ALT.VRS. FSD. TURBO BOOST SENSOR

[wild billyb]

I have a 99 SUB with a 6.5 Bone stock where is my FSD located, and please do not tell me it is under the intake manifold. the problem I have been having is the turbo boost sensor and then I get a lot of black smoke out of the tail pipe but only seems to happen when the AC is on and it looks like the voltage is low I went to the point of changing the ALT. to a 140 AMP. NO HELP!!!!!!!!!!!

[cudaaa]

wild billyb The fsd in mounted on the driver side of the injector pump. Bill Heath sells a great relocation kit that moves it out of the engine compartment. Cudaaa

[john8662]

The wastegate solenoid (that controls boost) isn't under the intake, its on the drivers side on a bracket just above the valve cover towards the rear. it has two vacuum lines and one two-wire connector going to it. The boost sensor (for the computer) is under the "Turbo Power" cover if equipped still on top of the intake plenum.

The FSD (Fuel Solenoid Driver) Or PMD (Pump Mounted Driver), both meaning the same part. is under the intake attached to the injection pump. This device controls the fuel to the injection pump, no turbo boost.

Most likely, lots of smoke, equals low boost, probably the wastegate solenoid, or low vacuum pressure by the vacuum pump. You also might want to check for check engine codes, you'll need a code reader for that year model (check with autozone for a free scan).

[Fredeberle]

wild billyb,
It is under the intake manifold on injection pump,
front of engine drivers side, behind upper radiator hose connection.
You should see round fuel shut off solenoid and probably a bar code on FSD. Need good light looking in there. smile.gif
Connector can be pushed off with long screwdriver
(lift tab) if you want to leave it there for now and just connect new harness to relocated new FSD.
Just removed my FSD from there today and it is a PITA. :(
Hope this helps,
Fred

[Kennedy]

For the black smoke deal, first try spraying some WD40 in the vacuum hose at the turbo while idling. This sometimes helps free things up.

If not, then I'd verify vacuum pump operation, and replace wastegate solenoid if need be.

Personally, i prefer the std 105 amp alternator as it has better low RPM charging capability.

[wild billyb]

I need to understand how the system works, so let me get this straight, the engine gets to 1800 rpms the computor sends a signal to the waste gate controler and closes the waste gate wich turns on the boost and when the boost gets to hight the sensor tells the computor and the computor sends a signal to the waste gate controler and it opens the waste gate and turns down the boost. what I need to know is when does the temperature of the air charge come in to play. oh and by the way if I have not told everyone thanks for the help understanding how this works.

[JohnC]

The pcm controls the waste gate by varying the duty cycle of the wastegate control solenoid. Greater "dwell" means more vacuum is applied to the wastegate controller and the gate is held more tightly closed. Less dwell, less vacuum, easier for the exhaust pressure to push the gate open.

Below 1800 RPM the PCM doesn't care. It's impossible for the turbo to generate too much boost. Also, below some fuel rate, which I can never remember, but like 20 mm3, for example, the PCM also doesn't care. Not enough fuel to generate too much boost. Under these circumstances the PCM runs the wastegate solenoid at a fixed duty cycle, around 80% IIRC. When both of these limits are exceded the PCM worries about too much boost and watches manifold pressure. It reduces the duty cycle on the solenoid to keep the boost under the limit. This lowers the vacuum and allows the exhaust gasses to push the wastegate open more. It's not an off-on thing. It opens gradually until there is a balance between the vacuum in the controller and the pressure in the turbine housing. If the PCM cannot keep the boost to a safe level it releases the vacuum entirely which generally allows the wastegate to open fully, and it reduces the maximum fuel rate to what it considers a safe level for no boost.

[wild billyb]

WOULD LOW VOLTAGE EFFECT HOW THIS OPPERATES

[rjwest]

JohnC I installed a turbomaster manual control.
I get a " Defuel " condition when I get to
high a boost ( I think) I lose power, and
can not get it back unless I turn off ign or clear codes from my laptop. ( Note no codes are set.)
as soon as i clear codes i get power back.
Is this the overboost sense doing this?
Is the a hidden condition being set that does not turn on a code?

( 96 dually)

[JohnC]

It should set DTC 78, or the ODB 2 equivilent. The defuel should stop as soon as the conditions are gone for a few seconds, i.e. if you take your foot off the pedal. It comes back if the conditions return for ~20 seconds. The code is stored in memory. ('96 may operate differently)