Holley HP Engine Control

Despite following Holley’s instructions to the letter
and using Holley harnesses, my Holley HP would not work properly.
The problems were:

1. In the version I have (summer 2015), Holley
   mislabels PSIG (or the commonly used PSIG we call “PSI”) as  PSIA. PSIA actually starts
   at zero for perfect vacuum, atmosphere is ~14.7 psi, and 20 lbs. boost would
   be 34.7 PSIA. Holley actually uses PSIG (called PSI on the street). PSIG has a negative number for vacuum, atmosphere
   is at zero psi, and boost is
   a positive number greater than zero. Naturally, when I
   programmed things based on PSIA, all sort of bad and confusing things happened. Once I
   learned PSIA was a label mistake by Holley, and it actually should be PSIG, all went well.

2. Holley has some serious ground loop problems in the
   TFI harness, and in their wiring instructions. Holley is very firm about
   wiring the power ground to the battery, but that actually is a very unsafe
   thing to do. Wiring to the battery negative also aggravates ground loops,
   opposite of what people think the battery negative would do. I’ll explain this below,
   because this problem actually extends outside the Ford TFI system.

3. The Holley fuel cut limiter is useless. The engine
   RPM oscillates wildly over a wide range.

Fortunately,  once understood, the first two
problems above were easy to correct. The fuel cut issue is in the Holley
programming, and Holley must correct it.

Holley Ground Loops and PIP / Spark Trigger Issues

 I
assumed my first dyno test of the Holley would a success, since I used the OEM
Ford TFI distributor and ignition system quite successfully with 15 psi boost at
7500 RPM with Ford’s EEC-IV (both A9L and A3M) system. My first Holley dyno pull
at 10 psi with the Ford TFI interfaced to the Holley was completely
unsuccessful.

Using the Holley system and Holley harness adaptor with
the Ford TFI distributor, my car would not pull over 5500 RPM without spark
scatter and spark drop. The effect was much like valve float or spark blowout,
or an RPM limiter. A quick switch to an MSD 6AL style CD ignition box only
allowed 6000 RPM before the same symptoms appeared:

Testing the Holley RPM limiters, the fuel cut caused wildly
varying RPM. The spark cut was scary, it caused terrible backfire banging and
popping. The spark cut
noise sounded like a cannon going off, and I feared for severe turbo, engine, or
piping damage. I initially assumed this horrible behavior was due to a poor RPM
limiter algorithm. A storage oscilloscope test showed the ignition spark problem was
from false triggering of the ignition by ground loop noise induced into the
Holley PIP input.

This ground loop problem was traced to three things:

1. Holley instructions and labels insist customers
   connect the black negative chassis ground and power lead to the battery
   negative, yet that negative is the ONLY chassis ground and signal ground for
   the Holley. This is a very serious mistake

2. Holley uses a long small gauge harness wire for the
   distributor PIP signal input
   return, and that return is grounded at both ends. This is a minor mistake

3. Ford connects the PIP and TFI grounds to a
   distributor pin common to the engine block. This is perfectly acceptable if
   the EEC has a differential input for signal, but the Holley uses a very poor
   single-ended input that is common grounded to the negative power bus and
   chassis of the Holley

I initially followed Holley’s instructions, and grounded
Holley power (and chassis) to the battery negative. I normally would not do
that, because my training and experience is that accessory device negative
connections must never connect to the battery negative post, battery negative
terminal, or share a common bolt or fastener with any factory battery ground.

As a matter of fact, European regulations for mobile communications, audio, and
ancillary amplifier equipment that I design and/or write instructions for
specifically prohibit connections to battery negative posts or battery negative
cables! Battery negative connections are prohibited because of vehicle fire and
electrical equipment damage concerns.

The sole exception to the rule above would be if the negative
bus in the connected device does not have a path to ground through any
connections, including the chassis or cabinet, although a battery negative
connection still would be prohibited in European countries in CE regulations.
One exact European regulation is:

If Holley had followed the same directive that applies
to European ancillary equipment, one that Ford also uses, they would have a
safer installation!! 

Ford TFI/PIP/EEC Power

Ford avoided ground loops in Fox Mustangs by using a
“chassis-centric ground” for all electrical systems except the starter,
alternator, non-critical engine sensors (i.e. analog instrument cluster gauges),
and TFI ignition coil primary ground return. Below you see a Ford OEM
negative pigtail. The negative lead below uses the
large heavy cable for block-common-ground devices like the starter, alternator, and
other engine-grounded devices. The smaller lead supplies battery negative to the
vehicle chassis, which is the common ground for signal and low-noise load
grounds. The EEC harness ground, which has some noise from injectors and
other switched devices, returns to the vehicle chassis very near the front-mount battery.

With Ford’s wiring, should the battery connector or any
ground open or go high resistance, there is little fire risk or damage risk to
electrical system hardware or components.   

If we examine Ford’s wiring, we see Ford complies with the European
directive (even though the directive applies to aftermarket accessories, and not
to OEM equipment). Ford connects the EEC as close to the battery chassis ground
as possible, and not to the battery. The only Ford OEM connections to the battery
negative
are the vehicle chassis and the engine block. The Ford EEC harness ground is a good idea because
the battery terminal, the engine block, and the chassis grounds are all close
together, and the battery negative is off by itself.

WARNING:
This would not apply to a trunk mount battery, because the trunk is too far from
the engine block for a reliable low-noise EEC ground or low resistance starter
or alternator wire connection ground.

The overview of the Ford system is:

Ford uses the chassis (C) as ground reference for all loads (E, F) except things
grounded directly to the block (A). Ford does this for noise reduction and
ground loop avoidance. The PIP signal enters an EEC-IV differential input (B)
through a shielded wire pair. Traditional noise shielding and mitigation
dictates grounding at a noise source and shielding at the noise source area. The distributor cap, with
high voltages and constant internal arcing, is the major electrical noise
source. The distributor base ground and the foil shield eliminates electric field
coupling into the PIP wires, while the use of paired PIP wires to a differential
input eliminates magnetic field noise coupling into the PIP, as well as
eliminating ground loop coupling from the block ground on PIP wires. The block
is grounded two ways, to the battery negative through a very large short length
cable because of high currents and noise, and from a head (D) to the firewall
(F) near the computer chassis ground.

Ford is block-centric for high current sources and loads that originate high
level noise,
and chassis-centric for all other power sources. All voltage and noise critical
sensors and triggers are only grounded at one point, the other end of the path
is differential between the wires. The chassis is the best noise-zero ground. The only connections to the
battery negative should be (and are) the vehicle chassis and/or the engine
block.  Grounding any accessory device to the battery post increases
likelihood of damage and noise problems.

My TFI spark break up and RPM limiter issue (that could have damaged the engine
had I used it) was completely cured by ignoring Holley’s advice. I removed the Holley negative wire from
my car’s negative battery post, and grounded the Holley power (which is also the Holley
chassis) at the firewall near the old Ford ground point. This point is within a foot or
of Ford’s OEM passenger-side cylinder-head ground point.

I considered a block ground for Holley power. I
decided against it because my engine is on rubber mounts. I did not want a connection between
very high starter and
alternator currents and the Holley chassis if the block should ever develop a high
resistance ground.

From Holley Instructions, the very first Holley “Do” sets the system up for damage and
ground loops:

There are two problems with Holley’s instructions shown above: