MPFI to SFI

[Supreme Cutlass]

What would be required (from an electronics standpoint) to take out my old (3.1) MPFI engine and ECM and putting in a new 3400 and it's ECM? most 3400 write-ups only deal with swapping to replace the 3100 how does this affect the things as far as the computer is concerned Vs. the UB3 cluster, etc.

[Robby1870]

You can run a 3400 with the 3.1L ECM. Its just wont be SFI, it'll be MPFI. I dont know if your set on SFI or not, but that might be easier. Switching from OBD1 to OBDII isnt easy. Someone on 60v6 board is just about done with his swap over, but its taken him a while.

[Supreme Cutlass]

Just use the 3400 wiring harness on the old computer?

[Brian P]

Switching from OBD1 to OBDII isnt easy. Someone on 60v6 board is just about done with his swap over, but its taken him a while.

 

you ain't kidding!!

[Robby1870]

Just use the 3400 wiring harness on the old computer?

 

Yeah. You might have to lengthen and shorten wires. Plus, the 3.1L ECM isnt going to need the cam sensor that the 3400 ECM does. Also, I cant remember this exactly, but I think you might have to use a different crank sensor, but Im not sure. Maybe someone can shed some light on that.

[OldSkoolGP]

I was the one doing that swap, and if you're going to run a 3400 it's definitely worth it. You don't want puddle fuel injection on a 3400. The hardest part in your case would be repinning the C100 connector to your car's pinouts. Also, if you plan to use the same tranny you have now, that will require doing wiring changes on the harness, or you can just use the tranny for the 3400, and you're set. There really wouldn't be much more beyond that. Mine was a PITA because I had to convince my ECM that it's controlling a tranny when it is in reality a 5 speed.

[99RegalGS]

Here's an idea. How about using a 94,95 3100 ECM? It's SFI and still OBD 1.

[GP1138]

Here's an idea. How about using a 94,95 3100 ECM? It's SFI and still OBD 1.

 

Actually, it's OBD 1.5, which is different from OBD 1. I don't know if there was ever an OBD 1 3100 car, but I could be wrong. Might see if you can find a '93 CS with the 3100.

[slick]

Here's an idea. How about using a 94,95 3100 ECM? It's SFI and still OBD 1.

 

Actually, it's OBD 1.5, which is different from OBD 1. I don't know if there was ever an OBD 1 3100 car, but I could be wrong. Might see if you can find a '93 CS with the 3100.

 

Really? Becaue when I had my 94' 3100 GP, I coulda sworn that I was able to read the codes with the paperclip method?

[99RegalGS]

Actually, it's OBD 1.5, which is different from OBD 1. I don't know if there was ever an OBD 1 3100 car, but I could be wrong. Might see if you can find a '93 CS with the 3100.

 

Well, It may be a hybrid, but it's still OBD1. So He'll still be able to get a free PC Tuner Program, and Just build a cable (or buy one for $30). Buy a EPROM burner (there are some for $40) and he can tune his own car. Unlike the OBD2 programs which are much more expensive.

[GP1138]

Here's an idea. How about using a 94,95 3100 ECM? It's SFI and still OBD 1.

 

Actually, it's OBD 1.5, which is different from OBD 1. I don't know if there was ever an OBD 1 3100 car, but I could be wrong. Might see if you can find a '93 CS with the 3100.

 

Really? Becaue when I had my 94' 3100 GP, I coulda sworn that I was able to read the codes with the paperclip method?

 

Hey, like I said, I could be wrong. :laugh: It wouldn't be the first time.

[ToroToro]

Actually, it's OBD 1.5, which is different from OBD 1. I don't know if there was ever an OBD 1 3100 car, but I could be wrong. Might see if you can find a '93 CS with the 3100.

 

The '93 3100 used the exact same ECM as the 94-95 models.

[GP1138]

Actually, it's OBD 1.5, which is different from OBD 1. I don't know if there was ever an OBD 1 3100 car, but I could be wrong. Might see if you can find a '93 CS with the 3100.

 

The '93 3100 used the exact same ECM as the 94-95 models.

 

I know that you can't pull codes with a paperclip with OBD 1.5. I know that for sure. And most '94's I've seen are OBD 1.5, that's what made me think most 94's aren't OBD 1. OBD 1.5 and 1 aren't compatible, they're different.

[ToroToro]

ALL '94s are OBD 1.5. As are the '93 3100 cars.

[Guest TurboSedan]

I was the one doing that swap, and if you're going to run a 3400 it's definitely worth it. You don't want puddle fuel injection on a 3400.

 

is that really an issue? not doubting you just never heard of that being something to worry about.

[Brian P]

considering sfi runs as MPFI above 3000rpm and under WOT too, I'm curious as well.

[GP1138]

In that case, I think I was right, then. OBD 1.5 is a hybrid of 1 and 2, but it's not the same as 1 at all. It's incompatible.

