Tbi Tpi Mpi Sfi, C4 Efi.

[Patton]

I thought all of the LT-5's used tuned port injection.
According to this chiltons book I have here, They all used Multi Port Fuel Injection.

I'm gonna have to take that plate off of my cigarette lighter door. :icon_scra

Can anbody confirm or deny this?

[Aurora40]

Multi Port and Tuned Port are basically the same thing. There is an injector in each intake port. As opposed to Throttle Body Injection, where there is one or two injectors at the throttle body (like an electronic carburator).

The ZR-1 is actually sequential also, meaning the injectors are fired individually. On TPI L98's they are all (or several are) fired at the same time, meaning fuel will pool a bit waiting for a piston to hit the intake stroke.

Edit: I wish they'd put some other lettering on the molding than "Tuned Port Injection" for the 1990. Something to differentiate it from the L98 car.

[Patton]

Kick@ss Port Injection has a nice ring to it....


Thanks for shedding some light on that for me. I love reading crap like that, Let me write exatly what it says.

YEAR | VIN | Fuel Sys |
1984 | 8 | TBI
1985 | 8 | TPI
1986 | 8 | TPI
1987 | 8 | TPI
1988 | 8 | TPI
1989 | 8 | TPI
1990 | 8 | TPI
DOHC | J | MPI
1991 | 8 | TPI
DOHC | J | MPI
1992 | P | MPI
DOHC | J | MPI
1993 | P | MPI
DOHC | J | MPI
1994 | P | SFI
DOHC | J | MPI
1995 | P | SFI
DOHC | J | MFI
1996 | P | SFI
LT-4 | 5 | SFI

[Aurora40]

Yeah, in 1984, it was the Crossfire injection. It was two throttle bodies, each with an injector. There was a mechanical linkage connecting the two throttle bodies. It was really like having dual electronic carbs. The fuel amount was just more precisely metered.

I think GM used "Tuned Port Injection" just to describe the L98 and whatever the 305 version was called. They seemed to use "Multi Port Injection" to describe other motors with batch-fired injectors, one per cylinder. I don't know if there was a real difference between MPI and TPI. But the LT5 would be considered SFI.

Sequential Port Fuel Injection is really like an advance in engine managment capability. PCM's are like your desktop computer in a way. They just get faster, better, and cheaper. More controller power meant that each cylinder could be controlled individually, and each injector is pulsed independently. Prior to that, I think it was really that hardware to support didn't exist or was too costly to be feasible. SFI is really what you think of when you think port fuel injection. One injector per cylinder, being controlled specifically for that cylinder.

Even though you'd think that about TPI, all those injectors would be fired at the same time, even though some cylinders weren't on the intake stroke. So the fuel would just sit there and wait. But it was better than throttle body injection.

I guess what I'm saying is that TPI, MPI, SFI, TBI, these are just terms GM came up with for fuel injection. What really matters is how the fuel delivery and control is implemented on your car, not what name it has. The LT5 is pretty good, especially given the time period.

I believe there are still improvements since then, though. I believe the LT5 ECM can't make control decisions on a per-revolution basis? It sees things as a 25 rotation window or something? I thought I recalled reading that somewhere. And it can't control the primary and secondary injectors independently. They pulse the same as the primaries (which is probably not a big area for improvment anyway). I believe in the last year or two, GM has started putting in a new-style oxygen sensor that has a much wider field of view than our style of sensor. All sorts of things that continually improve.