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Thread: Tune runs too lean in closed loop and changes in different weather

  1. #1
    Fuel Injected!
    Join Date
    Nov 2016
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    34

    Tune runs too lean in closed loop and changes in different weather

    I'm trying to get my '90 C4 corvette to run correctly. I've been having to drive it in open loop set for 27lb injectors lying to the ecu because it's really running 32lb injectors. I did that because for some reason I had to max out the VE tables to get the AFR's close to being right when I had tunerproRT set to 32lb. Telling it 27lb injectors adds more fuel to all the maps everywhere and so allowed me to lower the cell numbers while still getting goof AFR's. I think the issue with that is the ECU now removes too much fuel in closed loop because it thinks it's running 27lb injectors.

    So today I started it up and it runs about 13.5 AFR as it warms up and I had closed loop turned off as I always have to run it that way. If I try to let closed loop operate the engine runs so lean it is un-drivable. I tried setting the ECU back to 32lb and raising the cell values but had no luck still lean. So next I tried an experiment, I set it to the factory Bin with 22lb injectors and VE maps, in open loop it was very rich 10's as expected. However in closed loop still 17's or leaner! What's going on?


    I also suspect changes in weather are messing up my tune. Last night I had to remove -4 from the 80-100 kpa cells to lean them out
    to achieve 13.0 AFR at wot. But today during the heat of the day the whole map was too lean once the car was warmed up in open loop. I need better consistency. Is there an air temp map or something to adjust for air temps in tunerproRT? If so will that take effect in open loop? I'm using the $8D mask.

  2. #2
    Fuel Injected!
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    30
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    I am by no means an expert HOWEVER I do have a 1990 Corvette I am working on that had some of the same issues. I am in the process right now of tuning it as well so we may be able to help each other. Here is what I have learned so far about my car.

    To start, the car started as my fathers. Hes still actually the owner however its been sitting for 2 years after he became frustrated when he couldn't get it to run. I have a C6 Corvette with H/C/Supercharger that I am working with HpTuners on. I recently started messing around with the 1990 because the car is beautiful and its never going to go back on the road unless I finish it. I has the same issue with the injectors. The injectors HE purchased were 24lb injectors. What I didn't know was that he purchased them from Ebay. I couldn't get the car to run at all using 24 as my value. After months of reading I found a complaint online about the seller of the injectors he purchased. This other customer had them flow tested and they flowed at around 18.99lb/hr. Input that value, and I was in business. Car started and ran... and was ready to be tuned. First thing I would do is verify the injectors. The second thing I would do is verify the fuel pressure. The TPIS miniram he installed on the car has a fuel pressure adjustment screw. Although the fuel pressure was in spec I do remember him messing with the screw blindly. As luck would have it fuel pressure was OK, but if it was too high or too low... well, the car isn't going to run with the values that are input. All injectors are rated at a certain fuel pressure. If you look up the injectors you can find the values. BTW... 18.99 lbs isn't enough for a 305... but dad's frustrated so I tuned it so he could lightly drive it around town... but at WOT i'm getting 15.0 and big doses of healthly knock LOL. Also, I know a lot of guys tuning with widebands in open loop. It does work, no disputing it, but you'll get better fuel economy out of a carburetor. Its best to leave the car in closed loop, fully warm and tune using your narrowband. The narrowband is going to help you take advantage of the fine tuning ability of the type of sensor it uses, which a wideband can't really accurately do. Also, Are you running long tube headers??? If so... you will need to swap to a heated O2 sensor. Our stock sensor is not heated and again, I found out the hard way... you can't get an accurate read.

    I hope some of this helps you. I am no expert; I'm in the process of learning just like you. This site is amazing and so far everyone on here is exceptionally nice! Please keep posting your tactics and results as I am doing the same car and we can learn from each other. Also take the time and read as much as you can on here. Lots of good information I haven't been able to find anywhere else.

    Dan
    Last edited by Danspeed1; 1 Week Ago at 05:05 PM.

  3. #3
    Fuel Injected!
    Join Date
    Nov 2016
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    34
    I can tell you're new to this. You don't want to tune in closed loop. You'll end up fighting it. the ECU will flip between closed loop and open loop. Turn closed loop off under scalars 'closed loop enable min, temp'. Adjust it to the max so it never comes on. Don't use a narrowband for tuning either. It's meant to keep the car stoich and won't give you an accurate reading for wot or to tell you how far out from stoich it is if the tune is off. That's what widebands are for.

    I didn't get my injectors from ebay, they were supposedly tested and flow matched and they seem to be right or they wouldn't have supported the power my engine is making. My fuel pressure is fine, I have a gauge on the regulator. I do have long tube headers but I seriously doubt I need a heated O2, those headers get very hot. However I do suspect that O2 is bad from being old and this running lean condition in closed loop is probably what wrecked the engine before it was rebuilt. I happen to have a narrowband wire built into my wideband that I can use to send the sinal to the ecu instead of the oem O2. That's the next thing to try.

  4. #4
    Fuel Injected!
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    I don't know,... my BLM's are all between 127-129 and the car runs smooth. I've only used a wide band for WOT tuning, but hey.... I'm new to this so... I can only offer my experiences and what I have posted are my experiences so far. I am surprised you don't agree with the heated 02 sensor... seems to be posted just about everywhere....

    Good luck

    Dan

  5. #5
    Fuel Injected!
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    That reminds me. Where am I able to view the BLM's?

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