Sudden boost pressure drop request from ecu.

[FatblokeVRS]

Hi All

Got an issue with the car dropping boost when accelerating. Tuning guys testing on dyno have narrowed it down to ecu requesting a drop in pressure mid acceleration (2100 rpm)for no reason. Vagcom etc shows no sensor issues. Testing shows MAF and MAP sensors ok.

Any ideas??

Dave

[FatblokeVRS]

Anyone??

[faboka vrs]

We talking tdi? If so log group 11 using 3rd. Foot down from 1500 to 4500 rpm and post the results.

Also do another log of group 1 and 8.

[FatblokeVRS]

It's a 2010 CR. I don't have vagcom. Is there another way to do logging?

[FatblokeVRS]

The ECU is asking for approx 1.5 bar and then around 2100 rpm it asks for approx 0.5 bar. It then asks for 1.5 bar again. It does this several times until around 2500 rpm then it accelerates normally. MAF, MAP, DPF and exhaust temps are all spot on. No errors thrown up for anything. The turbo seems to be doing everything it is asked for so they don't think it's the turbo. It is just the ECU asking for a normal boost pressure then suddenly a low one several times at the same rev range and every time not intermittent.

They did logs and are going to speak to Bosch to see if they have any idea.

[faboka vrs]

Is it mapped?

Not an expert on the cr but it's guess work without VCDS logs I'm afraid.

On the ppd170 if the turbo overboost past the limiter then the driver wish map reduces fuelling which in turn reduces boost request. End result you get a horrible stutter.

[sniper29a]

ECU wouldn't ask for such a boost difference...that's pish. If any limiter is reached, it drops by 200mbar for example. NOT 1000mbar, unless it is in limp mode.

 

This kind of behaviour happens if some of limiters are reached. Turbo boost is limited by MAF, MAP, ambient pressure/altitude.

 

My guess is actuator/vanes are stuck. How old is your turbo?

 

If vanes/actuator is dead, you could do simple test. Drive your car on third gear, let engine revs drop to around 1500rpm. Then floor it (WOT - Wide Open Throttle). At around 1800rpm you must get boost and your car must accelerate hard.

 

If nothing happens, vanes in turbo are damaged or dirty. Take out your turbo and clean it.

 

 

An other option is someone has screwed ECU remap very badly!!!

Edited 20 October, 2015 by sniper29a

[faboka vrs]

ECU wouldn't ask for such a boost difference...that's pish. If any limiter is reached, it drops by 200mbar for example. NOT 1000mbar, unless it is in limp mode.

 

 

Here is an example of a Siemens PPD ecu dropping 700mbar due to overboost

[FatblokeVRS]

It's a 2010 with 67,000 miles. They took logs and it shows the requested boost pressure suddenly dropping several times in the rev range.

It's a revo map used on countless other identical engines. They took the map off and it still behaves the same although the pressures are slightly lower.

The car accelerates quickly but there is a drop in acceleration before it accelerates hard again at 2500 upwards. It almost feels like its an automatic box changing gear but its a manual.

There must be something telling the ECU to request much lower boost but there are no errors whatsoever.

[faboka vrs]

You find these type of things don't through up faults. You have to log and know what to log to try and found out the cause. Like said above could be sticky vanes. Could have had a replacement turbo with incorrect actuator settings. Could be a dodgy sensor which hasn't completely died so not showing as faulty.

 

Trip to the dealers?

[FatblokeVRS]

We have had the vehicle since it was 8 months old with 11,000 miles on it. It has had the oil and filters etc changed every 5000 miles and never had a turbo replacement.

Thinking it must be a dodgy sensor somewhere. The guy diagnosing it considered the turbo vanes but there are no other symptoms. The turbo seems to be doing exactly as it is asked, it is just the ECU asking for sudden low pressures. That is the only thing showing up.

I am hoping Bosch come up with something.

[sniper29a]

Here is an example of a Siemens PPD ecu dropping 700mbar due to overboost

you compare apples with bananas.

 

If you have overboost...that's the limiter working.

[sniper29a]

We have had the vehicle since it was 8 months old with 11,000 miles on it. It has had the oil and filters etc changed every 5000 miles and never had a turbo replacement.

Thinking it must be a dodgy sensor somewhere. The guy diagnosing it considered the turbo vanes but there are no other symptoms. The turbo seems to be doing exactly as it is asked, it is just the ECU asking for sudden low pressures. That is the only thing showing up.

I am hoping Bosch come up with something.

If you don't know how to drive properly - your turbo dies within 20k km period. Learn to drive from this article. I see this phenomenon everyday and people don't believe me if I tell them my turbos last 100k km of racing-style driving.

 

You can't beat physics and mechanics !!!!

 

Stuck turbo vanes usually report overboost/underboost limiter as on my Fabia HRI...it was faulty MAF and dying turbo. 1.4TDi has got small turbo and there is no vanes, just one small waste-gate.

[FatblokeVRS]

I do know how to drive properly, years of experience, many different vehicles, an engineering/physics background and never had a turbo fail yet.

It's nothing to do with way the car is driven or has been maintained, it is getting the fault consistently both on the road and on the dyno with no other errors. Bosch have not seen this fault before either but they have now asked the tuning guys to do more diagnostics and get live data from the car to try and find out what is wrong. It is now with the tuning guys for a few days so hopefully they can get to the root of the problem. I am pleased Bosch have taken an interest are are trying to help.

[faboka vrs]

Are you able to get the logs and post here?

I would ask for the following.

Group 1 - fuelling

group 3 - MAF

Group 8 - torque limiters

Group 9 - more torque limiters depending on Ecu

Group 10 - atmosphere and intake pressure

Group 11 - requested and actual boost along with duty cycle

I would do each in 3rd gear using wide open throttle from 2000 to 4000 rpm.

[FatblokeVRS]

Looks like they have fixed it. Sticking turbo vanes seemingly. They originally didn't think it was that as the turbo seemed to do everything asked of it. They put some cleaner through it and did something else and it seems to be OK now. No flat spot and smooth acceleration. They got logs the last time it was in too and everything was in spec. They checked the MAF, MAP, DPF, exhaust temps etc and nothing looked out of the ordinary. The only thing that showed up was the ECU asking for a roughly 1bar drop in boost then changing it's mind several times between 2100rpm and 2500rpm then accelerating as normal. There was no error codes from any sensors. There was no under or over boost flagged up as far as I know.

I will find out more when we collect the car (current info via SWMBO) but they did say its worth cleaning the turbo vanes again.

Is cleaning the vanes something that's easy to do?

Edited 6 November, 2015 by FatblokeVRS

[sniper29a]

amateurs of modern era. too many computers but lack of basic skills -"I can't troubleshoot" and "computer says nothing" age ;-)

 

yep, it is easy. you take turbo out and clean it properly.