Stock ECU able to handle induction mods?

[bernie lomax]

have read that the stock ECU of say a 78 L28E w/ N47 may not perform accurately if the induction system were modified w/ CAI, 60mm TB, intake ported to match...am thinking of going forward w/ this modification but wanted to get some opinions (in the future, mild porting of the head may make sense also)...overall, the goal would be to achieve better low-mid range (2000-5000rpm) torque. (which maybe these mods takes me in the opposite direction) appreciate your thoughts & time

[z-ya]

The stock ECU is not all that intelligent. It will not automatically compensate for modifications to intake/exhaust etc. You need to screw with the AFM and the coolant sensor resistance to compensate for modifications.

 

Pete

[FlatBlack]

Ive done the 60mm swap and I'm using the stock AFM/ECU. I originally didnt have to do anything, but since then I have toyed with my AFM because I have 3 of them in my parts bin.

[Daeron]

There is a subtle art involved in tweaking an old L-jetronic system to accommodate "hard" performance mods. There are very few inputs to the computer, and it makes its fueling decisions based on these. By changing the fuel injector flow rate and/or pressure (in other words, changing how much fuel you squirt into the manifold every time the computer says "open") and ALSO modifying the input signals from the air flow meter and the CTS to attempt to match your fueling to the way the engine breathes after your intake/exhaust/cam/port/polish/pistons.

 

Unfortunately, since the car is equipped with at best a narrowband O2 sensor and a computer designed in 1974, you can't *really* know you have it tuned well without either dyno time or a wideband sensor and a gauge... which between them cost about 200 bucks. You can megasquirt an L28 for ~$800 if you take all the easy ways out, more like 5-600 if you do extra assembly yourself (both assuming you need pretty much everything; if you happen to have, say, a trigger wheel or ignition system you can re use, a GM MAP sensor, a wideband O2 sensor and controller, these things shave off of that rough figure.)

 

 

Twenty years ago it was worth it to try and enrich your maf a tiny bit, and maybe install a potentiometer or resistor inline with the CTS to give it the right amount of gas... but the results were hazy, and the procedures were a shade more involved than many feel like working with electronics. This is why most people scrapped the FI and threw SUs, a 4bbl, or triples on the cars for so many years. Now replacing the stock FI with a MS system is at least an equally viable option.

 

Find the EFI bible and read it through; it will teach you alot.

[z-ya]

Daeron, nice detailed write up.... (OK, I was a little lazy).

 

Even with adjustments to the coolant sensor resistance and or AFM tweaking, the chance of getting a flat AFR across all RPMs and loads is not likely. You will most likely end up with areas in the power band that are too lean or too rich, with no way of tuning them out. This is where a programmable ECU comes into play. In either case, you need a WBO2 and or dyno time.

 

Pete