3.4L DOHC Fiero Engine Swap Guide
page 6
At this point you can elect to do continue on several different ways. I decided to get on the A/C and wiring. For the A/C system, I used the A/C compressor from a 94-up 3.4L DOHC engine which was R134a compliant. I also got a set of A/C lines that fit that compressor. I took the compressor lines and matched them up with the stock Fiero lines and noted the length and orientation. I have heard that some people were able to get stock 4 cyl lines to work with this swap, but due to clearances between the firewall and compressor, I could not get it to work without some more fabrication. I checked into custom A/C lines and Ace Radiator of Fort Wayne, Indiana said they could do them for around $100. I took them the lines along with my schematics for orientation and length (they would have preferred to have the car) and they welded on some new connectors (for the hose) and crimped on new A/C hose -- all for less than $100.
With the A/C done, I continued on with the wiring. The stock 91-93 3.4L DOHC ECM will fit in the stock Fiero ECM location, but the wiring connectors are different so you will have to splice the harness and connectors together. I recommend solder and shrink tubing to ensure a positive, weatherproof connection.
Using the stock Fiero 2.8L harness and manual transmission, you will only need to add a few wires to make this ECM function properly. You will need to add the following wires and components to this ECM:
Knock Sensor wire
1 of the 3 EGR solenoid wires (you can use the existing Fiero EGR control and Diagnostic wires for the other two solenoids)
EVAP solenoid control wire
Clutch Switch wire
A/C hi-side pressure sensor (3 wires)
I also elected to wire up 2 separate fan relays to the existing Fiero fan relay circuit in the car so the ECM fan relays are independent of each other and either only serve to activate the existing fan relay in the Fiero. The A/C clutch control relay has to be rewired to match the schematics of the 3.4 DOHC ECM otherwise the ECM may not control it correctly. The A/C hi-side pressure sensor is a 3-wire transducer that screws onto the hi-side port (located in the front spare tire compartment). Without this sensor, the ECM will not activate the A/C clutch and will not turn on the radiator fan once the A/C head pressure gets high enough to request it.
As far as the engine wiring the stock 2.8 Fiero harness is plenty long for use on the 3.4 DOHC engine. I had to change the following connectors on the 2.8 harness to be compatible with the DOHC engine:
Ignition control (DIS)
TPS
IAC
EGR
Aside from that, all you need to do is wire-in/shorten the injector plugs, MAP sensor, coolant temp sensor, the IAT sensor can stay in the stock location, EVAP, VSS, knock sensor, etc. The only wires I did not have to shorten on the 2.8 harness was for the MAP sensor which were just about the correct length.
With the wiring done, you can move on to the cooling system. I regret I don't have any pictures of what I did for the cooling system. Basically all I did was take measurements and note the orientation of the water outlet, inlet, heater hoses, and bypass and went to the local parts store and bought molded radiator and heater hoses that met my specifications (most parts stores will let you walk behind the counter and inspect the hoses they have in stock).
With the cooling system all hooked up, I moved on and finished the air induction. I used the stock Fiero airbox but modified it for better flow.
I used air induction tubing from a 3.1 W-body car to connect the throttle body to the air filter assembly. There was a hole in the top of the air tubing for the crankcase vent system (which I didn't need since I routed mine to the stock fiero aircan) so I plugged the hole with an IAT sensor.
I did have some other small clearance issues with the wiring harness at the bulkhead pass-thru and oil filler cap. To remedy this problem I cut the bulkhead out and moved up and rotated the wiring connector pass-thru to give me a little more room to get the oil filler cap out.
I ordered a Fuel Rail cover for a 95 Lumina Z34 which is a little different than the earlier versions but I think it looks better. Aside from that I think that pretty much wraps up the major points to this swap. If you have any questions about anything pertaining to this swap please feel free to drop me an email.
