fuel cut - never ignore the impossible

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felt i had to post this - light entertainment for some and a 'check the unlikely first' for others.

so, after buying the car i stuck on discs n pads all round, stainless downpipe on, some brake pipe, handbrake, re-wire of fog lamp blah blah, then gets it MOT'd to find im getting fuel cut on boost. A stop by these forums, make a list of items to check, order a temp sensor, and go start to work round the list of possible problems.

the car was boosting, but not holding well, and obviously fuel cutting around 4K on hard acceleration, but..... running stock with no boost adjustment gizzmo's. After checking all 20 or so vacuum pipe connections i finally end up here, at the rear turbo actuator, and cant beleive what im seeing: surprise.jpgsilicone hose split.jpg

the only uprated hose on the car and its split in half!!! replaced it, run up the road on full throttle and yes, no more fuel cut!

Questions for the knowlegable:
would this 'open' hose have been causing poor fuel consumption?
how in the **** did that silicone hose just tear itself in half?!

[Wobble]

good job finding it .

yes it will cause awful fuel consumption

i had a some vacume pipe that was sitting around abit from another member and that split probably due to age

[Nick Mann]

It could well be causing overfuelling. On light throttle the ecu should tune the car to the same fuel ratio regardless of small leaks, but on boost you would have an air leak so would be getting fuel for the air in the cylinder plus the air that has escaped.

I hate silicon hoses. They change shape and seem to split a lot more easily than standard piping. As they swell under pressure they seem to be a ridiculous option for pressure control lines too. In my mind that makes them even more daft when the owner has fitted a hard pipe kit!! Personally, I would suggest fuel injection piping for anything you need to replace.

[sabreuk]

that hose on the actuator mate opens it to stop the turbo boosting, if the pipe is not attached depending on actuator the valve would be open allowing the boost to escape, if its stuck closed it would over boost and kill the turbo amongst other things. yes i t would cause poor fueling as the car thinks its boosting when it actualy isnt thus ups the fuel to compensate.

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hi Sabre, not sure what you meant there? you mean if the actuator is jammed shut having this hose reconnected could case a turbo problem? either way now i re plumbed the boost guage hose into my blitz turbo timer so i could measure peak boost to check (there was a 'Savage' gauge in there - now in the bin!!). the peak is reading 0.61kg's (8.6psi) so i guess thats about right, so im guessing all is well.
im just a little suspicious of how this hose became cut in two..................

[Wobble]

spot on stock boost for an auto

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the standard boost is different? mine is a manual....

[sabreuk]

it might of just gone brittle from the excessive heat causing it to split mate. if you reconect the hose it should boost properly not over fuel. the actuator is vac run when the turbo boosts the actuator opens to release the pressure at set quantitys for example if you have a 1bar actuator when the pressure hits 1.1bar the valve opens so it doesnt damage anything. if the valve is shut the pressure can not release and will overboost making your turbo/engine work harder than it can take and things will break. so from your snapped hose the valve was shut and the pressure couldnt release thus overboosting and using more fuel. check the actuator though as they can seize which could of coused the hose to split also if it couldnt take the pressure that built up.

[Wobble]

in that case you should peak at 11.5 psi for stock manual.

[sabreuk]

to check the actuator make sure engine is cold so you dont burn your mits and there is a longish bar that comes from the back of the actuator to either or manifold or downpipe and simply try moving the bar back and forwards if its loose you need a new actuator. if there is a fair bit of pressure but you can move it that is normal and if if you cant move the bar at all then it might be seized all together causing the hose to split.

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interesting... ill give it a proper test tomorrow with better road and see what i get. the cheapo boost gauge i just ripped out was showing over 10 at some stages, and that was with that hose in half.
ill check peak again in the morning after pushing it all the way in each gear just to make certain, then if its still 9psi with this actuator hose fixed then i guess there is a problem of some kind there somewhere (perhaps what sabre was trying to mention?!)

[Nick Mann]

The actuator hose being off will cause the car to over boost, yes. As the actuator never sees the pressure to open the wastegate. That is why fuel cut was happening, to save the engine when the ECU thought there was too much air flow.

Rich running under those circumstances is due to the air loss through the broken hose. The fuelling is based on the volume of air entering the engine, as measured by the MAF, so if you lose air after that point the fuelling will be incorrect.

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to check the actuator make sure engine is cold so you dont burn your mits and there is a longish bar that comes from the back of the actuator to either or manifold or downpipe and simply try moving the bar back and forwards if its loose you need a new actuator. if there is a fair bit of pressure but you can move it that is normal and if if you cant move the bar at all then it might be seized all together causing the hose to split.

aha, ill do that before my morning test drive!! thanksman, will report back tomorrow

[sabreuk]

no probs bud, hope its just that and nothing more sinister

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i assume these actuators are non adjustable? so if its siezed it can be freed up then refitted without the need to set it up?

[Nick Mann]

Checking the actuators won't hurt, but I'd suspect the silicon hose has simply overheated and gone brittle in that very hot part of the engine bay. Even the heat protection mat on the bulkhead blisters in that area.

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OK, so, i grabbed and moved the actuator arm. it does move, by a few centimeters - im not sure how far its meant to move but im guessing less than 90degrees to open the gate its attached to? if it was seized im thinking it wouldnt be moving at all, as opposed to partly stuck.
hopefully Mr Mann is completely correct as these things do seem to run very hot, albeit theres no evidence on the silicone hose of heat damage, though i guess it regains most of it shape and visual appearance once it cools again anyway.

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OK, so, took it to end of road and back now and keeping a little back from the red line in each gear according to Mr Blitz its hitting exactly 11.5 peak. so i guess all teh problem was all along (previous owner) was that busted hose.
makes me think further, the car had and still has, a AFC2 installed and it had each range screwed down a fair bit, i wonder if this was an attempt to save some fuel whilst badly overfuelling due to that split hose...... seems an extreme length to go to, but seems ill benefit - AFC2 now zero'd until i can somehow read data to see my now current fuelling