Low power

We have 2001 Jetta with approximately 180,000 miles on a replacement used engine, (the original engine had a rod snap), 340,000 miles on the car total, and we have been experiencing a low power problem for quite some time now. The engine starts, runs just fine with normal cruising around town there are no noticeable problems. But, when pushed, it seems to accelerate well until around 2000 RPM where it starts to bog down and the power flattens out. At highway speeds, when climbing hills, the turbo will sometimes kick out, necessitating shutting the engine off and restarting. I have beat on the catalytic converter and there are no rattles. The car has been into the local VW shop several times where the MAF, fuel filter and all the vacuum lines have been replaced, the intake manifold cleaned, the fuel pump timed, all with no success. The shop says that the turbo itself is operating normally where they are stumped also by this problem, suggesting that I just drop the car off so they can experiment as time permits, but before I do that I would appreciate any further thoughts and ideas?

Thanks,

Bill

There should be a stored code. Sounds like classic limp mode, various causes, not sure why the shop isn't finding it. Does the OBDII system function correctly after the engine swap (this could interfere with codes)?

Make sure fuse #34 isn't blown, and put a vacuum gauge at the farthest point away from the vacuum pump--solenoid for EGR-- is a good place to start. IME if the engine accelerates well to 2000 RPM and then falls flat, there is vacuum loss to the turbo at that time. Sometimes due to exhaust volume the turbo will spool up w/o the vacuum assist.

The shop has not mentioned any codes or problems with the OBDII system...........

Fuse #34 is good, I would think that replacing all the vacuum hoses should have remidied any vacuum problems, but I may have to purchase a vacuum gauge just to double check that system?

http://aaronsautowerks.com/

Thanks,

Bill

wjfyfe said:

The shop has not mentioned any codes or problems with the OBDII system...........

Fuse #34 is good, I would think that replacing all the vacuum hoses should have remidied any vacuum problems, but I may have to purchase a vacuum gauge just to double check that system?

http://aaronsautowerks.com/

Thanks,

Bill

Click to expand...

You shouldn't have to unless you find evidence of leaky vacuum. More likely it's one of the vacuum operated controls, like N75, turbo actuator, etc., or even electric signals to those devices.
If it's going limp and not triggering a code, that should narrow down the cause. I'm not mechanic enough to know what though.

wjfyfe said:

The shop has not mentioned any codes or problems with the OBDII system...........

Fuse #34 is good, I would think that replacing all the vacuum hoses should have remidied any vacuum problems, but I may have to purchase a vacuum gauge just to double check that system?

Click to expand...

I would recommend a vacuum pump, not just a gauge.
You can test more with it s/a when the turbo actuator starts to move, it hits full open and if it holds vacuum.
The brake bleeder style also lets you prime the fuel system during filter changes or loosing prime.

Search for the 'limp mode' testing thread in the stickys how to diagnose it.

OK, just another lil new tid bit, if it means anything at all, I was just playing with vacuum lines trying to understand what goes where and why when I stumbled across if I remove and plug the vacuum line to the air filter housing, power improves noticeably. I am assuming that this line senses vacuum within the intake system? Anyways, does this mean anything?

Bill

Not trying to hijack the thread but I have a similar problem on my ALH and suspecting a leaky turbo actuator and only wondering for how much time should it hold vacuum? Mine drops it very slowly? Could that be the cause?

EDIT:Not getting any limp mode just severe power drop right after 2300rpm. Also logged some boost drop right in that area.

wjfyfe said:

OK, just another lil new tid bit, if it means anything at all, I was just playing with vacuum lines trying to understand what goes where and why when I stumbled across if I remove and plug the vacuum line to the air filter housing, power improves noticeably. I am assuming that this line senses vacuum within the intake system? Anyways, does this mean anything?

Bill

Click to expand...

Should tell us something. That line tees into ports on the N18 and the N75. Perhaps one of those devices is dirty or failed allowing vacuum escape. Or maybe the vac system is leaking some and the plug simply allows a bit more vacuum.
There are a couple check valves in system, been know to fail and cause issues.
See this diagram
If you need to buy one of those check valves look hard for an alternative source like Huge Peters, Grangers.

wjfyfe said:

OK, just another lil new tid bit, if it means anything at all, I was just playing with vacuum lines trying to understand what goes where and why when I stumbled across if I remove and plug the vacuum line to the air filter housing, power improves noticeably. I am assuming that this line senses vacuum within the intake system? Anyways, does this mean anything?
Bill

Click to expand...

Well you can't run it that way because that hose allows vacuum to be relieved so
that the actuators can cycle on and off. That's pretty good evidence that there is a
vacuum leak or weak vacuum pump function, though.

FWIW, I don't have any of those check valves anymore. They aren't absolutely critical.
I was able to correct my N75 by blowing it out with air. You can bench test the valves.
As Bob wrote, any of the parts of the vacuum system can leak and cause problems.

wjfyfe said:

OK, just another lil new tid bit, if it means anything at all, I was just playing with vacuum lines trying to understand what goes where and why when I stumbled across if I remove and plug the vacuum line to the air filter housing, power improves noticeably. I am assuming that this line senses vacuum within the intake system? Anyways, does this mean anything?

Bill

Click to expand...

Now, after thinking about this a bit more, why would a "hot" vacuum line be connected to an open air source, (it is not supposed to be "hot", is it?)

Bill

No, that's the vent line to release vacuum for the egr and turbo. The charged lines and that one go to the solenoids.
There's a check valve that is supposed to stop vacuum from reaching it.

