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Discussion Starter #1
Okay, this problem may need the Dr.House of tdi knowledge. I bought my 2002 Jetta TDI about 2 months ago. When I bought it the engine light was on and it was a P1556 problem. From there I took apart the intake and replaced it with a new one, and replaced all the gaskets with new ones when I put it back together. The intake was clogged pretty good, but still no boost from the turbo. From there I replaced the N75 valve with a new one, and replaced all the vacuum lines, as well as a new bosch fuel filter(air filter is clean). It seemed as if that fixed the problem but the code would still reoccur and the boost would only last a few seconds then cut out. I was never able to go completely down a freeway onrap without it cutting power. I restarted the engine and it would seem to come back for a minute, but then I havent felt boost after the first few time doing this. In other words, I definately do not feel any boost at all now. Finally, I replaced the actuator with a new one. I also replaced the MAF with a new bosch one.
Then, I realized I was probably doing the diagnostics in reverse order. First I should see if there is vacuum, and why it is not reaching the turbo actuator. I made my way to the hard line from the brake booster which has a type of T which I beleive supplies vacuum to the system. However, with the engine running (at idle) there is no air flow comming from the T that is inline of the brake booster line that comes out to the side of engine. There is no obvious leak near the brake booster, and my brakes operate normally.

Shouldn't this location offer a constant vacuum?
Also, any other ideas on what I could test next to get my boost going?

I appreciate any help you guys can offer. I have been up and down every forum, website, and search engine and have found nothing similiar to my issue. I have only a simple scanner that allows me to read and erase codes.
 

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Discussion Starter #2
Please help w/ a unique p1556 code

Okay, this problem may need the Dr.House of tdi knowledge. I bought my 2002 Jetta TDI about 2 months ago. When I bought it the engine light was on and it was a P1556 problem. From there I took apart the intake and replaced it with a new one, and replaced all the gaskets with new ones when I put it back together. The intake was clogged pretty good, but still no boost from the turbo. From there I replaced the N75 valve with a new one, and replaced all the vacuum lines, as well as a new bosch fuel filter(air filter is clean). It seemed as if that fixed the problem but the code would still reoccur and the boost would only last a few seconds then cut out. I was never able to go completely down a freeway onrap without it cutting power. I restarted the engine and it would seem to come back for a minute, but then I havent felt boost after the first few time doing this. In other words, I definately do not feel any boost at all now. Finally, I replaced the actuator with a new one. I also replaced the MAF with a new bosch one.
Then, I realized I was probably doing the diagnostics in reverse order. First I should see if there is vacuum, and why it is not reaching the turbo actuator. I made my way to the hard line from the brake booster which has a type of T which I beleive supplies vacuum to the system. However, with the engine running (at idle) there is no air flow comming from the T that is inline of the brake booster line that comes out to the side of engine. There is no obvious leak near the brake booster, and my brakes operate normally.

Shouldn't this location offer a constant vacuum?
Also, any other ideas on what I could test next to get my boost going?

I appreciate any help you guys can offer. I have been up and down every forum, website, and search engine and have found nothing similiar to my issue. I have only a simple scanner that allows me to read and erase codes.
 

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The first step is to get a Ross tech VCDS. http://www.ross-tech.com/Merchant2/merchant.mvc?Screen=CTGY&Category_Code=VAGCOM Although it costs 250, it's a lot cheaper than spending money and time chasing down problems. Then you can read the sensors and really know what's going on. Not sure the line you are talking about but the TDI has a vacuum pump that supplies vacuum because diesels doesn't have a throttle which gives vacuum in a gas car.
 

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Exactly^^^ Get the correct tool and stop throwing money and time at it. Go through this checklist:
http://www.myturbodiesel.com/1000q_how_to/multi/limpmodetdi.htm

It requires the VCDS cable and software. Some things are harder to diagnose and won't be found with a code scanner.

You could have put a vac line on the wrong nipple or have a loose EGR pipe. Whatever it is, it sounds like it's getting worse. Follow the vacuum pump at the end of the camshaft to the vac lines. You should feel vacuum with the engine at idle.
 

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Maybe the actuator isn't adjusted properly? You could have replaced a bad one with a new one that wasn't adjusted to the right length. The turbo vanes could be stuck too.
 

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Discussion Starter #6
Thanks for your input guys. I think I will invest in that tool to try and save some money in the future. Im starting to wonder if the owner before me messed up the vacuum line some way and thats why replacing them did me no good. Any one have a good picture of how the lines should be routed, the picture under my hood is all torn up and I cant see the lines.
 

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Discussion Starter #9
Thanks for the excellent diagram. I have some new symptoms that occurred on my way home. I have been driving around with the line from the n75 to the turbo actuator disconnected for a few days (awaiting a new).
When I got on the freeway today the turbo suddenly kicked in and started working for about a good 10 minutes. Id hit the gas and the power was instant. After that it shut down and it now works when I restart the car but shuts off when I get a heavy foot.

I bought and just received a new Vag-Com and I replaced the vacuum line going down to the actuator with a new one.

Now the question is, how do I diagnose limp mode using th Ross Tech Vag-Com tool?
 

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Read the link I posted earlier. First do a full scan and see if there are any error codes.

Then do each test. Since it sounds like you've already tried a few things, each cause of limp mode is equally likely.
 

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Discussion Starter #11
Driving around the past two days and there is no boost at all, not even when I restart the car. any thoughts?
 

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When you did the tests, what were the results? Any more advice I say is just guessing until you say what the test results were? What is the injection quantity? When does the vac actuator open? What is the MAF sensor reading?
 
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