weird ficm voltage

speedinpowerstroke · Dec 30, 2012

So I brought my truck to my buddys shop and he hooked it up to his computer and the ficm would read 48 volts then drop to 42ish then back to 48 then 40 sumthing then back to 48 it kept dropping then going back to 48 and the idle is weird. When the truck is cold it starts great when its hot it starts rough i know my #2 and #4 injectors are bad but with the ficm should i get mine rebuilt? or should i get a new one? and if new one 48 or 58? is there really a differance? thanks in advance

POWER-STRUCK · Dec 30, 2012

sounds like you need to get it repaired and options all depend on how much you want to spend

bboteler · Dec 31, 2012

Definately get it fixed. 58v and 48v there are two schools of thought, some guys swear by the 58 some say its not worth the $. I have one of each. Spare is a 48v tuned by KEM, one on the truck is a Swamps 58v tuned by PHP...can't say i've ever seen a difference in performance between the two.

Atsah · Dec 31, 2012

IMO, either send it out for repair or do what I did and buy a heavy duty 48V from swamps..

Lassie · Dec 31, 2012

A 58V FICM should not perform any better than a 48V, or even a 200V FICM if the system is working correctly.

In a DC system, P=IE (Power = Current x Voltage). When the circuit to the injector is closed, the injector coil will use the power it needs, no matter what. If system voltage is low, such as with weak batteries, more current will flow to make the power level needed. Current causes heat, and current ratings are based on heat.

The FICM converts 12V to 48V using a DC power supply. This is a dumb device that simply uses electronic parts to multiply the voltage x 4. If battery voltage drops to 10.5 volts, the FICM will convert that to 42 volts. Power needed for injector operation remains constant, so when the circuit closes, current will increase to maintain injector operation. This increased current does the damage to the FICMs and injectors because the systems are not rated to dissapate that amount of heat. The 58V FICM should maintain current levels down throughout normal operation, and should provide damage control with low system voltage. The same drop to 10.5 system volts should only drop injector voltage to 50.7 volts.

Now the other part.....Voltage ratings are based on insulation construction. Thickness of insulation, distance between components, type of insulation...etc. The 58 FICMs being built may have components with 58V rated insulation, but maybe not. The harnesses and injector coils are not changed, and they need to be rated at 58V and above also. These may be rated high enough, but this is what has always scared me away from the 58V FICM. If a wire or coil body (injector) becomes dirty or starts wearing, systems with the 58V FICM will track through to ground earlier than the stock 48 system. An injector with an occasional loss of signal to ground through a carbon track wouldnt be fun to find.