L98 ignition timing
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L98 ignition timing
I decided to reset my timing on my 1987 L98 after I put a new cap and rotor in it. I read in a few forums before doing so so I had a good idea of what to do what I did was I started the car and let it get up to temp I unplugged the tan/black wire thing and instantly the car started running rough so I quickly moved the distributor until it smoothed out after that I set it to 8 degrees advanced and shut the car off tightened the distributor down and I started the car to make sure I didn’t move it and it was still good so I shut it off plugged the tan/black wire back in and unhooked the battery for about 5 minutes and when I started it back up I checked the timing and it’s showing 30 plus degrees advanced what did I do wrong?
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30 sounds high to me too, but keep in mind this is with the ECM controlling the timing now. Just checking, your comment wasn't clear, you did recheck after tightening the distributor, before reconnecting the..I forget, the tan/black thing.
One key point, DON'T unplug tan/black with the ignition on and certainly while the engine is running! I'm not 100%, but that certainly sounds risky to the ECM. Unplug, start up, set timing and finalize. Then stop, disengage battery and reconnect tan/black (boy, forgetting the name for that is bothering me!).
Finally, where did you get 8 degrees timing? I ask because my '87 calls for 6 degrees. The timing and how to set it should be listed on a sticker on the left side of the radiator, as it can vary due to options, etc.
One key point, DON'T unplug tan/black with the ignition on and certainly while the engine is running! I'm not 100%, but that certainly sounds risky to the ECM. Unplug, start up, set timing and finalize. Then stop, disengage battery and reconnect tan/black (boy, forgetting the name for that is bothering me!).
Finally, where did you get 8 degrees timing? I ask because my '87 calls for 6 degrees. The timing and how to set it should be listed on a sticker on the left side of the radiator, as it can vary due to options, etc.
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From: Hartford WI
I decided to reset my timing on my 1987 L98 after I put a new cap and rotor in it. I read in a few forums before doing so so I had a good idea of what to do what I did was I started the car and let it get up to temp I unplugged the tan/black wire thing and instantly the car started running rough so I quickly moved the distributor until it smoothed out after that I set it to 8 degrees advanced and shut the car off tightened the distributor down and I started the car to make sure I didn’t move it and it was still good so I shut it off plugged the tan/black wire back in and unhooked the battery for about 5 minutes and when I started it back up I checked the timing and it’s showing 30 plus degrees advanced what did I do wrong?
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Joined: Dec 2018
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30 sounds high to me too, but keep in mind this is with the ECM controlling the timing now. Just checking, your comment wasn't clear, you did recheck after tightening the distributor, before reconnecting the..I forget, the tan/black thing.
One key point, DON'T unplug tan/black with the ignition on and certainly while the engine is running! I'm not 100%, but that certainly sounds risky to the ECM. Unplug, start up, set timing and finalize. Then stop, disengage battery and reconnect tan/black (boy, forgetting the name for that is bothering me!).
Finally, where did you get 8 degrees timing? I ask because my '87 calls for 6 degrees. The timing and how to set it should be listed on a sticker on the left side of the radiator, as it can vary due to options, etc.
One key point, DON'T unplug tan/black with the ignition on and certainly while the engine is running! I'm not 100%, but that certainly sounds risky to the ECM. Unplug, start up, set timing and finalize. Then stop, disengage battery and reconnect tan/black (boy, forgetting the name for that is bothering me!).
Finally, where did you get 8 degrees timing? I ask because my '87 calls for 6 degrees. The timing and how to set it should be listed on a sticker on the left side of the radiator, as it can vary due to options, etc.
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You set the base timing, which is 6-8 BTDC, with the EST disconnected.
Once you plug that back in, the ECM can now add its timing advance. Typically the total timing will be 30-45* depending on load/temperature/RPM conditions, these modifiers are added onto the timing the ECM normally runs from its memory in the chip.
So you did it right, sounds like. If you drive with a scanner connected and watch closely you'll see how it advances and pulls timing out.
Once you plug that back in, the ECM can now add its timing advance. Typically the total timing will be 30-45* depending on load/temperature/RPM conditions, these modifiers are added onto the timing the ECM normally runs from its memory in the chip.
So you did it right, sounds like. If you drive with a scanner connected and watch closely you'll see how it advances and pulls timing out.
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You set the base timing, which is 6-8 BTDC, with the EST disconnected.
Once you plug that back in, the ECM can now add its timing advance. Typically the total timing will be 30-45* depending on load/temperature/RPM conditions, these modifiers are added onto the timing the ECM normally runs from its memory in the chip.
So you did it right, sounds like. If you drive with a scanner connected and watch closely you'll see how it advances and pulls timing out.
Once you plug that back in, the ECM can now add its timing advance. Typically the total timing will be 30-45* depending on load/temperature/RPM conditions, these modifiers are added onto the timing the ECM normally runs from its memory in the chip.
So you did it right, sounds like. If you drive with a scanner connected and watch closely you'll see how it advances and pulls timing out.
