91 F250 460 EFI stock 5,000' alt base timing 10 or 14?
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5th Wheeling
Joined: Aug 2017
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91 F250 460 EFI stock 5,000' alt base timing 10 or 14?
when the rain stops and I get some time I am wanting to check my timing. I did install a new roller chain recently at 125k. Sadly the new chain had more movement than the old one. 3/8" vs 1/4"
So just to verify I remove the sprout and set the timing on a warm engine. I tend to buy the 91 octane as I have had some pinging in the past with the 87, I see 10 degrees everywhere but also 14 for altitude... Do I need to check the timing at other RPMS and adjust anything else... Idle is real good and she starts fine
So just to verify I remove the sprout and set the timing on a warm engine. I tend to buy the 91 octane as I have had some pinging in the past with the 87, I see 10 degrees everywhere but also 14 for altitude... Do I need to check the timing at other RPMS and adjust anything else... Idle is real good and she starts fine
Logistics Pro
Joined: Aug 2014
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If everything mechanical is in proper working condition, and every sensor is in proper working condition there is zero reason to change the base timing of 10* as that is what the EEC-IV expects is 10*, nothing else.
Since you already mentioned you have a slack in the timing chain, you already have a mechanical issue that may be causing the EEC-IV to behave inconsistently. You can't tune out or adjust timing to fix the mechanical issues.
The system has sensors to auto adjust and compensate for altitude. The MAP sensor was calibrated at sea level, and will give the EEC-IV information to adjust air/fuel mixture when adding altitude.
If it idles great, then I wouldn't change anything.
Since you already mentioned you have a slack in the timing chain, you already have a mechanical issue that may be causing the EEC-IV to behave inconsistently. You can't tune out or adjust timing to fix the mechanical issues.
The system has sensors to auto adjust and compensate for altitude. The MAP sensor was calibrated at sea level, and will give the EEC-IV information to adjust air/fuel mixture when adding altitude.
If it idles great, then I wouldn't change anything.
Logistics Pro
Joined: Aug 2010
Posts: 3,718
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From: Chillicothe
If you have ping at 5000 feet on 87 you have other issues. You need to check actual TDC with a positive stop tool and find true TDC on your balancer. To make sure the timing is accurate to the piston location not the balancer location.
You lose about 3.5 percent by volume O2 per 1.000 feet. So at 5,000 that is like what 16 or 17% compared to sea level. Rich mix alone should help stifle detonation unless the timing is way off. That is why 85 octane is available in the mountains, because it lights off easier.
Always check codes too. As they don't always trip the CEL.
You lose about 3.5 percent by volume O2 per 1.000 feet. So at 5,000 that is like what 16 or 17% compared to sea level. Rich mix alone should help stifle detonation unless the timing is way off. That is why 85 octane is available in the mountains, because it lights off easier.
Always check codes too. As they don't always trip the CEL.
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5th Wheeling
Joined: Aug 2017
Posts: 40
Likes: 1
I was disappointed with that new timing chain assy. I really thought about going to get a different one. looking back now I may really regret that considering how easy it is to change when its all opened up. The occasional ping which has not been an issue for 2 years since I started buying 91 and it was only when its real hot and under a load. of course at 4.20$ a gal for 87 and 10 MPG I may be wanting to try the 87 gas again.
Cargo Master
Joined: Mar 2007
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The way I see it, it's not hard to just adjust it and see what works for you. Asking this question is just going to get a lot of opinions based on experiences from all over the world. Denver is different than Seattle [except for the politics]. Every one is not right or wrong.
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5th Wheeling
Joined: Aug 2017
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I got a new timing light and it has this changing angle feature. I Pulled the sprout after I found it down low on the fender near the firewall. The light started at 10 degrees? I guess that was the default and what I want ? the mark on the harmonic is running on the drivers side of the indicator about an inch... when I change the timing light advance number to 0 the mark is right on the indicator. My RPM is 700
So to me this means the timing is currently set to 0 advance. I read you need to rotate the distributer CW to advance until the mark is on the indicator when my timing light is adjusted to 10. I got it set lined up at 10 on the timing light seemed to work fine for a few minutes and tries but the new light seems to have died it has intermittent flashing..Let me know if this sounds correct. I locked it in and will test drive it.
If I was set at zero timing would that explain pinging or running hot? I have since read that zero would make it run real hot at idle.. this may have been the big part of my cooling idiosyncrasy's
So to me this means the timing is currently set to 0 advance. I read you need to rotate the distributer CW to advance until the mark is on the indicator when my timing light is adjusted to 10. I got it set lined up at 10 on the timing light seemed to work fine for a few minutes and tries but the new light seems to have died it has intermittent flashing..Let me know if this sounds correct. I locked it in and will test drive it.
