Hey all. I'm about to do a manual swap on my 88. It's got a 2.5 Duke and an auto trans currently. I'm putting in the Isuzu 5 speed in place of the 3 speed auto. My main question is will I need a different ECM for the swap? It's staying a 2.5.
Hey all. I'm about to do a manual swap on my 88. It's got a 2.5 Duke and an auto trans currently. I'm putting in the Isuzu 5 speed in place of the 3 speed auto. My main question is will I need a different ECM for the swap? It's staying a 2.5.
yes. different chip or whole ecm and you gotta swap the harness to a manual one. you can convert the harness but its a real pain in the butt
Dennis LaGrua: What I would do is to replace the automatic with the 4T60 a 4 speed automatic w a shift kit. Thats a much easier almost bolt in conversion.
------------------ Original Owner of a Silver '88 GT Under 'Production Refurbishment' @ 136k Miles
Actually, all that needs to be done with the wiring is to eliminate the Neutral Safety Switch on the automatic transmission. It's a very simple procedure.
Cut and join the heavy gage yellow and purple wires. Cut the blue and green wire for the backup lights and wire a plug for the backup light switch for the Isuzu. Cut and insulated the orange/black and black/white wire ends.
WARNING - The modification eliminates the Clutch Safety Switch feature on the OEM wiring, so the car will be able to be started without depressing the clutch pedal. The car will be able to be started IN GEAR, you need to be aware of that.
Actually, all that needs to be done with the wiring is to eliminate the Neutral Safety Switch on the automatic transmission. It's a very simple procedure.
Cut and join the heavy gage yellow and purple wires. Cut the blue and green wire for the backup lights and wire a plug for the backup light switch for the Isuzu. Cut and insulated the orange/black and black/white wire ends.
WARNING - The modification eliminates the Clutch Safety Switch feature on the OEM wiring, so the car will be able to be started without depressing the clutch pedal. The car will be able to be started IN GEAR, you need to be aware of that.
Change the ECU or the EPROM.
I have a question about this. Could the existing neutral safety switch from the automatic be wired to the clutch pedal safety during the swap and act like the factory safety switch on the 5 speed cars?
Going from an automatic to a manual, as others have said, it should work just fine. You actually don't even need to swap out the ECM... you just have to deal with the Neutral Safety Switch.
A couple of things (some are already addressed):
- You will not have a clutch safety switch (meaning you can start the car in gear) - You will not have use of the shift light, since this is ECM programming
Going from an automatic to a manual, as others have said, it should work just fine. You actually don't even need to swap out the ECM... you just have to deal with the Neutral Safety Switch.
A couple of things (some are already addressed):
- You will not have a clutch safety switch (meaning you can start the car in gear) - You will not have use of the shift light, since this is ECM programming
I'm not sure if the automatic EPROM needs to see the 12v signal from the automatic NSS that is carried on the orange/black and black/white wires.
I have a question about this. Could the existing neutral safety switch from the automatic be wired to the clutch pedal safety during the swap and act like the factory safety switch on the 5 speed cars?
No. The clutch safety carries the solenoid signal to the C500, then to the starter. The NSS sees the signal from the C500 and closes to allow signal to solenoid.
So I saw a few ECMs on Rockauto and I'm wondering if one of those would work.
I have a diagram somewhere, but the ECMs are the same across the board for certain years... it's the EPROM / PROM that's different, and the wiring harness.
Let me see if I can find it:
EDIT: Yeah... so the ECMs are the same for all years except 1985. The 1985 ECM is actually a bit nicer (I'm told) than the other years, and has provisions for a knock sensor to be installed... just lacks the leads on the wiring harness, and a bit to be flipped in the PROM. But what you'll want to do is get a new PROM.
[This message has been edited by 82-T/A [At Work] (edited 03-04-2025).]
Originally posted by 82-T/A [At Work]: I have a diagram somewhere, but the ECMs are the same across the board for certain years... it's the EPROM / PROM that's different, and the wiring harness.
Let me see if I can find it:
EDIT: Yeah... so the ECMs are the same for all years except 1985. The 1985 ECM is actually a bit nicer (I'm told) than the other years, and has provisions for a knock sensor to be installed... just lacks the leads on the wiring harness, and a bit to be flipped in the PROM. But what you'll want to do is get a new PROM.
That's for the v6s, this is for a 4cyl, probably the same situation though
That's for the v6s, this is for a 4cyl, probably the same situation though
Shoot... sorry. Yes, it's the same deal with the 4 cyls. I know I have a diagram for it somewhere, but I can't find it now.
But yes... buy the PROM that you need, the ECMs are the same.
I wish I had known, I had a complete 5-Speed wiring harness, but it was from an 88 (slightly different). I ended up selling it on eBay for basically nothing (just didn't want to throw it out).
Originally posted by 82-T/A [At Work]: Shoot... sorry. Yes, it's the same deal with the 4 cyls. I know I have a diagram for it somewhere, but I can't find it now.
But yes... buy the PROM that you need, the ECMs are the same.
I wish I had known, I had a complete 5-Speed wiring harness, but it was from an 88 (slightly different). I ended up selling it on eBay for basically nothing (just didn't want to throw it out).
If using a manual transmission engine harness when performing an auto to manual swap, the engine side C500 plug would need to have the SOLENOID wire moved from E2 to A4 to match up with the automatic transmission chassis side C500.
This one here says it's for a 1987-1988 Fiero 2.5 / Manual Transmission: https://www.ebay.com/itm/146260148870 for $49 bucks. That one should work, and you should be able to swap it out with the one you already have.
If you look at the ECM you have now, there's a little panel on the face of it. It's held on by two 7mm screws. You remove those two screws and the panel comes off the front, and you'll see the chip. Be very careful, but you pry the old chip out, and install the new chip. MAKE SURE you look at where the original chip was installed. You CAN accidentally install it backwards, and it will ruin the chip. There's a notch on the chip holder, and also a notch on the chip socket (on the motherboard). The notches need to line up.
Here's an image I found (not mine) that shows a Fiero ECM with the panel off... you can see where the chip is (the larger one at the bottom). Take note of the notch, and make sure you install the new chip in the same direction with the notch facing the center.
