Re: Low boost problems -- at wits end -- HELP!

[Mike Posner <posne@cts.com>]

At 09:55 PM 7/7/99 -0400, Gisli Ottarsson wrote:
>
>Gurus:
>
>I recently purchased an '87 5KTQ with 180k miles on clock.  Condition
>is much better than milage suggests.
>
>When purchased, the car had a punctured Michelin-man hose between the
>intercooler and intake manifold.  After replacing this part, the car
>suffers from low boost, which maxes out at 1.1 bar according to
>in-dash pressure gauge.
>
>In troubleshooting this problem I have relied on Scott Mockry's
>excellent Troubleshooting Tips <http://www.sjmautotechnik.com>
>Is this guy *king* or what?!
>
>A list of my experiments follows in the hope that it will benefit
>someone and that someone might spot a hole in my reasoning.
>
> 1) ECU fault codes:  
>
>    Test drove vehicle for > 15 minutes.  Wide Open Throttle in
>    third gear.  Performed ECU fault code dump.  Only 4444 was
>    blinked.  Ergo:  No faults were stored.
>
> 2) Does Waste Gate work?
>
>  a) Applied 20 in Hg vacuum to Waste Gate.  Waste Gate held the
>     pressure.  Ergo:  Diaphragm does not leak.
>
>  b) Quickly removed vacuum.  Heard an audible "CLUNK".  Ergo: Waste
>     Gate is not stuck open.
>
> 3) Does Waste Gate Solenoid work?
>
>    Connected vacuum gauge to the hose that connects WGS to WG.
>    Unplugged Throttle Switch Connector and shorted two lower
>    connector pins.  Observed large swings on vacuum gauge.
>    Ergo:  ECU is speaking to WGS.
>
> 4) Multi-function temp sensor defective?
>
>  a) Based on experiment 3) I conclude that pin 2 is not sending false
>     ground to ECU.
>
>  b) Coolant temperature gauge holds steady at midspan.  Over-heat
>     warning symbol is ordinarily off but proved itself to be working
>     during a near overheat incident.  Ergo:  All seems well.
>
>    Are there other tests available for Multi-function temp sensor? 
>
> 5) Does Air Temp Sensor work?
>
>  a) Disconnected ECU and measured resistance across sensor.  I
>     measured 500+ ohms at ca. 77 degrees Fahrenheit.  Ergo: Sensor is
>     good (?)
>
>  b) Reconnected ECO and measured again.  Resistance had dropped to
>     420 ohms.  Ergo:  Sensor has a good connection to ECU.
>
> 6) Vacuum/Boost leak in hoses?
>
>    
>    
>  
>?

>
>    in performance was observed when Michelin-man hose was replaced
>    and boost comes up quicky.  Ergo:  All is well?
>
>I assume you werre not getting proper boost prior to new Mich. man.

What is your vacuum reading  at idle? Do you have any exhaust leaks?
ie cracked manifold, though they usually self seal when they get hot.
Check for hose leaks on the pressure side  from intercooler to throttle
body. also look for cracks in the intercooler pipes.  Also dont count on
the  digital pressure guage to be accurate. see what your reading is 
with another guage.  Is the vehicle at operating temperature?  Hows your
Cat?  If its clogged, it will impair boost, as will a clogged air fillter,
fuel filter.   ie everything needs to be clear going in and coming out.  Kind
of like the digestive system.  Its an ongoing problem with boost, there are
 so many things that can affect it..  . Mike Posner.   

>

>
>
>
>Gisli Ottarsson, PhD                     
>Mechanical Dynamics Inc.            gisli@adams.com    
>2301 Commonwealth Blvd.             Tel: 1-734-913-2550
>Ann Arbor, Michigan 48105           Fax: 1-734-994-6418
>
>
>
>