Welcome to CPGNation.com! Log in or Sign up to interact with the CPGNation community.

Throttle body harness

Discussion in 'FAST Support Forum' started by J.K., Jun 30, 2018.

  1. J.K.

    J.K. Member

    Joined:
    Aug 7, 2016
    I've had my share of electrical gremlins since installing my efi system. Even though my cars electrical was all sound, it was sound to period correct standards. Which obviously isn't good enough for these sensitive systems in today's efi's. I have moved wires, shielded wires, cleaned up grounds and added grounds and what not over the time I've been running this efi. In all my car runs quite decent now, but still seems like something's not quite there yet.

    Other than going to a sportsman ECU, there's just one area of electrical that's nagging at me a bit. Anyone have any thoughts on the proximity of the throttlebody harness to the distributor on a sbc? I tried to keep the harness away from the distributor as much as possible, but there's only so much one can do. It is my understanding that delicate low voltage sensors are quite sensitive to noise, and there must be a ton of noise inside that distributor cap. Am I just over thinking it, or is there any benefit to shielding the whole throttle body harness?
     
  2. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    The TBI harness does need to be away from the distributor. You should route it across the valve cover away from the distributor. It shouldn't need shielding in this position.
     
  3. J.K.

    J.K. Member

    Joined:
    Aug 7, 2016
    A A, how are your primary and secondary blades set up? According to the manual they should be set up as close to 1:1 as possible. I have tried it like that and seemed to work ok till it had time to learn. I find the low speed drivability to be better with a progressive linkage set up. I checked the other day and my current set up begins opening the secondary blades at 7% tps.
     
  4. J.K.

    J.K. Member

    Joined:
    Aug 7, 2016
    I assume the 2.0 throttlebody only runs four injectors until all 8 are in demand. Does anyone know what determines the last four injectors to come online. Does that go based on tps %?
     
  5. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    They all fire bank to bank.
    Both of mine came from the factory the same as yours are set - with the secondary not opening until after the primaries have partly opened.
     
  6. J.K.

    J.K. Member

    Joined:
    Aug 7, 2016
    Also for other electrical interference possibilities, I have my ecu power and ground to battery. Msd power to alternator and ground to block. There is a stretch where both these power wires are running alongside each other in separate looms. Is it an issue for these power wires to be next to eachother even though connected to power at separate locations?
    How about the electric fan leads. I have the power wire for the fans connected at the same battery terminal as the ecu, as well as the power for the nitrous relay solenoid feeds. Although I haven't really used the nitrous in a long time, so that one really isn't a concern for the current tuning issues. Possibly the fans though?
     
  7. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    I would get the +12 power for the fans coming from a connection point away from the battery terminal. Fans will create interference. The fans should also have a good chassis/engine ground. You want to avoid direct connections to the ECU direct +12 battery terminal connection.

    Power wires have magnetic fields that can induce interference. Cables crossing at an angle should be no problem, but any length of MSD power cables running parallel to ECU cabling could be causing an issue. Move the MSD wiring away from any ECU wiring. You could power the MSD from the starter solenoid, or a power block coming from it on the firewall, if that helps the wire routing.
     
  8. J.K.

    J.K. Member

    Joined:
    Aug 7, 2016
    Another thing I'm wondering is what an expected fuel pressure should be at idle. It's another thing that doesn't really make sense to me. I would think at an idle the engine needs the least amount of fuel. Increasing demand as engine speeds up. However due to low vacume at idle, and vacume increasing with moderate engine load it would appear it does the opposite. It takes more fuel out at a cruise than it does at idle.

    I get about 39psi at an idle right now and one thing I noticed is the engine has a hard time achieving target idle afr. Always tends to want to be a couple points richer than target. During brief moments that it does hit target I also notice the idle pressure momentarily dropping to 38 psi. So got me thinking maybe its having issues running on the richer side because of too much idle fuel pressure?

    I recently messed with idle timing, I increased it from 18 to 25. It seems to really like that. Less off idle lean outs, more responsive, and even lowered my map to 59-60 at 800rpm. Same rpm I was doing 62-65 on the map with 18. I dont own a vacume guage but my understanding is a lower map equals higher vacume. Interestingly it had zero effect on lowering the idle fuel pressure. Still hangs around 39 psi.

    Just curious if that's a fairly normal pressure or is my vacume reference not functioning properly.
     
  9. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    The engine is under less load at steady cruise speeds and light presses of the throttle. Fuel pressure increases with a quick press of the throttle from idle and can be seen raising correspondingly on the handheld. That's what the vacuum line on the regulator is all about.

    Just keep the fuel pressure adjusted the way FAST states in the instructions. If the O2 reading is showing points away from zero at idle with a fully warmed engine out of gear, you need to adjust the idle F/A until the O2 reads zero at idle. Steady throttle at cruise RPM can be set the same way out of gear. WOT should be 12.6. If the WOT isn't fat enough at 12.6, drop it to 12.5.

    Try using 10 degrees of vacuum timing at 45% load with 22 degrees initial and mechanical all-in set to 32 @ 4000-4200.

    After these settings have mapped, you can make further adjustments to the accel fuel, cold start, and cranking fuel as needed.
     
    Last edited: Jul 15, 2018
  10. J.K.

    J.K. Member

    Joined:
    Aug 7, 2016
    Thanks AA. Another thing is my IAC. When it's set in the green box (I set it so it's around 15 on the handheld), simply revving the engine up once or taking a drive...it always settles on 5 and the idle hangs 100 rpm higher for a bit. If I reset it back in the green, then just turning the car off and restarting it puts the IAC idling in the 25-45 range. But a quick rev puts it back to pegged out at 5. What am I missing with this inconsistent setting?
     
  11. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    IAC only remains steady at warmed idle out of gear. The ECU sets the idle higher at start and decel to help prevent stumble or dying.
     
  12. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    Lower your idle to at least 750.
     

Share This Page