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Description
Holley HP EFI ECU and Harness Kits 550-604MPFI HP ECU AND HARNESS KIT Looking for a plug and play alternative for your stock or built late model factory EFI engine? How about a replacement ECU for your older Holley C950? Holley has you covered. HP EFI ECU and harness kits are designed to be used with popular factory EFI engines as an alternative to the factory ECU and harness or as a replacement for your C950 ECU. The HP allows you to accurately control the fuel and ignition of your engine
MPFI HP ECU AND HARNESS KIT
Looking for a plug and play alternative for your stock or built late model factory EFI engine? How about a replacement ECU for your older Holley C950? Holley has you covered. HP EFI ECU and harness kits are designed to be used with popular factory EFI engines as an alternative to the factory ECU and harness or as a replacement for your C950 ECU. The HP allows you to accurately control the fuel and ignition of your engine along with additional controls for nitrous, boost or water meth.
Features:
- Optional 5.7” full-color touchscreen LCD allows easy on-the-fly tuning, data-logging or can be used as an easy to see graphical gauge panel
- Eight sequentially driven 8:2 peak and hold injector drivers, capable of driving up to 16 low or high impedance injectors as a standard feature. Multiple staged injector strategies
- Eight channel Distributorless Ignition (DIS)outputs capable of directly driving “Smart” ignition coils or Holley DIS coils. Will drive 2 wire coils with the addition of PN 554-112 high current coil driver module
- Integrated single channel wide band oxygen sensor control. Works with NTK or Bosch sensors
- Internal data-logging standard with a huge 2GB of memory
- 4 Stage progressive nitrous control
- Turbo boost control
- Integrated water/methanol injection control
- Self-tuning fuel table strategy greatly simplifies tuning process
- Individual cylinder fuel and spark control allows you to unlock your engine’s potential
- Works with 4, 6, 8 cylinder engines
- Unique lb/hr based fueling strategy greatly simplifies and commonizes tuning
- Advanced idle, closed loop, and enrichment strategies allow for very stable operation
- ECU is fully potted and can be mounted in the engine compartment or interior
- Sealed automotive and marine grade connectors
- Allows for use of common OEM sensors as well as customer sensor calibration input
- Ignition Plug and Play with GM HEI, Ford TFI, magnetic and hall effect trigger, and other ignition systems. New Plug and Play applications in process. Custom settings can be configured to allow many other applications
- 1-5 Bar MAP sensor capability
- Two channel knock control sensor Inputs for both one or two wire knock sensors
- Dedicated fuel and oil pressure inputs
- Controls both stepper and PWM Idle Air Control (IAC) motors
- Speed density, Alpha-N, or combination fueling strategies
- 4 Programmable high or low Pulse Width Modulated (PWM) outputs and 4 fully configurable inputs can be configured for use
- 4 Stage nitrous oxide control
- Fully featured nitrous control eliminates the need for a separate nitrous controller device
- Can be configured “Wet” or “Dry” with closed loop feedback
- Progressive control based on time, RPM, or boost, requires part # 554-111
- Lean or rich safety cutoff
- Full timing retard/control configurability per stage based on RPM or time
- Integrated Water/Methanol injection control
- Uses Holley Water/Meth solenoids specially designed and calibrated for use with this EFI system to allow the user to enter Water/Meth flow as a percentage of fuel injector flow for Water/Meth tuning precision unmatched in the industry
Application
-
Universal
Specs
| Brand | Holley EFI |
|---|---|
| Emission Code | 3 |
| Ignition Type | Coil - (No Timing Control) |
| Ford TFI | |
| GM HEI Small Cap | |
| Holley Dual Sync Distributor | |
| Injector Connector | Jetronic / Minitimer (Bosch) |
| Product Type | HP EFI Kit |
| Part Number | 550-604 |
Shipping Notes
- Free Standard Shipping on $100+ Orders to the USA.
- Except Preorder products are shipped in 48 hours.
- Delivery to the USA:
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Exchange/Return Notes
- We offer a 30-day return/exchange service after receiving.
- Final sale items are not eligible for returns or exchanges.
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4.8 ★★★★★
Based on 11 reviews
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Product Reviews
★★★★★ 5
Now I want to hike the PCH!
Format: Paperback
Such an incredible story, actually several stories. Very inspirational. I can’t help but want to join the adventure and experience some trail magic of my own. Thank you for capturing these experiences, Scout. Well done
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Reviewed in the United States on November 25, 2025
★★★★★ 5
A community 3 feet wide and 2650 miles long
Format: Paperback
One of the aspects of long-distance backpacking on our National Scenic Trails that those who haven't done so are generally unaware of is the tight-knit sense of community that binds hikers together, even hikers who've never met. These folks are average people with a vast range of life experiences and circumstances, and not simply a generic array of "professional hikers" involved in some sort of athletic competition. In the "real world," you can know someone for years without *really* knowing them at all, but on the trail, a single day can feel like weeks, and months can feel like years. You can bump into someone in the morning, and have a new "old friend," soulmate, or savior by the end of the day.
In "Journeys North," Scout brings this community to life on the page vividly and emotionally, drawing us into not just his own life and experience, but of many others in his trail family- all making that journey north in a literal way collectively, as well as in their own personal ways figuratively. Along the way, he relates the highs and the lows of not just life on the trail, but of life in the "real world" as well. It's a crash course in empathy, determination, and sometimes just plain stubbornness.
When I received the book and flipped through it quickly, I was at first surprised at the lack of photos- just a single page at the end with a handful of shots of the "main characters." But as I read the book, I quickly realized that Scout's richly descriptive prose paints a far better picture than any actual pictures could, and was grateful for the space he made for my imagination to play a part in his story.
While no book could ever substitute for the actual experience of hiking a long trail, "Journeys North" serves as great inspiration for those who aspire to, as well as reassurance for their friends and family that they won't simply be disappearing into the wilderness alone.
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Reviewed in the United States on August 1, 2020
★★★★★ 5
Basics for the Hike
Format: Paperback, Format: Paperback
This is a nice, short book that gives you the basics of hiking the Camino de Santiago.
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Reviewed in the United States on March 8, 2026
★★★★★ 5
If you are thinking of the Camino, This book is for you!
Format: Kindle
I just had a friend who walked 32 days on the Camino, and I chose this book to learn more about what it would be like. This was an excellent choice. The author outlines what pilgrims can expect and how to prepare for the experience. I had not realized there are six paths: The French, Northern, English, Portuguese, Orrigonal, and Silver Ways. It turned out that my friend was on the Portuguese way. The different paths range from three hundred to a thousand kilometers. The author goes through each of the "ways" and does a daily highlight of the number of kilometers one walks and the sights to expect. This book whetted my appetite to consider a walk like this; it would be a great resource for any pilgrim.
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Reviewed in the United States on October 22, 2024
★★★★★ 4
Basics for a successful pilgrimage
Format: Paperback
Brief but useful info
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Reviewed in the United States on January 26, 2026