No boost

9dreizig · 07-27-2008, 06:49 PM

I thought i'd start a new thread on this since I think I've got my CIS leak issues fixed ( but who knows?)..
Anyway I am getting almost no boost - .2-.3 bar.. I just have the tach/boost guage but it's running like a dog so am quite sure it's accurate.
I went through and snugged up all the screws on the intake as well as double checked all the hoses around the intake so am pretty sure that isnt' it as well.
I also checked the wastegate diaphram in that I pressurized the hose that goes into the intercooler and could hear/feel the spring engaging/disengaging.
Unfortunately it looks as the wastegate has not been removed since it was installed at the factory in 86.. so I've just started the PB Blaster routine.. But my question is ... is it possible or does it often fail half open ?? So that amount of boost is all that can be developed ?? Could I have a bad turbo ?
That is a ton of boost to be missing and I'm quite confident it's not disapearing in the intake section..
Comments ?

DSPTurtle · 07-27-2008, 07:07 PM

I once had my up pipe from the turbo to the IC spun a little to one side or the other... that allowed boost to leak out because it did not mate securely to the IC. Two minute fix, but I had to stare at it a little while to figure it out.
Other possibility is a bad seal between the IC and throttle body or IC and up pipe or up pipe and turbo outlet. Those are some sneaky seals...

RarlyL8 · RarlyL8's Garage

I assume your engine has the stock '86 heat exchangers. The waste gate spring can fail which would allow an exhaust leak past the valve.
What muffler do you have? Stock '86 as well? Does the waste gate pipe connect to the muffler?
The reason I ask is because an exhaust leak-by at the W/G would be very loud if the W/G is not piped into the stock muffler. You can pull the exhaust pipe off and have a look at the valve. It should be seated firmly shut when the engine is not on boost.
The other place to look is downstream of the turbo as DSP stated. The up-pipe and throttle body seals as well as the BOV seals can leak boost into the atmosphere or around the throttle plate.

9dreizig · 07-28-2008, 07:29 AM

Brian,
Yes it's all stock.. the waste gate has one of those little mufflers on it so no doesn't go into the muffler. I'll certainly double check the seals , but my experience is that the engine won't run if there's not a good seal from turbo-intercooler.
Any chance of the turbo going bad ? what would those symptoms be ?

beepbeep · 07-28-2008, 09:24 AM

Disengage the hose from wastegate and plug it. Do the run. This will allow boost to skyrocket as wastegate will be shut off. If you cannot get boost past 0.3 bar even then, you have big leak somewhere else. Probably intercooler O-ring.

Be careful not to boost more than 0.9 bar.

9dreizig · 07-28-2008, 09:30 AM

Beep beep, that won't eliminate the possibility of the waste gate being open will it ?

fredmeister · fredmeister's Garage

Quote:

Originally Posted by 9dreizig

Brian,
Yes it's all stock.. the waste gate has one of those little mufflers on it so no doesn't go into the muffler. I'll certainly double check the seals , but my experience is that the engine won't run if there's not a good seal from turbo-intercooler.
Any chance of the turbo going bad ? what would those symptoms be ?

If you have bad leaks between the intercooler and turbo you in effect have a massive vacuum leak under idle.....causing poor running or no idle. You are correct.
I would remove the wastegate and see how the valve surface looks. It is possible you have a piece broken off of it or dirt/carbon has prevented it from closing. Also, your rubber diaphragm may be slightly torn allowing some boost build up or the spring could be broken. Once the wastegate is off the car you can tear into it to check.
Be careful as the spring tension for stock 0.8 bar boost spring is about 90-100lbs force so when you undo the 6 little bolts around the flange that holds the wastegate halfs together have it locked down in a vise or press or you will be making a trip to the dentist.

fredmeister · fredmeister's Garage

Oh yeah, get yourself another boost gage that is actually accurate.
One that mounts in the clock position is best....the OEM gage in the tach is useless.

beepbeep · 07-28-2008, 04:47 PM

Quote:

Originally Posted by 9dreizig

Beep beep, that won't eliminate the possibility of the waste gate being open will it ?

No it won't. If valve is stuck open it will lead to sluggish boost build-up high up in rev range. But it's fairly uncommon.

Also, ruptured wastegate membrane leads to overboost, not loss of boost (except the little that seeps trough membrane).