Base Timming??

[scotch1]

Base Timing??

Hi.
Does anyone know what the proper method of checking and adjusting the timing of my 1990, L98 coupe??
I have over 122K Mi. on it and it deserves a check-up and a tune up ??
Please help shed some info, looked in the service manual couldn't find any procedure.

Tom.

 

[XtremeVette]

I can offer a little help

You can't...well here's what I mean:

Straight out of my 1990 HELMs or GM service manual....THE BIG BOOK lol

All spark timing changes in the HEI (EST) distributor are done electronically by the Electronic Control Module (ECM)(your computer), mounted in the left rear corner of the engine compartment. The ECM monitors information from various engine sensors, computes the desired spark timing, and signals the distributor to change the timing accordingly. A back-up spark advance system in incorporated to signal the ignition module in case of ECM failure. No vacuum or mechanical advance is used.

So basically your at the mercy of your computer and its sensors, make sure all your sensors and the ECM is up to snuff and your fine. Not like the old days where you need to turn your distributor to get better timing. This at least applies to the 1990 and 1991, before or after that is a whole different ballgame.

Jeff

 

[Jeb]

Base timing should be listed on the emissions control lable located on the radiator shroud. I believe it is 6 degrees BTC for an L98.

 

[oldvet]

Base timing should be listed on the emissions control lable located on the radiator shroud. I believe it is 6 degrees BTC for an L98.

on my 89 that is exactly true.

 

[sxyvet]

Hi.
Does anyone know what the proper method of checking and adjusting the timing of my 1990, L98 coupe??
I have over 122K Mi. on it and it deserves a check-up and a tune up ??
Please help shed some info, looked in the service manual couldn't find any procedure.

Tom.

hi there scotch1,
this how i go about adjusting igntiion timing on my 1991 l98 engine!
i first warm up the engine ,turn it off!
grab a timing light and connect positive then negative wire to battery!
connect pick up wire on timing light no 1 cylinder on left hand side front of engine!
start engine up,
point timing light down at balancer on lower pulley!
see what reading says!
as the guys stated it should be set on 6 degrees btdc.
if not disconnect the tan/white wire - black plug near left hand side of fire wall and then loosen single bolt on distributor just enough to move distributor around!
while the engine is running put your hand on top of distributor and while still pointing the timing light at balancer move the distributor around to get correct timing!
once set,turn car off.
retighten distributor bolt.
connect tan/white wire-black plug back!
disconnect negative wire on battery for 1 minute to clear code that may be sent beacause you dissconnected the tan-white wire
your done!
glen
sxyvet
australia

 

[Jeb]

hi there scotch1,
this how i go about adjusting igntiion timing on my 1991 l98 engine!
i first warm up the engine ,turn it off!
grab a timing light and connect positive then negative wire to battery!
connect pick up wire on timing light no 1 cylinder on left hand side front of engine!
start engine up,
point timing light down at balancer on lower pulley!
see what reading says!
as the guys stated it should be set on 6 degrees btdc.
if not disconnect the tan/white wire - black plug near left hand side of fire wall and then loosen single bolt on distributor just enough to move distributor around!
while the engine is running put your hand on top of distributor and while still pointing the timing light at balancer move the distributor around to get correct timing!
once set,turn car off.
retighten distributor bolt.
connect tan/white wire-black plug back!
disconnect negative wire on battery for 1 minute to clear code that may be sent beacause you dissconnected the tan-white wire
your done!
glen
sxyvet
australia

Not so fast, Dood!

He's not done until he rechecks the timing and sees that the distributor didn't move when he tightened it back up.

 

[sxyvet]

Not so fast, Dood!

He's not done until he rechecks the timing and sees that the distributor didn't move when he tightened it back up.

fair enough!
i cant be expected to remember every little detail!
at least i tried to give some lite on the topic.
i didnt see you write up fully on how to do it!
so not so fast dude...
glen :eyerole

 

[Jeb]

LOL

I was just rattlin your cage, Dood.

To be honest, I've never screwed around with the base timing on mine so I didn't want to post something of a detailed nature and make matters worse. I just didn't want him to think nothing could be done. I think the earlier poster who said that nothing could be done might have missed the L98 reference in the original post.

 

[scotch1]

Thanks alot guys.
I am now trying to find the tan /white wire , Black connector.
About where is it on th fire wall??
Tom.

 

[Jeb]

It's at the rear of the left valve cover down near the bottom of the distributor.

It should be found sticking out of a cable shield that runs from the bottom of the distributor.

 

[sxyvet]

Not so fast, Dood!

He's not done until he rechecks the timing and sees that the distributor didn't move when he tightened it back up.

scotch1,
once you have finally found the black plug dont forget to do the following above as would you believe i forget to mention,how dum was i!!!!
good luck mate.
glen

 

[Vettefan87]

Just make sure you reconnect the wire once you get the base timing set, then I reset the computer to clear the code, and you are fine once you get it all tightened up, just make sure you reconnect that wire back up or your car won't run very well.

