Hello everyone, I'm relatively new here, so bear with me. I've never owned a German car, and this is my first Turbo car.

I have a '98 A4 1.8t 5-speed non-quattro, it's got high miles, but it's been well maintained and runs great. . .

Anyway, I thought I was having a boost issue, so I bought a boost gauge and installed it this afternoon. At idle, the gauge is reading about 10 inHg. At around 3500-4000 RPM's, the gauge is reading between 0-1psi of boost, which seems off to me.

From what I've gathered here through several searches, my car should be sitting around 20inHg at idle, and 4-6psi at 4k RPM's. I'm at a loss as to where to begin looking, I'd like to get this straightened out by next weekend, we're supposed to be going on a trip, and I'd like to take my car (better gas mileage than the alternative).

Just in the interest of full disclosure, it does have a CV axle going out (left side), I ordered the new one today, and will be replacing it on Monday. The car has only been in my possession for about 3 weeks, and it's come a long way since I got my hands on it. I just want to get it running 100% before I decide whether to mod it or not.

I'm going to replace the vacuum hose at the front of the intake manifold (where I teed into for the boost gauge) tomorrow, I've already replaced the air filter and did an oil change on it (full synthetic 5w40), bought new plugs (then found out the previous owner just put new plugs on), and installed the boost gauge. There are no mods done to the car, it is completely stock, and it just seems to have no power at all.

Any tips, tricks, ideas to figure out the boost issue would be greatly appreciated. Great forum, I've been lurking for a few weeks, and I'm hoping to glean some more info from you guys. This place really is a wealth of knowledge!

 

Ah, forgot to mention, I do have a diagnostic computer (MacTools scan tool), hooked it up, and there were no codes, no CEL's, nothing. The car idles smoothly, and aside from a minor exhaust leak behind the catalytic convertor, it sounds completely stock. I'll be taking it in to get the exhaust leak fixed Monday as well.

 

Do a boost leak test, its somewhere to start. Also check all piping twice to make sure all are snug and not crack/ripped in some odd place.

 

I'll give that a shot. You're talking about the tennis ball test, right? I'll try that next week (I'm working tomorrow and will be working on getting the new CV Axle installed on Sunday) and report my findings. . . Just seemed odd that I'd be getting low readings both for vacuum at idle AND boost at 4k RPM's, there's got to be a leak somewhere. I can't complain too much though, the car runs great, has 183k miles, and things are starting to wear out on it, so it's not unheard of for a rubber hose to crack somewhere.

Thanks for the tip. Any place in particular I should start looking for leaks? Any known problem areas?

 

Something is very wrong, boost should be 9-10psi at WOT from 2500 till almost 5000 rpm for stock ECU and if it is chipped around 15-16PSI.

You car must be running very slow if it has no boost. Normal vacuum at idle is 20inHG.

Is car accelerating good, maybe just boost gauge is faulty? Do you hear turbo at WOT?

 

I hear no turbo at WOT, it IS VERY SLOW all the time, almost dangerously so. I've been told by the previous owner (a mechanic, go figure) that these cars only run 3-5psi stock. . . I'm hoping to chip it at some point, but it's got a top end noise (loud tick, sounds like a collapsed lifter), and at this point, IDK if I'll even be keeping the car long. . .

I'm going to try to pinpoint the boost leak tomorrow, I'll be pulling all of the rubber hoses from the intercooler to the intake and inspecting for damage, as well as replacing the vacuum line that I teed into for the boost gauge (just to make sure it's not cracked somewhere along the line). If I can get this car to move out of it's own way, I'd have MUCH more fun with it, and I wouldn't be looking to move up to a newer A4 (post-facelift) with Quattro AWD. . .

Funny story actually, I had the car for 3 weeks before my Mom asked me to take her for a ride (that's a new record, she usually asks to drive my car a day or two after I get it), and now she wants to buy it from me to replace her Blazer as her DD. . .


Anyways, it's making boost, as evidenced by the 1psi at WOT. It's most likely got a leak somewhere along the line (as evidenced by the abnormally low vacuum at idle), and I'm looking for the most common issues. If the car needs a new turbo, I can order a replacement (probably do the K04 upgrade) soon, but I need to make sure the one that's currently in the car is bad before I'm going to drop $300 on a new unit.

So, give me some ideas as to what to start checking out (besides the obvious, check for cracks in rubber hoses and vacuum lines, check for obvious boost leaks, etc.), and I'll make sure it's checked out. I'll be out working on the car all day tomorrow anyway, trying to track down the reason for the pathetic power output, and replacing the CV Axle that's on the way out.

 

I think that you should first check diverter valve. Bad idle vacuum is suggesting, that it may me totally ripped and you can`t hold/make boost. So, DV or big boost/vacuum leak, other than that only turbo can be dead, but you would notice that easily.

It is a cheap part(30$). Buy 710n version it will last forever on stock ECU or even chipped. When I had bad DV, idle vacuum was 14inHG but it was holding stock boost (9-10psi).

90% chance is that DV is the problem. If you want to chip the car, you must have 710n valve anyway...

Here is part number 06A 145 710 N...

Good luck

 

Is that something I can get at the local parts stores, or would I have to order online or from a dealer?

 

I think you will have to buy online or from audi/vw dealer.
Also you must go below car to change that, it`s 10min job, but it is hard to get there.

 

I just read a write-up on how to do it, seems easy enough. Definitely easier than the CV Axle replacement I'm about to start. . .

Cheapest I found the part was for $50 (including shipping) online, I'll get that ordered soon. Hopefully I can get this thing boosting as it should before Friday, we are taking the car on a little road trip to a family reunion, and it'd be nice to have a little power on the way. . .

I'm going to inspect all the hoses for cracks, and try disconnecting the battery for a few minutes to see if it's just stuck in limp mode or something. I'll get the new DV ordered later this afternoon.