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Thread: Running very rich on cold start

  1. #1
    Tuner in Training
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    Running very rich on cold start

    Hey guys. I have a 2001 Pontiac Grand Prix GT with a SS M90 supercharger kit. I live up in Canada, and it's freezing cold right now. Whenever I first start my car in the morning, my AFR goes extremely rich (I forget the exact number, but somewhere between 10.5-11.5). I can smell gas as well. I am still new to tuning, so I am not exactly sure what tables to modify to solve this. What should AFR be for a cold start?

    Here is a copy of my tune.

  2. #2
    Do you have a cat? A majority of that extra fuel is to help warm the cat. You'll notice your timing is really low too when you first start it (unless its colder than 0*C or something like that). This is so that the extra fuel burns in the cat, helping it heat up.

    Ideally, and the way I have my car tuned, is you would tune the warmup AFR correction and decay tables in such a way that the AFR hovers around 14.7:1.

    Fuel doesn't condense the same when it's hitting cold surfaces. Therefore, less fuel is actually making it into the cylinders when the engine is cold (for a few seconds, not nearly as long as they make it from the factory), which is why you need to squirt a little extra than stoich (besides the cat of course). It needs more fuel as it gets colder.

    Personally, I would ignore the cat and make warmup leaner and disable warmup spark correction. Best I could find on the net said that it only made it warm up 5 seconds faster. So you're putting out pollution for 5 extra seconds...

    My car warms from 20*F to 180* (operating temp) in just about 3 miles which is pretty crazy I think. So it saves gas mileage too.

  3. #3
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    I don't have a cat. I have headers. So which tables would you recommend changing? Thanks man!

  4. #4
    Awesome, that's good news. So you need to figure out what OSID you have. It's under Calibration Details or something like that. Then, ask someone on CGP for a .bin for that OSID. You'll probably need help with that part since the serial number wont match and HPT will ask you to buy 2 more credits. Just PM me if you get that far and I'll help you out.

    Then, open your .bin with TinyTuner and find the table for "Warmup Spark Correction" or something along those lines. You set the max run time to 0 seconds for the whole table. You don't need all that BS if you don't have cats, it just makes the engine run like poop.

    Then, after saving the file, re-open it with HPT. Copy everything in your tune over to it. The tables that control startup AFR are under "Fuel Control" and are (aptly named) Startup AFR Correction lol.

    The way they work is, the PCM takes the "Base Open Loop AFR" (which you can't see in HPT) for whatever the ECT is and then SUBTRACTS the "Initial vs Startup" adder to it to get your final AFR during startup. So if the OL AFR is like 14:1 at 20* C ECT, and the adder from that table is 2.1, the PCM will command 14-2.1:1 during warmup. IDEALLY, you want the wideband to read 14.7 for any given temp.

    The car is setup from the factory to be extremely rich, so keep that in mind. You can take away quite a bit of fuel. I set my base OL AFR to 14.7:1 for ALL temps and started from there. You only need warmup correction for roughly 10-30 seconds depending on how cold it is. I'm commanding 14.7:1 in this cold 20*F weather within 30 seconds of starting IIRC.

  5. #5
    Senior Tuner Russ K's Avatar
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    Using the beta shows your open loop afr vs coolant temp.

    Make the changes as shown to enable closed loop sooner and at a lower coolant temp.

    But no cat is going to cause a fuel smell, install a high flow cat.

    Russ Kemp

  6. #6
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    answered my own question with a bit of searching, Ive sent a e-mail to Bill "I HOPE"... lol Could not find "support" but I think I sent it to the right place
    Last edited by MMGT1; 12-21-2010 at 07:03 PM.

  7. #7
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    Thanks guys!

  8. #8
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    Hey Russ, does this mean we can now tune non-PE regions of our MAF with a WB in the v-6's having access to the OL commanded AFR?

  9. #9
    Senior Tuner Russ K's Avatar
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    With the open loop tables, you can set the tune to command 14.7 without having to set the PE to 0%.

    Not all V6's have the open loop tables yet.

    Russ Kemp

  10. #10
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    I got the Beta last night and it is available to me. Im going to set up my start up tomorrow morning actually. I can't wait, no "gassy" start up will be nice! I think the start up has killed two sensors on me now cuz this thing has been that rich when I fire it up

  11. #11
    I would tune the car in open loop (if you didn't know that already). Set closed loop enable temp to some unreachable temp and clear the fuel trims. Use the wideband to calibrate teh maf table.

    It's going to take you some time to tune startup, only because it requires a big temperature range and winter only gives you -10 - 30* lol. Only use scans from an engine that has sat overnight as a warm engine will skew the readings. Unless you're doing 100+ as the ambient temp will never be 100* so it will always be attained with some heat in the engine.

    I would set the entire decay table to .015 and your eventual goal is to get the whole open loop base afr table to read 14.7 (while appropriately adjusting the adder tables) but doing so will require scans for some of the ect's as outright setting it to 14.7 might cause it to run lean at startup.

    Let me know if you need any help

  12. #12
    Tuner BlackZJ's Avatar
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    I'm "fighting" against the same problem. My AFR is below 10:1 at startup (PCM commands 8.5:1).
    I can change the base open loop AFR table but it's really annoying that we can not change the spark at startup.

    Does someone have a bin of OS ID: 9352828 ?

    - Mat
    '97 Jeep Grand Cherokee ZJ, 5.2L (Canada Import), 2" Lift
    (CAI, Modded Kegger, Ported TB, 3" Cat-Back, SCT Custom Tune)

    '98 Jeep Grand Cherokee Limited ZG, 5.9 V8, Stock

    '03 Skoda Fabia, 1.4L 16v

    '98 Chevrolet Camaro V6, 3.8L, Targa, ZZP GT1 Cam, Dynomax Cat-Back [sold]

  13. #13
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    HPT.... Guys, thank-you!

    Got the beta and finally had a quick go at my start-up with the new OL tables, WOW!! What a difference, just touch the key and it fires right up, no "spinning over" to get it to fire, and not afraid to "light a smoke" within the first 5 mins of starting it... lol Seriously though, thanks dudes.