ECM won't advance timing like it should

[dlivewyer]

'94 c1500 with a new 355 blueprint engine. I used the original TBI with 80 lbs injectors, vortec fuel pump and FPR, with a custom tune. It runs good, but it's not advancing the timing like it should. With a scanner hooked up, it shows 10 degrees of timing at idle and when the motor is raced up, it will advance the timing to about 22-23 degrees. BUT, when you put it in gear with a load on it, it drops timing to 0 degrees and will not advance it when accelerated. It has a new distributor, knock sensor, MAP sensor, and temp sensors. Does anyone have a clue what could be causing this thing not to advance the timing with a load? Thanks.

 

[Schurkey]

What is the scan tool showing for knock sensor activity?

WHO did the "custom tune", and what are they saying about lack of spark advance?

 

[dlivewyer]

What is the scan tool showing for knock sensor activity?

WHO did the "custom tune", and what are they saying about lack of spark advance?

No knock sensor activity. Randy @ Prevat performance in Tulsa did the tune and he is stumped. He said he worked on it all day trying different stuff and could not find any reason for it to be pulling timing. He thought it was something in the distributor or ICM. My mechanic has replaced the distributor and ICM and checked wiring and is now going to try a different ECM. He is very knowledgeable and has a lot of time trying to diagnose this thing and believes the only thing it could be now is the ECM.

 

[PlayingWithTBI]

He is very knowledgeable and has a lot of time trying to diagnose this thing and believes the only thing it could be now is the ECM.

And make sure the EPROM (chip) is seated properly with no bent prongs.

 

[L31MaxExpress]

'94 c1500 with a new 355 blueprint engine. I used the original TBI with 80 lbs injectors, vortec fuel pump and FPR, with a custom tune. It runs good, but it's not advancing the timing like it should. With a scanner hooked up, it shows 10 degrees of timing at idle and when the motor is raced up, it will advance the timing to about 22-23 degrees. BUT, when you put it in gear with a load on it, it drops timing to 0 degrees and will not advance it when accelerated. It has a new distributor, knock sensor, MAP sensor, and temp sensors. Does anyone have a clue what could be causing this thing not to advance the timing with a load? Thanks.

The timing table in the chip. If the idle vacuum is lower than stock, it will fall into an area in the timing lookup table that is much lower than the normal idle area. TBI advance curve is a solid 10* less than Vortec heads require under load. TBI timing map is actually up to 4-6* negative in places.

 

[dlivewyer]

I think I'm just gonna get rid of this TBI set up and convert it to a carb and vacuum advance distributor and be done with it. I've spent a lot of money trying to get it to work and I'm sick of messing with it. I should have just done this to begin with.