overboost

[Rice crispy]

Never had a problem before I adjusted the short shift earlier today took the car out for a run after and when it warmed up gave it the beans and experienced fuel cut. All i did was remove the boost hose from inner wing to inlet to plenum and moved the header tank out the way ?? is there anything i could have disturbed ?? i know its not the wastegate as ive checked it is free ?? could a leak in the hose cause it ?

Thanks
David

[tigerdog]

A leak in the boost circuit hoses can definitely cause overboost. Remember, the wastegate is pressurized through these hoses. When pressure reaches the wastegate default (5PSI, I think) the wastegate opens. The boost solenoid works by introducing a controlled leak that bleeds some of the pressure and causes the gate to open later. If you have a leak in the boost hoses, you get overboost because the wastegate isn't pressurized when it should be. As a precaution, especially on cars with Mountain chips or MBCs, I strongly suggest securing the ends of the boost hoses with one or two small nylon zip-ties.

[steve matthews]

their is not much left to check.
Steve

[hodge]

I agree, check the connections on the hose that feeds the wastegate actuator (under the corrugated air inlet hose) and the one going from same T junction to the boost control valve (down behind the air filter dustbin).
If they're all secure and the problem persists I'd check out the connection on the M.A.P plug. I had overboost symptoms (fuel cut and dash light) caused by a dodgy earth connection within the map plug. You may have disturbed the connection while focusing on your short shift.
I've yet to fit my shortshift, how did it go?
Do you like?

[trig]

. All i did was remove the boost hose from inner wing to inlet to plenum and moved the header tank out the way ?? is there anything i could have disturbed ?? i know its not the wastegate as ive checked it is free ?? could a leak in the hose cause it ?

Thanks
David

my moneys on the hose you removed being the problem , I had the same thing happen to me and it was a poor seal on the inner wing side of the hose ,,it now has two jubilee clips and no more probs

[Rice crispy]

All, thanks will re-check the connections today. Hodge, I already had it fitted by my mechanic 2 years ago but decide to try the shortest setting (mine is the AB version which is adjustable) and its a great MOD

David

[rip]

You may have disturbed the connection while focusing on your short shift.

Unlikely but not impossible. Adjusting the AB shortshift is a matter of releasing a bolt & connecting it to somewhere slightly different. It is easy to get at once you have removed the wing-plenum hose & moved the expansion tank out of the way.

I've yet to fit my shortshift, how did it go?
Do you like?

Slightly
I have the same shortshift as Dave. Mine ran on the longest setting for about a year until I got some AB cables. I then adjusted it to the shortest setting & fitted a slightly shortened gear lever.
I have read that this can feel a little extreme for everday use on the shortest setting but I completely disagree. I think it feels great & have had no desire at all to adjust it again.

[Rice crispy]

rip dont foget im ham fisted so anything is possible

[Rice crispy]

Replaced the circlip on the hose to the plenum and all seems good

[tigerdog]

Replaced the circlip on the hose to the plenum and all seems good

Hooray!

[Rice crispy]

Circlip was only £1

[bobbrown]

I assume you mean hose clip as circlips look like this.

circlip-internal.jpg

[Rice crispy]

yep hose clip

[rip]

I assume you mean hose clip as circlips look like this.

circlip-internal.jpg

I was wondering where on the wing-plenum hose I would find a circlip

[Rice crispy]

Hmmmm went for a spin tonight and no fuel cut but it doesn't feel like its as quick as normal, i know its warmer than it has been but gauge only showing .5 bar where it usually is .75 (i have everest chip) so how do i check the map plug and boost control valve ( all connections and hoses are in place and i can see no leaks

David

[norman lovie]

maybe you've induced a bit of negative adaption in the ECU with the overboost issue, if you disconnect the battery for a while and try again

[hodge]

Take a look at Jon T's thread 'not making expected boost' in same section as this which covers a lot of the problems in this area. On the second page it has a nifty simple technique for pressurising the system to check for leaks.
I had same hose blow off as you (foot down) after repairing large leak elsewhere, there was loss of power/boost along with loud, gasping, rushing air sound (strange that. . .)
As Rip says, the map plug sounds unlikely - but it did happen to me and as it's not one of the usual suspects I thought I'd give the heads up.
I didn't see it mentioned anywhere when it happened to me and it's an easy check.
The plug wasn't inserted far enough for the plastic plug 'catch' to engage.
One of the long metal contacts inside the plug was misaligned so you couldn't insert it fully.
This meant it didn't take much to dislodge it as it inserts vertically and was being held only by friction - the wires going to it were cable wrapped to others lower down, any movement of these would tug on the plug.
The MAP is mounted on the bulkhead behind the plenum. To check it simply unplug it, and take a gander at the condition of the contacts ( they should all look the same length and clean) and re insert making sure the catch latchs.
Good luck.

[hodge]

ps actually after re reading your last post I don't think checking the MAP plug is relevant any more as your current symptoms are now different.

[Rice crispy]

Well checked the map and boost control and both plugged in fine, went to the meet tonight and was all ok ? ? So wonder if it was the boost control plug or i have an intermittent problem. Car doesn't miss a beat just seems to lack boost ? wondering if its worth replacing boost control valve as a precaution

[hodge]

You could test the boost control valve by putting car in service mode (short out black and white wires on ALDL plug) if you switch ignition on and off (without starting engine) the boost control valve should open and close (open in service mode).
If you have a helper to switch ignition I think you can hear the valve open and close if you're stood near it. Alternatively disconnect the boost control hose at wastegate end and try blowing thru it when ignition is switched in service mode - it should be open and let air pass ( to the air filter bin output).