misweetrevenge
Registered Member
Planning to do MSD wires/cap/rotor when I do my tune up. Is there any advantage to advancing the timing while I'm in there?
Completely stock 91 TBI 350
Completely stock 91 TBI 350
CK5
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Advancing Timing
- Thread starter misweetrevenge
- Start date
chulisohombre
1/2 ton status
The tbi computer advances the distributor itself. It would hurt your engine to do so. It needs set at zero tdc and the computer makes adjustment as needed. It would be good to check to make sure it is at the correct position though after you change everything.
You unplug the EST wire, which is tan and have engine at a warn idle speed, set timing to 0/TDC, plug EST wire back in and your done.
You unplug the EST wire, which is tan and have engine at a warn idle speed, set timing to 0/TDC, plug EST wire back in and your done.
misweetrevenge
Registered Member
Ok cool thanks guys. My first Chevy 350. I'm used to MPFI on OBDII systems. How would I change the timing to 0 if need be? (i know what wire you are referring to. I saw a picture in another thread)
Unplug EST bypass wire (tan/blk?) single connector somewhere near the brake booster. Start truck, turn distributor until you hit 0* at the timing tab. Turn off, plug EST wire back together, remove ECM fuse if CEL illuminated, reinsert fuse, run it.
*Normally* you can get about 2* more out of the stock numbers, but since you are CA and I expect not emissions exempt, I'd leave it at 0* unless you want to change it for testing only. You can always try 2* extra and see what happens. If advanced too much, you'll "hit" the knock sensor under load/acceleration, and performance will fall off.
*Normally* you can get about 2* more out of the stock numbers, but since you are CA and I expect not emissions exempt, I'd leave it at 0* unless you want to change it for testing only. You can always try 2* extra and see what happens. If advanced too much, you'll "hit" the knock sensor under load/acceleration, and performance will fall off.
misweetrevenge
Registered Member
I just smogged it and flew way under the average. I'll probably leave it at 0* though so I don't risk hurting anything until I do more research on it
check out our injection section for efi info . eagle mark is the mod in there and also a tunner guy for chips and flashing pcm's on newer stuff.
if I recall some have had good luck going to 4* from 0* mark .
if I recall some have had good luck going to 4* from 0* mark .
misweetrevenge
Registered Member
There's a guy I've read about that I've heard real good things about with his TBI tunes. I'll look more Into advancement. I'm looking at the performer manifold with some cams and headers. What do you guys suggest for a cam in a DD type truck with minimal towing?
The problem with adding spark advance at distributor is the ECM does not know about it. I've seen lots of times it's OK to add 5*... it's not!
Yes it will run better when warm, but there's a few spots it will get knock counts and retard timing by more then you added. Also that extra 5* is killer when you have another table called "SA - Coolant Comp Spk Adv" which adds 10* when cold, depending on ambiant temps.
Then add 5* when in PE "Power Enrichement" and again, it's OK in spots and causes knock in others.
There's also a ESC "Electronic Spark Control" test done in these ECM when you enter PE, it adds 11* timing to force knock! Now you added 5* to that... if that's not bad enough and you run high octane? It won't knock at 11 so the second test adds 22*, with your unaccounted for 5* that's 27*
I remove this ESC test. Not sure why anyone would want forced knock?
Newer OBDII systems have a High Octane and Low Octane table, it runs off High Octane until it see's knock activity, then reduces spark to low octane. Our systems don't have high octane or learn so the ESC knock test is just to prove the knock sensor works, at the worst time! WOT!
Here's what a stock spark advance table looks like for 90-91 5.7L
Here's what the engine likes! Now with a table like this you do have to remove the ESC test, some Coolant spark adder and PE to make it safe for all conditions of daily driving and towing.
Yes it will run better when warm, but there's a few spots it will get knock counts and retard timing by more then you added. Also that extra 5* is killer when you have another table called "SA - Coolant Comp Spk Adv" which adds 10* when cold, depending on ambiant temps.
Then add 5* when in PE "Power Enrichement" and again, it's OK in spots and causes knock in others.
There's also a ESC "Electronic Spark Control" test done in these ECM when you enter PE, it adds 11* timing to force knock! Now you added 5* to that... if that's not bad enough and you run high octane? It won't knock at 11 so the second test adds 22*, with your unaccounted for 5* that's 27*
I remove this ESC test. Not sure why anyone would want forced knock?
Newer OBDII systems have a High Octane and Low Octane table, it runs off High Octane until it see's knock activity, then reduces spark to low octane. Our systems don't have high octane or learn so the ESC knock test is just to prove the knock sensor works, at the worst time! WOT!
Here's what a stock spark advance table looks like for 90-91 5.7L
Here's what the engine likes! Now with a table like this you do have to remove the ESC test, some Coolant spark adder and PE to make it safe for all conditions of daily driving and towing.
