Pro Flo 4 Edelbrock

[89 sport truck]

Hello everyone. Forgive me if I am posting this in the wrong section.

On my 89 chevy (TBI 350, NV3500, RWD) I am swapping in a sbc 400 with Edelbrock’s pro flo 4 port efi system.


I think I can get away with entirely unplugging and removing the oem PCM. Because mine is a manual trans truck, all it is doing is engine management. Going thru the OEM wiring diagrams and comparing it to Edelbrock’s new wiring, The only outputs that the oem PCM has that Edelbrock’s doesn’t is my Speedometer and HVAC controls. Is there a workaround for making these continue to work? I want to keep the oem gauges/ controls. Is it even worth bothering to remove the oem PCM? Would it be simpler to leave it in, and let it be in limbo and only use 2 of its outputs? Or would that cause problems? If I left it in, I would more or less depin everything (to clean up wiring) except for the few things I need.


Hopefully my question makes sense. I think anyone who has done a standalone ECM would be able to help, not necessarily just the pro flo.



THANK YOU THANK YOU THANK YOU

 

[PlayingWithTBI]

The only outputs that the oem PCM has that Edelbrock’s doesn’t is my Speedometer and HVAC controls. Is there a workaround for making these continue to work?

It seems to me, you don't need either of them. The speedometer is fed directly from the VSSB behind the dash which also feeds the ECM. The Control Panel sends a signal to the ECM when the A/C comes on so it can adjust the idle but the A/C doesn't need anything from the ECM to work. At least that's how it works in my 88. YMMV

 

[b454rat]

IIRC need 12 volts to the DRAC and the speedo will work. It's behind the glove box, white box.

 

[PlayingWithTBI]

IIRC need 12 volts to the DRAC and the speedo will work. It's behind the glove box, white box.

For 88 - early 91 "Moonie Dash" the VSSB is behind the cluster. Later years switched to the DRAC behind the glove box.

 

[b454rat]

I was close lol

 

[89 sport truck]

Thanks for the input guys. So as far as I can tell, I should be able to completely remove the oem ecm without issue? I just need 12v pwr to the VSSB?

I would think everything in your 88 would be the same as my 89. To my knowledge there were no changes between those two trucks. (other than option packages each truck has)

Thanks guys.

 

[PlayingWithTBI]

I just need 12v pwr to the VSSB?

I don't even think you need that, you should already have power to it. @someotherguy has a thread somewhere which explains how to calibrate your speedo and probably could answer this question too.

I would think everything in your 88 would be the same as my 89. To my knowledge there were no changes between those two trucks. (other than option packages each truck has)

yeah, AFAIK there's some minor differences like, the 88 dash trim is all black and the 89 has grey in it. The 88 Moonie gauges are a little different too, I think the 89 has hash marks on the dials - stuff like that...

 

[L31MaxExpress]

The ECM tuning on it is garbage. Hopefully runs better for you than it did for me.

 

[Komet]

You can completely remove the factory ecm and make all your stuff work. I'm guessing the Edelbrock has no speedo out because it doesn't tap into the VSS, does it have an input for A/C kick? That's the only thing the ecm would really need to know about from the chassis other than ignition on. The HVAC runs independently from the ecm.

 

[L31MaxExpress]

You can completely remove the factory ecm and make all your stuff work. I'm guessing the Edelbrock has no speedo out because it doesn't tap into the VSS, does it have an input for A/C kick? That's the only thing the ecm would really need to know about from the chassis other than ignition on. The HVAC runs independently from the ecm.

No ac input or park/neutral switch input both of which contribute to the disaster it is especially since you cannot get it to run with enough timing advance at idle to get an absolute stable idle. Retarded idle ignition timing plus no load compensation results in frequent stalling when load is added to the engine.