How do I go abouts setting timing on my 90? Will I need a timing light?

 

Yep, you'll need a light! Instructions will come with it. Here is a tech tip of the steps:



How to Set Ignition Timing -- 1 of 1
Date Published: 2004-06-06

Submitter's Name: JAKE
Email Address: jakejr266@sbcglobal.net
Corvetteforum.com Member Alias: JAKE

Here’s a step-by-step on how I set the initial
ignition timing. I start the engine and let it run
until it's warmed up. I then shut it down, and
disconnect the EST wire, (it's a SINGLE wire that
is tan in color with a black stripe and is located
just under the power brake booster/windshield
wiper motor area). I get out my 3/8" ratchet and
distributor wrench, adjust the ratchet to the
loosening position, and place it on the passenger
side tire. The distributor wrench is shaped like
an "L" and makes getting to the distributor bolt
much easier than using a straight 9/16" open
end/box end wrench. I then connect my timing light
to the #1 spark plug wire and the other two clips
to the battery; red to positive and black to
negative. I don't have a self-powered timing
light; mine uses battery voltage. I then start the
engine. It may be a little difficult to keep
running at first with the EST wire disconnected.
That's the reason I let the engine warm up first;
makes it a little easier to get it to idle by
itself. Once the engine settles down and idles by
itself, I point the timing light at the harmonic
damper and see where the groove in the harmonic
damper aligns with the timing tab on the timing
chain cover. The stock setting is 6 degrees Before
Top Dead Center (BTDC). Each little line on the
timing tab should equate to 2 degrees. If the
timing needs adjustment, I walk to the passenger
side of the engine and loosen the bolt that
secures the distributor to the intake manifold
(you have to access it from the passenger side). I
loosen the bolt just enough to allow me turn the
distributor with my hand. I adjust the ratchet to
the 'tighten' position and leave the ratchet and
distributor wrench in place, kind of standing up
but still on the head of the bolt. I then return
to the driver's side of the engine, point the
timing light at the damper again, pull the trigger
and turn the distributor with my hand while
watching the groove on the harmonic damper move.
Once the mark on the damper aligns where I want
it, I reach over and give the ratchet a turn to
tighten the distributor hold down bolt. I then
check to see that the timing I'd selected hasn't
moved. It will sometimes as you tighten the hold
down bolt. If it has moved, I loosen the bolt,
make the necessary adjustment by turning the
distributor (again) in the require direction. Then
I tighten again. Once I have the timing set to
where I want it. I walk over to the passenger side
of the engine again and tighten the bolt
completely. I then go back to the driver's side
and verify that the timing hasn't moved. Then, I
shut down the engine, re-connect the EST wire,
remove the timing light connections and disconnect
the battery (just one cable) for about 30 seconds.
This clears the code that gets automatically set
when the computer detects the engine running with
the EST disconnected. I try to work as fast as I
can because with the engine idling with only 6
degrees of timing advance, the headers/exhaust
will begin to glow red due to the engine not
having enough timing advance. Once the engine is
re-fired with the EST re-connected and code
cleared, the timing mark should be just off the
scale of the timing chain cover tab. up near the
12 o'clock position. You can re-connect the timing
light if you want to check it. That's it. Figuring
out the timing marks has tripped up a lot of guys,
so don't fret. Most timing tabs are marked in
two-degree increments. Each little hash line on
the timing tab indicates two degrees difference
from the hash line nearest it. You mau not see
actual numbers, like 2, 4, 6, etc., all you may
see are just little lines cut in the timing tab.
Tabs differ, but there is usually ONE spot on the
tab that is marked ZERO, has the letter "0", has a
deeper notch or longer hash line than the others.
Something that makes it different from all the
other marks on the timing tab. That's the sucka
you have to identify first; all changes are made
in direct reference to it. The damper has a groove
cut in it which is 'supposed' to coincide with the
#1 piston being at TDC (Top Dead Center). This
isn't always accurate, but unless you want to go
to all the trouble of verifying it, just accept it
as being cut in the correct place. Most guys mark
those spots (ZERO on the tab and TDC on the
damper) with something that will make them stand
out when the timing light is flashed at it. I use
red fingernail polish, others use whiteout, etc.
The ignition advance is determined by where the
groove in the damper aligns with the little hash
mark on the timing tab. If you are standing on the
driver's side of the engine, those marks on the
timing tab that move away from you, which also
causes it to move away from the ZERO mark (in a
counter clock-wise direction) are advance marks.
Those that move toward you (in a clock-wise
direction from the ZERO mark) are the retard
direction. So, for each little hash mark on the
timing tab that you move the damper groove you've
changed the timing two degrees. If you move the
damper groove counter-clock-wise (away from you)
you're advancing the timing and if you move it
clock-wise (toward you) you're retarding it. With
the EST disconnect, the engine will idle
noticeably better as you advance the timing and
noticeably worse as you retard it. Do be fooled;
sticks to the stock setting of 6 degrees, or at
best 8 degrees. Modified engines may call for more
initial advance that 8 degrees, but for a
basically stock setup, stick with a max of 8.
Remember, the directional references I listed are
with you standing on the driver's side of the
engine. If you can picture yourself standing
directly in front of the engine, facing it (which
won't do a lot of good since you wouldn't be able
to see any of the timing marks from THAT
position), clock-wise and counter clock-wise
applies. Hope this helps explain it. Jake




