1227747 with 7.4 injectors AND knock retard

[clarkent5477]

Hello, apologies in advance for the newbie question: I'm continuing my quest to use 7.4 injectors on my old Cadillac. Is it possible to use the 1227747 PCM for it's knock retard capabilities AND use the 7.4 injectors with it? Or do adjustments need to be made? Many thanks in advance!!

[dave w]

What Cadillac engine are you working with?

The bore diameter is one of the factors for determining which Knock Sensor to use.

[clarkent5477]

What Cadillac engine are you working with?

The bore diameter is one of the factors for determining which Knock Sensor to use.

Hi Dave. It has a 4.125" bore with a 4" stroke. Will the 747 PCM pair with 454 injectors though? Would PCM interpret the exhaust stream as rich since it's pumping more fuel into the engine?

[NomakeWan]

If the injectors you intend to use have a different flow rate from the injectors that were used on whatever calibration is in your 1227747 PCM, then you will of course need to make changes to that calibration to account for the different injector flow rates. That's true for all ECMs in all cars.

[dave w]

So it's the Cadillac 425?

The SBC 400 has a 4.125 bore but did not use a knock sensor.

The SBC 5.7 has a 4.00 bore / 3.48 stroke.

The BBC 454 has a 4.250 bore / 4.00 stroke.

I'm not sure which knock sensor (5.7 vs. 7.4) is the better choice for the Cadillac 425. I'm guessing the 7.4 because the stroke is the same as the Cadillac 425.

The '7747 is a simple ECM and can be setup to use 7.4 injectors and a 7.4 knock sensor. The 5.7 knock sensor is mounted into the block coolant drain so the knock sensor would come into contact with the coolant. If I recall correctly, some 7.4 knock sensors were mounted to the BBC block and did not come into contact with the coolant. Some early (1987 Models) '7747 454's did not use a knock sensor.

I'm thinking a 1987 454 '7747 chip (without knock sensor) would be a good starting point. Once everything is up and running, add the knock sensor and update to a 1989 454 '7747 chip.

[dave w]

So it's the Cadillac 425?

The SBC 400 has a 4.125 bore but did not use a knock sensor.

The SBC 5.7 has a 4.00 bore / 3.48 stroke.

The BBC 454 has a 4.250 bore / 4.00 stroke.

I'm not sure which knock sensor (5.7 vs. 7.4) is the better choice for the Cadillac 425. I'm guessing the 7.4 because the stroke is the same as the Cadillac 425.

The '7747 is a simple ECM and can be setup to use 7.4 injectors and a 7.4 knock sensor. The 5.7 knock sensor is mounted into the block coolant drain so the knock sensor would come into contact with the coolant. If I recall correctly, some 7.4 knock sensors were mounted to the BBC block and did not come into contact with the coolant. Some early (1987 Models) '7747 454's did not use a knock sensor.

I'm thinking a 1987 454 '7747 chip (without knock sensor) would be a good starting point. Once everything is up and running, add the knock sensor and update to a 1989 454 '7747 chip.

Gearhead-efi link for 1777747 information, including .bin files: http://www.gearhead-efi.com/Fuel-Inj...Information-42