of and came across a faulty MFTS sender.

I replaced the sender with 4x new ones (1 from gsf, 1 from euro parts, 1 from andrew pages and another from the main stealers) with no success at all

I meatered out each sender at the time i had it installed and each give a diff reading at the same temp... so after tearing my hair out for around 2 weeks trying to work out the prob i just dissconected so i could run the car temp.

And relyed on watchin the oil temp gauge (i no thats bad but it was the only idea of temp. i had)

Does any 1 know what readings you should get from a MFTS, Say at fan cutting in temps and also from cold???

If i remember rightly, however it was a while ago i did this the sender works on resistance to voltage??? and has 1 out put to the dash warning system and 1 to the ECU, as i said i cant be sure as i have not looked at it for a good while.

[bigdan]

Right, an update!
Now, a couple of months back i discovered that i was loosing coolant down the side of the block - it was a blown cyl head gasket. i was not loosing compression, just water, and the water was leaking out, not in.
Sooooo, i chucked in a bottle of k-seal as a temp fix untill i had the time to change the cyl head gasket. It fixed the leak, and blocked my main rad

In the meantime, she has failed an M.O.T, one of the issues was 'emissions test not carried out' - because she overheated!
I thought that this was now a sensible time to change the head gasket, obviously!
I had 10thou skimmed off the head, re-ground the valves, replaced the stem seals, replaced the MFTS, changed timing belt and idler, thermostat and all gaskets concerned etc.
I tested the coolant temp sensor on the back of the block and the intake air temp sensor against the specs on s2central.net. They were found to be working well. I cleaned the MAF, and fitted the correct NGK spark plugs (the existing ones were incorrect)
After all this work, i felt sure that i would have cured my problem... it wasnt to be - exactly the same as before.

Tonight i just happened to be studying my fusebox (in the engine bay) and i noticed this
20022009286.jpg

Now, i understand that the missing fuse is at location 25 - which i understand to be 'lambda probe heating'!
My question is, if this fuse is missing, would it cause the problems ive had? i.e boost cut back when the engine gets up to temperature?

For now, i have fitted a 10a fuse, but will not be able to drive the car untill after the weekend as it is in work. I dont want to build my hopes up unnecessarily

Dan