I have a 91 Z28 with a 383 and Procharged D1SC. I have know clue or time on how to wire the FAST XFI so I had Jannetty Racing do it for me. They removed the old ECM and installed my FAST XFI to power the car but found out I lost my speedo/trip/odometer.

After 2 years of using my GPS for a speedometer I had enough. After a bunch of searching for clues and help from this site and chevythunder.com I finally decided to dive in and see if I could fix this.

I have a VSS buffer unit out of an 88 GTA but I read somewhere that it was suppose to wire it into my ECM so I figured that was out since I didnt have one powering the car anyhow. So I decided to use the original ECM and go that route first.

This was the mess I had to start with


After some serious wire checking and clean up


The XFI is now up in the dash and zip tied securely. I removed the dash pad to get at everything and secured everything down. I removed the original ECM bracket since it is going to be relocated in the rear of the car.

Items in the rear for mockup



Wires ready for plug in:


Bracket secured with screws ECM installed and zip tied to make sure no movement:


Got in the car fired it up, started rolling down the driveway and had movement. Got out on the road and everything is working perfectly. Checked speed against GPS and it was spot on, trip and odometer are rolling too

Here is how I wired it up:


Many thanks to this site and I hope this helps someone out with the same issue.

Lol,

Should have come to us first...

Maybe go back to Jannetty Racing to square it away...

Yes, I have no sympathy. You paid them, get them to make it right. After all , they are the ones that got the money.

Not looking for sympathy, just sharing how I fixed my issue. I think I did message you and was referred to Bob in Long Island to help me out but I didn't have the time to make the trip out there, deployments tend to hamper that. Either way its done.

How's it run with the XFI? Any issues at all? How much time into the tune so far?

Oh I see it's a fairly mild build so it should run ok.

Yeah nothing huge, Golen 383 engine and installation and tuning by jannetty racing. No issues except for the above.

I vaguely recall this. If you can wire in the OEM ECM, you could have easily wired in a 4-out buffer box. Which is also much smaller, is a cleaner install, and runs a lot cooler.

RBob.

Where would that Brown wire coming out of the Buffer Box (F-post) gone to if not the ECM A10 pin location?


Seems like over kill wiring up both units to each other when ECM can do it by itself without buffer box which is what I did. I think it is a clean install but to each his own I guess. No issues with cooling so i dont see the problem there. Wish I had all this great advice prior to fixing this instead of just a referral.

Jeff

That is where it goes for the '7165 ECM. Since that ECM can't buffer the magnetic VSS, the 4-out buffer box is used. I guess the XFI box doesn't have a VSS input? May be able to send it to it.

With the 4-out buffer there is no need to wire in the original ECM.

Need to check your thread:

https://www.thirdgen.org/forums/dfi-...echnician.html

You were the one looking for someone to do the work.

RBob.

Has anyone got a photo of the buffer box, as my speedo doesnt work and i dont know what im looking for. Is this the simplist wiring diagram to work to, photos would be great. Thanks

https://www.thirdgen.org/forums/tpi/...-location.html

The above shown wiring is partly correct. The A - H terminals are in the opposite order. You will see that in the picture in the thread.

RBob.

So why is there a port coming out of the buffer box to goto an ECM? Why did they waste the time to add that port if its going no where and does nothing.

Huh, funny when you look for post and show how I asked for someone to do the work and then you know how to do it but couldnt be bothered with it until I fixed it then all of a sudden there's input lol. Seems like if you know how it's wired you could have made a sticky post diagram and just directed me to it and we would have never had this conversation. Either way people with my type of issue now know they dont have to get a buffer box and they can just use their original ECM. Personally I like the way it came out and I have no worries either way. Cheers!

But it does do something. In the vehicles that the 4-out buffer was used, the ECM is not capable of buffering a magnetic VSS. So the 4-out buffer was used. It provides the VSS pulse streams to the cruise control (when required), speedometer, and the ECM.

The only 3rd gen f-body's with an ECM capable of buffering a magnetic VSS are the '90 - '92 TPI and MPFI equipped vehicles. Even the '90 - '92 TBI f-body's had the 4 out buffer as the ECM used was not capable of buffering the VSS (among other 3rd gen f-body cars).

And there is the issue, you didn't ask how to wire in a 4 out buffer, or what you could do to solve the issue. You apparently knew that a 4 out buffer would do the job as you mentioned having one.

In your thread you asked for information regarding whom could wire it in for you. Read your thread, I posted the link.

You received several replies of offers to wire it in.

If you asked how to wire it, the responses would have been different. Not only that, there are other threads that show the wiring for it.

RBob.

Great, I glad we got that cleared up. Yeah I did say I was looking for someone to do the work as I was in the weeds looking at all those wires. It would have been nice to see....."just do this, this, and this and you'll be good to go." Guess I gotta be more specific next time.

Since my ECM can take care of what I need, then I'm good. Some may not like it because its not easier, cooler, cheaper, etc., etc. to each his own. Like I said, I'm a novice but I think I did good for what I needed to be done and I learned a lot from my Chiltons book and chevythunder.com

It may be a good idea to post how to specifically wire up your buffer box version with a diagram since there are numerous questions dealing with this topic. This way you can just say see......< >post and be done it.

Jeff

Wow I could see why you were asking for help that's quite the rat nest lol! Looks like you got it working either way, good job.

I appreciate it. Learned a lot.