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EZ EFI 2.0 Throttle Body System Vehicle #2 - An '81 GMC

Discussion in 'FAST Support Forum' started by A A, Jun 5, 2016.

  1. J.K.

    J.K. Member

    Joined:
    Aug 7, 2016
    So I tried 14.4 idle, 14.7 cruise. Bumped up the idle to 900 for the time being. Sounds a bit fast but it keeps the map around 57-60 idling. How does one determine the ideal idle afr? Trying to understand why some efi guys are getting very lean idle afr, some in the 15's....while others tune for the low to mid 13's at idle. That's such a broad range.

    Back with my carb I would get idle about 14.5, but any leaner would cause the motor to die. Best idle afr tended to be in the 13.5 - 13.8 afr. This gave the best off idle tip in quality. Obviously the efi will want to keep itself running, so I find it harder to know where that sweet spot is. It doesn't just stall out like a carb to let me know it's too far.
     
  2. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    Use a vacuum gauge to initially determine idle A/F while tuning the idle (initial) timing adjustment also. You want the highest steady vacuum using both adjustments. The front and rear throttle blades may also need adjustment. While juggling settings, the MAP will lower as vacuum increases. Later, you use the color of the outer half of the inner ceramic firing end and the O2% reading. O2% should settle close to zero at a steady fully warmed idle with the correct idle A/F. Idle A/F tends to be richer at idle due to slower runner speeds there. A camshaft design that also lowers power at idle (performance cam that increases power later in the RPM band) requires more fuel at idle. Most all engines need more fuel at idle to maintain more power at idle.

    With your extreme FI camshaft, you should be getting a MAP of 57-60 or less at 750. Something isn't tuned correctly. Your rear throttle blades may be opened too far at idle - this will prevent proper IAC control and will give a false adjustment correction setting. With everything set correctly, your fuel maps should correct to easily allow a lower idle.

    What you're describing happened to my 406 at idle - during my earlier tuning after changing to a single plane intake. The dual plane intake would never allow an idle below around 900 regardless.

    I had to keep the idle higher until the plug heat range, initial timing, and rear throttle blades were correctly adjusted with the new Vic Jr intake. I also had a third factor that happened during this time - bad fuel from a local gas station near my home. Once I replaced that fuel with fuel from a different station, I was able to quickly correct the plug heat range and adjust all settings for a smooth 750 idle in and out of gear - even as low as 700 without problem. Before that, I was getting all kinds of misleading readings that appeared to be what the engine wanted. If my other vehicles hadn't started running rougher than their usual smooth as silk, I might have overlooked the fuel as an issue. I had been buying most of my fuel from that nearby station for years without problem. I haven't bought fuel there again, and I haven't had any more fuel problems.
     
  3. J.K.

    J.K. Member

    Joined:
    Aug 7, 2016
    It's a bit frustrating that these throttle bodies are shipped incorrectly set up in the first place. Mine came with the secondary linkage rod set up in the top hole of the primary lever, and set loose on the secondary so that it would function just like a Holley double pumper carb would. Me being new to efi, I certainly didn't know better and ran it like that for a while. It was by lots of efi searches on the internet that I just happened to stumble across a proper FAST throttle body linkage set up procedure on a site that had nothing to do with FAST products. Then is when I realized it was set up completely wrong and the secondary was suppose to move the same time the primary moved.
    I have fine tuning to do, but it does run and drive so much better than it did in the beginning. Back then I was ready to chuck it in the scrap. Now it's drivable and pretty decent, just not perfected yet. I still plan once I can afford it I will get the xfi ecu. This way I can go back to my xr294hr cam. The xfi cam I have does the job but I still feel as I made alot more torq in the mid to upper rpm with the other cam. And to me it had a much angrier tone once in it's rpm happy spot than the xfi cam does. Also the xfi cam makes for much noisier valvetrain. My other cam not nearly as noisy.
    In the meantime would you set up idle with both butterflies closed, and both opened equally for proper set up? I think mine are close, but primary probably open slightly more than secondary. My secondary I think was set to just touching the screw, so as to not have the blades bind in the bores.
     
