TOYOTA PREVIA 91-97 REPAIR MANUAL

1-36 GENERAL INFORMATION AND MAINTENANCE

As you accelerate from idle, the speed of your engine (rpm) increases.
The increase in rpm means that the pistons are now traveling up and Jown
much faster. Because of this, the spark plugs will have to fire even sooner if
the mixture is to be completely ignited as the piston passes TDC. To
accomplish this, the distributor incorporates means to advance the tirjiing
of the spark as the engine speed increases.
On fuel injected vehicles there is no centrifugal advance or vacuunji unit
to advance the timing. All engine timing changes are controlled electroni-
cally by the ECU. This solid state "brain" ECU receives data from many
sensors and commands changes in spark timing based on immediate idri-
ving conditions. This instant response allows the engine to be kept at;
performance and economy throughout the driving cycle. Basic timing and
idle speed can still be checked and adjusted on these engines.
If the ignition timing is set too far advanced (BTDC), the ignition a
expansion of the air/fuel mixture in the cylinder will try to force the p
down while it is still traveling upward. This causes engine ping, a sound
which resembles marbles being dropped into an empty tin can. If the Igni-
tion timing is too far retarded (after, or ATDC), the piston will have already
started down on the power stroke when the air/fuel mixture ignites and

;peak

expands. This will cause the piston to be forced down only a portion
travel. This results in poor engine performance and lack o" power.
Ignition timing adjustment is checked with a timing light. This ins
ment is connected to the number one (No. 1) spark plug of the engin
timing light flashes every time an electrical current is sent from the d

)fits

The

ptrib-

cale,

ththe

ming

ow

utor through the No. 1 spark plug wire to the spark plug. The crankshaft
pulley and the front cover of the engine are marked with a timing poi ter
and a timing scale.
When the timing pointer is aligned with the 0 mark on the timing:
the piston in the No. 1 cylinder is at TDC of it compression stroke. V\e running, and the timing light aimed at the timing pointer and

scale, the stroboscopic (periodic) flashes from the timing light will a
you to check the ignition timing setting of the engine. The timing ligf
flashes every time the spark plug in the No. 1 cylinder of the engine ires.
Since the flash from the timing light makes the crankshaft pulley see|n to
stand still for a moment, you will be able to read the exact position ojllthe
piston in the No. 1 cylinder on the timing scale on the front of the enipine.
If you're buying a timing light, make sure the unit you select is rat$d for
electronic or solid-state ignitions. Generally, these lights have two w res
which connect to the battery with alligator clips and a third wire which con-
nects to the No. 1 plug wire. The best lights have an inductive pick-ijp on
the third wire; this allows you to simply clip the small box over the wire.
Older lights may require the removal of the plug wire and the install;lion of
an in-line adapter. Since the spark plugs in the twin-cam engines ars
deep wells, rigging the adapter can be difficult. Buy quality the first t jne
and the tool will give lasting results and ease of use.

INSPECTIONS ADJUSTMENT

2TZ-FE and 1991-95 Models

I See Figures 98 thru 103

This service procedure is for setting base ignition timing. Refer to
hood emission sticker for any additional service procedure steps an^or
specifications.
These engines require a tachometer hook-up to the check connec
see illustrations. NEVER allow the tachometer terminal to become
grounded; severe and expensive damage can occur to the coil and/o
igniter.
Some tachometers are not compatible with this ignition system, c
the compatibility of your unit before using.

1. Warm the engine to normal operating temperature. Turn off a
   trical accessories. Do not attempt to check timing specification or id
   speed on a cold engine.

under-

nfirm

elec-

2. Connect a tachometer (connect the tachometer (+) terminal to the
   terminal IG- of the check connector) and check the engine idle speed to be
   sure it is within the specification given in the Tune-Up Specifications chart
   or underhood emission sticker.


3. Remove the cap on the diagnostic check connector. Using a small
   jumper wire or Special Service Tool SST 09843-18020, short terminals TE1
   (test terminal No. 1) and E1 (earth-ground) together.


4. If the timing marks are difficult to see, shut the engine OFF and use
   a dab of paint or chalk to make them more visible.


5. Connect the timing light power source terminal to terminal 30 of the
   starter and test probe to the No. 1 spark plug wire (light blue).


6. Start the engine and use the timing light to observe the timing
   marks. With the jumper wire in the check connector the timing should be
   5° BTDC (refer to underhood emission sticker as necessary) with the
   engine fully warmed up (at correct idle speed) and the transmission in cor-
   rect position. If the timing is not correct, loosen the bolts at the distributor
   just enough so that the distributor can be turned. Turn the distributor to

IG0

Fig. 98 Attach the tachometer to the battery and check connector

terminal IG—1991-93 models

Tachometer

Battery

Fig. 99 Attach the tachometer to the battery and check connector

terminal IG—1994-95 models