Boost issues

[danjohns88]

Hi all,

New to this forum so not sure what to expect!

I've recently picked up an 2003 LCR AMK. I'm having boost issues when under full throttle. The car seems to boost and then dump, boost then dump - like it's cycling on/off. In all gears and is more prevalent from lowish revs. Seems to dump on high boost and it's quite a sharp decrease in power.

Up to now I've done the following:
Replaced the original DV for an 'uprated' Forge 007. No difference.
Replaced the N75 valve for an OEM (through TPS) new part. No difference.
Bypassed the N249 valve, no difference (I have a new one to fit tomorrow but not hooeful on that).
As far as I'm aware, the car has not been mapped.
The car has been into Awesome Gti in Manchester and there's no faults at all, so it's not an easy find

Has anyone had this issue previously or am I chasing my tail? My next port of call is to book the car in with R-tech and let them work their magic.

Thanks in advance, Dan

 

[Alexis27]

Try unplugging the N75. Your boost will be capped at 5psi, but is it smooth or does it still kangaroo?
Also try another run with the MAF unplugged

 

[danjohns88]

Try unplugging the N75. Your boost will be capped at 5psi, but is it smooth or does it still kangaroo?
Also try another run with the MAF unplugged

I'll have a look this afternoon. I've still got the N249 to change and then I'll have a go at this and update. Cheers

 

[MLBrett]

I'll have a look this afternoon. I've still got the N249 to change and then I'll have a go at this and update. Cheers

Any progress on this? I'm having the same issue on my cupra 180 and can't figure it out.

 

[danjohns88]

Any progress on this? I'm having the same issue on my cupra 180 and can't figure it out.

Nope. I've changed the N75 & N249 and still the same. It's like it's dumping boost as soon as it hits full. I'm wondering if it's either a dodgy remap (I'm unaware that it's had one) or possibly a dodgy wastegate on the turbo? It's going in again, to another garage to have a look at it and hopefully they can find something. Will update when I get an answer

 

[mty12345]

Nope. I've changed the N75 & N249 and still the same. It's like it's dumping boost as soon as it hits full. I'm wondering if it's either a dodgy remap (I'm unaware that it's had one) or possibly a dodgy wastegate on the turbo? It's going in again, to another garage to have a look at it and hopefully they can find something. Will update when I get an answer

You need VCDS to get to the bottom of it really. Log it under boost and see if the fueling is ok, also check boost requested vs boost actual. With an unknown map that complicates things. If it's some generic crap downloaded from the internet etc, then it could be that. Could also be a weak fuel pump unable to supply the fuel needed at high revs and full boost, but only looking at the fueling would answer that.

If you only have access to an OBD2 level scanner, then looking at the short term fuel trim when the issue happens could also help. If the trim is maxed out, then that could point to a weak fuel pump too.

 

[danjohns88]

You need VCDS to get to the bottom of it really. Log it under boost and see if the fueling is ok, also check boost requested vs boost actual. With an unknown map that complicates things. If it's some generic crap downloaded from the internet etc, then it could be that. Could also be a weak fuel pump unable to supply the fuel needed at high revs and full boost, but only looking at the fueling would answer that.

If you only have access to an OBD2 level scanner, then looking at the short term fuel trim when the issue happens could also help. If the trim is maxed out, then that could point to a weak fuel pump too.

Cheers bud. It's going in on the 6th Jan and I'll pass this information on. I don't have access to VCDS but once I get a new laptop, I think I'll invest and swat up on it as I've got a few niggly issues at the moment!

 

[mty12345]

Cheers bud. It's going in on the 6th Jan and I'll pass this information on. I don't have access to VCDS but once I get a new laptop, I think I'll invest and swat up on it as I've got a few niggly issues at the moment!

You're welcome mate, I'm sure R tech will be able to sort it easily enough once they are looking at the live data.

Yeah sounds like a plan, VCDS is definitely a good investment if you plan on keeping the car long term.

 

[danjohns88]

Update:

Following some diagnostic work a couple of weeks back I was advised to change both the N75 & N249 valves; I changed the N75 valve a couple of weeks ago and it made little to no difference.

This morning I've changed the N249 and it seems to have cured the issue. Acceleration now feels smooth and I'm not getting lumps of power, more of a smooth curve up through the revs. Will keep an eye on it and update in a week or so

 

[mty12345]

N249 has the ability to open the DV, so that would make sense. Glad you have it sorted.

 

[danjohns88]

N249 has the ability to open the DV, so that would make sense. Glad you have it sorted.

Yeah when I thought about it, I should have gone straight to it but I wanted a proper process of elimination (being an engineer, it's how my brain works).

Hope this post helps others though!