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VW MKIII-A3/B4 TDIs This is a discussion about MKIII-A3/MkIII Jetta/Golf (<99.5) and B4 Passats (96,97) TDI's. Non TDI related postings will be moved or removed.

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Old December 7th, 2017, 09:52   #1
2006PSDSD
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Default Intermittent limp mode

I've read quite a few threads here from search results on this matter, but none of them specify my issue. My car: 1998 Jetta TDI 5spd with 279k

This happens when the ambient air is around 15 degrees. The car is going great, as usual then it feels like it's losing fuel pressure suddenly and power is reduced. I thought this could be bad fuel or a dirty filter, so I cycled the ignition while I was going down the highway and it runs great again for a mile, maybe 10. This is on my way to work in the morning, but on the way home I don't get so much as a hiccup from the engine. No CEL either. I don't have a Vagcom either

TIA
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Old December 7th, 2017, 12:41   #2
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Likely limp mode due to boost pressure out of spec for a time. That you can get another mile after cycling the key pretty well confirms it.

There is a code set, just not one that an OBDII reader can see - you would need VCDS.

Can you plumb in a boost gauge and determine what boost levels you are seeing?

Alternatively you can get under the car and work the wastegate to see if it is functioning properly. Easiest is with a cheap bicycle foot pump plumbed into the actuator.

Lastly, The N75 (wastegate control valve) is fairly common as they get slow when they age - you can run an actuator test (again with VCDS) or just replace it once you have eliminated everything else.
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Old December 7th, 2017, 13:04   #3
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Also possibly the boost line going into the ECU. Or the boost line inside the ECU. I had the exact same issue a few months ago, even changed the fuel filter and checked inside the tank for debris. Turns out I forgot to plug the boost line back in after working on it.
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Old December 7th, 2017, 14:30   #4
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Quote:
Originally Posted by Windex View Post
Likely limp mode due to boost pressure out of spec for a time. That you can get another mile after cycling the key pretty well confirms it.

There is a code set, just not one that an OBDII reader can see - you would need VCDS.

Can you plumb in a boost gauge and determine what boost levels you are seeing?

Alternatively you can get under the car and work the wastegate to see if it is functioning properly. Easiest is with a cheap bicycle foot pump plumbed into the actuator.

Lastly, The N75 (wastegate control valve) is fairly common as they get slow when they age - you can run an actuator test (again with VCDS) or just replace it once you have eliminated everything else.
Shoot, I wonder if I should just drop it off at a shop, but then again, I'll save money on teh next repair if I just buy the VCDS. Would this one be a good unit (3 car version)? https://store.ross-tech.com/shop/vchv2_ent/

I can try and plump a boost gauge, but I'm not really in a place to spend the money on mych of anything at this point after spending 7k to repair my truck. How hard is the boost line to plumb in?

I'll look into the actuator, hopefully this weekend


Don't you find it odd that the car runs fine in the afternoon though? The issues you talked about seem like it would be a constant issue

Quote:
Originally Posted by thechoochlyman View Post
Also possibly the boost line going into the ECU. Or the boost line inside the ECU. I had the exact same issue a few months ago, even changed the fuel filter and checked inside the tank for debris. Turns out I forgot to plug the boost line back in after working on it.
Where's that boost line located?


Thanks for your help guys
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Old December 7th, 2017, 20:20   #5
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Nope, sounds normal to me. It could be condensation in the N75 or a small hole in a boost line. Could be the EGR hanging up as well. I doubt it's anything major and is just an annoyance.

Boost gauges are super simple, just a T off the hose going from the intercom cooler piping to the ECU and then run it into the car.
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Old December 7th, 2017, 21:37   #6
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Limp mode is triggered by over boosting for a period of time (about 5-10 seconds). This is the most common issue. its usually caused by a bad vac (boost) line to something that causes the waste gate actuator to not work properly when commanded.
Common issues and the fix for them.

Vacuum lines or boost lines: Inspect or replace them all. usually 3mm, 4mm and 5mm hoses. dont use cheep ones, get quality silicone or VW braided lines from IDparts.com or where ever. Not sure about your ECU but on MK3's there is a boost line going into the ecu and inside the ecu to the MAP sensor and it needs replacing too, if you have one.

N75 Valve: you should have a slight clicking from it, kinda like a CCV valve. some times you can clean them, they are not very cheep ($75) for an OEM. usually replacing it is best.