And a detailed topic of it:


Member Since: Aug 2004
Florida
Default L98 timing?
------------------------------------------------------------------------
I'm going to check the timing today on my '86E coupe but I have a few
questions first. Where should the timing be set? I was told 6 before TDC
with the EST wire disconnected. Next, where and or what is the EST wire
I have to disconnect? Yes, I know I need a manual but I have twin baby
girls due in a month and the wife has cut ALL Corvette funds for now.
Please help me ASAP, I'd like to get this done before she comes home and
catches me with the new timing light.



------------------------------------------------------------------------
You can usually find this wire by the vacuum booster. Has a bullet
shaped black connectore that pulls apart. 6 degrees is correct. I like
to run mine around 8
Default
------------------------------------------------------------------------



------------------------------------------------------------------------
Its located at the back of the engine near the brake booster. It looks
almost like a black in-line fuse holder (its usually a brown wire).

When I time my Vette, I let the engine get up to normally operating
temperature, then with the parking brake engaged, I put the car in
Drive, disconnect the EST and set the timing. When its set, reconnect
the EST and you're good. I run mine at the stock 6.


------------------------------------------------------------------------
Hmmmm, I was thinking it was the "tan" wire at the dist cap? All I run
is premium gas and what will moving it to 8-9 do for me? The car has
minimal mods, the "free" L98 stuff, K+N filter w/open airbox, Hypertech
HO cap rotor and coil, precats cut off.
------------------------------------------------------------------------
my "tan" wire has faded to brown

------------------------------------------------------------------------



The warmup is important. Drive the car around for a while and then reset
the timing.. This is important because the car will go into open loop
and you will get the correct timing advance for warm condition.

I don't know if putting it in drive when setting it is necessary though...

--------


You need a timing light and, it will be easier, a 9/16" distributor
wrench, which is shaped like an 'L' .

You should first bump the engine over until the TDC mark on the harmonic
damper can be reached. Wipe off any grease and dirt and mark the TDC
mark on the damper with something that will make it stand out and be
easier to see. I use fingernail polish, but about anything will work,
like chalk, yellow grease pencil, etc.

Warm up the engine then shut it down.

Disconnect the EST wire, which is a brown or tan wire with a black
stripe located near the power brake booster. It's a single wire with a
weather-pak connector; just separate the two at the connector.

Connect the timing light to the battery; red to positive and black to
negative. Connect the other timing light connector to the #1 spark plug
wire; anywhere along the wire will work. It just clamps over the plug wire.