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You set the base timing, which is 6-8 BTDC, with the EST disconnected.
Once you plug that back in, the ECM can now add its timing advance. Typically the total timing will be 30-45* depending on load/temperature/RPM conditions, these modifiers are added onto the timing the ECM normally runs from its memory in the chip.
So you did it right, sounds like. If you drive with a scanner connected and watch closely you'll see how it advances and pulls timing out.
Once you plug that back in, the ECM can now add its timing advance. Typically the total timing will be 30-45* depending on load/temperature/RPM conditions, these modifiers are added onto the timing the ECM normally runs from its memory in the chip.
So you did it right, sounds like. If you drive with a scanner connected and watch closely you'll see how it advances and pulls timing out.
What you did is exactly how I set up my race car. Im at 8-10° initial and then let the computer do the rest. Since there is no load on the engine at idle it can handle a surprising amount of timing. I think I am around 40°+ at idle and 36-38° at WOT.
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For a backyard hack, people have just cranked up the distributor but for a race car, would it not be better to change the advance in the eprom program?
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From: Mission Viejo CA
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From: Hartford WI
Don't disagree with the base timing but what I am curious about is why not set it for whatever and build the chip with that in mind? IOW, if you set base timing to 0 instead of 6 and build the program for with that in mind, would it not work? Say the engine needs 36 degrees, it puts the advance to 30 plus 6 base timing. Or could you not set it to 0 base and set up the advance to 36 thus giving it a total of 36? Or out another way, is there more than 1 way to skin the cat? Always wondered why GM chose 6 degrees base.
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From: Hartford WI
The OP's car is stock, so the factory ignition curve should be fine. Why the confusing talk about custom chips, custom race car specs, and arguing with GM's decision about base timing? These issues don't help the OP one bit! Please start your own thread if you want to fight with GM.
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From: Mission Viejo CA
Would it be any easier to set the base timing to 0 deg, than setting it to 6 deg.? Please don't answer this rhetorical question.
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From: Hartford WI
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Let's think about this. How can the ECU know where the "base" timing is set? There's no cam or crank position sensor in the L98 (or L83), so how can it know? Answer: It can't!
If the "base" timing is advanced X deg. from the factory recommended setting, the entire ignition curve will be advanced X deg. The various engine sensors will enter into the calculations for the final spark timing, but the factory curve will be whatever was programmed into the chip, with no consideration for the initial "base" timing! And there is nothing inside the distributor that advances the timing, unlike earlier HEI systems that had weights, springs, and vacuum. The final spark timing is strictly a function of the ECU.
If this were not true, you could set the initial "base" timing anywhere, and the engine would run exactly the same as if the "base" timing was set correctly! This is obviously not true.
If the "base" timing is advanced X deg. from the factory recommended setting, the entire ignition curve will be advanced X deg. The various engine sensors will enter into the calculations for the final spark timing, but the factory curve will be whatever was programmed into the chip, with no consideration for the initial "base" timing! And there is nothing inside the distributor that advances the timing, unlike earlier HEI systems that had weights, springs, and vacuum. The final spark timing is strictly a function of the ECU.
If this were not true, you could set the initial "base" timing anywhere, and the engine would run exactly the same as if the "base" timing was set correctly! This is obviously not true.
Team Owner
Joined: Jul 2004
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From: Hartford WI
Let's think about this. How can the ECU know where the "base" timing is set? There's no cam or crank position sensor in the L98 (or L83), so how can it know? Answer: It can't!
If the "base" timing is advanced X deg. from the factory recommended setting, the entire ignition curve will be advanced X deg. The various engine sensors will enter into the calculations for the final spark timing, but the factory curve will be whatever was programmed into the chip, with no consideration for the initial "base" timing! And there is nothing inside the distributor that advances the timing, unlike earlier HEI systems that had weights, springs, and vacuum. The final spark timing is strictly a function of the ECU.
If this were not true, you could set the initial "base" timing anywhere, and the engine would run exactly the same as if the "base" timing was set correctly! This is obviously not true.
If the "base" timing is advanced X deg. from the factory recommended setting, the entire ignition curve will be advanced X deg. The various engine sensors will enter into the calculations for the final spark timing, but the factory curve will be whatever was programmed into the chip, with no consideration for the initial "base" timing! And there is nothing inside the distributor that advances the timing, unlike earlier HEI systems that had weights, springs, and vacuum. The final spark timing is strictly a function of the ECU.
If this were not true, you could set the initial "base" timing anywhere, and the engine would run exactly the same as if the "base" timing was set correctly! This is obviously not true.
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The OP's car is stock, so the factory ignition curve should be fine. Why the confusing talk about custom chips, custom race car specs, and arguing with GM's decision about base timing? These issues don't help the OP one bit! Please start your own thread if you want to fight with GM.
Would it be any easier to set the base timing to 0 deg, than setting it to 6 deg.? Please don't answer this rhetorical question.
Would it be any easier to set the base timing to 0 deg, than setting it to 6 deg.? Please don't answer this rhetorical question.