If I was set at zero timing would that explain pinging or running hot? I have since read that zero would make it run real hot at idle.. this may have been the big part of my cooling idiosyncrasy's
Last edited by elkski1; Apr 29, 2026 at 09:30 AM.
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Cargo Master
Joined: Aug 2012
Posts: 2,875
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From: Kaufman TX
I got a new timing light and it has this changing angle feature. I Pulled the sprout after I found it down low on the fender near the firewall. The light started at 10 degrees? I guess that was the default and what I want ? the mark on the harmonic is running on the drivers side of the indicator about an inch... when I change the timing light advance number to 0 the mark is right on the indicator. My RPM is 720
So to me this means the timing is currently set to 0 advance. I read you need to rotate the distributer CW to advance until the mark is on the indicator when my timing light is adjusted to 10.
Let me know if this sounds correct.
So to me this means the timing is currently set to 0 advance. I read you need to rotate the distributer CW to advance until the mark is on the indicator when my timing light is adjusted to 10.
Let me know if this sounds correct.
Logistics Pro
Joined: Aug 2014
Posts: 3,573
Likes: 855
I got a new timing light and it has this changing angle feature. I Pulled the sprout after I found it down low on the fender near the firewall. The light started at 10 degrees? I guess that was the default and what I want ? the mark on the harmonic is running on the drivers side of the indicator about an inch... when I change the timing light advance number to 0 the mark is right on the indicator. My RPM is 700
So to me this means the timing is currently set to 0 advance. I read you need to rotate the distributer CW to advance until the mark is on the indicator when my timing light is adjusted to 10. I got it set lined up at 10 on the timing light seemed to work fine for a few minutes and tries but the new light seems to have died it has intermittent flashing..Let me know if this sounds correct. I locked it in and will test drive it.
If I was set at zero timing would that explain pinging or running hot?
So to me this means the timing is currently set to 0 advance. I read you need to rotate the distributer CW to advance until the mark is on the indicator when my timing light is adjusted to 10. I got it set lined up at 10 on the timing light seemed to work fine for a few minutes and tries but the new light seems to have died it has intermittent flashing..Let me know if this sounds correct. I locked it in and will test drive it.
If I was set at zero timing would that explain pinging or running hot?
Normally to read straight up, set the dial to 0, chalk mark on your balancer at 10*, Spark Output(SPOUT) unplugged, start the engine light strobes at 10*, if off then adjust distributor.
So, if your mark on the balancer is at 10*, timing light at 0, your strobe light and mark is right under the indicator, PERFECT!! no adjustment needed, and your dist is timed correclty.
Turn off engine, plug SPOUT back in, continue with your day.
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5th Wheeling
Joined: Aug 2017
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timing light is an amazon Autolumen store qz6803 digital with digital advanced timing.
I figured the groove in the harmonic that still has a white stripe is 0 degrees. when this is aligned with the timing light at zero advance it was lined up.to the indicator bracket.. Perhaps the guy I hired to do a tune up many years ago set it wrong or new timing chain changed it.
So now after I turned the distributor CW about 1/4- 3/8" with the timing light set at 10 advanced that white groove is right at the indicator. with sprout out...
Just checked the timing light on a different vehicle and it is not lighting on each fire.. its going back.
I figured the groove in the harmonic that still has a white stripe is 0 degrees. when this is aligned with the timing light at zero advance it was lined up.to the indicator bracket.. Perhaps the guy I hired to do a tune up many years ago set it wrong or new timing chain changed it.
So now after I turned the distributor CW about 1/4- 3/8" with the timing light set at 10 advanced that white groove is right at the indicator. with sprout out...
Just checked the timing light on a different vehicle and it is not lighting on each fire.. its going back.
Last edited by elkski1; Apr 28, 2026 at 02:45 PM.
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5th Wheeling
Joined: Aug 2017
Posts: 40
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Seems to be running well. and I think it is cooler in the engine compartment. I did fill up with regular gas yesterday.
Latest issue is the drivers power window wouldn't' open one morning then later that day it worked and no not at all. Maybe wire in the hinge. I recall that before... I'm glad for wing windows.
Latest issue is the drivers power window wouldn't' open one morning then later that day it worked and no not at all. Maybe wire in the hinge. I recall that before... I'm glad for wing windows.
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