[CBR600RRider]

What would cause my ignition timing to go from 40 when on the gas to -10 when left off?
having some weird issues while freeway driving and trying to track down causes.
Engine came out of a 97' tahoe 5.7L vortec.
thanks!

 

[oldeerslayer]

What year truck is it in and what computer and programming are you using?
The computer will advance and retard the timing as it deems necessary. 40° seems like a lot for a Vortec under load. Even at higher rpms, but with these low compression engines if the PCM thinks it's right I won't argue. Dropping to -10° when you back off makes sense. You need to talk to a tuning guy.
What issues are you having?

 

[CBR600RRider]

What year truck is it in and what computer and programming are you using?
The computer will advance and retard the timing as it deems necessary. 40° seems like a lot for a Vortec under load. Even at higher rpms, but with these low compression engines if the PCM thinks it's right I won't argue. Dropping to -10° when you back off makes sense. You need to talk to a tuning guy.
What issues are you having?

The engine originally came out of a 97' tahoe. I swapped it into a 88 S15.
The PCM from the 97' tahoe was tuned by Blackbear to get some stuff taken off. Specifically the post Cat 02 Sensors and to put their base performance tune on the truck.
When driving on the freeway it handles great at 60+ but as soon as i let off the gas the truck starts to slow down after about 3 seconds and it retards the timing to -10. Truck feels like it almost goes into compression. I can go from 60MPH to 35 before it goes back to +40 ignition timing.

 

[bk2life]

was tuned by Blackbear .... to put their base performance tune on the truck.

Your answer is right there. Contact black bear and ask why it does it. That's why mail order tunes 'suck'. They're made for someone, somewhere, and gets reused for similar vehicles...this doesn't work for every circumstance.

But, i would contact them to see what they have it go negative like that. There could be many different reasons, and, being i do tuning as well, I dont want give my thoughts.

 

[CBR600RRider]

Took them a bit to get back but Blackbear is stating its a deceleration fuel cut off. Not sure what that is to be honest. Going to do some google searching tonight to see if i can bypass what ever is happening.