Check engine light in '86 5kcstq when accelerating

[Bernard Littau]

Luke wrote:
> I am pretty sure that the starting problems are caused by the check valve,
seeing how i can't start the car at all now.  It must have been slowly going
bad.  But as regards the light it doesn't come on once and a while, its all
the time, but only when i step on the gas.   i got the ECU codes and they
were,
>  the intake temp sensor or inclusive wiring, (could this be why I am only
getting 1.2 on the boost?)  the hall sender in the Dist.  and the RPM
sensor.  Any help would be appreciated!!  TIA

Hi Luke,

The only code of those three that is engine load related is the Intake Temp
Sensor.  Usually, if the wiring for the Intake Temp Sensor has an open
connection, the check engine light comes on when you hit 0.8 bar boost, as
the ECU ignores the temp input below 0.8 bar. Yes, this would be why the car
does not go above 1.2 bar, as the ECU will not try to add boost with the
Intake Temp Sensor failure.

I would start with the Intake Temp Sensor.  The splices often can go bad.
I would cut the splices out, and check that the sensor is measuring the
correct resistance in free air.  The Bentley has a graph you can use to see
what value should be expected.  Scott's site might also have that same graph
somewhere.  If the sensor itself is OK, add some wire and new splices, and
you should be good to go.  otherwise, find a new sensor and wire it up.  In
a pinch, just add a resistor to fool the ECU into thinking the sensor is
working so you can debug the rest of the problems while you wait for a new
sensor.

In any case, set the engine at TDC via the 0 mark on the flywheel, and check
the alignment on the distributor.  (If you are 180 or so degrees off, rotate
the engine to TDC again, one turn later)  Set the distributor so the finger
points to the mark on the distributor housing (under the dust cover).

It is odd that both the Distributor and the Speed Sensor are "bad" at the
same time.  I almost wonder if you do have a bad ground somewhere between
the engine and the ECU.  Check the ECU ground on the engine carefully --
clean it and WD40 it.

I would just do all three of the above.  The splices are a problem point on
the Intake Temp Sensor and could likely user refreshing, and checking the
sensor is no big deal with a VOM.  Also, the Intake Temp Sensor is not
directly dependent on the ground between ECU and engine, so I think it is an
independent problem.  Aligning the Distributor is simple, as is the ECU
ground freshening.

Do those fixes, then see what you find in terms of running and codes.

Best,

Bernard Littau
Woodinville, WA
'88 5ktq