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Holley EFI 550-601 Question

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Old 06-10-2018, 10:19 PM
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Holley EFI 550-601 Question

Hi all!

Before I ask the stupid question, I just wanted to say that I have read a million posts about switching to an aftermarket EFI system and I get all kinds of different information on one simple question (at least I thought it would be).

1987 GTA came with a 305 TPI and 700R4. Same setup except I have a 5 speed in it now. Supercharger too, but I'm not dealing with that until I have it working right without it first. ;-)

If I am using a Holley EFI 550-601, do I completely remove the stock ECM and thus the wires that go to it? I know there are many that a linked to other wires, so I don't mean literally all of them, but most of them?

I currently have a HUGE mess and it seems scary to start cutting. I've disconnected all connectors that are part of the new Holley harness and have them hanging out of the engine bay, but there are plenty of wires left that still go to the stock ECM. Trying hard not to make too many mistakes.

Last one for now... is there an installation manual from Holley that steps you through it all easily that I'm not finding? NO... I have not called them YET. Figured while I was posting I would just ask...

Thanks for any information you may have and I know I should probably take it somewhere to have an intelligent person do this, but how else will I learn? :-) Try to take it easy on me please...
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Old 06-11-2018, 09:25 PM
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Re: Holley EFI 550-601 Question

Abubaca recently did a Holley EFI conversion to his TPI. You might ask him since it is all fresh in his mind.
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Old 06-11-2018, 10:12 PM
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Re: Holley EFI 550-601 Question

Originally Posted by QwkTrip View Post
Abubaca recently did a Holley EFI conversion to his TPI. You might ask him since it is all fresh in his mind.
Thanks for the info... i sent a PM.
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Old 06-11-2018, 10:47 PM
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Re: Holley EFI 550-601 Question

Happy to help.

So please keep in mind that from year to year, there ARE differences in our thirdgens. Mine is an 89. That being said, I think all my answers should be accurate.

If I am using a Holley EFI 550-601, do I completely remove the stock ECM and thus the wires that go to it? I know there are many that a linked to other wires, so I don't mean literally all of them, but most of them?
I short, yes. You remove them all. Basically that kit will run everything, so long as you supply power. Ithink that your 87 may be easier to seperate engine harness from chassis harness. Mine was a BEAR!!!!!!!! ...and still I didn't get em all. Just be careful when cutting. If you're able to remove the engine harness by iteself....without cutting....I would do so. In 89 I could not. The CAR may need something, so be careful, but the Holley does not. Keep in mind this means Evap cannister control too, as the Holley cannot control it. I built a charcoal canister for smell, but it does vent to atmosphere. Actually found that from Factory Five forums.

Last one for now... is there an installation manual from Holley that steps you through it all easily that I'm not finding? NO... I have not called them YET. Figured while I was posting I would just ask...
Did you get the disc with the kit? It's got a step by step, but it's more how to "technically" install the kit and get started, not how to physically install it in a thirdgen. Honestly once the old wires were out....the physical install was pretty easy. I laid the harness out on the floor and identified everything. Recognized most of it, but had to look up a few things. It's basically the same quite honestly, just nice, new and clean! Once you know what's what, lay it out on the engine. Zip ties are your friend. LOTS of zip ties. Figure out how to get through the firewall and start routing your harness. It takes time, but it's not really hard. The ECU actually fits/mounts in the factory ECM bracket. Just drill a few holes to mount the ECU and then the whole bracket mounts in the factory location.

Don't kid yourself, it takes some time and focus, but nothing was really hard. Getting everything to FIT right, and have the harness tuck in nice and neat took more time and trial and error than any of the tech stuff.

...and before you call....check the forums. SUPER helpful. Danny Cabral is SUPER helpful. He's always on. I once had a reply on a Sunday in less than an hour.
https://forums.holley.com/forumdispl...?13-Holley-EFI

...and feel free to hit me up. I love this stuff. ...and these guys here on TGO have helped me more than I could ever repay, so I'm here to help where I can. Ask away.
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Old 06-13-2018, 11:16 AM
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Re: Holley EFI 550-601 Question

I appreciate the info! I'm not sure mine is going to be any easier to separate the harness than your's was. :-)

I would like to ask for a little clarification. When you say "In short, yes. You remove them all. Basically that kit will run everything, so long as you supply power." Do you mean only the wires that are replaced by the Holley ECU or ALL wires that go back into the cabin through the fender that attach to the stock ECM connectors? Don't worry... not going on a cut-fest, just trying to see what I am really working with.