MAF: this is the sensor on the intake air duct right after the filter. ONLY CLEAN WITH MAF cleaner. A cold air intake usually is the culprit for killing them. Check out this link to understand why. Disconnect it and if driving conditions do not improve then its bad. (only after you make sure you have no boost leaks and all your lines are perfect shape.) http://forums.tdiclub.com/showthread.php?t=290373

Boost leaks: Check all your pipes after the turbo to and from the intercooler and to the intake manifold. take them apart, and put back together to make sure no cracks etc. inspect the intercooler too. You will see some oil on the pipes. Its normal. Just wire off the parts your connecting with a light amount of brake clean on a rag. DO NOT spray it into or on the pipe. it could cause a temporary runaway. Happend to me lol, i was lucky, kinda.

When you take your intake pipe off the intake manifold, inspect the intake and see how much soot and crud is caked up. This is caused by the CCV (crank Case Vent) it mixes with the EGR (Exhaust Gas Recirculate) and caused crap to build up. A small amount is ok. Recommend a EGR delete and a tune or hack to remove the CEL (Check Engine Light.) This wont cause limp mode unless its Really bad to the point of causing an over boost. the ECU knows the engine to take in enough air and charges the turbo to supply. This is very uncommon but eh its worth a look.

thats about it. Fix and inspect those items. in that order one at a time with test drive in between to make sure you dont jsut thorw parts at it.

Get someone with VCDS and a VAG-COM connector, or you can autozone it with one of the diagnostic computers they lone you, or a amazon Bluetooth OBDII device. Look up the code you are getting. Limp mode usually does not trigger a CEL (check engine light.)
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Old December 8th, 2017, 07:25   #7
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Wow, thank you for your time and thorough thoughts on fixing my car! I will report back as soon as I have this unit fixed and tell you what fixed it. Now, I'm off to replace the head gaskets on my 2006 Powerstroke!

Do you guys have a vendor you prefer for the EGR delete and tunes? I don't have emission laws where I live
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Old December 8th, 2017, 08:05   #8
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Rocketchip, TDtuning, and Malone are the big three - all have their fans and would be able to provide a tune for your car. Search each and make a choice.
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Old December 11th, 2017, 14:40   #9
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Does a tuner increase fuel mileage? I know Powerstrokes, but not much about the TDI's.

I sure don't want to decrease that since that's the biggest reason I own it
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Old December 11th, 2017, 18:04   #10
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If you do it right, yes. So if you add power without changing the GPH (gallons per hour) of the fuel consumption than by definition you are burning more of the same fuel that goes into the car. In a TDI you get more power buy burning more of that fuel in each combustion. Now new nozzles are usually more efficient then stock, upping the boost helps too. I have a very less than ideal set up that most and I went from 90hp to 200-215 is HP and was getting 43mpg now I get about 48 with the way I drive, if I stay on the highway. I drove across 450 miles nonstop at 70mph~ behind a truck drafting and got 66mpg. But when I autocross I get about 8mpg including the drive there and home because racecar, scan gauge and logs say I get about 1mpg when I’m at WOT at 11GPH. When I am driving I get about 2.6ghp on the flat
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Old December 26th, 2017, 14:02   #11
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Well, I think I'll keep it stock for now, with the exception of the EGR delete maybe. My money pit now is my F350 LOL. Moddifying the TDI is also costly after the VAGCOM, injector nozzles, EGR delete and on and on. My wife won't like having two money pits taking my time and our money! The ROI isn't really there
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Old February 17th, 2018, 13:48   #12
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I think I figured it out! I just now got a chance to take a look at this thing. I took advice given, and started by taking the intake piping apart. What I think the issue is, is two loose intake to turbo bolts! They were sooo loose, oil was all over from the CCV system (with I plan to ditch). I haven't tested anything to see if this is the fix, but I'm ordering the parts now. EGR delete, CCV mod and intake parts that I need. Thanks for the pointers!
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Old February 25th, 2018, 09:50   #13
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Before going down the EGR delete path I would verify that your car is exempt from diesel emissions testing. If you go and modify a bunch of things and then have to go in for inspection there's no telling whether it will pass or not.

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Old February 25th, 2018, 12:42   #14
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Seems to me the test is simply to tighten the two loose bolts?
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Old February 26th, 2018, 05:19   #15
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Well, that didn't work. Back to the drawing board

I'm probably not going to do the EGR delete, not because of the emission restrictions (which I don't have) but because I don't want to spend the money and she has been running for 281k with it intact
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