[RFI] 2002, Ford 4.6L V8 RFI, Need Help

wng@daimlerchrysler.com wng@daimlerchrysler.com
Tue, 8 Oct 2002 14:43:37 -0400


We have had significant experience with this problem with coil-on-plug
systems.  The most severe noise is due to the primary current being
interrupted by the ECU to make the spark.  Often, the engine wiring
INTERNAL geometry is not controlled by the ignition system designer.  If
the circuit from battery/ alternator to engine relay to coils to ECU to
battery/alternator is permitted to be a large area loop, the edges will
couple through mutual inductance to other circuits and even to body
sheetmetal!  It is necessary to locate the switched feed to the engine
components (coils, injectors, &c.) and reroute it to the immediate vicinity
of the engine controller and bypass it there with a low impedance (stacked
film) 0.5uF capacitor.  The feed to the engine must be spliced as close to
the capacitor as possible, and then routed along the coil returns to the

This causes the secondary current (the actual spark current) to return
common mode along the engine harness.  The spark currents are typically
much smaller, but they are AC, at the self resonant frequency of the of the
secondary (This gives a good hot, blue spark.)  In order to control them we
use one or more ground straps from the engine to the block.  It is a very
tedious process to find the best location for the grounds, but it is
usually successful.  The ideal solution would be to relocate the engine
control unit to the engine, but I cannot recommend this course, since I do
not know whether your controller can handle the temperature, vibration, &c.
It is also possible to choke the secondary currents by using several LARGE
ferrite cores between the ECU and the engine, but they must be a very high
initial permeability (type "J" or 77 material).  Type 43 is largely useless
at this low frequency.

Try bytemark.com for parts (and technical information on ferrites , if you
are interested).

Bill Gilmore WB8FPQ
EMC Technical Lead
Dodge Truck Electrical/Electronic Engineering

                      "Paul J. Pagano"                                                                                              
                      <wa4aa@netscape.n        To:       <rfi@contesting.com>                                                       
                      et>                      cc:                                                                                  
                      Sent by:                 Subject:  [RFI] 2002, Ford 4.6L V8 RFI, Need Help                                    
                      10/07/02 08:47 PM                                                                                             

As suggested in an earlier posting, I ordered 16, snap-on, split, ferrite
beads (#43) from Amidon. I placed one around each, of two wires, located
above each spark plug. Unfortunately, It did not help at all. Have any of
you received confirmation from other Ford Motor owners,(same engine and
year) that this solved their RFI problems, specifically ignition noise? If
so please have them contact me.

Ground strapping everything is my next step! I'm not sure how to go about
grounding all the side panels and doors. The vehicle is leased and I can't
drill any visible holes. Can anyone reference an established procedure for
this strapping process?

I am sharing this message with all members of the Forum; as I'm interested
in hearing from any 2002 Ford owners who've had this problem and have
successfully resolved their RFI issues. Thanks in advance for your useful
comments. Please e-mail any helpful recommendations to me at:
Thanks again and again....Paul

 J. Pagano

RFI mailing list