Holley HP Engine Control
Holley HP Engine Control
This article is still under construction…in monthly
editing (last rev 1/10/16)
The article was either hacked and deleted, or
accidentally deleted, in mid-October. I am restoring it now
Holley ground loop design problem
I’ve used stock and clocked A9L and A3M ECU’s, as well
as the MegaSquirt PNP, in my Fox Mustang. I primarily used the Tweecer system
with various software packages, and found it good for mild builds. The lack of
failsafe, unreliable logging, and dependence on multiple external devices has
made the Ford ECU system troublesome in high power builds. Just one small
problem, like a loss of connection or even a hose failure, has destroyed pistons
in a matter of seconds.
In an attempt to work around that, I used a
Safeguard. I really like the Safeguard. It is more than spark
retard, it also has internal RPM limiters. While the J&S helped a great deal with failures like poor fuel, too much
heat, or too much advance, the J&S could not prevent piston damage in severe lean conditions.
Problems with tunes and logging caused me to constantly add on devices.
To solve the nagging log system failures, I added an AEM AQ-1 logging system. To
solve air measurement system failures, connection failures, or tune failures, I
designed and built an L-Warn system. That system monitored throttle position and
sensor voltages, and shut the engine down if it was lean when throttle was more
than 60% open, and ignored lean if the throttle was closing or a stage limiter
I did the circuit board layout, electrical design, and
construction of my warning system here. This system bridges across the stock
sensors, and watches the voltages for abnormal conditions. It activates warning
lights when close to danger and a failsafe shutdown when danger points are exceeded.
As a second function, this board also allows some standard gauges to bridge from
EEC system sensors. It can sample voltage from the sensor for the gauge circuit
without affecting the EEC use, allowing one sensor to drive multiple circuits
without harmful interactions. My
home made warning and buffer system looks like this:
Using the stock ECU with my 700-800 HP SBF engine rolled
$4000 in accumulated engine repairs, many months of down time, and hundreds of hours
trying to learn how to tune or patch around problems. I have a mountain of books
and papers on tuning, many of which put me to sleep trying to find something
useful. The stock ECU required:
A MAF meter sized for power
J&S knock detector and external RPM limiter
Aftermarket wideband O2 system that outputs logging
signal or logs
Laptop in the car for logging or monitoring.
Clicking on a “start logging” icon is a terrible nuisance in the staging
lanes, and having a heavy laptop on the passenger seat is unsafe at
An external logging system, independent of the
laptop, that always logged when making a pass (because service port logging
Learning which of a complicated flow of program
tables and scalars were important, and which were not
“Saving money” by using the Ford ECU
probably cost me $5,000-$10,000 and a year of fun racing out of the past 5 years. The
good thing is the time I wasted using the stock EEC gave the Holley EEC time to develop and mature.
The Holley System
I initially worried about aftermarket system cost, and I
did not want to cut my car up. It turned out the opposite was true. In reality,
the Holley ECU system has been one of the best choices I’ve made for aftermarket
parts. I use the Holley HP and Holley Digital Dash in concert with my own homemade instrument cluster.
I decided to ditch my standard instrument cluster. With a Hughes Superglide style transmission, my car lost
normal speedometer functionality. RPM range is well beyond the Ford factory tach, and I never
had time to look down at gauges in a pass anyway. With the loss of most gauges, I
opted to build my own cluster with two large digital red LED displays,
six multi-color (off/red/yellow/green) LED warning lights, a bright blue
high-beam indicator, and green LED turn signal indicators. I used the following layout:
I still use an analog tach with super bright RED LED shift
lights (on the right side of the tach), along with an analog boost gauge. There simply
isn’t time to watch any other gauges, mandating warning lamps for lean, fuel
pressure, fuel level, proper boost (staging), and shifting. My homemade instrument cluster does
not illuminate unless a problem or alert appears.
One example of a warning is battery voltage. With a 12V
battery, 12.6 volts is a fully charged float voltage, and anything from 12.5 to
13 volts turns the battery warning LED off.
Less than 12.5 indicates some loss of charge, illuminating the red/green
with a mix of red and green to produce yellow. The yellow turns progressively
redder (by reducing green) as battery sags below 12 volts.
