Hi guys I'm new to the site so forgive me if I'm asking something that's already covered. Just point me to the right thread if so. I'm putting an XFI in my recently acquired 92 Z28. My question is if I remove the stock computer what other functions than engine control do I lose? I'm fine with losing the dash gauges since I'll probably put aftermarket in it anyways. I've got a lot of experience with the FAST stuff, just none with putting one in this generation of GM ecm's. Thanks in advance for any and all help.

 

If it was originally a TPI then you lose the VSS signals to the speedometer and the cruise control.

If it was originally a TBI you lose nothing.

RBob.

 

Thanks for the info. It was a 305 TPI 5spd so cruise is probably the only issue. I believe there's a way to get cruise another way too. I'm putting a 4L70E in it next week and will be able to send that VSS to the speedo but will probably need to change the speedo since it was a manual car originally.

 

I have a 91 Z28 with a 383 and FAST XFI in it and I'm having he same issue right now. No speedometer/odometer/trip/crusie. I want to keep the factory gauges. There's gotta be a way to get the electronic signal from the vss to the speedometer. Anyone had this issue that solved their problem without changing gauges.

 

Find and use a "4-out buffer" box from a '90 - '92 f-body with a TBI set up. The later MAF TPI Firebird cars also used this box. Along with some TBI Caprices. It is yellow or white, under the dash on the passenger side.

The VSS gets wired into it, and there are four outputs available for the speedo, cruise, ECM, and a spare.

RBob.

 

i put the FAST EZ efi in my car and my ECM is gone but all of my gauges work along with the cruz. when i installed i was careful to cut only what wasnt needed. i know this isnt the XFI but it still deals with the same issue.

 

Being a later TPI MAF Firebird car it has the "4 out buffer" box in it from the factory. In the '90 - '92 TPI and MPFI f-body's the ECM does the VSS buffering. Which is why the VSS signals go away when the factory ECM is removed.

Under the dash on the passenger side, look for a flat yellow (sometimes white) plastic box with a paper label that has "4 OUT BUFFER" on it.

RBob.

 

Rbob, think the instruments would work if the ECM was left alone and only the needed items to run the system were used?

on the EZ i tapped into the fuel pump system and the heavy red wire for the dizzy, everything else was more or less left alone. glad you educated me on the 90-92 cars as a friend has a healthy motor in his Heritage Z and the shop that the tune was done at is gone and the guy that does the tuning is dang near impossible to contact his only option is to go with the EZ system or the XFI.

right now i hae him likeing the EZ and id hate to finally get him tuned but lose all instruments.

 

Can leave the factory ECM to provide for the VSS buffer. Just need the battery+, ignition+, and ground to it. Along with the VSS input and outputs.

Another option for tuning is an EBL P4 Flash in the stock '7730 ECM.

RBob.

 

RBob i'll make note of this as i'll probably run across another car that will need this done to.

 

I got the 4 out buffer box and hooked up power, ground, VSS PRP & YEL but not sure what colors for speedo and cruise. Are they in the same clear connector as the pnk/blk and ground?