3.2L injector impedance

[70SWT]

I know this has been visited all over the place, e.g.:

Fuel Injector - Low or High impedence in '85 3.2?

alternative fuel injectors for 3.2

...however, I need a bit more info from anyone who has experimented with different injectors on a 3.2L car. The situation:

My '88 runs great. I have taken many bolt-on items off the engine to address oil leaks, maintenance and general clean-up. I found that the car came to me with Ford (Bosch) injectors, specifically the following item:

https://www.injectorplanet.com/products/bosch-0280155715

These appear to be high-impedance injectors, whereas most info I see says the car should have low-impedance injectors.

Again, the car runs great at all RPMs with these injectors; a guy running a local Porsche repair shop remarked how strong it runs, and speculated what else has been done by POs to the car.

So, might high-impedance injectors simply be OK with a stock 3.2?

Or, I wonder what DME (or hidden engine) mods the PO might have done in which his tuning efforts led to using those injectors (he is not available to contact, so I cannot verify!)

If DME changes that relate to the injectors appear possible, what should I look for? Have certain chips been found to work better with different injectors? I see that MS likes high-impedance, but this car (presumably) has the stock DME.

The car has a number of other (awesome) mods, including 930 brakes, suspension upgrades and more. So since I see a long, grey cable coming out of the DME and connected to nothing, I would not be surprised if I have some kind of chip or other DME mods. I wonder what is going on inside that box...

[ischmitz]

Sal is the most knowledgeable guy here when it comes to alternative fuel injectors for the 3.2. He can probably tell you how well these would work in an otherwise stock 3.2 DME. To really know what if anything has been done to the DME you'd have to open it and read the EPROM and compare it to a stock EPROM.

Historically, at the time when these DME systems were designed low-impedance injectors had more desirable characteristics compared to their high-impedance counterparts. Their dynamic range (smallest reliable amount of fuel per pulse/largest flow rate) was just better and that's why they were chosen for high-end applications. In addition the 3.2 DME drives all six injectors in parallel and this presented some unique challenges to the driver electronics. The DC resistance of all six injectors is sub 1 Ohm and there is a significant amount of energy flowing back into the DME when the injectors are turned off. All this has to be handled and resulted in a fairly complex injector stage.

In general changes to the DME can be one grouped into one or the other:

- simple map changes in the 2D and 3D fueling maps (that what most do)
- changes to the injector calibration curve and code changes to how the fuel duration is calculated (here is where Sal is the man)

Most "tuners" only change map entries to richen or lean out areas in the fuel maps to accommodate different VE at certain load/RPM areas due to modifications of the intake or exhaust. This methods isn't really suitable for accommodating different injectors. Keep in mind that the closed-loop function of the 3.2 DME also affects overall mixture unless your WOT.

The more preferred way would be to change the injector constant and calibration to match the DME to a different type of injector. And once you change the air metering from AFM to MAF the calculation of injector duration has to change. This is what Sal has done for this MAF kit and it seems to work exceptionally well.

Cheers,
Ingo