loss of boost after 2800 rpm

[BLOWNSVT1]

Long time mechanic but new to these beetles. Just bought my wife a 2000 1.8 turbo car with 100k on it. Replaced the timing belt and water pump just as a precaution! Has ran great for several weeks. the other day I noticed the boost was going in and out while pulling through the gears. now the car pulls from a stop just fine until 2800 rpm and the turbo boost cuts out. It's almost like a blow off valve or waste gate dumps off the boost. Do these cars have some type of boost controller on them? I can hear the turbo spool up and them dump the boost after 2800 rpm. These cars are complete dogs without the boost. Any ideas? Also, no codes or ect light does not come on! Runs good other then no boost!

Thanks in advance!

[Fl_bug]

Originally Posted by BLOWNSVT1

Long time mechanic but new to these beetles. Just bought my wife a 2000 1.8 turbo car with 100k on it. Replaced the timing belt and water pump just as a precaution! Has ran great for several weeks. the other day I noticed the boost was going in and out while pulling through the gears. now the car pulls from a stop just fine until 2800 rpm and the turbo boost cuts out. It's almost like a blow off valve or waste gate dumps off the boost. Do these cars have some type of boost controller on them? I can hear the turbo spool up and them dump the boost after 2800 rpm. These cars are complete dogs without the boost. Any ideas? Also, no codes or ect light does not come on! Runs good other then no boost!

Thanks in advance!

My boost problem came from the stock vacuum lines and a faulty diverter valve. The lines were cracked and splitting and not holding pressure to well. The diverter valve threw a CEL code that my friend's VChecker & Vagcom both picked up. After I replaced them with silicon tubing & a Forge 007 Diverter valve, i've not had any more boost problems. Not sure if the same with you.

You should check your vacuum lines out to make sure they're all ok and not cracking and the like.

[Too Cold NB1.8T]

The very first thing I would suggest is that you check for any fault codes in the ECU, then please let us know what they are if any.

2. Check all vacuum/pressure hose and connections for the smallest leaks, the fastest most effective way to do this is with a good smoke keak detection machine, like the Smoke Pro.

3. Check for a bad N249 solenoid.

4. Check for a bad N75 valve.

5. Check the Map sensor.

6. Check that the Waste Gate is not sticking or that the diaphram is not leaking.

[Winterbeetle]

I actually had this problem as well and it turned out to be plugs.

I had pulled them all originally and they looked good but after replacing them the car is running normal.

I had the same issue on my pops volvo s40 turbo and it was also the plugs.

Might not be your issue but it's food for thought

[Too Cold NB1.8T]

Well that is one more of many possible causes to add to the list.

If the spark plugs are fouled or defective then the boost could be blowing them out like a candle which would cause the symptoms that are being experienced, low voltage/current to the coils can cause the same problem as in the case of a failing charging system, good call Winterbeetle.

BLOWNSVT1, put a new set of plugs in and see what happens, be sure to use only (OEM) NGK's or the Denso equivalent and make sure the gap is at .032, anti-seized and torqued to 22ft-lbs.

[BLOWNSVT1]

Thanks for all the comments. The plugs are good, there is no codes in the ecu. The power loss is constant. As soon as the rpms reach 2800 the boost is lost. Prior to this happening, the boost was in and out and then no boost after 2800. I have checked all the lines and intercooler hoses, nothing found. I think the waste gate is dumping off the boost, but you would think this would set a code or you would hear the boost being dumped, but I dont. The engine runs fine, idles real good and has good accel off of idle until 2800. the engine still will pull to redline but without boost, very sluggish motor off it's juice!!!!

[Too Cold NB1.8T]

You say that the plugs are good, how did you determine this or did you change them?

[3beetles]

I also think I am having a boost issue. Upon acceleration it bogs out at around 2500 rpm or so, but picks back up. Am very new to these cars so will be doing as suggested. Will also post any findings that I come across.

[BLOWNSVT1]

plugs were replaced! I am baffled. I thought maybe the intercooler hose was not tight and bleeding off boost under pressure, but it's tight. I looked and felt, checked every vac. hose on the back of the motor. I am sure it is a valve or something that is stuck and bumping the boost, but you would think this would set a code for some type of vac. loss. Like I said....the engine does not cough, spit or sputter, it pulls to red line but there just is not any boost after 2800 rpm. Very puzzled

[Too Cold NB1.8T]

OK:

1. There very well might be a bad valve somewhere, however, vacuum/pressure leaks can be extremely difficult to find and where this engine is concerned, the smallest vacuum/pressure leaks can cause crazy negative results.

The only true way to make sure that no leaks exist is with the use of a good smoke leak detection tool, believe me I know, some leaks I could find through common methods like spraying carb cleaner or using propane gas but even after weeks of searching, these methods left some leaks undiscovered, also, just because a clamp is tight does not mean that a leak is not present, sometimes an over tightened clamp can create a leak.

I finally did some intense research before purchasing the best system "Smoke Pro" had to offer and with-in five minutes of use it revealed three vacuum leaks, valve cover gasket, adjustment screw on my HKS SSQV (I have since upgraded to the new non-adjustable version) and an injector seal, it also located a leak where the turbo and exhaust manifold meet, the three bolts had backed out some.

The car ran like a Bat out of hell after I completed the repairs, it is an expensive tool but it is well worth the cost, it paid for itself after three uses and without the hassle of going around and around with some shop that "might" be of help but will charge hundreds of dollars in the process.

FYI, none of the above issues triggered a fault code either yet they caused the car to run a bit erratically, including surging under boost.

[Smileybug]

Do you have a boost gauge?

[Bob Kontak]

First post - Howdy. I have almost the identical symptoms on my 02 Turbo Beetle. Cripes - Need to look at the plugs - 75k miles and never changed.

Not trying to make this my thread but I will throw a little of my data into the mix.

I get a whooshing sound also that comes from around the charge side. Inner fender coming off now to inspect.

I interpreted the Turbo in an out symptom the poster is experiencing to the transmission but the turbo fluttering sounds like a real possibility.

Will post more to this thread as I gain some experience with the problem.

[Too Cold NB1.8T]

Just curious as to why you are removing the inner fender, there is nothing on either side in there that is related to the turbo or the engine, except, in the left fender there is the plumbing for the stock air box.

[Bob Kontak]

It was news to me when I found out but the inter-cooler is near the passenger side inner fender. You can see it without the liner out - but not all of it - you get a real good look at it and can check for leaks better with the liner out.

That said I did find a leak in the charge side, behind the engine (of course), near where the metal charge tube turns down 90 degrees towards the inter-cooler - actually just inside and down from the L bend in the pipe. I just put a few pounds of air pressure into the system by sealing off the big hose ends with duct tape on the air filter side and the intake manifold side. I have not isolated it yet - I have a tiny mirror and it is not helping much.

Will report back asap.

[Bob Kontak]

Found it - It is a 1" hose that has a big hole in it - almost looks like it was melted by something. Won't know till I get it out. I am embarrassed to say I don't know what it is. It originates on some cylindrical "frammitz" valve and enters the metal air charge tube.

Note to poster - All of my hoses looked great too! You never know. Check the same hose on your car.

Hole is just to the right on the bottom by my thumb. Cant get a good pic of it. Second pic is the hose from a better viewpoint showing tie-in to valve part.

[Bob Kontak]

Diverter Valve hose

1C0145712E Pressure control line - Official name and number - $55

[BLOWNSVT1]

thanks for the pics, I will check my hoses once more. Question, does the divertor valve need vac. to keep the valve closed to build boost or is the loss of vac under acc. close the valve to build boost????