Only .5 Bar Boost
 

Hello again fellow Pelican Heads! First post in quite some time. After rebuilding the 930S motor and trans last year I decided to "just drive it" for awhile and not mess around with it. Well, I guess she got jealous of me working on the other cars cause the other day she started to stop making full boost (like that combo of words :)). Out of the blue... the digital boost gauge now only lights the led's up to .5. I pulled the IC and reseated all of the o-rings. Still only .5 bar. Today I pulled the wastegate... not a 10 minute job as described in a older post. I could not get a wrench on the 4th nut tucked next to the exhaust pipe so I had to cut it off... yuck.
Took the WG apart, the spring looks nice and tidy, the diaphragm appears in good shape and the valve seems to seat pretty well.
As some of you know, I have the 930SE muffler on the car (quad tips with the WG muffler installed). I also have the WG muffler removed so I could actually hear the WG opening when the gauge was reading .5 bar.
Prior to this new symptom, the car always lit the gauge to .8 and even .9 if it was nice and cold out. One day everything was fine, a few days later, went out for a ride and noticed that the kick was not quite as hard.
Ideas please!!! Hopefully there is a cheap fix cause I am saving up for a Zork :)

I'd recommend pressurizing the line from your intercooler to the WG input and verifying it will hold .8-.9 bar.

Also, if they haven't been done recently, replace the O-Rings all the way from the turbo outlet to the throttle body housing with new rings.

Be sure to replace the T-Body O-ring (you need to take out the recirculation valve to do it). I made the mistake of replacing all but that one because of the hassle involved w/ pulling the recirc and didn't get the result I wanted until I replaced that last O-ring (sides were flat).

Lastly, make sure all of your intake manifold nuts are tight. Some of the nuts on my intake manifold were loose, particularly the ones above cylinder 5 and the opposite cylinder (2), right under the recirc valve piston area.

On my car, the intake manifold bolt under the recirc valve, above cylinder 2 and closest to the fuel injector was completely loose (not even finger tight). I could see where pressure was escaping (oily stain) between the manifold and the phenolic spacer.

I checked the manifold nuts. Still nice and tight since I put on the nylocks last year during the rebuild. I replaced the BOV seals (internal) about two years ago and the TB o-ring at the time I rebuilt the engine.
Since I broke the first law of stud removal (tighten before you loosen) I now have the cast iron portion of the WG all buggered up. Either I drop it at a machine shop or buy a new Tial. Being that it is a factory ROW slope, I think I may go to the machine shop to fix the hole I buggered. Although, I am wondering if there are any internal WG parts I should order as preventative maintenance before I put it back together???
Still have not solved the "lack of boost" issue, but now I have just gotten myself into a different dilemma :) I love these cars...

Dose it pull like it is only getting .5 bar (gage)?

If not you may have a restriction (Air Filter?), the turbo is going, or you could have an intake leak.

Test for leak first with with a vac gage at idle. Then by spraying carb cleaner at suspect areas and see if idle increases. It is possible that these will not find it and you will only be leaking on boost.

Do you have AFR monitoring? If you have a leak and are leaking air under boost, you will go very rich.

I really am just guessing.

The fact remains that I can hear the WG opening when the boost gauge is only showing .5bar. Yes, it is much more nose heavy under acceleration then normal. I took the WG apart and all the components appear within tolerance. Is there something in there I may be missing? There is a little valve wobble side to side but nothing too bad I think.

Are you running rich on boost?

That's a great question... and I don't know the answer. And, unfortunately, won't know till I get the WG back together :(

Greetings:
Similar issue here also...After not driving the car for a while and getting alot of internals changed(ignition-msds& coil,plugs,fuel accumulator,fuel pumps,oil &gas filter,replaced gas-emptied)
I checked connections,lines,intercooler,wastegate.,timing,et c..
I couldn't find why i couldn't boost...under load....poss..5bar not much...It then was getting worse...until the car was going to stall out....
In the end it was the FUEL HEAD-the piston was getting stuck...
How did I Know--MY AIC-HKS FUEL Enrichment..Was kicking in,(good pull on test mode & no pull when off) but not rest of my fuel system..No fuel---starving...It was really frustrating and it took alot of chking..
Maybe this could be the cause..

Walt

"...Prior to this new symptom, the car always lit the gauge to .8 and even .9 if it was nice and cold out...."

Could it be too much heat sink?

Mine loves cold temps (below 60*) and don't boost the same during hot days.

Try taking off the elbow off the intake of the turbocharger, inspect and try to turn compressor vanes with your finger. Don't spin it, but note the amount of drag to turn it.
While you're in there, with your thumb and forefinger, grab the nut and check for lateral play. It should be absolutely minuscule.

Do you have the stock exhaust/cat on your car?

I finally tracked down the cause of ALL the issues I've been having with boost on our '86 930.. a plugged up original catalytic converter.

Symptoms:

* Boost wouldn't go above .8Bar, even with the MBC turned all the way up.
* WUR cold control pressure had to be dropped to richen up mixture and the car would still only idle @ 500RPM until it warmed up.
* A/f had to be set rich or idle was terrible
* Car started running about 20% warmer than normal
* Boost gauge connected to booster hose was showing 30% or more LESS boost than the gauge connected to the wastegate line (Vac was OK though)

I had a new catalytic converter installed, reset the air/fuel mixture and all my boost problems, low boost, lag, heat - disappeared.

Too bad you can't just run without the damn thing, but I guess Johnny Law at your friendly emmissions testing station won't let you get away with it. Run with a bypass, then install the CAT only at test time. Save some weight and gain some performance.

Sorry I have not posted back in a few days. I broke a stud on the WG and just got too PO'd to think much about it. The spring appears fine, the diaphragm appears fine too. Once I get the cast iron piece back from the machine shop where they are installing an oversized stud to fix my drill bit walking debacle, I will put it all back together and look someplace else. As for the exhaust, I have an SE muffler so I am pretty sure that back pressure is not the issue. Although, I am still trying to get my hands on a Zork... anyone heard from RarelyL8 lately?
I am still hesitant to think it is the turbo since I can hear the WG open when the gauge reads .5bar. I guess the next step will be to figure out how to hook up a different gauge and see if it reads something different. The old LED 935 style gauges are apparently not known for their accuracy :(

Where is the gauge tapped into?

Are you running a Catalytic converter?

In my situation, the wastegate line was showing .8Bar, but the brake vacuum booster/intake (past the throttle body) indicated .4Bar.

Have you tested the wastegate with .8Bar compressed air directly the WG input line?

Just somethng to be aware of: Puting .8 bar air pressure from an external source to the wastegate usually won't open it unless the engine is also running. Need a little bit of exhaust pressure to be present as well, as it's the combination of boost pressure and exhaust against the WG valve that opens it. Seems it took me something like 15-18 psi to get the WG to open on the bench. Of course, your experience may vary depending on the condition of the valve guide and seat.

DSPTurtle,
Do you know where the sender for the 935 Style boost gate resides? I think most factory senders screw into the IC. Check to make sure that there is a good ground between the IC and chassis ground. If there is not a good ground, it will throw the readings at the gauge way out.

Good point Mark, mine has a stock spring (.7Bar?) and the WG opened wide at 12-14PSI using compressed air.

I believe both the overboost switch and the gauge sender are tapped into the BOV. But don't quote me on that since I am nowhere near the car. I do know for a fact, that I do not have to remove any wires to take the IC on and off the car... I have that process down to under 60 seconds.