[Robby1870]

considering sfi runs as MPFI above 3000rpm and under WOT too, I'm curious as well.

 

Yeah, seems like a lot of extra work for nothing. I know the guy on 60v6 board was doing it for tuning reasons, but outside of those, I dont see the benefit.

[THe_DeTAiL3R]

Check out this guys' car. I beleive he is an active member at 60* (I don't go there that often).

http://www.3100mpfi.com/3100.html

 

He's got a 2000 3100 engine in his 1988 Cutlass...

[99RegalGS]

considering sfi runs as MPFI above 3000rpm and under WOT too, I'm curious as well.

From what I understand SFI isn't about all out performance. It's about smoothness and economy. My old cutlass used to sound like it had cams in it just idling. vs my dad's SFI 3100. MUCH smoother. Also it is proven that SFI is more efficent than MPFI, so when you're below 3000rpm's you're getting better gas milage. I'm not sure about you guys, but my car says under 3000rpm's most of the time. So why would I not want to have my engine to be as efficent as it can be where I use it most?

 

In that case, I think I was right, then. OBD 1.5 is a hybrid of 1 and 2, but it's not the same as 1 at all. It's incompatible.

How's it not compatible? The Hybrid OBD1 "OBD 1.5" Uses OBD2 standard codes ex: P0123. and they require a scanner to access the codes. Also, they have a EEPROM like OBD2 cars. I'm sure there are a few other things that were changes, but OBD 1.5 is more similar to the regular OBD1 than you think.

[SleeperRed90TGp]

What would be required (from an electronics standpoint) to take out my old MPFI engine and ECM and putting in a new 3400 and it's ECM? most 3400 write-ups only deal with swapping to replace the 3100 how does this affect the things as far as the computer is concerned Vs. the UB3 cluster, etc.

 

Yea changing ECM's would be a nightmare. :evil:If you stick with your old ECM and wireing harness the swap to a 3400 is a drop in. All wires will fit all sensors on the 3400. If you don't have a cam sensor on your 3100 just cut the wire off the 3400. Depending on what year motor you get you may have to change injectors or wire on the smaller injector connectrs to your harness. Don't remember what year they started using the tiny injector that have a different connector but thats about all your going to run into.

 

Jud

[Brian P]

considering sfi runs as MPFI above 3000rpm and under WOT too, I'm curious as well.

From what I understand SFI isn't about all out performance. It's about smoothness and economy. My old cutlass used to sound like it had cams in it just idling. vs my dad's SFI 3100. MUCH smoother. Also it is proven that SFI is more efficent than MPFI, so when you're below 3000rpm's you're getting better gas milage. I'm not sure about you guys, but my car says under 3000rpm's most of the time. So why would I not want to have my engine to be as efficent as it can be where I use it most?

 

 

Oh yeah it is a little more efficient, but it's not going to make-or-break the engine, performance, or its dependability. It might be good for 1-2mpg across the board, and a smoother idle. The biggest difference would probably be that with sfi's and 3100's you'll never get the brief engine hesitation when initially hitting the gas from idle (like a MPFI 3.1 does often) I know two people running mpfi programming on 3x00's with no adverse effects, no idle issues any worse than mine, and efficiency is almost as good as mine (theirs are a little more beefed up than mine though)

[GP1138]

considering sfi runs as MPFI above 3000rpm and under WOT too, I'm curious as well.

From what I understand SFI isn't about all out performance. It's about smoothness and economy. My old cutlass used to sound like it had cams in it just idling. vs my dad's SFI 3100. MUCH smoother. Also it is proven that SFI is more efficent than MPFI, so when you're below 3000rpm's you're getting better gas milage. I'm not sure about you guys, but my car says under 3000rpm's most of the time. So why would I not want to have my engine to be as efficent as it can be where I use it most?

 

 

The biggest difference would probably be that with sfi's and 3100's you'll never get the brief engine hesitation when initially hitting the gas from idle (like a MPFI 3.1 does often)

 

Ugh, it'd be worth it to me. Going back and forth from the 3100 and 3.1MPFI I HATE that little hesitation. It's unsettling.

[Brian P]

I hear ya on that. I was never able to get rid of that 100% on my old '90. Got REAL close though especially after the oxygen sensor was changed.

[GnatGoSplat]

I don't know about OBD-1, OBD-1.5, OBD-2, but a 94-95 3100 definitely has the same type PCM as 96+.

No removable PROM, they are flash-memory based and very non-tuner friendly.

 

If you want SFI and a tuner-friendly PCM, look into a 94-95 3.4 DOHC PCM. They are SFI and can control a 4T60-E. They also use a MEMCAL with PROM like an old OBD-1 PCM. They differ in pinouts a bit, but I can't imagine there being too much work if you use a 3.4 DOHC harness. Maybe extending/shortening some wires at the worst. As far as making it run, I bet it'd run and start without any modification to the code. Making it run well would just involve tweaking some numbers in the code.