If the alternator is charging or supplying adequate
power to run the vehicle, the battery LED turns green. At 14 volts and above it
is bright green, because that means full charging. At 14.9 the LED goes blinking
red, indicating dangerous overcharge (regulator or battery boiling).
With a glance, I know my battery and charging system
My car’s cooling fans and pumps run in the accessory key
battery indicator logic design disables the accessory key position if battery
11.9 volts. This disables cooling fans (and radio) if the
ignition key is left on accessory to operate fans and water pumps for cool down
the battery becomes too low for restarting the engine.
The dash layout looks like this when installed. This is
with key on, engine off. In the picture below, the battery has dropped
below 12.5 volts causing a red warning lamp above the battery voltage. The
Holley digital dash wiring is not in the final location in the picture
Final wiring is seen below. Wires from the digital dash route through the dash vent
to the Holley:
My Holley system mounts on a plate behind the glove box:
Since I want to run fans and cooling pumps with the
ignition run off, I do not use the Holley for fan or water pump control. Wiring in picture
below around the fan controllers and ignition box cannot
be harnessed yet. I have a
temporary Flex-a-Lite fan controller (since removed and replaced with a Derale) hanging on the bracket while I wait for a
The Holley HP harness enters the engine compartment through grommets by the PS hood hinge:
Despite following Holley’s instructions to the letter
and using Holley harnesses, my Holley HP would not work properly.
The problems were:
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.
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.
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
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
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:
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
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
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 only battery post
negative connection should be to or from another battery negative, the
vehicle chassis, and/or the engine block. There should never be a direct negative post
path to accessory or ancillary equipment.
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:
Negative Feed Connection
In the case of negative earth return
For heavy commercial vehicles (>7.5Tonne GVW) only, and those
With certain equipment it may be necessary to connect the negative
this case an existing vehicle earth point must be used.
If Holley had followed the same directive that applies
to European ancillary equipment, one that Ford also uses, they would have a
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
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.
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
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
From Holley Instructions, the very first Holley “Do” sets the system up for damage and
There are two problems with Holley’s instructions shown above:
First, a power ground should never be connected directly
to a battery negative. Grounding to the battery creates an equipment damage and
fire hazard. The only things that should ever connect to the battery negative
are the vehicle chassis and the engine block, or another battery. The reasons for this are described
at this link Battery Negative Lead
If a battery negative lead to block and chassis ever goes high resistance or
open, all of the vehicle current will try to run through the ground of any
device connected to the battery negative.
This could cause a fire, or damage the Holley or things connected to the Holley.
Holley is setting users up for failure.
The second issue is the Holley TFI wiring harness
that Holley sells actually violates some of Holley’s “Don’ts”. The PIP wires in the Holley TFI harness are
not shielded, the TFI PIP ground is a chassis ground that is grounded at both
ends, which sets the TFI system up for noise and ground loops. I’m not sure if
things like this occur with wiring or adapters for other systems, but the TFI
harness is a recipe for disaster. This is especially true when using a battery
negative post ground to the Holley chassis, because of the battery negative to
chassis to block ground loop.
Holley gives a very bad
ground “Do” that can cause damage and ground loops, and Holley sells harnesses
and uses inputs that violate their very own “Don’ts”.
A proper correction for the
TFI PIP would be a differential input at the Holley for the PIP, like Ford uses,
as well as a chassis ground reference for the EEC/ECU system and negative power.
The positive connection does (and should) connect to the battery, but a fuse
belongs at the battery. A fuse at the engine control does not protect the
vehicle from short circuit fires between the battery and fuse.
I did not do a proper correction, because I got away with just grounding the
Holley to the firewall near where the head grounds. I could easily make a
differential input buffer for the Holley PIP input. This would improve any spark
trigger, as well as the PIP system, by reducing noise. I could have also used a
twisted pair inside a shield for the PIP signal, which Holley should have also
done. I got away with not rewiring anything, or cutting up a new Holley harness.
Based on what I have seen with my vehicle, following Holley instructions could
result in engine or electrical system damage. This is a great system, it’s just
too bad someone does not understand ground loops and wiring (and fix the fuel