Using the distributor wrench and, standing on the passenger side of the
engine, loosen the bolt that holds the distributor hold-down clamp,
which is located at the base of the distributor. Loosen the bolt just
enough to allow you to turn the distributor.

Start the engine - it may be a little difficult at first but play with
the throttle until the engine will idle on its own.

Point the timing light at the hamonic damper and pull its tiggger. The
light will being to flash. On the timing chain cover there is a timing
tab. These tabs are slightly different depending on the year of the car,
but you should see numbers on the tab. Look at the mark you made on the
damper and see which number the mark aligns with. That's your base
timing. If the mark is aligned with 6, you have 6 degrees before TDC.

To change the timing, all you need to do is turn the distributor. As you
turn the distributor (by turning the distributor cap) you'll see the
timing mark move.

Once you have the timing where you want it, tighten the disributor hold
down bolt, then recheck the timing to make sure it didn't move as you
were tightening the bolt. If it moved, loosen the bolt again and adjust
the distributor some more.

Once you have the timing where you want it, and the hold down bolt
tight, shut down the engine, reconnect the EST wire and disconnect the
battery for about 30 seconds. This will clear the error code that gets
set when the ECM detected the engine running with the EST disconnected.

Reconnect the battery, remove the timing light connections and you're done.

Jake
----------



Quote:
Originally Posted by proemtpff
Ok, just checked it 8 deg BTDC and I run super in it. Good? The car runs
great, I was just wanting to check it. What would make me want to make
it 6 deg over having 8 deg? IE: what should I "look" for performance wise?



It's all about cylinder pressure; the more you advance the spark, the
higher your cylinder pressure becomes, which equals more power (since
this pressure is what pushes the piston down).

Think of it this way--when the spark fires before TDC, the mix is
already starting to burn as the piston is finishing up its travel up the
cylinder. At TDC, you've already got a good fire burning and pressure is
rising quickly, pushing the piston down harder. If you advance your
timing even further, the fuel/air mix has an even longer time to start
building up pressure, meaning more pressure at TDC when the piston
starts traveling down, and therefore even more power.

Downside of all is this is that if you have too much advance, the
pressure and temperature get too high and you get detonation, similar to
what happens with a high compression ratio. Also your NOx emissions go
up because NOx levels rise with higher combustion temperature and
pressure. It was pretty typical for automakers in the 70's to not add as
much spark advance (as well as lower compression ratios) to lower NOx
emissions, since the catalytic converters of that period didn't remove
NOx emissions (NOx reduction is the 3rd part of a "three-way" catalytic
converter).

Also, theoretically you could start having misfires from having too much
advance, as the fuel/air mixture isn't compressed enough to light off.
But, I've never run into that happening--typically you'll get detonation
before you hit that point.

Finally, bumping up the advance shouldn't move the powerband around--it
should increase power at all RPMs, although the effect isn't as
noticable as at high RPMs since at higher RPM you're already running
around 35 degrees of spark lead--a couple extra degrees of advance
doesn't affect things as much as at low RPM when you've increased the
lead from say from 6 to 8 degrees (a 33% increase of spark advance).

Hope this helps!

Ben

 

Damn what some info. You shouldn't have any problems after reading that.

 

Excellent! I have a '90 as well and wanted to up the advance a little. I really appreciate the detailed information. Way to go, good job.

Question: Do you think it will have to be put back to 6 degrees before a smog in California or will this not be enough advance to hurt emissions?

Thanks Matt

 

If your car is running well at the 8 deg timing, are there any negatives to be concerned about?

 

I've been saving topics in a Corvette folder on my computer. Easy enough to copy and paste.

Draw backs to eight? Hmm could get ping going to higher altitudes, requiring premium gas, being more aware of ping on very hot days.

Eight and emissions, stock mine passed with soooo low numbers. I think you'll be fine.

 

Thanks Aardwolf, I will pickup a timing light and get to work. Very nice post, all the info I need.

 

Thanks I appreciate the info and will be uping my timing to 8 degrees TODAY!

Thanks Matt