Part Throttle Problem

[kyle'87]

This is a really weird problem that I can't decide if its a surging issue or something else but it makes the car undrivable.


If I give it more than 50% throttle the car accelerates fine and boosts as normal. Which is fine when you want to go faster.

However on a long trip yesterday I found that anything less that 50% or you know when you need to keep at a steady speed, which requires a fine amount of pressure on the throttle, that the car boosts to around 5/6psi then goes to 0psi as if you have lifted off the throttle (but not a vacuum) and then builds again to 5/6psi then drops to 0psi and will continuously do this eventually leading to a jerking motion and you have to come off the throttle.

Any ideas?

Recent updates are a FMIC, New N75 and new MAP sensor and running a stage 1 CC map. (Getting it mapped end of January)

Car is horrible to drive atm

 

[kyle'87]

UPDATE:

I have tried the car with the old N75 valve on and its the same. I have also turned the MBC down to the lowest possible setting with the weaker spring.

The boost issue still happens.

A better description of the problem would say 'Part throttle bucking'

I can't figure out what would cause this, the car sounds like it is dumping even though it's on throttle, currently run the green spring in the 007p, is the yellow one needed?

Will try and get logs on vagcom later and also a video, anyone know the best banks to log?

 

[kyle'87]

UPDATE2:

Got the car checked out on Vagcom earlier and the fault code thrown was 16622 and according to rosstech...

16622/P0238/000568 - Manifold Pressure/Boost Sensor (G31): Signal too High

Possible Symptoms
Malfunction Indicator Lamp (MIL) active
Possible Causes
Wiring/Connector(s) from/to Manifold Pressure/Boost Sensor (G31) faulty
Manifold Pressure/Boost Sensor (G31) faulty
Possible Solutions
Check Wiring/Connector(s) from/to Manifold Pressure/Boost Sensor (G31)
Check Manifold Pressure/Boost Sensor (G31)

This is the MAP sensor, It's brand new, could it really be throwing this code?

Here is the youtube video to show whats actuaklly happening...

http://youtu.be/GQyB2Agny8w

Any idea guys?

 

[tom w]

I take it you have ruled out boost leaks causing it to over boost to compensate as you have recently fitted a fmic ?
Sticky wastegate open/ closed ?

 

[kyle'87]

I take it you have ruled out boost leaks causing it to over boost to compensate as you have recently fitted a fmic ?
Sticky wastegate open/ closed ?

I' haven't looked for boost leaks as I thought that as it boosts fine when on 100% throttle?

The turbo is a brand new refurbished model so the waste gate should be fine.

I'm going to start searching for boost leaks though as I am at a loss.

 

[Berg]

"part throttle bucking" and that exact fault code was due to my map sensor when i had those problems

 

[kyle'87]

"part throttle bucking" and that exact fault code was due to my map sensor when i had those problems

Looks like I'm ordering another new one

Would it make a difference that my whole piping system for the intercooler is 63mm and the map sensor pipe from forge is 60mm so it fits my forge relocation kit?

Just a thought as the pressure is going to increase due to the pipe size reduction, shouldn't should it?

 

[Berg]

I cant see that making a difference tbh

My old pipework was 63mm but was using the standard map sensor pipe and never had a problem with that

 

[kyle'87]

I cant see that making a difference tbh

My old pipework was 63mm but was using the standard map sensor pipe and never had a problem with that

Cheers Berg, will get the MAP sensor ordered tomorrow and see what happens once its fitted.

 

[sm_cupra]

Definately a map sensor fella, i had the same issue. when you do change the pipework for the IC from 60mm to 63mm or drop down your map sensor should automatically be able to adapt to the flow of air otherwise just disconnect the battery for a few mins and connect it back up and you should be ok.

 

[kyle'87]

I haven't yet diconnected the battery, it is another thing I will try. Meanwhile I have ordered another MAP sensor just incase.

What I don't understand is that my current MAP sensor is literally no more than 100 miles old? Maybe I killed it when removing the old pipework. Should it only have 3 wires going to it?

 

[sm_cupra]

I haven't yet diconnected the battery, it is another thing I will try. Meanwhile I have ordered another MAP sensor just incase.

What I don't understand is that my current MAP sensor is literally no more than 100 miles old? Maybe I killed it when removing the old pipework. Should it only have 3 wires going to it?

Hmm, map sensors are pretty sturdy but even then you would never know if you recieved one out of a bad batch, try the battery job and see how you get on and yeah you should have 3 wires going in to it.

 

[kyle'87]

Hmm, map sensors are pretty sturdy but even then you would never know if you recieved one out of a bad batch, try the battery job and see how you get on and yeah you should have 3 wires going in to it.

Yeh thats what I was thinking, Will reset the battery and see how it goes.

Cheers

Kyle

 

[kyle'87]

This is now solved

Went in for a map today to get a jabbasport stage 2 map. After talking with the guy (Micheal?) he knew what the problem was and it turned out to be my actuator was set to tight (so to many threads wound down on it) this was confusing the N75 causing the 'boost bucking'.

It has now be adjusted and works perfect !!!

 

[PhilW]

It's because you're running a MBC.

 

[Berg]

It's because you're running a MBC.

My car seems to run better with a MBC fitted??

Or is it because its T'd in with my N75, fitted it just to stop boost spikes

I did fit mine without N75 and it was well irratic lol

 

[kyle'87]

It's because you're running a MBC.

I think you are right Phil.

Fitting the MBC to control the spikes seemed to exaggerate the problem, MBC removed now.