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Old 10-09-2012, 11:23 AM
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Advanced Timing Question for built 4.3

I'm going to redo my timing today. My 4.3 TBI has a mild comp cam in it, bored over .060, and a MSD ignition system. Anyhow, the speed shop who built my motor suggested 10 BTDC initial time, and 37 BTDC total time. I know how to set initial time, however, how do I do total? He instructed me, after setting the inital time, to rev the motor to 1500 RPM and adjust the distributor to 37 degrees BTDC. Does this mean just adding 27 more degrees, or 37 by the light/gun?
Also, comp recommends 6-8 BTDC on initial and no more than 34 on total. Trying to figure out why the builder suggested 10 initial and 37 total.... Here are the cam specs: 09-412-8 - Magnum
Note* When this was first done, I did what he said, and kept getting piston rattle on his recommended settings, so basically what I did, was to set initial time, and then adjusted the distributor slowly on a hill. I would goose it in 2nd gear up the hill, and bump it an 1/8" advanced, until it wanted to stall. At that point, I backed it off an 1/8, and solved the ping. been running it like this now for about 7 months. I run 93 octane. Nothing else.

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Old 10-09-2012, 11:32 AM
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set your timing to 35 degrees at 3,000 rpm,rev engine higher to see if timing still increases? let the engine idle and see what you have for static timing.Road test car for ping.add 2 degrees at a time until it does ping.set back 3 degrees from there.That is your maximum timing.That does not mean its the best.

when you have figured the maximum timing and you know what the static timing is,come back and repost
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Old 10-09-2012, 11:37 AM
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Quote:
Originally Posted by vinniekq2 View Post
set your timing to 35 degrees at 3,000 rpm,rev engine higher to see if timing still increases? let the engine idle and see what you have for static timing.Road test car for ping.add 2 degrees at a time until it does ping.set back 3 degrees from there.That is your maximum timing.That does not mean its the best.

when you have figured the maximum timing and you know what the static timing is,come back and repost
Sorry to sound so ignorant... How do I check "static timing"? That's a new one to me. Once again, sorry to sound ignorant.
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Old 10-09-2012, 11:40 AM
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Is that timing with no load on the engine?
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Old 10-09-2012, 11:54 AM
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no load,no vacuum at idle,is the static timing.3,000 rpm in park,no load is full advance(or should be)This is just a starting spot and will get you very close if you follow this procedure.

recurving the advance takes time/or money.(both)
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Old 10-09-2012, 11:58 AM
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Quote:
Originally Posted by vinniekq2 View Post
no load,no vacuum at idle,is the static timing.3,000 rpm in park,no load is full advance(or should be)This is just a starting spot and will get you very close if you follow this procedure.

recurving the advance takes time/or money.(both)
So does this mean I should set my initial, then when I plug the ECM back up, do I take off the main vacuum/plug it? Then follow your steps?
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Old 10-09-2012, 12:08 PM
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Quote:
Originally Posted by vinniekq2 View Post
no load,no vacuum at idle,is the static timing.3,000 rpm in park,no load is full advance(or should be)This is just a starting spot and will get you very close if you follow this procedure.

recurving the advance takes time/or money.(both)
I also forgot to mention that it doesn't idle at factory. Factory is 750, it idles at 1250. All sensors and etc are new.
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Old 10-09-2012, 01:59 PM
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Advanced Timing Question for built 4.3

Read this article then you will understand how to set the initial, total, and with vacuum advance.http://www.crankshaftcoalition.com/w...EI_distributor
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Old 10-09-2012, 02:21 PM
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Quote:
Originally Posted by cdminter59 View Post
Read this article then you will understand how to set the initial, total, and with vacuum advance.http://www.crankshaftcoalition.com/w...EI_distributor
Thanks for the link.
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Old 10-09-2012, 03:00 PM
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Quote:
Originally Posted by cdminter59 View Post
Read this article then you will understand how to set the initial, total, and with vacuum advance.http://www.crankshaftcoalition.com/w...EI_distributor
Actually, this is a great link! Now I know why it idles at 1250 RPM. But what sucks, is that Comp Cam recommends 6-8 for initial time. However, I have it at 9 and it still idles high. I guess I will have to try between 10-12 initial to see if it cures my high idle.
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Old 10-11-2012, 12:38 PM
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OK, so after reading all of the links provided, and doing some research, I'm gonna go over the steps I need to take to set advanced time, and if anyone sees something amiss, please say something. I have a MSD distributor and coil, no vacuum advance on it.

Shooting for 37* BTDC Total Time

Setting the initial at 10* BTDC (unplug the ECM sprague wire to do this)
then, once initial is set, plug the ECM back up to the distributor, here's where things are iffy for me, Put the light to the engine, rev up to 3500 RPM, or until mark moves no longer, then adjust (twisting the distributor) to 37* BTDC, and that's it? Doesn't that change the initial time? Then Static Time is with no load at idle?

Quick question. If my idle is too high, that suggests initial is too low. Do I advance it a bit more to solve that issue? The cam company recommends 6-8* BTDC, but that just ain't cutting it.

