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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:
- Standard Shipping : 3-10 business days
- If time is of the essence, please consider selecting expedited delivery for faster service.
Exchange/Return Notes
- We offer a 30-day return/exchange service after receiving.
- Final sale items are not eligible for returns or exchanges.
- To process your return/exchange, please contact us at [email protected]
- Please click here for more details>>> Return & Exchange Policy
4.1 ★★★★★
Based on 1625 reviews
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Product Reviews
★★★★★ 5
Pleasant Scent, Effective Cleaner
Scent: Lemon Verbena Concentrate, Size: 32 Fl Oz (Pack of 2)
I love the delicate verbena scent in Mrs. Meyers Clean Day Multi-Surface Cleaner. It’s very mild compared to other common household cleaner’s like Mr. Clean (Mr. Clean is one that knocks me over and I can’t stand the smell). Many years ago it was fine, but the scent has changed and become stronger, and NOT for the better. Manufacturers on the whole, use way too much scent in their products, whether it’s laundry detergent, fabric softener, hygiene products and anything else that scent is added to. Just take a walk down the detergent isle of your grocery store and if you aren’t immune to scent, you will find it overwhelming. This cleaner is not overpowering and smells just like verbena, a fresh, clean, green smell. I also love the way it cleans my wood floors, sinks, countertops, stainless steel fridge, stove & dishwasher, & everything else I clean with it. It leaves the surfaces “squeaky clean” without any streaks. Is it a good deep cleaning cleaner? I don’t know for sure since I’ve never used it to clean up muddy, greasy, grimy, dirty areas in my home. It does remove dark marks on painted walls but I haven’t tried it on heavy dirt and grime. I imagine it’s comparable to Murphy's Oil Soap, which is another brand I love and have used for years. If the scent of cleaners is an issue for you, and you like verbena, you should love this cleaner. A little bit goes a long way in a bucket of water (for washing floors, etc.). I usually use allot less than is recommended (in everything from laundry detergent to household cleaners). Especially my laundry detergent. I used to use the recommended amount and found with concentrated products, the amount recommended is way too much. I could feel the soap in my clothing after the wash cycle finished. I had to re-rinse all my loads. Then I got smart and cut way down on detergent and included vinegar in the final rinse cycle. Manufacturers love to sell more product, so don’t go by what they state on the container. Use your own wise judgement. On a side note, I love Costco’s Industrial Strength powdered laundry detergent but I cut way back to 1/4 cup per med to large loads. The white dress shirts and tee shirts are much brighter & whiter compared with many other detergents I’ve used in the past. I highly recommend this product for all of the above reasons. Give it a try at least once. You may love it too!
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Reviewed in the United States on June 17, 2024
★★★★★ 5
Excellent cleaning product, but lavender is a bit too strong for me.
Scent: Lavender Spray, Size: 16 Fl Oz (Pack of 3)
I bought 3 bottles of the lavender cleaner, and have used it to clean a number of different surfaces. In one of the bathrooms, I used it to clean dust from 6-panel doors, the cabinets, the counter and sink, the inside and outside of the tub area, and the outside of the toilet. When I was done, everything in the bathroom looked so clean. Even the dust that collects in the corners of the 6-panel doors was gone.
Next, I tried to clean stainless steel refrigerator in the kitchen. The refrigerator wasn't dirty, but it had streaks from water dripped from the ice maker and fingerprints. This cleaner didn't work as well on the refrigerator. Although it did remove the fingerprints and water streaks, it left streaks that I had to clean using another method. Actually, a clean washcloth and warm water worked very well to remove the streaks. This cleaner also left streaks on my built in stove that has a glass front. So, I don't believe this cleaner works well on reflective surfaces such as mirrors, glass, or stainless steel. Although it does clean these surfaces well, it leaves a residue that causes streaks.
The last surface I tried cleaning today was some of my kitchen cabinets. These cabinets collect not only anything in the air from cooking, but, since I am a smoker, they also collect some nicotine. On the cabinets that I cleaned, this cleaner did remove stains from both as was evidenced by the washrags I was using. To-date, the only cleaner I have found that would effectively clean these stains was Windex. So, I was impressed at how well this cleaner worked. It was working so well, I wanted to keep going, but, unfortunately, ran out of time.
Overall, I would recommend this cleaner for anything but mirrors, glass, and stainless steel. The lavender scent of the bottles I got was a nice scent, but a bit overwhelming in my opinion. Once I use up the bottles that I have, I will be trying one of the other scents, possibly the honeysuckle or lemon scents.
UPDATE 05/21/25:
We don't use our dining room which is furnished with a 40 year old solid wood dining room set. All too often the table is used for keeping appliances or other items that I plant to get rid of or need to find a permanent storage place. I finally got the table clear off and saw a decent layer of dust on it. So, I decided to try this cleaner on it. This cleaner not only removed all dust and spots on the table top but also the layers of old furniture polish. I was so pleased that the table was clean with a natural shine that did not feel oily. Now all I have to do is clean the rest of dining room furniture. I will definitely be using this cleaner.
I hope this review was helpful for you.
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Reviewed in the United States on April 23, 2025
★★★★★ 4
Smells amazing while cleaning, light lasting fragrance
Scent: Peppermint, Size: 16 Fl Oz (Pack of 1), Scent: Peppermint, Size: 16 Fl Oz (Pack of 1)
I really enjoyed using this Mrs. Meyer’s Clean Day Multi-Surface Cleaner, especially because of the peppermint scent. It smells incredibly fresh and pleasant while you’re cleaning, not overpowering, just very clean and uplifting.
I tested it on multiple surfaces including countertops, tables, and other everyday areas, and it performed well across the board. It cleans effectively without leaving residue or streaks, and it feels gentle enough for regular use.
The only reason I’m giving it four stars instead of five is because the scent fades fairly quickly after cleaning. While it smells amazing at first, the fragrance doesn’t linger for very long. That may be a plus for people sensitive to strong smells, but if you’re looking for a long-lasting scent, this might fall a bit short.
Overall, it’s a solid multi-surface cleaner with a beautiful scent and reliable cleaning performance. I’d definitely repurchase, especially during seasonal releases.
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Reviewed in the United States on February 7, 2026
★★★★★ 5
Bang for your buck
Scent: Lemon Verbena Concentrate, Size: 32 Fl Oz (Pack of 2), Scent: Lemon Verbena Concentrate, Size: 32 Fl Oz (Pack of 2)
The amount of spray bottles you get from this concentrate is actually insane. I won’t have to buy surface cleaner until next year. No but seriously, this is a great price point and you get so much from it. All of the Mrs Meyers products have awesome conscious ingredients that I feel comfortable having around my kids and pets (and they’re insanely gross creatures too) The scent is just a cherry on top!!
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Reviewed in the United States on May 26, 2026
★★★★★ 5
a miracle in a jar
Scent: Earthy, Nutty, Refreshing, Size: 4.06 Fl Oz (Pack of 1)
This item did exactly what it was expected to do, and I couldn’t be happier with my purchase. It works as described, is easy to use, and the overall quality exceeded my expectations.
The price was great for what you get, making it an excellent value. Everything about it—from performance to convenience—has been spot on. My sister has noticed an extreme growth in her hair since using this product.
I’m very satisfied and would definitely recommend this to anyone looking for something reliable and well worth the money!
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Reviewed in the United States on May 5, 2026