87 5KTQ - Boost Question

[Cody Forbes]

> Hi,
>
> I just bought my Dad's (original owner) 87 5KTQ.  It has between
108-109K...
> the odometer died last week.  I just brought it out to Colorado (5,300'
> elevation) from Kentucky (+/- 300' elevation).  The fuel cut off for the
> turbo boost would kick in between 1.5-1.7 bar in Kentucky.   In Colorado
it
> has been kicking in between 1.3-1.5 bar.
>
> a. what is the typical / correct boost pressure?  years ago...  if I
> remember it correctly... between 1.7-2.4

Stock its actually 1.4bar. It could be chipped in which case it should be
1.8bar. Stock cut-off should be 1.55, chipped cutoff is 1.95 usually.

> b. is it typical for the the computer / wastegate to compensate for
> altitude?

AFAIK the stock copmuter will always shoot for 1.4bar.

> c. if the fuel cut off is cutting in too early... what should I start
> checking... wastegate... sensors... etc.

Well to start with your wastegate diaphram could be bad. To check it you can
disconnect the hose that runs from the top of the wastegate to the little
solenoid and try sucking on the hose (disconnect at the solenoid side, leave
the wastegate side attached). If theres resistance (to the point where it
hold a slight vacuum) then the diampram should be ok, but if you can suck
air through then you are in need of a diaphram. It is possible that it's a
small break in the diaphram that will still not give in to the very little
ammount of vacuum that a human can produce, so if you have a handheld vacuum
pump that would work much better. Another way to test is if you have a
bicylce tire pump you can disconnect the lower wastegate hose from the
intake manifold and the upper hose, then give it just a little bit of
pressure. If the air that you pump into the bottom comes out the top then
it's got a break.

> d. if I need to replace the wastegate... any recommendations on an after
> market stock/oem equivalent part... or an after market high performance
> part.

You almost definately don't need a whole wastegate, just the diaphram
inside. You can get a diaphram for under $40 either from a dealer or from
http://www.sjmautotechnik.com. It's a fairly simple fix if thats the case,
and instructions are on that SJM site too.

-Cody Forbes
http://www.5000tq.com
'86 5ktq EFI
'87 5ktq 380whp
'88 80 4cyl
'88 90 4cyl