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Injector Latency Testing and Calculation (Open Time or Dead Time)
This method for determining injector latency compares two sets of pulse width values from two running conditions. The contrast between the two conditions is the number of injections, per injector, per-cycle. If we adjust the running in each condition to the same AFR/Lambda at the same load and RPM, the total fuel flow is assumed to also be the same, and the difference between the values of the two conditions is the effective injector latency.
Set Speeduino to the number of injections, per-injector, per-cycle, to the cylinder count; e.g., 4-cylinder = 4, etc. Select 2 per-cycle if your system is limited to that. Speeduino cannot be in sequential mode for this testing unless your code version allows multiple injections-per-cycle in sequential mode.
Bring the engine up to temperature and allow to stabilize, including voltage. In neutral gear, hold engine speed at a specific target rpm (e.g., 2500 RPM), with EGO (AFR/Lambda) corrections ON. Using a throttle stop, clamp, or wedge may be helpful to hold target RPM steady. As the AFR will slowly waver, the corrections should vary back and forth across zero correction. If necessary, temporarily tune the VE Table cells you are testing in close to the AFR target, so the corrections are smooth and relatively slow. Log stable running at the fixed rpm for several zero-crossings. Review the log and note the injector pulse-width at zero correction as "PWa".
Repeat with minimum injections-per cycle, which is usually "1, simultaneous" or "2, alternating". Again read the pulse width when the O2 correction crosses zero, recording this time as PWb. !! DO NOT DRIVE WITH THESE SETTINGS. RETURN TO YOUR ORIGINAL TUNE SETTINGS BEFORE LOADING THE ENGINE !!
Calculation to separate the known correct fuel flow from the unknown latency (open or dead time):
(#a * PWa) - (#b * PWb) / (#a - #b) = Latency
#: Number of injections (per injector, per-cycle)
PW: Pulse Width (at zero crossing)
Example using a 6-cylinder engine and system code limited to 1 or 2 injections per-cycle:
Test "a": Set-up Speeduino for 2 injections per-cycle simultaneous (2 per-injector per-cycle). Run, fully warmed, at fixed 2500 rpm while logging. On log review, when the EGO correction to the target AFR is zero, the PW is 1.6ms.
Test "b": Speeduino is reconfigured to 2 injections per-cycle alternating (1 per-injector per-cycle), and run under the exact same conditions. On log review, the PW at zero correction was 2.3ms.
(2*1.6) - (1*2.3) / 1 = 0.9 ms
Notes: 1) Most injectors exhibit non-linear (odd) latency time at very small pulse widths. Engines with very large injectors may require loading the engine at a steady load and RPM in order to bring the injectors into the linear operating region.
2) MegaLogViewer (free or registered) is suggested for reviewing logs and test results easily and accurately, and with greater safety when not running or driving the vehicle. Registered versions of TunerStudio are able to review logs.
3) If your system is not capable of switching injection modes, simple change of injections-per cycle works well also, e.g., testing at 2-squirts and then at 4-squirts per-cycle. Remember, the point is to make two (or more) tests with exactly the same conditions, except for number of injections per-cycle, revealing differences caused by incorrect latency across a different number of injections.
4) After completion, the comparative test may be repeated with a loaded electrical system (reading lower voltage), finding the first value of the injector voltage correction table.
Its a ceramic heater, its unlikely to have burnt out, it most likely cracked, its usually caused by bringing the power up too fast when cold or while condensation is present. There its also an issue with some LSU4.2 controllers that copied the schematic from a leaked preliminary datasheet. Its worth investigating the problem or it could get expensive.
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