Thanks again!
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Old 06-13-2018, 12:00 PM
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Re: Holley EFI 550-601 Question

I took out my entire ECU. It's not even in the car. What I can NOT say, because frankly I don't remember...it whether or not there are OTHER wires that come from the engine bay, through the passenger fender, and down to the passenger side footwell. They may ALL be ECU related, and removable, but honestly I don't remember.

What I did to clean up the engine bay was to pick a connector and wires, say for example the injector connectors and wiring, .....and trace them as far back as I could and cut 'em. I did that for every wire connected to the TPI. Injectors, TPS, IAC, EGR, Knock, Temp, etc. etc. All those wires are no longer visible from the engine bay. I cut them down inside the fender by removing the inner fender well. They ARE still inside the fender and running through the firewall. Then I simply unhooked the ECU and removed it.
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Old 06-13-2018, 07:14 PM
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Re: Holley EFI 550-601 Question

Pocket has a thread that I used to trim my harness down a lot before installing my Holley Terminator EFI. I think it's in the LS swap section IIRC. I think there were a few ground circuits that did come back through the passenger side pass-through.
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Old 06-22-2018, 10:28 AM
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Re: Holley EFI 550-601 Question

Originally Posted by Abubaca View Post
Happy to help.
...and these guys here on TGO have helped me more than I could ever repay, so I'm here to help where I can. Ask away.
I second this comment. Most members pretty much bend over backwards to help. Some like to just stir the pot and rile people up- but they're part of the flavor of the site. Keeps things interesting.


I personally am interested in your experience with the Holley controller. I can visualize the conversion, probably about the same for any ECM. How does it tune, perform and do the things you want it to do?
I'm using EBL and am very impressed with it's capability. For a OEM based 80's era ECM it is awesome. But there have been a lot of improvements in the past 30+ years like sequential fueling, faster communication rates and a lot of things that make me wonder if a newer system would be worth the conversion. I am mostly looking for part throttle and cruising improvements and possibly live wide band feedback. Sequential, CnP and the like would be desirable features for a classic SBC.
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Old 06-28-2018, 12:38 PM
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Re: Holley EFI 550-601 Question

I am mostly looking for part throttle and cruising improvements and possibly live wide band feedback. Sequential, CnP and the like would be desirable features for a classic SBC.
Well I can't speak to the EBL. ....I actually purchased it, but sold it in favor of the Holley before I ever hooked it up. ....The Holley has impressed me at every turn, and for the most part, that's what I hear from other Holley owners. As for the specifics of part throttle/cruising, I haven't had any issues, so I have not had to specifically address it withing the tables. That being said, what I HAVE played with with very easy to read and manipulate. As for Sequential/CNP, it's definitely an option, but I'm still running a distributor so not an option unless I purchase the additional sensors, which right now I don't feel is necessary for my set up.
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Old 06-29-2018, 09:36 PM
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Re: Holley EFI 550-601 Question

I also removed my entire ECM and harness completely for a holley system. There is only a few wires that go elsewhere other then the motor. Get a wiring diagram and mark the ones you need to keep and cut them from the harness. Like TCC for auto and Fuel pump . I mounted my ecm to the oem bracket and added a fuse panel above it to wire in the accessories and keep it neat.

I also had to extend some wires and touch up the holley harness as I didnt like the way it was layed out.
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Old 06-30-2018, 10:03 AM
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Re: Holley EFI 550-601 Question

I mounted my ecm to the oem bracket...
Yup!
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Old 06-30-2018, 02:25 PM
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Re: Holley EFI 550-601 Question

I did the same thing.

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Old 07-01-2018, 10:15 AM
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Re: Holley EFI 550-601 Question

Of course I cant find pics of mine!!
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