85 GT 3.4 (Page 1/1)
mnicolia OCT 02, 11:11 PM
I bought an 85 Fiero Gt few months ago, and the previous owner had the Fiero Factory upgrade the engine in it to 3.4 93-95 Camero/Firebird. Since I've got the car the speedo isn't correct it runs about 10mph faster than the car is actually going, nor the shift light correct. So I'm assuming when they put the 3.4 they used the donor computer? I don't know really anything about these swaps. So if anyone can help me understand the swap, and knows what I might be able to change to correct the speedo, not as worried about shift light. Also the Fiero has a 5sp and the rear seal on the drivers side is leaking, I replaced it about 200 mi ago and now its back leaking. The axle shaft didn't look in bad shape, anyone know what might be causing the new seal to leak again after about 200 miles?

Thanks
Michael

[This message has been edited by mnicolia (edited 10-02-2022).]

fierofool OCT 03, 07:23 AM
The swap uses the stock Fiero computer. The only thing that changed in the swap is bore and stroke. The 3.4 is otherwise the same as the 2.8 so that wouldn't affect the speedometer.

JGunsett on this forum recalibrates gauges. You might contact him. Changing vss gears wouldn't fix the variation.

How is the shift light not correct?

[This message has been edited by fierofool (edited 10-03-2022).]

fierofool OCT 03, 07:29 AM
Also, the shift light wont work in 4th if it has the 85 ecm. The speed variation is probably due to tire size if the 5 speed came from an 86 or later gt. 4 speed cars had 14 inch tires. GT 's had 15s.
Blacktree OCT 03, 12:12 PM
IIRC, the '85 GT didn't come with a 5-speed. So they probably swapped the trans as well. That may be why the speedo and shift light are acting strange. You could swap in an ECM from a v6 5-speed car, or reprogram the existing one.