Limp Mode.... Again!

[EZ Tutty]

Hey guys,

i keep getting a re-occuring problem....

In 4th n 5th gear, when i hit 20psi, it instantly drops to 10psi, i understand this as limp mode, i normally find playing with the actuator i can get it boosting normally again (normally peaks at 20, and drops to 14, then gradually tails off).

however this is about the 3rd time this problem has come back in the past month, and this time i've slackened the actuator off a couple of turns and it's made no difference, maybe more would sort it, but i can't see why i need to keep adjusting it

I've also tried just unplugging the MAF to see if that made a difference, but nothing

Any advice would be greatful?

Cheers

EZT

 

[evans1089]

when was it last serviced? not letting the petrol light come on are you?

 

[EZ Tutty]

just done a run with the N75 unplugged to find what my actuator is set at, and 8 psi was about the highest constant value i saw.

However i tried to wind the actuator out slightly, and it was boosting really slow (i assume the wastegate was being held open?)

I only seem to be able to get too much boost, or it takes ages to boost.

 

[EZ Tutty]

^it gets serviced every 6months (last done 2 months ago), and it's got about half a tank of petrol in now.

 

[old yella]

Mine used to go into limp quite alot and i just put it down to not being used much only 300miles a year for the last 2 years, but ran a fault code check and found temp sensor code replaced that with a modified one from seat and now its fine. got to be worth a check, sensor took second's to fit and i think less than £10..

 

[EZ Tutty]

i've already scanned the car with VAG-COM, no faults listed...

also my Coolant Temp Sensor is already a new green top one... cheers for the suggestion tho.



done some further tinkering today, i tested the actuator (using a calibrated gauge, and a varible pressure source) and i've set it so it just starts to open at 6psi (stock is between 5 and 7psi), i also leak checked it fully open, and it didn't leak at all, and i've checked the vac hoses, and none are split..... however none of this made any difference

i've just cleaned and lubricated the N75 valve (as IMO things are pointing that way), however i can't see it making any difference, it is electrically working, however i could do with another to try, i would buy another but there not cheap if it's not the fault, plus my valve is only less than 6months old

 

[EZ Tutty]

anyone have any other suggestions before i cough up 60quid and change my N75 ?


btw forgot to mention at the start, i'm running a N75J valve.

 

[tarzan]

anyone have any other suggestions before i cough up 60quid and change my N75 ?


btw forgot to mention at the start, i'm running a N75J valve.

then the n75j is the problem.hade the same problem after 3 months with it on changed back to the f valve and diden`t come back if you do a search on the n75j valve you can see that it works for someone and not for others.

 

[EZ Tutty]

was kinda hoping you wouldn't say that car pulls soooo well with the J valve on.... when it's working that is, which it has for some time now, which is why i can't understand whats goin on.

 

[EZ Tutty]

Been reading on VWVortex and a few other forums about the clamping the Map sensor reading (to 17psi) using a zener diode (at 4.7v) which would stop the limp mode from happening, and allow me to use my N75J valve, and have it peak at what ever it wants to.

once it drops below 17psi the MAP sensor will read as normal, therefore the Boost will control as normal too.

this should make no difference to fueling, as thats done by the MAF, Lambda's, and Temperature Sensors. The MAP sensor is only for boost control.

The only problem i can see is from a safety/protection point of view, if something went wrong the turbo could boost up to what ever it wanted, and the ECU wouldn't try and sort it out.

Has anyone else done this mod?

 

[tarzan]

Been reading on VWVortex and a few other forums about the clamping the Map sensor reading (to 17psi) using a zener diode (at 4.7v) which would stop the limp mode from happening, and allow me to use my N75J valve, and have it peak at what ever it wants to.

once it drops below 17psi the MAP sensor will read as normal, therefore the Boost will control as normal too.

this should make no difference to fueling, as thats done by the MAF, Lambda's, and Temperature Sensors. The MAP sensor is only for boost control.

The only problem i can see is from a safety/protection point of view, if something went wrong the turbo could boost up to what ever it wanted, and the ECU wouldn't try and sort it out.

Has anyone else done this mod?

nope haven`t done it but would like to try it. some info here
http://forums.vwvortex.com/zerothread?id=2901711&page=1

 

[EZ Tutty]

I've got a couple of 4.7v zeners sat in the garage by chance, also got some 3pin plugs, so i can do the wiring in them to make it nice and easy to remove.

The more i read the more i think it's the answer i'm looking for, only thing to bare in mind is there is no limit to overboost, so if something should go wrong, the ECU will never know, so it's worth keeping an eye on ye ol' boost gauge.

might even rig up some sort of 'over' pressure switch on a buzzer as a safety to warn me, be easy enough to do.

 

[daves ibiza]

Put money on n75

 

[EZ Tutty]

yes i know it's the N75 valve?

it's because i have a J valve fitted, the peak boost is higher than the ECU expects, and is therefore going into limp mode.

The valve is not faulty...

 

[tarzan]

I've got a couple of 4.7v zeners sat in the garage by chance, also got some 3pin plugs, so i can do the wiring in them to make it nice and easy to remove.

The more i read the more i think it's the answer i'm looking for, only thing to bare in mind is there is no limit to overboost, so if something should go wrong, the ECU will never know, so it's worth keeping an eye on ye ol' boost gauge.

might even rig up some sort of 'over' pressure switch on a buzzer as a safety to warn me, be easy enough to do.

do itor get it mapped again with the n75j valve

 

[EZ Tutty]

yeh i'll give it ago when i'm next off work.... when i eventually go ko3s (hopefully next year) i'll get it mapped to suit, untill then, zener clamp it is

 

[ibizacupra]

do you get a boost deviation fault code?
clamping the map sensor wont help if thats whats upsetting the ecu

 

[EZ Tutty]

nope, no codes at all

 

[R4cup]

EZ was it your N75 after all?

 

[EZ Tutty]

nope, zener clamped the MAP sensor, and all is well

Boost controls perfectly.