View Single Post
GJF GJF is offline
Slantnose from HELL
GJF's Avatar
Join Date: Dec 2004
Posts: 809
Justin the reason you fire big injectors (over 55-60 lbs) in sequential mode is to be able to acheive decent idle AFR's. If you try to fire the injectors in batch (all fire simultaniously) you will not be able to acheive a desired AFR at idle. It will be too rich because the injectors can't be fired low enough not to over fuel the engine in batch. So by setting up the EFI to fire each injector for every spark event (sequential) you will be able to acheive a respectable idle AFR. This is from Electromotive's web site from the TEC GT manual.
High vs. Low Impedance Injectors
The TECgt is equipped with 6 fuel injector channels. These channels are pull-to-ground outputs, meaning that they provide a ground connection for the injectors when they fire.
The injector channels can be configured to run in one of two modes – either 2 amps peak with 0.5 amps hold for one low impedance injector per channel or 4 amps peak with 1 amp hold for a pair of low impedance injectors per channel.
To differentiate between high and low impedance injectors, simply measure the resistance across the two terminals on the injector. If the resistance is around 2.5 ohms, it is a low impedance injector. If the resistance is around 1.2 ohms, it is a throttle body-style injector. If the resistance is above 12 ohms, it is a high impedance injector.
Low resistance injectors are used when the injector is large and finer control of the low opening time is required. Most OEM injectors are smaller and are of the high resistance type.
When selecting your output from the 4/1 or 2/0.5 type you should match the output to your injector configuration. (see Figure D.1. 1 for parallel wiring instructions).
As a rule, always use the 4 amp setting for running injectors in pairs.
Use the 2 amp setting to run injectors individually one per driver.
The one exception to this rule would be the 1.2ohm injectors found in throttle body injection (TBI) setups. These injectors should be wired with only one injector per driver in the 4amp mode.
High impedance injectors can be used in place of low impedance injectors at any time, as a rule, use the same logic to adjust your outputs.
When the injectors are wired such that the circuit will flow more than 5 amps, the TECgt fires them in peak-and-hold mode. When this is happening, the injector current ramps up to approximately 4 amps very quickly, then drops to 1 amp for the remainder of the pulse width. See Figure D.1. 2 for details on peak-and-hold mode.
When an injector circuit is wired so that the circuit will flow less than 2amps, the injectors will be fired in saturation mode. When this happens, the injectors will ramp up to the maximum amperage determined by the circuit (should be less than 2amps), and keep the current at this level for the remainder of the pulse width.
The bottom line here is that the injector channels should never be required to remain turned on (in “hold-mode”) at a level greater than 2 amps. As long as the circuit is capable of flowing more than ~ 5 amps, the TECgt will enter peak-and-hold mode, thus limiting the current output. Care must be taken when using injector circuits that flow less than 5amps, since they will not engage the peak-and-hold mode. As a result, the injector channels will remain on full current for the entire pulse width. Also, if a low impedance injector resistance measures less than 2.2ohms when cold, its resistance may increase when warm, so it should not be used on a one-injector-per-driver basis.
87 911 Carrera platform
Twin Garrett's, Big Valve, Xtreme Cylinder Heads, JB Racing cylinders and machine work, custom JE pistons, GT2 EVO cams, GT3 oil pump, modified 3.2L intake, 80mm TB, custom Intercooler, equal length headers, DFI, KEP Stage 2 custom twin disc, G50 custom gear set, LSD, Tilton trans pump, Fluidyne cooler
Old 11-09-2008, 02:56 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #7 (permalink)