CARSNPLANES

1987 Turbo Quattro wagon, or any audi turbo, The numbers on the boost gage in Bar, 0.0 to 1.4 (I only see 1.1 tops). Are they a portion or percentage of atmospheric pressure? Since atmosphere is 1 bar, does anything below 1 bar mean there is no boost happening? And the time real "boost" is happening is above 1 Bar? To get max boost , you have to mash the pedal to the floor (full throttle) and be close to 3000 rpms or higher. Your really never mashing down too long because the car will catch up and then you let your foot off to change gears. It seems "boost" is hardly happening. If this is the way it's supposed to work, then it seem there is more unboost range(0.0 to .9) than boost range(1.0 to 1.4)Is this correct? OR... is a turbo charged engine alway in "boost" just very little at times, hence the .x number value as opposed to the 1.x value?
Feedback?

MarkPan

if youre only getting 1.1bar, the electronics side is probably fuct, and that is just mechanical (from the wastegate spring).

yes. 1bar = atmospheric pressure.. but you must realize that normal aspirated cars do not run at one bar, they run at a vacuum (i dont know what.. but <1 bar)

the car is designed to only give you lots of boost when you mash the pedal.. saves gas

so.. your wastegate freq valve, or full throttle switch, or air temp sensor, or multi function temp sensor, or a boost leak is causing your lack of boost.

Will Ng

yes, you are correct.
The reading used is a bit confusing since it's absolute, therefore below 1.0 bar, it indicates vacuum.

A turbocharged car's characteristics is determined by the manufacturer. Under most driving conditions, you are not at boost. Boost can be dialed in most agressively, where upon each dab of the throttle means you're dipping into boost. Some sportscars and sportycars are set up that way, ie. DSM turbos, WRX.
But being constantly on boost also reduces gas mileage significantly. Bear in mind, the type 44 turbo was a luxury cruiser, not sportscar. Audi has engineered the ECU to govern how the boost builds so that the throttle is smooth not abrupt.
The frequency valve is cycled between boost and vacuum to control the wastegate for 1.4 bar indicated. Otherwise, it begins to crack open quite early. If you don't see 1.3 or 1.4 bar, something is defective. First check for leaks at the hose to the top of the wastegate. Then look at the turbo hoses. Feel for cracks and oily spots, especially the michelen man hose.

Of course, most of us are interested in the power.
;-)
And a swap to a stiffer wastegate spring will provide that push-you-in-the-back transition you want. Boost will be reached much quicker, car will accelerate better, mileage will fall, grins bigger. Until the michelen man house blows.
(can't ignore the Audi Gods.)

CARSNPLANES

Thanks. Well, I may not even have a boost leak. I posed the question as a general question about "boost" theory to see if I might have a problem. I never really had the pedal down that long to see if 1.4 ever comes up, (car has 195000 mi). It may be possible to get it but truthfully, I'm afraid to go there. Should I be? Except for a nuisance oil leak between head and front of block, the engine seems to run very well, idles well etc. If I had boost problems at high power, would evrything else look ok or perform ok? It seems like eternity to have the pedal down full to wait for 1.1 or 1.2 to show up and then I'm reluctant to keep it there.

Will Ng

Everything would appear OK, or may be OK, it's just the boost control that's not allowing 1.4 bar.
Or a leak somewhere is limiting you to 1.2.
It shouldn't take forever to hit 1.2 bar, almost instantaneous if you floor it.
Sounds like a possible boost leak.

Some other things that limit boost....
1. low octane gas may cause detonation triggering the knock sensor to retard ignition timing.
2. Bad MFTS gives false temp reading to ECU thus it stays in cold engine mode.
3. cracked hoses.
4. vacuum leaks.
5. leaking intercooler.
6. frequency valve dead.
7. frequency valve hoses cracked.

Are you sure the oil's leaking between the head and block? I would check to see if it's actually the valve cover gasket. At that mileage, it should be all cracked like mine was.
If it is leaking from the head/block, I'd be concerned. Otherwise, feel free to try to hit 1.4 bar. I have 211k miles, and have no trouble with 1.4 bar and with regular 87 octane.

CARSNPLANES

I forgot to mention that the MM hose is new, the intercooler doesn't appear to be leaking, I have checked for vac leaks at WG upper chamber. Freq valve is clicking during output tests. I'm not sure about the air sensor though ,checking??
Yeah it's not easy even getting to 1.1.

I always use high octane just to make sure no pings. Else??

Sleeps 4 at 120

First - My '87 5kCSTQ Avant has over 200k and I didn't start messing with the boost until about 197k. I've found the engine to be rock solid.

So! You want to see if the car will boost up? If you do the following and the car still will not build boost you definately have a boost leak somewhere, and possibly other problems. Take a clamp and clamp off the upper wastegate hose. This will prevent the wastegate from opening, so if you mash the throttle in third gear you should hit 1.8 around 3500rpm, and then either hit the fuel cutout or bounce the rev limiter. Never hit the fuel cutout before? You'll come close to ****ting your pants the first time 'cause it isn't the most graceful experience. With that said...

WARNING!!! - This isn't the 'safest' thing to do, and I don't recommend clamping the WG and driving around with your foot on the floor everyday, but it is a decent test to see what the car is capable of. I've done this with no problems.

boxerfan

This will supply boost directly to the back of the diaphragm and hold the WG closed.

Clamping off the hose should only allow 1.2 bar as this is when the factory spring will let go. That is unless your diaphragm has a leak and allows boost to the back on it's own.

CARSNPLANES

OK i suppose Ii might dare it. What is the deal with third gear. I've heard of this many times before. Will boost only work in third gear?
I'd like to understand the goings on at the wastegate. Is the upper chamber in vacuum or pressure during boost?. What about the bottom chamber. I understand if the bottom hose is leaking, it will be in full boost. Right? wrong?
Freq valve, pressure going to and through
it during boost?
Thanks

boxerfan

This assists the spring in holding the WG closed. Not sure about the bottom hose as I haven't had to dig in there yet. The lower hose connects to the cylinder head and so I think it should see pressure so a leak should reduce boost.. I think.

3rd gear seems dialed right in for these cars. Mat it and off you go. Boost will climb rapidly as will your speed.