VWALH said:

Not trying to hijack the thread but I have a similar problem on my ALH and suspecting a leaky turbo actuator and only wondering for how much time should it hold vacuum? Mine drops it very slowly? Could that be the cause?

EDIT:Not getting any limp mode just severe power drop right after 2300rpm. Also logged some boost drop right in that area.

Click to expand...

I experienced similar issues recently. No codes, just flat power in the same place as you. My N75 slowly dropped vacuum when I tested it. Replacing the valve restored long-lost power...

OK, vacuum at the vent port of the N75 and N18, I am assuming this is telling me that both solenoids have gone bad?

Thanks folks,

Bill

Swap the n75 and n18 to see if it clears up.
Also check the check valve to ensure it inly flows in one direction.

eddieleephd said:

Swap the n75 and n18 to see if it clears up.
Also check the check valve to ensure it inly flows in one direction.

Click to expand...

To confirm, there should be no vacuum from the vent ports of the N18 and N75, correct, (I have vacuum in both lines)?

Thumbs up on the check valve, black towards vacuum, white towards solenoid!For grins I just tried switching it around, the car goes no where!

Bill

wjfyfe said:

To confirm, there should be no vacuum from the vent ports of the N18 and N75, correct, (I have vacuum in both lines)?

Thumbs up on the check valve, black towards vacuum, white towards solenoid!For grins I just tried switching it around, the car goes no where!

Bill

Click to expand...

Aw, heck with it, the car is almost 17 years old now, and has over 300,000 miles on it, it's probably a a good idea just to go ahead and replace both of those solenoids anyways so they are on order!

Thanks everybody!

Bill

wjfyfe said:

To confirm, there should be no vacuum from the vent ports of the N18 and N75, correct, (I have vacuum in both lines)?

Thumbs up on the check valve, black towards vacuum, white towards solenoid!For grins I just tried switching it around, the car goes no where!

Bill

Click to expand...

I don't thing I agree with 'no vacuum from the vent ports'
As is a vacuum it doesn't vent, it sucks air in.
When I plug the vent at the air filter box the car runs bad or stalls.
Clearly there should be vacuum in the line.

I sprayed a bit of penetrating oil in my N75 lines and lightly blew it out.
The car was more responsive after that.
My replacement is here, I just didn't have time to install it this weekend.
had to much fun changing my timing belt and a few other things.
Started about 10:00 AM, finished around 5:00 AM
Probably next weekend.

OK, that is interesting, when you plugged your vent line the car ran bad and stalled, when I plugged the vent line, the car ran noticeably better, so which of us, if either, actually has a bad valve? Or, maybe both valves are bad for differing reasons?

Bill

I stated that wrong, it relieves the vacuum pressure so you don't stay at full boost. Otherwise, there is no way to control it.

There shouldn't be vacuum if it's not connected to the valves and when it's not running.

wjfyfe said:

To confirm, there should be no vacuum from the vent ports of the N18 and N75, correct, (I have vacuum in both lines)?

Thumbs up on the check valve, black towards vacuum, white towards solenoid!For grins I just tried switching it around, the car goes no where!

Bill

Click to expand...

What do you mean by it goes no where? It should run and drive, you will just have no boost and it will throw a code.
Put mine in backwards once and that's what I experienced.

Lol, you took my post too literally, with the check valve in backwards it was very, and I mean VERY, lethargic, there was absolutely no mistaking that something was not right and you were not going to be going too far with it!
Bill

I figured, however, I have learned not to assume.
It will definitely go nowhere fast with it in backwards
Curious about the injectors though.
Ever replaced/rebuilt?

It is interesting that you ask that question where the injectors in it now are the original, but some folks have asked whether the engine originally was "in front of" an automatic or manual transmission, stating that there is a difference, I dunno.

Bill

OK, just some added info if anybody is following this. I replaced the the N75 and N18 valves today resulting with the car being "snappier" around town, noticeably improved acceleration on the highway, but on steep hills it is still initially bogging down, but now it will pick up where you can feel the power coming on slowly with some surging. I could not get it to kick into limp mode this time. We seem to be sneaking slowly up on the real issue but are not quite there yet.................

To recap, the intake is clean, we have replaced the fuel filter, MAF, vacuum lines, N75 and N18.

Bill

Have you checked the actuator function and adjustment?

Are you talking about the actuator accessible underneath on the turbo, if so, it is operating but I am unsure about adjusting it?

Bill

There's mention of the intake having been cleaned, but not of the intake ports on the head OR the EGR cooler.

You say that the turbo actuator is working. Can you qualify this? We need to hear some metrics, as without them what you think is OK might not be OK (others can say/confirm).

If this is a higher RPM issue then start looking at fuel blockages (work from the tank forward).

BUT... Really need to see some VCDS logging, otherwise we could be at this guessing game for quite a long time.

When the initial power problem diagnosed by the shop the initial suggestion was to clean the intake manifold, which I gave permission to do, but when they got into it they said that the intake did not require cleaning, further stating that the turbo was working, so that was not the problem. Obviously stumped themselves, they then suggested my just leaving the car with them a week or so and they would play with it on their free time, (saving me shop time), but we really cannot do without the car for that long. The actuator appears to be operating freely with application of vacuum.

Thanks,

Bill

So, you said that the intake was cleaned, now you say it was not.

Sorry, but I'm questioning the shop at this point. This should really have been figured out rather quickly: folks here are struggling because we're doing this virtually- having hands on this thing should get this resolved quickly- there are only a few things that could cause this. This seems like you're fishing for help for the shop.

Like I said, run some logs. THAT will get us real data (everything thus far has been with little/no qualification, just "it works" or is deemed OK).