as title. So, what would cause this and how do I test to find out? This came up rather suddenly from what I can tell. Blocked catalytic converter? Downpipe crushed since I wrapped my headers and increased the heat it sees?

 

I would say you have a vacuum leak. This is the spring pressure of the stock wastegate approx.

 

I had a similar problem a long time ago and it turned out to be a restriction in the cat converter.

It's always a good idea to test vaccum though - these cars are notorious for leaks.

 

If it was OK then suddenly not its more likely a problem in the cycling valve circuit. The cycling valve directsts boost pressure away from the wastegate. If its not working correctly boost is limited by the wastegate spring which is approx 6psi. Crimp the pipe to the wastegate, drive very carefully and see if you get increased boost, Be very careful as you have no boost control so if you get carried away, you will cause damage. If that shows the engine is cabale of developing boost then the next step is probably the cycling valve its self. Unfortunately this is buried under the intake manifold. After that your talking about wiring, KLR etc.

 

I deleted they cycling valve some time ago.

 

Irrespective, you have to find out if the engine is capable of developing boost, with the boost control bypassed. You must have some form of boost control. Bypassing it or isolating it will at least give you an idea where to go next.

 

k, I will clamp the tube from the accuboost to the wastegate tomorrow and let you guys know what happens. fyi - none of the vacuum lines are disconnected and I have 18 in hg at idle when at operating temperature.

 

Be careful doing that - even a "lowly" k26/6 can build quite a bit of boost at maximum - more than enough to do damage.

 

Ok, clamped the hose between the banjo and the accuboost and went over 6psi easily. Took the clamp off and back to 6psi. The accuboost should be fine, I was getting 16psi before this, last I adjusted it, after my head work.

 

I had a TurbXS boost controller on my car for a time. I ended up blowing a head gasket, burning three valves and broke the exhaust. It turned out the controller had drifted out of adjustment and I was running well over 20psi before the head went. It was quite a ride while it lasted. Well the good news is that the motors probably Ok, not a damaged turbo or exhaust system. I think I would be looking at the accuboost next.

 

6psi or so is all the boost you will build if the blowoff valve does not have boost pressure to the top of it's diaphram, I'd double check the the vacuum line going to it. Also if the diaphram is torn, same 6 psi, swap for a new one.

For clarification of various systoms listed earlier, 4 psi is usually all you will get if the cycling valve is inoporative.

Good luck.

 

I'll have to check that blowoff valve. It's not much more than a year old but it would be a nice excuse to get a forge to upgrade as I have some overtime cash available :-)

 

sigh - dopey me - turns out my accuboost loosened up even though I had tightened down the locking nut. Commence with the laughter.

 

So at anytime you should be able to clamp the WG line and should see tons of boost? And if not there is a leak somewhere???

 

No that's not exactly the right interpretation. Clamping the wastegate line prevents the wastegate from being opened from the available boost pressure. With a good engine and wastegate etc you will quickly overboost the motor with the wastegate clamped, hence great caution is required to avoid any damage. But its the quickest and easiest way to see if its a major mechanical engine problem that means that it just can't build boost, or if its a boost control problem. Its just the first step of troubleshooting. If you can't get boost it could be bad wastegate, bad turbo, major leak or something else.