fuel trims?
fuel trims? After a lot of searching. I finally found a vacuum leak in my H/C car. The problem is that my car had been tuned before i found the vacuum leak. I took it to a friend of mine at the dealer after finding the leak and he set all of my fuel trims back to factory default. I was a little worried because I thought that the trims were part of the tuning process. He said that the computer would relearn what it needed. Now my car is running superrich. What's going on? Do I need another tune now?
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From: Denver International Airport, Colorado USA
MD:
Well first off, how are you determining if it is rich? Wideband or subjective?
I am only asking this because the trimming function is designed to keep your idle and part-throttle AFR at ~14.7, so determining if your rich would take either software or a wideband.
Resetting them to 'factory default' is somewhat of a misnomer. I am sure that all that was done was to simply re-set the Trims to zero. That is a very common tuning technique. The normal Trim process is always occurring, so there is nothing 'lost' from your previous tune. In fact the same thing happens if your battery runs down or loses power.
If you are still running closed-loop and your narrowband O2 sensors are in good shape, your Trims will readjust to the previous level in a fairly short amount of time.
If your saying your rich at WOT, that is another matter. Do you have tuning software? Fuel Trims are a pretty simple adjustment and you can learn a lot watching how differing throttle and weather conditions effect them.
Hope this helps.
..WeathermanShawn..
Well first off, how are you determining if it is rich? Wideband or subjective?
I am only asking this because the trimming function is designed to keep your idle and part-throttle AFR at ~14.7, so determining if your rich would take either software or a wideband.
Resetting them to 'factory default' is somewhat of a misnomer. I am sure that all that was done was to simply re-set the Trims to zero. That is a very common tuning technique. The normal Trim process is always occurring, so there is nothing 'lost' from your previous tune. In fact the same thing happens if your battery runs down or loses power.
If you are still running closed-loop and your narrowband O2 sensors are in good shape, your Trims will readjust to the previous level in a fairly short amount of time.
If your saying your rich at WOT, that is another matter. Do you have tuning software? Fuel Trims are a pretty simple adjustment and you can learn a lot watching how differing throttle and weather conditions effect them.
Hope this helps.
..WeathermanShawn..
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Joined: Jul 2008
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From: Columbus Ohio
This unfortunatly is an example of how tuning gets screwed up when the car being tuned isn't right. **** happens, and it sounds like you need to go back to your tuner and have it looked at/fixed.
Think of it like this, if you have a vacuum leak, you'll be getting extra air. When you take the extra air away now it's rich. It will cure itself for the most part when you're just driving it around with the fuel trims, but I'd bet WOT is all screwed up. This really shouldn't be too hard to fix, because once the VE table is brought back in line the rest of the tune should be fine or really close.
Think of it like this, if you have a vacuum leak, you'll be getting extra air. When you take the extra air away now it's rich. It will cure itself for the most part when you're just driving it around with the fuel trims, but I'd bet WOT is all screwed up. This really shouldn't be too hard to fix, because once the VE table is brought back in line the rest of the tune should be fine or really close.
When I say rich, I mean that I can smell fuel at idle when I didn't before. After the the initial cam install and questionable tune, I would get headaches when driving. Then, the tuner changed the A/F ratio and the car smelled right for two years. The tuner recently changed some parameters to try to fix the intermittent bucking. It made no difference. I found that the AIR line was uncapped and the line to the ac/heater vacuum tank was broken(but intermittently sealing). A friend at GM set my fuel trims to zero about 4 hours after I fixed the problem( before I could stop him of course). Now my car is PIG RICH at idle.
