I'm new to tuning so I thought I'd put this in the Getting Started forum. I have a '10 LS3 crate motor in a '67 GTO.
I'm getting high fuel trim numbers (turning on the lamp), a slightly rough idle and exhaust popping on deceleration. Could somebody point me in the right direction as to things to look at? My tune is attached along with a 45 sec. log file (car idling, warmed up). It's a Speartech tune, that was tweaked at a local dyno tuner. E38 ecu.
I am new to this too, but after messing with HP Tuners for a few months I have reached the conclusion that if you really want your car to be tuned, you have to do it yourself. That is, you tweak, log, tweak, log, etc. In order to do that, I think you probably need to have a wideband O2 sensor so that you can see what is really going on.
I honestly didn't think fuel trims that high were even possible, but if that is an accurate reflection of what is going on, I think it means that your calibration is way too lean and the fuel trims are having to compensate a lot for it. I have an E67 with a GMPP tune so it is MAF only, but I think yours is VE plus MAF. If that is true, I think both have to be calibrated, ideally using a wideband.
I thought of something you might try that you wouldn't need a wideband for. I have attached the config file I have been using. I have set up histograms (#3 and #8) that will plot LTFT's (#3) and total FT's (#8) v. MAF cells that correspond to the MAF Hz. table in VCM Editor (and throttle position on the y axis, just for additional info).
You could log and see in the histogram display which MAF cells have high (positive) fuel trims. Those cells are "lean". Then go to your MAF calibration table in Editor and increase the airflow numbers correspondingly. For example, if the 4200 Hz cell in your datalog shows 20% fuel trim, multiply whatever number is in the 4200 cell by 1.2, and then do another log and see if it helps.
The thing is, all I know is the MAF side of things--you probably also have a VE table that needs fixing, and I don't know anything about how to do that, but I think the concept is similar.
Thanks. I ordered a wideband - seemed like a worthy investment for the shop. Can this type of tuning be done on the road? Don't really want to pay for dyno time.
I think if you are tuning for maximum WOT power, you probably need a dyno, but for everything else, which is the vast majority of it, you can do it on the street.
I just thought I'd run through the instructions - it says to copy the High Octane Spark Table over to the Low Octane Spark table to get it into SD. Well, I opened both and they're identical already?
Wow, I just found a vacuum leak. Trims are back to normal. I'm still interested in fine tuning though and your config file will help. One thing though is the #8 histogram isn't working. Should I have something set differently in my table?
Glad you found the vacuum leak. That makes sense, and it shows you that it probably was in fact really lean, hence the high fuel trims.
I haven't read Banish's book, but it seems popular so it must be pretty good.
A couple of your statements above don't make sense to me... I am no expert, but this is my understanding of it:
The purpose of tuning the MAF is to calibrate it such that the MAF output frequency to the ECM is an "accurate" reflection of the intake airflow. You can accomplish this by logging AFR with a wideband 02 sensor OR by using fuel trims, but with the latter you cannot calibrate WOT operation. It isn't a matter of tuning the MAF or the trims--rather you use the trims to tune the MAF.
I believe that tuning VE is done in much the same way, but instead of MAF signal, you are looking at the MAP sensor output instead (not too sure as I haven't done this).
I think that SD mode means that your MAF is "disabled" and the engine is operating exclusively off of the VE calibration. I wouldn't think that changing your spark tables would have any effect on which mode (SD or MAF) you are running in.
I think that the low octane table comes into play only when your knock sensor detects knock beyond some pre-set threshold. Otherwise you are running in the high octane table. From what I have read, it is best to not mess with your spark timing until you get your A/F issues worked out.
All of the parameters in the histogram must also be in table view, and they need to be "valid" parameters. This is just a guess, but I am thinking that you have a different operating system and things won't be identical--so most likely you will have to tweak it some to get it to work. For one thing, with an E38 do you have a cable operated throttle? If so, that could be the problem because I have the electronic throttle control position on the y axis. Maybe you could try eliminating that axis from the histogram and see if it works.
Last edited by daniel76309; 09-25-2013 at 01:51 PM.
Forget they dyno until you get your MAF and VE tables tuned. You tune each independently of the other in Open Loop (O2's disabled and Fuel Trims disabled) using Wideband O2 sensor. I highly recommend one of these. to properly dial in your MAF and VE tables.
Your VE tables are dialed in by comparing calculated airflow to measured / true airflow (Wideband O2) at each MAP sensor reading and RPM range.
Your MAF is tuned by disabling VE table lookup in Open Loop and comparing measured / ture airflow against Hz reading on MAF. You adjust by % the difference.
ONLY after you get these tuned do you need to visit a dyno. The dyno is there to tune WOT and figure out what Spark Timing and AFR your car makes most power at. Spend your time there with your VCM controls and set a spark timing of say 22 to be safe and try AFR settings in different increments 11.5, 11.8, 12.1, 12.5, etc. Once you find out where you make the most power with AFR, then keep AFR the same and work on timing. Hope this gets you going in the right direction.
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