Injector dead time relative to injector health?

Specifications, applications, part numbers, and prices for various OEM fuel injection components.

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ScottRS
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Injector dead time relative to injector health?

Post by ScottRS »

I have a set of older injectors (probably 15-20 years old) that I am using, and was just checking for dead time to get my tuning dialed in. Following the Microsquirt help info, dead time for high-Z (mine are 14 ohm OEM Ford 24lb injectors, as found in Mustang Cobras, 460 trucks, and a number of other applications) was suggested as 0.9ms.
My testing of them points to a dead time of about 2.2ms.
I set my injector dead time to 2.2ms, and the idle and engine behavior improved noticeably over the starter 0.9ms setting I had before.
My curiosity on this is, is this normal? I'm seeing spec sheets for new Accel injectors that look to claim 0.6-0.8ms dead time for the same size injectors as I have, one would hope higher quality than what I have (at least newer anyway), so less dead time maybe?
And the real bottom-line question in my mind: does this long of dead time mean my injectors are nearing end of usable service life? Or is it more a matter of "check again in a year and see if it's changed" and reevaluate then?
Scott's Megasquirt adventure V2.0: It's a Jeep! Sort of. It's just a tube car that pretends to be a Jeep, hiding an MS3ProEvo, Ford 351W, two HX40 turbos, 42lb injectors, the kind of goodies my KOH car wishes it could've had back in the day.
slow_hemi6
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Re: Injector dead time relative to injector health?

Post by slow_hemi6 »

Modern injectors do seem to open faster than old designs. It would have been interesting to know what the dead time was for your injectors 20 years ago. Then you could gauge any change a bit better. Have you had them cleaned/serviced?
Find the Manuals up top under Quick links: Manuals. :RTFM:
Cheers Luke
ScottRS
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Re: Injector dead time relative to injector health?

Post by ScottRS »

I agree that I'd be interested to know what the dead time was for these same injectors new. I have not had them cleaned/serviced; pro cleaning runs about $200 for all 8, or I can buy reputable brand outright new for under $300. With that level of cost difference, my leaning is that if I'm removing 20-year-old parts, I'd rather replace with new than gamble on the remaining lifespan of the cleaned old parts. If they were only a couple years old, I'd probably be more inclined to try having them cleaned.

I'm definitely thinking this is something that on an individual-engine basis, is worth noting and rechecking periodically; I suppose at some point, the dead time could theoretically increase to where it's no longer possible to cycle the injectors fast enough to keep up with high engine RPM, at which point you'd be forced to replace them or watch performance deteriorate.

On a side note, I'm wondering if dead time creep (if it's even a "thing") is partly responsible for the notoriously surging idles of older EFI Fords. If my thought on it is in line with reality, as the injectors age, dead time increases (due to wear, age, dirt, whatever) and as the dead time increases, the computer's calibration gets increasingly farther off. The AFR is adjusted in real time, closed loop, but it's by narrowband O2, and the dead time is a programmed constant. As the AFR keeps going out of whack because the narrowband keeps telling it to correct, and its correction steps are the wrong size, particularly at the short pulse widths at idle, the AFR then goes out the other direction, tries to recorrect back, and the idle surges. Ford doesn't have a means in the OEM hardware to adjust for dead time (that I know of) so the "fix" is usually to get the hardware back in sync (new injectors with dead time close to original) rather than tuning around it. The problem I have with this theory, is GM used the same Bosch injectors in many of their TPI engines, but their injection systems don't typically suffer the same surging idle problems that Fords typically do. I know GM used stepper IAC's and Ford PWM's (not to mention speed density vs. mass air strategies) in those years, so a lot more to the dynamic than just injectors.
Scott's Megasquirt adventure V2.0: It's a Jeep! Sort of. It's just a tube car that pretends to be a Jeep, hiding an MS3ProEvo, Ford 351W, two HX40 turbos, 42lb injectors, the kind of goodies my KOH car wishes it could've had back in the day.
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