1.4 TDi PD Limp Mode - +ve Boost Deviation - Boost/Duty Graphs inside!

[edbutler]

Hi All,

I have a VW Lupo 1.4TDi which is remapped to approx 100BHP. The car pulls well for its slender weight, however has an issue going to Limp mode. It hits limp mode usually going up hill and a constant partial (30-80%) throttle for around 5secs. If you modulate the throttle, even slightly, it will be fine.

The error logged is a Positive Deviation error (i think, i actually forgot!). The N75 makes a LOUD ticking noise audible from the cabin when the ignition is on (not engine running) - is this a problem? Ive had a visual/audible check for boost leaks and cant seem to see any at all.

Here are my logs at full/part throttle hoping to find what is going on. Notice that the car meets (and exceeds) requested boost at 100% and as such the duty cycle reduces (goes up on the graph)... At part throttle however, the duty cycle is almost maximum (Low on graph) but Actual never meets Requested!!

Any ideas please shout! Many thanks all for reading!

Full Throttle:

~50% Throttle:

[MiiTCH-TDi]

My n75 makes noise with ignition on

[RS6plusMTM]

Ticking seems to be normal.

Funny enough i have the same issue ever since owning the car but just change my driving style not to use full throttle more that 6 seconds up hill (I've lived with it for nearly 2 years this way - lol)

Recently had a snap on diagnostic on it to start to track down the issue but it just says the same thing to check as a vagcom for negative pressure, boost leaks, n75 etc...

I replaced the n75 (thinking the ticking was a fault was causing the issue) and it didn't change anything, if fact the brand new n75 ticked louder than my old one.

Just havnt had the spare time to diagnose any further, but was going to start to replace a few of the old vacuum pipes just incase it's one of those leaking.

Sorry I couldn't help any further, other than to say not to worry about the ticking.

Cheers

Gary

[MiiTCH-TDi]

I also had a tiny split in my boost pipe which cause this

[Derv]

I had this problem last summer. After driving at WOT in 5th for about 10 minutes, I had to lift when a car pulled into my lane. When it moved out of my way, I went straight back to WOT and the car immediately went into limp mode. Luckily I wasn't far from a service area, so I pulled in cleared the code, and drove on. And the problem has never come back. But I can't say that I have had the chance of a long WOT run since.

I do find I have to replace the intercooler - inlet manifold hose on a yearly basis. The metal retaining barbs always wear out.

[vinay]

Replace the Maf sensor I had a big lag as when I put my foot down up a hill

[north wales loop]

mine did this had a crack in the intercooler. look for a boost leak

[electricracer]

there is a difference in positive deviation and negative deviation , one is boost leak one is vacuum leak, cant remember which way round. do your fault codes again,

[edbutler]

Thanks for all your responses! Ill keep at it and bring back a solution if i find one! Fingers crossed!