FiTech - Lessons Learned, Mystery "Lean-Spike"

Discussion in 'High Tech Retrofits' started by redriderjf87, Jul 5, 2018.

  1. redriderjf87

    redriderjf87 Veteran Member

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    This is a long-time coming and I'm a bit late in posting my findings, but hopefully this will be of some value if there is anyone else is fighting the dreaded "lean spike to rich bog" issue at low RPM's on tip-in. Below is my eventual root cause fix, in addition to new RPM-specific accel pump adjustment from the newest T198 software rev.

    I should note that although I found a lot of helpful FiTech info on here and the Chevelles forum, I hadn't seen this specific fix mentioned (nor in FiTech's documentation). FiTech's only suggestions were "turn up the accelerator pump 30%" and to plumb a fuel line inside the car so I could watch for a pressure drop on tip-in.... (would've been nice if, ya know, there was a way to read this pressure to the computer)

    My Setup: Naturally aspirated SBC, GoEFI 600 TBI, Tanks Inc in-tank pump with Walboro 255 LPH pump connected to the orange harness wire.


    The Fix: Adjusting PWM threshold RPM

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    Under the PWM fuel pump control in Pro-tuning settings on the handheld, I had to turn down the threshold RPM for the internal relay to turn on the pump 100%. Default setting was 2500 RPM, I had to change it to 1500. In my understanding, this setting should've been covered redundantly in the fact that FiTech does recommend disabling the PWM in my scenario, by setting the low/mid/high flow PWM values to 100%.


    Honorable Mention: RPM-specific accel pump adjustment

    I mention this because it did help band-aid the lean spike only at lower RPM's, and the default values were set much lower at low RPM's than higher rev's. Again I did not really see this documented anywhere but this gives a lot more flexibility than just kicking up the general accel pump and fast accel. Right now mine are set too high, now that I found the PWM issue I'm dialing them back. That being said, we'll see where the sweet spot is for my car at low RPM's, and how that compares to the default values (which were about 40 instead of the ~240 they are now). Getting this setting in the handheld requires a firmware update to the T198 or newer software, which you normally have to request from FiTech, or can access from the Pro-Cal software.

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  2. Ihada70Z28B4

    Ihada70Z28B4 Veteran Member

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    Thanks,I will bookmark this in case I run into this problem. For the fuel pressure monitoring.. I'm going to try and tap the fuel inlet plug on the front for a schrader and see how that goes. I'm surprised they actually recommended plumbing pressurized fuel into the cockpit, wtf? On the Buicks we'd just temporarily duct tape a gauge to the windshield base outside the car and test.
     
  3. redriderjf87

    redriderjf87 Veteran Member

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    Gotcha, yeah I couldn't believe he suggested it either. I tried to bust them a little for not having a pressure sensor to read it but oh well. I was trying to think of a creative way to mount a go-pro with a light in there to watch my inline gauge i put right before the TB, but thankfully better judgement kicked in and it didn't end up being my issue.
     
  4. hoppin5478

    hoppin5478 Veteran Member Lifetime Gold Member

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    I run a pressure sensor on my fuel line and data log it along with a whole bunch of other information and it makes trouble shooting way easier. I'm sure there is a pretty inexpensive way to set up an electronic gauge so your not trying to read a mechanical one under the hood. The pressure transducer's I use are less than 20$ bucks at Amazon and have been very reliable. I'm sure for under $50 you could probably put something together.
     
  5. redriderjf87

    redriderjf87 Veteran Member

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    Gotcha thanks I hadn't thought about that, I may try hooking one up. At this point I'm just glad it seems to be working correctly. Still kind of sour at FiTech for not adding it to begin with haha.
     
  6. redriderjf87

    redriderjf87 Veteran Member

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    Sorry I know I'm updating an old thread, but I wanted to add the actual "fix".

    From my previous post,fiddling with settings I could kind of get the tip-in fuel better, but would still always lean out, worse on quick tip-in, and/or at lower RPM's. Contrary to FiTech's techs, no amount of accel pump enrichment would change this, other than making it richer after the fact. They didn't seem to have any other ideas, outside of low fuel pressure (which I proved was ok w/ transducer) and then stopped answering my emails.

    After beating my head against the wall, I stumbled upon a thread mentioning slack in the secondaries linkage, specifically in the threaded rod connecting to the primaries. Mine did in fact have a good amount of play at idle (not on the sec's stopper either), and to the point of being noticeably not straight up at WOT.

    I took a couple turns out of the rod so that there was 0 play off of the primaries from fully closed, and now it actually works. For the first time I can step into it at-will, and the motor never goes lean (per datalog). Now I just have to slowly dial out my maxed out accel pump settings to not go rich.

    I also documented this at the original thread on the FiTech EFI Tuning Forum if I'm allowed to link there ( https://fitechefituning.com/fitech-efi-tuning-forum-2/topic/secondary-adjustment/?part=2#postid-4646 ), which had some other useful/relevant info on the secondaries adjustment.

    If you have any weird issues, I highly recommend checking out the linkage. Mine shouldn't have gotten shipped out like it was, and I feel like it should at least be on their basic troubleshooting instructions to have people check.


    Also, for the fuel pressure monitoring, I bought a 0-5V transducer from Amazon and I verified my pressure reading into an Arduino M5Stack unit. Modified an example program to do the math and show it as a gauge. Still working on 3D printing a case and mounting it under the radio most likely. I had a noise issue to work out when the unit was getting powered via usb, but otherwise does the job.
     
    Last edited: Dec 29, 2019
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