The Mysterious Vacuum Issues

[Shizzell]

So the hunt continues. To summarize the problem, the car is not producing enough vacuum; it's resulting in failed power brakes. This vacuum system is causing some headaches, and I would just like some clarification on a few items.

1. Is my method of checking the vacuum OK?:
Using the vacuum gauge, I tee'd it into the middle bulbous side nob on the brake booster hose.
On my working tdi: ~12 inHG. (I believe this should be > 24 working correctly, I need to replace the hoses on this one)
On the non-working tdi: ~2 inHG.

2. Is my method of checking the vacuum pump OK?:
When I disconnect the hose from the tee from the vacuum gauge, and plug both sides, I believe this will check the vacuum pump directly.
Working tdi: > 28 inHG
Non-Working tdi: ~2 inHG

3. The steps I have taken:
A. Today I replaced the power brake booster with a used one.
B. I replaced the vacuum pump with another used one a month ago.
C. I swapped in a used N75 to check if there was any difference, and there wasn't.
D. I swapped the entire vacuum system with the used one that came with the engine I replaced.

4. My next steps in order will be to:
A. Replace the vacuum hoses.
B. Swap in the old vacuum pump I replaced it with.

5. The assumptions I can make:
A. I know vacuum pumps rarely go out, but I suspect it because of the vacuum pump test I did.
B. The brake booster looked physically better than mine, but it still could be an issue.

The vacuum hoses should be replaced no doubt, but what do you guys think about after that if I still have problems?

Thanks

 

[Seatman]

I think you should buy a heap of silicone pipe either 3 or 4mm and replace the lot. I just did today and the car's got back it's edge. The amount of crappy bits I found was unreal. Little almost invisible splits here and there that you just wouldn't notice looking at it. The whole thing is connected and any leaks will effect the brakes, that's what I found anyway. I bought 3mm stuff but it's really stretchy so I have it on the bigger fittings as well as the smaller ones.

I used these diagrams for mine, just printed off the one I wanted and followed it.

http://forums.tdiclub.com/showthread.php?t=290286&highlight=vacuum+diagram

 

[Shizzell]

I replaced the entire vacuum system hosing. The car now starts and jumps to about 12 and works itself slowly up to 17 inHG. When I hit the brakes, the pressure jumps all the way to 0. When I do that in my other car, the pressure will drop maybe 2 inHG.
What to do next?

 

[Seatman]

What about trying the pump from the other car and if there's still a difference at least you can rule out the pump.

 

[Shizzell]

This weekend I think I'm going to swap the vacuum pump. I'm pretty sure the one that we put on this was good though.. Anyways, I've noticed this issue:

There is oil getting sprayed from the... EGR? onto the valve cover. What to think of this? I just checked the mityvac vacuum on the EGR and the EGR actuator. They both hold.

 

[Seatman]

That's just a bad egr, they do tend to leak a bit of oil from the intake.
Your first post says you replaced the vacuum pipes with the ones that came with the engine, get new stuff and get silicone. It's made a huge difference to my car and mine looked fine. The boost is better, the brakes are better, everything is better.

 

[Shizzell]

Bad EGR as in, replace it? Would this cause any vacuum issues? (Or just a trivial oil leak?)
I replaced the vacuum hoses originally with ones that came with the engine, and then replaced those with a complete set of brand new ones several days ago.

 

[Seatman]

All I know on the egr is they start to leak oil like yours so people replace them. I've heard of the egr causing boost leaks too but not vacuum.

New pipes? I'll shut up about it then lol


Looking again at your first post, is it just bad brakes? The car still has plenty of power and doesn't go into limp mode or that?

 

[eb2143]

Bad EGR as in, replace it? Would this cause any vacuum issues? (Or just a trivial oil leak?)
I replaced the vacuum hoses originally with ones that came with the engine, and then replaced those with a complete set of brand new ones several days ago.

The only way to fix it would be to replace the EGR or modify it into a race pipe, or purchase a race pipe. Trivial oil leak as far as related to your vacuum issues.

I don't think vacuum pump problems on the A4 are all that rare. I've had to replace mine. Try wiggling the nipple on the pump and see if it affects how much vacuum it pulls—is that nipple pretty loose on your pump? This is why I had to replace mine.

I'm still a little unclear: do you have any power brakes or is it intermittent failure? Did you replace the hard plastic pipe between the pump and the booster that is usually vacuum troubleshooting numero uno due to hairline cracks at the bend? Even if you did replace this pipe, if you're using a used parts it's worthy of a close re-inspection.

 

[Shizzell]

The car has no troubles running, plenty of power. The brakes worked on this vehicle before it sat for 6 months as I replaced the engine. Right now its just an issue of getting the assisted brakes to function. You can tell you are getting assistance on the first brake pump, but after that there is nothing... you need to stand on the brakes to get them to work. I confirmed with a vacuum gauge that I lose total vacuum when pushing on the brakes. The vacuum will slowly work itself up to 7- 12 inHG after idling, and the assisted brakes will function with the little vacuum it has built up (Only to lose it on the brake again)

 

[Shizzell]

The hose connecting to the vacuum pump is more secure (however with a aftermarket clamp) than the other TDI that has a working vacuum system. I'm pretty confident it is not that hose, however I will probably swap it when I swap the vacuum pump. The vacuum is also not affected when the hose is wiggled.

 

[eb2143]

You can tell you are getting assistance on the first brake pump, but after that there is nothing...

Let us know if the new pump and hard plastic hose prone to cracking fixes things. If not, triple check to make sure the vacuum reservoir (round plastic ball) isn't somehow leaking or has a bad connection.

 

[whitedog]

Can you pull the vacuum tube off of the brake booster and block that while measuring vacuum with the engine running? That would isolate away the brake booster.

 

[greengeeker]

2. Is my method of checking the vacuum pump OK?:
When I disconnect the hose from the tee from the vacuum gauge, and plug both sides, I believe this will check the vacuum pump directly.

No and WD just explained why. You haven't isolated the pump from the booster.

 

[Shizzell]

Excellent. Thanks whitedog for the sweet troubleshooting technique. Turns out I had 2x bad vacuum pumps, and I was replacing a bad one with another bad one. I put a new one in, and the gauge shoots right up to 28 inHG in seconds. Brakes are working well now; we can consider this one closed guys.
Thanks a lot!

 

[whitedog]

MMMM. Chicken dinner for the winner! LOL!

Thanks for letting us know the results.

 

[BakoTDI]

The only way to fix it would be to replace the EGR or modify it into a race pipe

eb2143, this intrigued me! what do you mean by modifying the EGR into a race pipe? I live in California, which still calls for inspections on diesels 98 or 97 and newer, so moving to an actual race pipe would most likely be a cause for failure on inspection, even though I might try for the time in between my inspections. So, can you explain this a tad more please.

 

[flee]

WingNut has a thread in the performance stickies that describes his 'stealth race pipe' mod.

 

[BakoTDI]

WingNut has a thread in the performance stickies that describes his 'stealth race pipe' mod.

INDEED!! Here it is! http://forums.tdiclub.com/showthread.php?p=711141
Thanks flee!!