1990 TBI timing question.

[SoCalSlaughter]

I have a 1990 Suburban 5.7 TBI, just wondering what timing you guys are running. The stock 0 degree's or advanced? I've been told by a few Chevy guys that the engine loves advance, but I'm not sure with the TBI engines. Advancing to 6 degree's harmful/helpful? Thanks!!!

[JJLT1]

4-6* BTDC is usually purty safe, try a little at a time, and listen for pingin and rattlin..
I ran my 89/90 like that for years, but it did not like cheap gas, good 87 was ok..

[danheit]

I run 12 degrees on a 90 5.7 block that I removed the TBI and went carb on. Still have TBI heads, etc. Engine runs great with it (although I have a different cam), I only run non-Ethanol 93 in the truck though....

[Marv D]

If all the TBI and OBDI computer is in place,, you may not be doing yourself any favors. Intake air, Throttle position, Map/MAF/ Residual O2, and the knock sensor feedback to the computer is going to determine timing. When the computer runs out of advance or retard to get the feedback it wants,, your going to set a SES code.

I guess you could use that as your 'sanity limiter',,, keep advancing it till it sets codes,, then back off some till it doesn't.

But that just doesn't sound like a wise move to me.

[Bigdav160]

I set my TBI engines to 2º BTDC

[1990GMCVan]

I have a 5.7L in my G3500 van that I use for towing my trailer. Recently I had a coil meltdown. the carbon contact in the distributer cap broke and the coil arced from the terminal in the cap to the rotor button until the coil died. Now with the new coil, cap and rotor button, distributor(pickup coil was also trashed) the truck still does not run right. At closed throttle the old OTC scanner I have tells me I have 1.0 volts coming in from the MAP sensor which loosely translates to 8 inches of vacuum. I t'ed off the vacuum line at the sensor and there was between 19 and 20 inches of vacuum at the MAP while the OTC scanner read 1.0 volts (8 inches of vacuum). The TPS when closed is at .70 volts. When I open the throttle just a little, the MAP voltage indicates true manifold vacuum. The timing at idle is low but when the throttle is opened a little it jumps app 20 degrees. When the knock sensor picks up a knock the timing snaps back down 20 degrees or so until the knock stops (brakes locked up full throttle). According to the OTC Scanner the other sensors are giving reasonable indications but there is still a flat spot in the acceleration when going down the street. The timing is now set at approximately 20 degrees advanced with the timing connector disconnected. Before the failure the MAP would give a true manifold vacuum indication. I don't know how the timing performed, is it supposed to snap on and off like that instead of tracking the engines RPM. HELP