88 350 TBI timing

[Steven Petersen]

To be clear to the OP. Bone stock 88 TBI, set you timing to zero (with engine @ regular warmed up temps).

Thank you. I knew it was zero. I just hadn’t messed with one in over 15 years. I didn’t remember the engine being cold making a difference. Especially since you unplug the spark advance wire. How does it advance with the wire unplugged?

 

[HawkDsl]

Thank you. I knew it was zero. I just hadn’t messed with one in over 15 years. I didn’t remember the engine being cold making a difference. Especially since you unplug the spark advance wire. How does it advance with the wire unplugged?

unplugging the wire disables the computer control over the advance. The computer has a cold start routine that keeps the engine at a higher RPM until there is some heat in it.. this routine runs if it's unplugged or not.. that's why you should have a warmed up engine before setting the timing.

When it's unplugged, it can't advance or retard. It'll run whatever you have the timing set to. To change the timing you have to loosed the distributor bolt, and turn the distributor left or right... but you probably know all that.

Anyway, the plug is the computers connection to controlling the timing. She's gonna run the timing tables it has all the time, and that timing is always going to be different depending on temp, air temp, and etc. That's why you have to unplug it to set the base timing.

 

[tsr2185]

What is the timing supposed to be at idle and when hot idle when the brown wire is plugged back in, and the initial timing has been set to 0 prior?

 

[Nad_Yvalhosert]

What is the timing supposed to be at idle and when hot idle when the brown wire is plugged back in, and the initial timing has been set to 0 prior?

That doesnt matter, as its controlled by the computer. What matters is setting the engine to 0° at operating temp, with the connector unplugged.

 

[tsr2185]

That doesnt matter, as its controlled by the computer. What matters is setting the engine to 0° at operating temp, with the connector unplugged.

Isnt it good to confirm what the advance is after setting timing to 0? Like to know if the ecu is properly advancing the timing or whatnot? I thought I read somewhere that it's supposed to be advanced like 12deg after its set and the wire is plugged back in.

 

[PlayingWithTBI]

Isnt it good to confirm what the advance is after setting timing to 0? Like to know if the ecu is properly advancing the timing or whatnot? I thought I read somewhere that it's supposed to be advanced like 12deg after its set and the wire is plugged back in.

Just for sh*ts and giggles, I took a stock .bin (AMUR) for a 1227747 ECM (88 - 91) and looked. A simple answer - it s/b somewhere around 16.17 - 17.23* @ 600 - 800RPM. Note the flattened area where the blue dot is. That's to keep the engine from surging @ idle.

You must be registered for see images attach

 

[Schurkey]

How is that spark-chart modified by other programming in the computer?

For example, at light load and 3000+ rpm, would there be additional spark advance beyond what is shown in that graph?

Seems odd to me that they limit spark advance to ~30 degrees when an older distributor with centrifugal and vacuum advance might go to mid-40s, maybe even more advance.

 

[PlayingWithTBI]

How is that spark-chart modified by other programming in the computer?

For example, at light load and 3000+ rpm, would there be additional spark advance beyond what is shown in that graph?

There's nothing added other than for when the engine is cold, when it goes into PE (Performance Enhancement), EGR, and Hywy Lean Cruise. GM kept these conservative to reduce the possibility Knock Counts no matter what kind of fuel you use. Another good reason for a good tuner.

Seems odd to me that they limit spark advance to ~30 degrees when an older distributor with centrifugal and vacuum advance might go to mid-40s, maybe even more advance.

Keep in mind, if you take a distributor's rotation (360*), divided by 8 cylinders, you get 45* so, you don't want to advance too high or you'll be cross firing to the previous cylinder.

Here's a couple examples from my engine. Yes it's got a cam, aluminum heads, and other go fast parts but, this is just for illustration. Here's a spark map from a "mail order" tune based on my build. (This was with the 1227747 ECM)

You must be registered for see images attach

Here's what I have now after more research and using an Accel spreadsheet developed by a member on another site. You plug in your max SA at 3200RPM and WOT. Then retard % above that. Then I go out , data log, and fine tune based on Knock Counts and performance until I'm good. (This one is with the EBL Flash-II). I gained close to 1-1/2 seconds in 0-60 and 1/4 mile with this and my fuel tables over the "mail order" tune. HTH

You must be registered for see images attach

 

[kenh]

I can see who I'm going to look up when I get my engine built!!!! hahahaha I know zero about computer tuning but any idiot can see that top table is crap.
All those pits and valleys and rough terrain just doesn't look right at all. Should be a smooth transition like your bottom table. At least in my mind....

ken

 

[PlayingWithTBI]

All those pits and valleys and rough terrain just doesn't look right at all. Should be a smooth transition like your bottom table. At least in my mind....

Yeah, a table can wind up looking like that as you reduce/add spark to a certain cell but, you need to take the time to smooth it out some. I'm no expert but, since I'm retired, I have plenty of time to play with this stuff,