I'm installing a MSD timing tape to eliminate the need for an advanced timing light.
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Old 10-11-2012, 05:26 PM
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Checking the timing on a electronic injected engine is not what you are thinking here. Timing adjusts differently in closed loop than it does in open loop. AND the engine needs to be operating under load to be able to actually read the true timing that is being dialed in to the PCM..
If you have a scanner, it will read the amount of timing being adjusted into the system , just read the live data while driving.
Closed loop conditions are usually
At least 160 degrees engine temp
Gear selector in drive(if automatic)
Active O2 sensor
Then you can throw it into gear, stomp the gas, watch the roadspeed vereses the ignition timing and RPM on the scanner. Then you will be getting closer to what you need to know to start with
Also, if the knock sensor is hooked up and working, if it does get too much timing, the knock sensor will signal the PCM and back the timing off, roughly about 3 degrees each time it happens.Eventually it will"learn" where it needs to be.
The drive method you had for setting the timing in your first post was probably the way to go.
You can dial in more base timing, but the knock sensor should keep the advance curve from going to an excess , which could cause engine damage.
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Old 10-11-2012, 05:50 PM
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Quote:
Originally Posted by LATECH View Post
Checking the timing on a electronic injected engine is not what you are thinking here. Timing adjusts differently in closed loop than it does in open loop. AND the engine needs to be operating under load to be able to actually read the true timing that is being dialed in to the PCM..
If you have a scanner, it will read the amount of timing being adjusted into the system , just read the live data while driving.
Closed loop conditions are usually
At least 160 degrees engine temp
Gear selector in drive(if automatic)
Active O2 sensor
Then you can throw it into gear, stomp the gas, watch the roadspeed vereses the ignition timing and RPM on the scanner. Then you will be getting closer to what you need to know to start with
Also, if the knock sensor is hooked up and working, if it does get too much timing, the knock sensor will signal the PCM and back the timing off, roughly about 3 degrees each time it happens.Eventually it will"learn" where it needs to be.
The drive method you had for setting the timing in your first post was probably the way to go.
You can dial in more base timing, but the knock sensor should keep the advance curve from going to an excess , which could cause engine damage.
Thank you. I was thinking about getting a advanced timing kit for the HEI so I could change the fuel curve to do it's thing in the lower RPMs. I may go that route. I may have to advance it further to lower the idle to where it needs to be. Then adjust for total time. The one thing I am wondering... Doesn't Initial time change in the procedure? I mean, set initial, plug ECM back up, then adjust total @ 3500 RPM... Either way, the distributor is being turned... Does the ECM store the initial time setting and adjust for what it needs at that point?
Also, one other thing bothering me... If Comp recommends 6-8* and it's not working as far as idle goes, will advancing it to where the idle is proper damage anything?
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Old 10-11-2012, 06:13 PM
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Quote:
Originally Posted by S10BlazerBuilt View Post
Thank you. I was thinking about getting a advanced timing kit for the HEI so I could change the fuel curve to do it's thing in the lower RPMs. I may go that route. I may have to advance it further to lower the idle to where it needs to be. Then adjust for total time. The one thing I am wondering... Doesn't Initial time change in the procedure? I mean, set initial, plug ECM back up, then adjust total @ 3500 RPM... Either way, the distributor is being turned... Does the ECM store the initial time setting and adjust for what it needs at that point?
Also, one other thing bothering me... If Comp recommends 6-8* and it's not working as far as idle goes, will advancing it to where the idle is proper damage anything?
On a TBI engine there is no advance mechanism. Its all calculated by the PCM
You can add more timing to the base or inital timing to compensate for things like cam duration.Put a vacuum gauge on a manifold source to help you get it to a happy spot between Idle qaulity and speed.
Base timing , and computed timing are basically stored in the PCM algorythms. It does have an "Adaptive strategy" which will allow the timing to run further advanced if it detects octane will support it, and retaard the timing when the low octane fuel causes a knock or pre ignition, which is detected by the knock sensor.
Its a good thing to have the kock sensor hooked up and working. As you drive the vehicle , the PCM will advance the timing through all the rpm ranges, untill it gets to the point it detects a knock, or pre ignition, at which point it will retard the timing until it stops.After that, and a few drive cycles, the adaptive part of the pcm will run the timing based on strategy it has developed through it range of operation.
The amount of timing that the pcm is delivering is based on the initial or base timing being correct.Or factory spec as on the underhood sticker.
If you add some base timing, you will have to add the extra amount to the value of timing advance that you see being displayed on the scanner.
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Old 10-11-2012, 07:09 PM
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Quote:
Originally Posted by LATECH View Post
On a TBI engine there is no advance mechanism. Its all calculated by the PCM
You can add more timing to the base or inital timing to compensate for things like cam duration.Put a vacuum gauge on a manifold source to help you get it to a happy spot between Idle qaulity and speed.
Base timing , and computed timing are basically stored in the PCM algorythms. It does have an "Adaptive strategy" which will allow the timing to run further advanced if it detects octane will support it, and retaard the timing when the low octane fuel causes a knock or pre ignition, which is detected by the knock sensor.
Its a good thing to have the kock sensor hooked up and working. As you drive the vehicle , the PCM will advance the timing through all the rpm ranges, untill it gets to the point it detects a knock, or pre ignition, at which point it will retard the timing until it stops.After that, and a few drive cycles, the adaptive part of the pcm will run the timing based on strategy it has developed through it range of operation.
The amount of timing that the pcm is delivering is based on the initial or base timing being correct.Or factory spec as on the underhood sticker.
If you add some base timing, you will have to add the extra amount to the value of timing advance that you see being displayed on the scanner.
OK. I'm getting the point here, I think. So I can adjust the initial time to fix the idle by advancing it. No worries about any other issue because the ecm will compensate. As long as my engine starts just fine, no hang ups, then I am good. That's assuming I have no piston ping...
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