boost control issue has got me stumped

[ken.fresno-tdi]

My 98 Jetta AHU install into a 95 Eurovan has been great with one exception. I keep occasionally getting a 0575 code (boost control difference) and going into limp mode, but only when accelerating moderately in 4th or 5th gear up an incline. In regular hard acceleration on flat road it *never* happens. I had the engine prior to the transplant and it ran fine, but I added some mods during the transplant. Since the transplant I've only put on about 5000 miles.

For the transplant into the Eurovan I did the following:
- K03/04 hybrid turbo from KermaTDI
-Kerma tuned chip
-Bosio injectors

as well as:

-replaced all vacuum and pressure hoses with viton
-new FMIC with 2" pipes and tubing; pressure tested at 20+ PSI and no leaks
-new N75 valve
-replaced 3" hose inside ECU

I'm stumped. The only thing I haven't actually done is check the actuator but the turbo only has 5000 miles on it and is just a year old, and I live in a very dry part of California, so rust is not an issue. Like I mentioned, it ONLY happens occasionally on moderate acceleration while going uphill. So, for example, I went up 5000 feet yesterday and I had to reset limp mode using my Scangauge II at least 10 times. Very annoying.

Here's a link to logged data in a CSV file from about 7 minutes of driving with group 003, 008, and 011. I added column Q which is specified minus actual MAP values. edit: (I think) the engine went into limp mode at 411 seconds, when the difference was 703.8. There were several times before that where it was in the 700s, and often in the 300-400 difference range.

What is 'normal' difference between requested and actual MAP? What else to check?

Thanks for any help you can give me!
Ken

 

[BigAndy]

Do you have a boost guage installed that you can watch? You didn't have a leak before - but that was before. You might have one now. I'd go and check every connection - pressurize and test.

 

[Mongler98]

vcds take a log of when this happens report back probably a n75 issue or bad maf would be my guess. that or the tune chip is not working properly by expecting more boost or something, who knows, no one, thats who, so get a log and lets see whats going on!

 

[ken.fresno-tdi]

Thanks for the quick replies. I use Scangauge II for boost gauge. It is almost almost around 8 pounds when it kicks on limp mode. On same hill if accelerating at 12 or 13 pounds boost it rarely if ever goes into limp mode. I wrote to Kerma folks and they said first fix the boost differential before thinking about a possible chip issue. I did the boost pressure test just two weeks ago and it immediately had the same issue the next day. The VCDS log that I linked to is, I think, right up to the moment that I went into limp mode. I'm not sure because I wasn't looking at VCDS as I was driving (for obvious reasons). But when I looked at the VCDS screen it had frozen; I thought because it had gone into limp mode but perhaps before that... I should have clarified 'before' - I meant before I did the transplant - when it was still in my Jetta. But that was before the new FMIC and turbo and viton tubing. Question - how does MAF impact requested/actual boost pressure?

 

[Mongler98]

thats nice
how about some graphs
most of us have no idea what that stuff means and are also not willing to do the excell work to plot it.
upload a graph log, i should have clerified.

 

[BigAndy]

MAP Specified vs MAP actual - that's what we're looking for. MAF - is mass air flow.

When you say this:


It is almost almost around 8 pounds when it kicks on limp mode. On same hill if accelerating at 12 or 13 pounds boost it rarely if ever goes into limp mod

That tells me you aren't building the boost needed. I am going to guess it's asking for me (MAP specified) versus what it's getting (MAP actual). Graph it and show us.

If you aren't building the boost, something came loose maybe? If everything is tight - well, that rules out the easy stuff.

 

[ken.fresno-tdi]

I'll try to do a run this week and graph it. Column Q shows what the problem is - the boost deviation amounts.



I'm aware of the difference between MAF and MAP. Mongler98 mentioned that a bad MAF may cause the MAP specified/actual to deviate, but I didn't want to buy a new MAF until I knew that that was a realistic diagnosis. Since I had the same MAF in the Jetta and it worked fine there I assumed that it probably was not the problem. I don't think it is a N75 issue since I put a new N75 in.



What I meant by the 8 lbs versus 12 or 13 lbs was that if I go up a hill with moderate acceleration (8 lbs) it is much more likely to trip into limp mode than if I go under hard acceleration (12 or 13 lbs). The boost deviation seems more pronounced under moderate than hard acceleration.

