Low power no code or limp mode?

I have been trying to help a friend who has been having a problem with low power on his 1999.5 jetta tdi. It doesn't seem to have any power but does not throw a code or go into limb mode. In the lower gears (1-2) it will start out like it has some boost but as the rpm rises it almost feels like you are backing off on the fuel. I have Vag-Com and the MAP pressure starts out pretty close but as the rpm rises the actual drops off compared to the requested but it never goes into limp mode. I checked the turbo actuator with a hand vacuum pump and it is moving and holds vacuum. I put a vacuum gage on the control line for the actuator and you can see the vacuum change to the turbo with change in demand for boost. I thought I would try changing all the vacuum lines in case there is a leak somewhere. Is there a spot I could connect my hand vacuum pump to to verify the lines are vacuum tight.
Any other help would be very welcome. The car has about 150K on it and I replaced the head and turbo about 1 1/2 years ago as it had been overheating back then if that is any help.
Thanks

jjsbiggs said:

I have been trying to help a friend who has been having a problem with low power on his 1999.5 jetta tdi. It doesn't seem to have any power but does not throw a code or go into limb mode. In the lower gears (1-2) it will start out like it has some boost but as the rpm rises it almost feels like you are backing off on the fuel. I have Vag-Com and the MAP pressure starts out pretty close but as the rpm rises the actual drops off compared to the requested but it never goes into limp mode.

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The symptoms are consistent with a boost leak. My '02 had a cracked pancake pipe (between the turbo and intercooler) which leaked more as boost increased - enough to cause low power, but not bad enough to throw an underboost code. A plugged intake manifold is another possibility, but I assume it would have been cleaned when you did the head.

Is there a spot I could connect my hand vacuum pump to to verify the lines are vacuum tight.

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If you go to measuring block 11 while the car is idling and click basic settings, the ECU will cycle the actuator up and down continuously every 30 seconds or so. You can then reach down behind the engine and feel whether it has full movement (about 1/2" - see DBW's video), and if it's leaking down.

Simon

I went thru the same thing about a week ago. it was a Vacuum leak I replace all vacuum lines and power was back.

Also check the Vac hose from the vac pump in the engine to the brake booster, that hose is a hard plastic material and the ends are heat shrunk to the fittings, with time and heat it get brittle and cracks in both ends by the fitting and leaks vaccum.

Good luck!!!

See the link in my sig for low power / limp mode

Sounds like you're already starting down some of the troubleshooting paths. I recommend you test the maf before you go further

I will post again once I get to look at the car again. He drives the car to work everyday so it can be hard to get him to bring it over for me to look at. I cleaned the intake when I did the head and I look at it when I had it the last time and it looked good.
I also tried unplugging the MAP and it seemed to have no power all the time so I just plugged it back in. I think a vacuum leak is the most likely problem.

I was able to get a chance to take another look at my friend's 99.5 Jetta again. I replaced all the vacuum hoses and now it appears to hold vacuum after you shut off the car which I don't think it would do before. I cleaned and tested the one check valve I found in the system. It seems to restrict the flow in one direction but does not seal fully should it seat fully and not allow flow in one direction.
It still does not have the power it should and is not giving full boost. It does not throw a code or go into limp mode. Checking with VAG-com above 3000 rpm you can feel the power drop off all most like you are backing off on the fuel and when you are requesting 800 MAP it is getting about 600. I checked the intake lines to look for any signs of leaks like stains etc. but they seem to be OK. I also tested the turbo actuator and it starts to move at about 5" vac and it fully open at about 17". Does applying vacuum to the actuator increase boost?
Thanks for any help you guys can offer.

jjsbiggs said:

I also tried unplugging the MAP and it seemed to have no power all the time so I just plugged it back in.

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jjsbiggs said:

Checking with VAG-com above 3000 rpm you can feel the power drop off all most like you are backing off on the fuel and when you are requesting 800 MAP it is getting about 600.

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Those sound like MAF (mass air flow) numbers not MAP (manifold absolute pressure - boost). If the MAF is only reading 600 at 3000 RPM, the MAF is probably bad.

I suggest logging both MAF and MAP - detailed instructions here.

Simon

I will give that a try and see if I can post the results. Thanks

jjsbiggs said:

I also tried unplugging the MAP and it seemed to have no power all the time so I just plugged it back in. I think a vacuum leak is the most likely problem.

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Usually you unplug the MAF to test, are you sure you didn't mean to say MAF, or did you test the MAP rather than the MAF?

If you have not done so yet, please try unplugging the MAF and running without it.

I had the owner unplug the MAF and there was no change. I believe with no change or it runs better that the MAF is the most likely problem. I have read that here and on another site is that correct?

I think that if there is no change then it is inconclusive.