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Thread: Help 1990 Vette closed loop tuning

  1. #1
    Fuel Injected!
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    Nov 2016
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    Help 1990 Vette closed loop tuning

    I've got my 90 vette built 350 engine six speed manual running great in open loop only and typically only drive like that because closed loop pulls so much fuel it is beyond the scope of my wideband and pops and drives terrible. The narrow band voltage bounces around so fast from 0-800mv I can hardly read it! Is it supposed to be like that? It's always been that way and i've tried the old stock sensor (single wire) and new replacement and then a new three wire sensor, no change always crazy fast voltage reading and car still goes too lean. No matter what I do it seems nothing makes a difference it just keeps pulling fuel even though it's already too lean according to my trusted and proven wideband if I have closed loop turned on and it stays in closed loop even if I max out the min temp again until I turn the car off and back on again. Just messing around in the garage tonight I decided to test it and make some minor changes one at a time to a few closed loop parameters but no dice. It would be helpful if they were explained in plain English. The INT went down to 108 and the BLM started to follow it but I had to stop because it was going too lean beyond 16:1. Normally it runs 13.5:1 in open loop. The only other annoying issue I have is a random DFCO it almost never cuts fuel for engine breaking like a normal car, It's just kinda random. I'm using the $8D mask by the way.

  2. #2
    LT1 specialist steveo's Avatar
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    Quote Originally Posted by Turbo Nasty View Post
    The narrow band voltage bounces around so fast from 0-800mv I can hardly read it! Is it supposed to be like that? It's always been that way and i've tried the old stock sensor (single wire) and new replacement and then a new three wire sensor, no change always crazy fast voltage reading and car still goes too lean.
    no idea why it's going lean.. but.. it's supposed to quickly 'switch' back and forth from 'lean' to 'rich'. that's how narrowbands work. if it's not doing that, you have a problem. although i'd like to see 0mv to 900+mv, 800mv peak is a bit low

  3. #3
    Administrator
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    You might start with a couple of simple tests. 1) ensure O2 voltage on DVOM matches O2 voltage displayed on scanner. 2) Force the O2 voltage lean in CL and see if the ecm adds fuel. These two tests ensure that tuning time is not wasted due to another issue.

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