Trim Rich + Boost issue + EPC = Wtf?
02-11-2017, 06:49 AM
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Trim Rich + Boost issue + EPC = Wtf?
Ok Gents I'm new here but not new to VW/Audi. I've got a puzzle maybe you all can help me figure out. A few months ago my wife picked up a 2004 Quatro TT with the 225hp 1.8t (BEA Block). Bottom line up front: We are consistently getting a fuel trim rich code with CEL, and inconsistently getting a hard idol or EPC and traction control light paired with no throttle response on the highway (I think it's a failsafe, we pull over turn the car off to reset everything, then it starts and runs fine), we are also getting inconsistent boost. One of the problems is I've never driven the car when I knew it was working properly, so I don't know if I'm getting an intermittent over boost or only the boost too low issue. Of note, I am the only one that gets the EPC issue and I believe it only happens when using cruise control (the wife doesn't use cruise).
I suspect it's multiple issues so it's a royal pain to iron out. This is what I have done so far:
I suspect it's multiple issues so it's a royal pain to iron out. This is what I have done so far:
Checked spark plugs: they are clean and the proper type
Checked vacuum system: Replaced old lines, actuated valves with vacuum tester, and vacuum tested everything. There are no leaks.
Checked EVAP Purge Valve (N80): It was clogged so I replaced it, there was no noticeable change (I did not do anything with the charcoal canister)
Checked coolant temp sensor with VAG-COM: It was reading about 120 degrees high, so I replaced it (and fixed a coolant leak in that damn plastic flange)
Visually inspected fuel injector portion of wire harness: No abrasions or damage
Visually inspected coils and wires to coils: They do not match, so at least one has been replaced in the past otherwise nothing strange
Replaced all turbo clamps with T clamps (I was having issues with blowing boots off, made me think N75 was working intermittently causing overboost)
Swapped MAF sensors
Replaced brake switch: it was the old style and had an intermittent short, and I know they have caused cruise control issues in other vehicles
Recorded requested vs actual MAP: There is a significant difference during hard pulls to redline (sometimes making almost no boost)
There are no misfires when I've done recordings
My next planned steps are:Checked vacuum system: Replaced old lines, actuated valves with vacuum tester, and vacuum tested everything. There are no leaks.
Checked EVAP Purge Valve (N80): It was clogged so I replaced it, there was no noticeable change (I did not do anything with the charcoal canister)
Checked coolant temp sensor with VAG-COM: It was reading about 120 degrees high, so I replaced it (and fixed a coolant leak in that damn plastic flange)
Visually inspected fuel injector portion of wire harness: No abrasions or damage
Visually inspected coils and wires to coils: They do not match, so at least one has been replaced in the past otherwise nothing strange
Replaced all turbo clamps with T clamps (I was having issues with blowing boots off, made me think N75 was working intermittently causing overboost)
Swapped MAF sensors
Replaced brake switch: it was the old style and had an intermittent short, and I know they have caused cruise control issues in other vehicles
Recorded requested vs actual MAP: There is a significant difference during hard pulls to redline (sometimes making almost no boost)
There are no misfires when I've done recordings
Change N75 valve: I haven't checked it but if it is working intermittently it could explain the boost issues
Change Diverter Valve: It's cheap and could also explain the boost issues
Verify the wastegate is working properly (at about what PSI should it activate?)
Is there anything obvious that I'm missing? I'm new to the VAG-COM, so are there any other recordings I should do?
Change Diverter Valve: It's cheap and could also explain the boost issues
Verify the wastegate is working properly (at about what PSI should it activate?)
03-11-2017, 04:30 AM
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Problem Solved
The N75 valve was the problem. I've noticed as I searched for other people with the same or similar issues as I had no one comes back and explains what the solution was, so here it goes. The N75 pressure checked fine, but it wasn't actuating properly causing the wastegate to open intermittently at higher throttle. This also caused the car to periodically dump boost at steady highway speed, and I can only surmise the sudden power fluctuation while using cruise control caused the EPC and CEL as a failsafe. I've run it for about 2,000 miles to verify this was the only remaining issue, and it was. We also went from 17mpg to 30mpg average, so better fuel economy is always welcome.
The moral of this story is check that damn little boost control valve if your turbo is acting wonky, if you're getting low power and a fuel trim rich code, or if your car randomly throws EPC and CEL and looses all throttle control when using cruise control. This issue is probably why the previous owner sold the car, because it was a pain to figure out. Not to mention if you take it to a dealer you'll leave owing the shop fee with only a note that says "could not replicate issue" to show for it (fortunately I didn't have to play that game). Hopefully this saves someone else some time money and frustration.
On a side note thanks for the help guys, super insightful
. As there were no responses after a month and almost 200 views. I can only assume the problem I described exhausted the technical expertise of this forum, or this isn't the right "community" forum for me. This'll be my second and probably last post.
The moral of this story is check that damn little boost control valve if your turbo is acting wonky, if you're getting low power and a fuel trim rich code, or if your car randomly throws EPC and CEL and looses all throttle control when using cruise control. This issue is probably why the previous owner sold the car, because it was a pain to figure out. Not to mention if you take it to a dealer you'll leave owing the shop fee with only a note that says "could not replicate issue" to show for it (fortunately I didn't have to play that game). Hopefully this saves someone else some time money and frustration.
On a side note thanks for the help guys, super insightful
. As there were no responses after a month and almost 200 views. I can only assume the problem I described exhausted the technical expertise of this forum, or this isn't the right "community" forum for me. This'll be my second and probably last post.
03-24-2018, 09:21 AM
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Surge, thanks for the post. i posted a question---"disconnected battery, now problems" . I just had the N75 checked, ok, and checked or replaced the other things that you mentioned. I will try the N75. Also, i am getting views, but no replys. this tt is very well built mechanically, but the electronics seem f**ked up. thanks for your suggestion. artifacts [ chris]
03-25-2018, 12:27 PM
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Surge, thanks for the post. i posted a question---"disconnected battery, now problems" . I just had the N75 checked, ok, and checked or replaced the other things that you mentioned. I will try the N75. Also, i am getting views, but no replys. this tt is very well built mechanically, but the electronics seem f**ked up. thanks for your suggestion. artifacts [ chris]
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