 

[Mongler98]

Actually my point was that you dont know what part it is until we get some data. It could be a manifold pressure issue due to a fueling issue? Who knows. We dont. A graph of fuel, boost and so on will tell the story. My point was no what was the issue, the point was that it's pointless to guess. Not that it was a maf, I though that would be obvious enough to be a joke

 

[ken.fresno-tdi]

Charting 003, 008, 011 for TDI AHU

I was able to get out to the mountains near Fresno and graph 003, 008, and 011 in VCDS. I didn't actually catch it as it went into limp mode, but recorded it close to the conditions that it usually does go into limp mode (uphill with light throttle, 4th or 5th gear, boost around 8 or 9 lbs.) I used Malonetuning.com's website to make the graph. I haven't done graphing before so I hope the chart makes sense. It seems that MAP actual is always lower than specified, but also that MAF actual versus specified is completely different - specified hardly registers on the chart. But, like I said, I need someone with more knowledge than me to read and interpret the data. Ideas anyone?



https://imgur.com/65Zycfa

 

[BigAndy]

Based on the graph, it looks like boost is controlled down by 1/4 way across the graph - limp mode. 'Limp mode' is when boost is limited to 7psi by reducing fueling so you never exceed that pressure.

Your actual isn't close to your specified so the ECU responds to this 'boost deviation' by controlling boost to a level to not damage the engine, etc.

So with this low power issue, I would read this sticky:

How to Troubleshoot Low Power on A3's/B4's:

http://forums.tdiclub.com/showthread.php?t=75959

You've done some of the work - so it's time to get systematic.

 

[ken.fresno-tdi]

hmm. then I posted the wrong portion of the graph... I'll check this evening after work. It has plenty of boost (13 - 15) when running normally and I feel a distinct loss of power when it goes to limp mode. At that point the max boost is 6.9 and the 1550 code comes on. I'll check things out and update the graph...

 

[BigAndy]

Nahh - it was me - I was reading the wrong lines.

So yes, 7 psi is what the ECU will limit boost to when it detects a problem. It's clear boost never hits specified and why it goes into limp mode. Again, if you modulate the throttle going up hill - on hard, off, on hard, off never keeping the boost level the same, you won't hit limp mode - the ECU has a window - something like 5-7 seconds before it cuts boost down. Keep fluctuating and you can keep it from triggering.

But you do have a problem - it could be a badly clogged fuel filter, could be a worn out turbo - it could be a ton of things. Read the 'How to Fix' link and start at the top and work your way down.

Did Malone ever say what boost should be? 14 is the factory maximum from what I recall. You might be hitting 14, but the Malone tune might be expecting 18. Your graph says it to me you aren't generating the boost the computer thinks you should.

 

[ken.fresno-tdi]

I can finally close off this thread... After spending several hours double and triple checking the pressure and vacuum lines that could cause my limp mode at seemingly random times I decided to do the one thing that is mentioned toward the end of the very good
" How to Troubleshoot Low Power on A3's/B4's:" http://forums.tdiclub.com/showthread.php?t=75959, specifically a exhaust blockage. I cut the exhaust in front of the cat and drove around with vagcom measuring expected/actual MAP values. I went for a quick spin and under hard acceleration from 1500 - 3500 rpm everything lined up. Then I drove up towards Yosemite (in horribly smokey conditions because of our wildfires) and it never went into limp mode; actually better power than ever and I think better mpg's as well. Next step will be to replace the cat and see if that is it. I think it is, as when I hit it with my palm it rattles and seems to have lots of loose pieces inside... Anyway, good to solve a problem of many months... Thanks again for all the suggestions and tips.

 

[Mongler98]

You melted it. I would be suspect to see what egts you are running! Another reason to run an egt gauge.

 

[ken.fresno-tdi]

Good point and well worth having! I actually did install a egt gauge on the van when I first swapped in the TDI engine because I was worried about temps, since it was chipped and I knew the boost would run a couple psi more than stock. But even when climbing long hills with a van load of camping gear and 2 or 3 persons (total weight of around 5000 lbs/2400 kgs the egt never gets above 1000F / 540C), which seemed reasonable given what I read on other forum posts. The cat is also about 7 feet downstream of the header, which would also lessen the temps somewhat over a Jetta. What I didn't check was whether the cat was any good when I bought the Eurovan, since I bought it with a bad 2.4L 5 cyl gasoline engine before swapping in the TDI. My guess is that it was bad from the beginning and I have always been running with more back pressure then I should be.