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Are all Merc. Marauder injectors 24 lb/hr. ? And will these directly swap over to the NPI 4.6 in my '94 bird. ( Minus of course MAF recal. and a tune. )

Thanks, Paul
 

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last i checked all n/a 4V mod motors came with #24 injectors, so yea the marauder most likely has them.

and yes they are a direct swap(although the connector shape might be different for the newer injectors)
 

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you do not need to touch the MAF transfer function when you swap injectors....only the injector data needs to be changed

yea the marauder injectors are 24 #/hr.....im currently running them....you'll have to get the connector from a newer style harness (doesnt have to be specifically from a Marauder, im sure other vehicles run the newer, thinner EV6 type injector as well)......and you also definitely want to solder the connectors onto your car's injector wires....last thing you need is to drop an injector or two in the middle of stop-n-go traffic
 

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Discussion Starter #4
What do you mean by change injector data? I thought your MAF needs to be recalibrated for bigger injectors.
 

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that is one of the most common misconceptions in modern electronic fuel injection by enthusiasts

the MAF does not directly open the injectors in any way, shape, or form......it is not a processing unit.......it influences the injectors indirectly...........it only gives an airflow reading to the EEC....with this, the EEC figures out how much fuel mass is needed to attain the target air/fuel ratio......fuel mass injected is not just proportional to the 'pulsewidth' (time commanded to be open), because short enough pulsewidths (usually < 1 ms) seemingly make the injector behave larger than it actually is, due to the sudden release of fuel from the high pressure fuel rail and overshoot of the pintle when it moves off its seat.....larger pulsewidths do, however, have the injector flowing at its normal rate because that split second opening when the injector flows more-than-usual constitutes a lower percentage of the total time the injector is actually opened

this relationship between fuel mass and commanded pulsewidth is setup with the low-slope, breakpoint, and high-slope rating of the injectors.....as you can hopefully tell, the breakpoint sets the cutoff point between which the injector is in low-slope mode (higher flow-rating), or in high-slope mode (lower, actual flow rating)

there are other things that affect injector behavior such as minimum pulsewidth, injector offset, voltage compensation, etc....but that was just a quick run-down of how things work in the EEC in your car.....ALL of these things need to be changed when you change injectors.....and just as importantly the MAF signal needs to reflect reality.......if you change the MAF signal to 'show' less air coming in so as to try to trick the EEC to open larger injectors for a shorter time period, it throws off the Engine Load calculation........engine load depends directly on knowing how much air mass is flowing into the engine and the RPMs to determine what percentage of the cylinder is getting filled......this is important because there are tons and tons of functions and tables within the EEC that use the engine load value and work behind the scenes to give your car the smooth seemless operation it has without you ever knowing it
 

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On my Mach 1 swap I'm using the Mach 24lb injectors with the 95 computer. Everything is running fine except I'm running a little rich. Just solder the newer injector connectors on your harness and get a tune and shouldn't have any problems.
 

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without a tune you'd be running ~26% rich all the time with the 24 #'ers, but the adaptive strategy should be able to correct most of it....bad part is, you no longer have any more leeway in that direction for fuel control, should the EEC want to pull fuel for whatever reason.......so yea as you said, the best, and only correct way to do it is to get a tune for the larger injectors
 
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