    Last edited: Sep 23, 2017
  4. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    This new cam is correct. You needed it because of your compression ratio - to help control pre-ignition/detonation. It may cause a little more valvettrain noise due to the ramp design, lifters, and engine oil pressure. But, the benefits are far greater using it - including its ability to make more mid range and top end power over your previous cam - with improved idle due to its increased idle vacuum design.

    Engine exhaust tones are very deceiving. Compression, fueling, and timing have a lot to do with this. Some settings can make the engine sound stronger, but the reality is the engine is running ragged and erratic and producing lower torque. With the old cam, you were likely experiencing detonation - and that will give that "angrier" exhaust note,

    I've never seen a FAST throttle body come with the linkage set up wrong from the factory. I have seen the rear blade screw adjustment set incorrectly.The linkage is supposed to be progressive with the 2.0 TBI unit. If yours isn't, you've found the cause of more problems. - as this will not allow the adaptive learning to work properly at building fuel maps. You shouldn't need to fool with the rear throttle blades unless running over 500 cubic inches.

    The secondary linkage should be in the lower of the two holes on the main throttle. The linkage should be "loose", per design. This allows the rear throttle to close using its shaft mounted spring - and keeps the rear throttle closed during part throttle operation until the engine needs and can use the added air from the rear blade actually opening. Not having it set this way also affects engine deceleration operation while driving - further upsetting fuel maps.

    With the linkage correctly adjusted, the main throttle fully opened, the rear blade should be at a slight angle from straight in the rear throttle bore. Too much air from the rear throttle blade at part throttle will cause a stumble, and will not allow the adaptive learning to create proper fuel maps. Easier, the linkage adjustment will have the end of the rod slightly inside the back of the adjuster nut instead of sticking out the back of it
     
    Last edited: Sep 23, 2017
  5. J.K.

    J.K. Member

    Joined:
    Aug 7, 2016
    Interesting, I will have to look at that setting again. I was under the assumption since efi works different than carb, the front and rear blades needed to move the same for a balanced air flow. Maybe I'm misunderstanding the terms "progressive" and "1:1". I will look again at the manual, but I thought I read somewhere in the manual that the front and rear blades needed to be as close to 1:1 as possible.

    I found it in page 63, just a few lines down. It says a 1:1 set up is preferred over progressive. Yet they seem to be all shipped with progressive setting.
     
    Last edited: Sep 23, 2017
  6. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    Yeah, I see that on page 63. Crazy! The design of the throttle parts is for progressive movement not 1:1. All engines cannot accept the rear throttles opening at the same time as the main throttle begins to open - and will stumble. 1:1 basically will defeat much of the ability of the ECU controlled IAC.

    The angle of the rear throttle blades will basically look straight with the main throttle fully open.
     
    Last edited: Sep 23, 2017
  7. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    On one of my 2.0 throttle bodies, the rear throttle blades were sticking slightly open after some backfires once. With the slack the factory designed into the rear setup, I was able to find and correct this with the main throttle closed. Once the rear blades were again closing properly, I re-adjusted the IAC and TPS - restoring perfect running at idle. The problem has never re-occurred.

    As the main throttle opens farther, the setup does transition to more of 1:1, but this is still a progressive setup.
     
    Last edited: Sep 23, 2017
  8. J.K.

    J.K. Member

    Joined:
    Aug 7, 2016
    I'll give it a try. Mine is 1:1 now, runs pretty good though. Don't know till you try right? It may get better yet.
     
  9. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    Be sure to "blip" that rear throttle several times with the main throttle closed. This will let you know if the rear throttle is sticking open.

    Maybe this will allow the ECU build better fuel maps.
     

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