 

[scotch1]

Yes! I didn’t forget to reconnect the timing plug, thanks for the reminder. And, doubled checked the setting after tightening the distributor.

I also found the sticker on the hood describing the pug and 6 degrees BTDC, instruction settings.

And thanks again to everyone, for your input.

Consequently I found that my timing was way, way, off, much, much, too far advanced, don't know how it got that way, but my engine is running much better now with allot more pep and get up and go.

Now for the idle problem. Can’t get it to idle below 1500 RPM. Any suggestions?

Tom

 

[Volkspanzer]

Yes! I didn’t forget to reconnect the timing plug, thanks for the reminder. And, doubled checked the setting after tightening the distributor.

I also found the sticker on the hood describing the pug and 6 degrees BTDC, instruction settings.

And thanks again to everyone, for your input.

Consequently I found that my timing was way, way, off, much, much, too far advanced, don't know how it got that way, but my engine is running much better now with allot more pep and get up and go.

Now for the idle problem. Can’t get it to idle below 1500 RPM. Any suggestions?

Tom

Sounds like you need to reset your idle speed

 

[Volkspanzer]

i used this procedure to great success
--------------------------------------------------------------------------------

i used this.
Procedure
There are two electrical components on the TB that you will be working with: The TPS and the Idle Air Control Valve (IAC). Make sure that the connectors for these two components are easily accessible and that you can easily disconnect the IAC.
You will also be playing with the diagnostic connector under the dash. Remove the cover (if it's still in place). Bend your paper clip into a "U" shape. You will be playing with the two top right hand terminals ("A" and "B") in the connector.
First step is to set the minimum idle speed. If nobody has messed with this on your car before, the set screw will be covered by a pressed-in plug. It's located on the driver's side of the TB. Remove this plug if it's there.
With the IAC connected and the ignition "OFF," stick the paper clip into the diagnostic connector from "A" to "B." This grounds the diagnostic lead.
Turn the ignition to the "ON" position without starting the engine. Wait 30 seconds.
Now, with the ignition still in the "ON" position, disconnect the IAC connector at the IAC.
Remove the paper clip from the diagnostic connector.
Start the engine and allow it to reach normal operating temperature. The idle speed will probably be really low, and you may have to coax the engine a bit with the gas pedal to keep it running for a while.
If your car is an automatic, set the parking brake and put the transmission in "DRIVE." If your car is a manual, leave it in neutral.
Adjust the idle speed screw to obtain 400 rpm in drive or 450 in neutral.
Shut off the engine and re-connect the IAC.
That's it for idle speed. Now on to the TPS.
There are 3 wires stacked vertically on the TPS. You will need to be able to measure the voltage between the two top wires. You can either buy a special harness connector that breaks these wires out (from Mid America), or gently pierce the insulation of the wires with the pointy prongs on your volt meter. You can also stick a paper clip into each of the two top locations of the connector and clamp onto the paper clips to measure the voltage. Whatever is easiest for you.
Turn the ignition to the "ON" position without starting the engine.
Loosen the TPS Torx adjustment screws.
Set your volt meter to a low scale DC volt setting that will accurately read less than 1 volt.
Measure the voltage between the two top TPS wires.
Adjust the TPS by rotating its position until you get a reading of .54 volts.
Tighten the Torx screws and recheck the voltage. Re-adjust if necessary to make sure voltage is right at .54.
Turn the ignition "OFF."

 

[Bill Heygster]

scotch1,
once you have finally found the black plug dont forget to do the following above as would you believe i forget to mention,how dum was i!!!!
good luck mate.
glen

Sorry about this stupid question but I'm dying to know if your vette is right hand drive

 

[scotch1]

Bill.
No,standard drive, American, US, left hand drive, just an old 1990 L98 with over 120 thousand hard miles, I'm trying to refurbish and bring back to life.
New seats, Clutch, complete exhaust system, repaired radio, tune up, replace all sensors, and some body work to name a few.
Tom.

 

[sxyvet]

yep corvette is rhd!

Sorry about this stupid question but I'm dying to know if your vette is right hand drive

hi bill,
my 1991 corvette was converted to rhd!
cost $20,000 aus dollars and took 4 weeks to do!
thanks
glen
sxyvet
Australia

 

[Bill Heygster]

hi bill,
my 1991 corvette was converted to rhd!
cost $20,000 aus dollars and took 4 weeks to do!
thanks
glen
sxyvet
Australia

Glen

Ouch - love to see a picture of the interior - thanks for the answer

 

[scotch1]

Hi Again.

Thanks for the procedure!

I followed your instructions and then did it over again to fine tune my idle just make sure that I was doing everthing correctly.

My engine works fine now but only one problem, afterward my idle still returns up to about 1800 RPM.

I drove out to Carlisle, PA. to pick up a replacement top from Thompson Astro Tops, Got a great buy an he even adjusted it for me.

Tom.