can't get past 5psi


Jul 20, 2002
ok not sure where to start. so cold start 18". vac fuel press 42 line off. ttt 57 chip. 60lb inj 3"dp rjc 206 roller cam champ iron heads injs hot wired
scanmaster at cold idle 600-800m lv blm 128 130. iac 50s. temp 165. etc. 17 blade 9.5 lock up 3400 convertor bought used but just installed
stock 342 rear
ok so if I foot brake it it swings up to 5 psi then back to 0
when off idle driving at seems to stumble an hesitate slightly before taking off but once it hit 5 it swings back to 0
so tried at a 45 mph roll stepped into it hear turbo come on starts pulling an bam. back to 0 it doesn't fall on its face or anything strange just reads 0
the vac reading is a steady 18 no bouncing or anything like that

its a 64 66 dual bearing turbo aem Wideband. new gm 02 sensor new plugs. ac delco 42s gapped at 32 3.5 map an translator
could it be wrong convertor? I had a multi disc 9.5 an boost wasn't an issue just hated the chatter. thanks
Look for loose or missing fasteners on the headers. Particularly the 3 nuts holding the turbo on the header
Bad turbo or bad converter, just a guess from my sofa. Any noises when attempting to boost?
ok the wastegate holds 25" of vaccuum an opens when air is applied its a hd unit
the gauge is an autometer 30 30 tied into the vac line under the egr valve
it feels like its still pulling but definately not like it should wont even spin the tires
yes all fasteners are tight
the only thing i changed this year was the convertor it was a used unit i assume specd for the ta motor the fella was building
no odd noises when attempting to spool just the whistle of the turbo starting to spool then nothing
it has the larger wastegate puck an the alignment looks good.
I use a 40 lb adjustable regulator to test them here. If it just cracks open at say 5 lbs. It should make around 9 or 10.
Mine makes boost with the wastegate having only slight pressure holding it closed for testing and break in.
the gauge is an autometer 30 30 tied into the vac line under the egr valve
The EGR valve has/had a check valve in the original vac line.
You need to find a clean source for the gauge.
Have you checked the gauge?
It may be the boost is climbing but the gauge shuts off with boost on the check valve.
If that's the case, it may well be the converter has STB.
ok reouted boost vac line no more checks in ithe way
tested boost gauge read fine under boost an vac applied 5 10 20 an held it for a few minutes
wastegate started to move around 5 psi an slowly opened as i increased the air pressure
3400 convertor bought used but just installed
Your last post indicates it may be a boost control issue... either the solenoid, the programming, or the actuator itself.
One way to test is to wire it shut and see if it will build boost past the 5 psi. BE CAREFUL!
Another test is to check stall on the converter.
Engine and trans @ op temp. Park and foot brake applied. Check stall speed. Some use zero boost/zero vac as a test point. Where is the engine speed?
solenoind? if your meaning the one on valve cover ive bypassed it running tuner style hose from turbo to wastegate
not sure about programming tt chip?
ill try your suggestiong an get back to you
am i looking to see what rpm the boost start at?
Wasregates start to open 5 to10 lbs before they are full open depending on turbo to engine size and mods. So what happens is if you are set foe 15 lbs, the gate starts opening at say 10, and that slows the gain of boost for those last 5 lbs or so. A boost controller puts a positive pressure holding the gate totally closed until just before the set limit.
Put an adjustable small regulator on the W G and see when it starts to open and where it's fully open. I'm not saying that is your issue, but it is an issue.
My cheap way to overcome that is use a solenoid in the W G line to block all of the pressure and an adjustable Hobbs switch to control it. Say, set it at 14 if you want 15, and the gate sees no pressure till then. Something to think about.
Your situation I would try a regulator on the WG and see what it's doing.
It could have a hole or tear or be old and hard and causing issues. See when it starts to open and how linear it seems to be till full open. Just another place to start. Knowlege is power.
Take a string and tie the wastegate shut. See if it boosts up then. DON'T GO ABOVE 10psi the first time. You will have to modulate boost with your foot on the gas pedal, if you don't let off, it will boost to the moon and blow head gaskets or worse. Yes it will. No distractions, it takes self control, watch only the boost gauge (and traffic, ha).
Using my way with a regulator you don't need to watch for traffic or worry about head gaskets. Just bring the pressure up slowly with the actuator disconnected from the turbo and watch for smooth motion with no "hitches" or jerks. Do this raising up and slowly lowering the pressure. Then check the arm on the turbo and make sure it moves smoothly thru its entire range. Next reattach the actuator to the arm and repeat the test. If the diaphragm is torn or hard, it won't move smoothly on this test. If so, buy a new adjustable actuator.
You can observe more this way than while driving. Also, how about buying a new hose to the actuator. That's not your issue now, but it's cheap insurance for later.
Here is what I use for testing pressure stuff, inlet is a shop air fitting above the gauge, outlet is a rubber hose and barb off a piece of 1/8" NPT brass pipe, , adj. reg., and you don't need that big of a gauge but an accurate one always helps. Easy to set up and use. Adapts easily to various hose sizes.
What downpipe are you using? Make sure it's not slightly hanging up on something and not closing the flapper properly.
That's similar to what I use. Different brand, same stuff. Useful also for checking fuel regulator to make sure the pressure is rising with the boost.
thanks for all the great ideas fellas much appreciated if it wasnt our thanksgiving weekend id be in the garage see if i can disappear for awhile ha ha