Dead spot in the power curve

[Blue2000TDI]

Hi all, I've got a little question that I have been wondering about for awhile. It seems that my TDI has a bad weak spot in its power curve between 2700 and 3000 rpm's. It is more pronounced in 3rd-5th gears. I can tell the torque is doing it's job in the low end, but as soon as I hit about 2700 rpms it feels like the engine is being choked. I thas been like this ever since I've had it. It now has 74,000 miles, I bought it with 42,000. It gets excellent mileage, so I doubt it is a serious engine problem, it might even just be a normal low spot that every 5-sp manual tdi has. I don't know, but I would like to find out if it is normal or if it can be fixed. I've read quite a few of the MAF posts and I don't think(that could be a problem) that it is related. Any ideas where to look for an answer or what the problem may be. Many thanks in advance.

 

[Curious Chris]

VagCom required as you do need to check the MAF. Try the list above of VagCom people who will help you out.

Hesistation around 3000 rpm is a classic MAF symptom.

 

[Darren_J]

Yup, sounds like a classic symptom of a failing MAF. Change it, at that mileage you'll notice the difference.

 

[Frank M]

Hi all, I've got a little question that I have been wondering about for awhile. It seems that my TDI has a bad weak spot in its power curve between 2700 and 3000 rpm's. It is more pronounced in 3rd-5th gears. I can tell the torque is doing it's job in the low end, but as soon as I hit about 2700 rpms it feels like the engine is being choked. I thas been like this ever since I've had it. It now has 74,000 miles, I bought it with 42,000. It gets excellent mileage, so I doubt it is a serious engine problem, it might even just be a normal low spot that every 5-sp manual tdi has. I don't know, but I would like to find out if it is normal or if it can be fixed. I've read quite a few of the MAF posts and I don't think(that could be a problem) that it is related. Any ideas where to look for an answer or what the problem may be. Many thanks in advance.

unplug the maf and see if flat spot goes away.
if it does they it probably is MAF.
oh yeah, it will set a code when unplugged too.. and a CEL

best way to check MAF is with VAG

 

[deltafox]

Does the power come back at higher rpm? In other words, does the torque surge up and down slightly? If so, and it turns out not to be the MAF, peek into your EGR. Mine (96k miles) had the same symptom even with a new MAF, and it turned out to be badly (85%) clogged intake. After cleaning, the pull is now smooth all the way to redline.

 

[estwing]

I get power all the way up to 4400 where there is an incredible drop in power, like hitting the break. 2700-3000 rpm's are premo acceleration areas in 4th and 5th (and 1st, 2nd, & 3rd). It's awesome to go from 60 to 90 mph with no downshift and virtually no effort.

Not sure about MAF issues as I only have 1200 miles showing.

 

[weedeater]

Well, don't let the fact that peak horsepower is at 3750rpm slow you down.

Or that you should not exceed 3000rpms while breaking in the engine.

Just put the hammer down and go for 5k. Won't hurt a thing.

 

[compu_85]

I get power all the way up to 4400 where there is an incredible drop in power, like hitting the break.

That's where the rev-limiter starts.

-Jason

 

[Mike Morriss]

Hi!
I had what sounds like exactly the same problem with our '99 New Beetle. After a while, it got to where it would go into safe mode occasionally. Ray Gruelich, my trusted TDI mechanic, first found the ball linkage between the vacuum servo that controls the trubo and the turbo was REALLY badly worn. He fixed that and things got better but not fully cured. Then he adjusted the bolt that limits max boost slightly, a turn or so. He said VW recommends never adjusting that and never adjusting the length of the control arm that connects the two. Their story is that "It is set at the factory and should not be adjusted in the field." but Ray said as things wear the factory setting sometimes needs to be adjusted.

The result in Ray's adjustment is ever so slightly max boost under hard acceleration but my power curve is smooth - no flat spot at 3K RPM any more AND it has not gone into safe mode since )

So... I would recommend you do these things:
1. Inspect the turbo control servo and linkage to the turbo to make sure it is in good shape. Maybe lube the linkage at friction points with some sort of high heat thin lubricant, maybe silicon spray.
then
2. Try making the same adjustment that Ray made on my 99, a little at a time. If you can find someone with a VagCom, you can use it to tell how much boost you are sacrificing by doing this. I'd recommend making a small adjustment, test drive and repeat until flat spot goes away.

Please let me know how it goes.

Good luck.
Mike

 

[TornadoRed]

Then he adjusted the bolt that limits max boost slightly, a turn or so. He said VW recommends never adjusting that and never adjusting the length of the control arm that connects the two. Their story is that "It is set at the factory and should not be adjusted in the field." but Ray said as things wear the factory setting sometimes needs to be adjusted.
(skip)
2. Try making the same adjustment that Ray made on my 99, a little at a time. If you can find someone with a VagCom, you can use it to tell how much boost you are sacrificing by doing this. I'd recommend making a small adjustment, test drive and repeat until flat spot goes away.

Mike

When I had an upgraded turbo installed back in 2008, we had to make a tiny adjustment to the turbo actuator, lower it from the lift, take it for a hard drive to get a VAG-COM log, put it back up on the lift, tweak it again, lower it, go for another run, repeat, repeat... until it was perfect. I'm pretty sure the turbo has not been touched since then.

I don't think this should be attempted without VAG-COM/VCDS.

 

[Mike Morriss]

Thanks TornadoRed. I agree that having a VAG-COM to see what boost you are getting after each adjustment is very desirable, but if one isn't available, I believe with cautious (small, like 1/4 or 1/2 half turn at a time) adjustments and a little trial and error one can achieve a satisfactory adjustment without a VAG-COM. Ray as a VAG-COM (as do I). I expect he checked my beetle with his after the adjustment, but he has checked it on many visits over the past few years, so he knows the car's characteristics well.

Thanks again for the note. It is good advice for anyone wanting to try this adjustment.

Mike