Let’s begin this chapter by agreeing that the “LS1 PCM” is just an ECU that has the designed purpose of controlling the sequencing of ignition and injector events based on a variety of sensor inputs. We can then agree that this ECU is uniquely programmed so that combustion results are favorable so that the stoichiometric ratio of air to fuel (approximately 14.7 to 1) is achieved during normal operating conditions (and so on). Simply put, the ECU can be calibrated for any V-6 or V-8 engine because General Motors designed it that way.
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Injectors and Ignition Coils
A very common question goes something like this, “How can I use the LS1 PCM on my Gen I small-block engine when the firing order between the two engines is different?” To answer this question, let’s take a look at how General Motors addressed this issue.
In model year 2001, General Motors released Gen I small-block and LS-series engines that all used the same PCM (GM# 12200411). The firing order for the Gen I small-block engine is 1-8- 4-3-6-5-7-2. The firing order for the LSseries engines is 1-8-7-2-6-5-4-3. Notice that cylinders 4 and 7 have swapped, and cylinders 3 and 2 have swapped. When you compare this PCM’s fuel injector wiring diagrams for the Gen I small-block with the LS-series engines, you see something interesting: General Motors simply swapped injector outputs 4 and 7, and 3 and 2 within the engine wire harness to address the firing order change.
Now compare this PCM’s fuel injector calibration details for the Gen I small-block and LS-series engine. EFILive reveals that General Motors also changed the injection bank assignments table values to follow the wire harness fuel injector assignments. The PCM must be calibrated to know which injectors are assigned to bank 1 (cylinders 1, 3, 5, 7) and bank 2 (cylinders 2, 4, 6, 8) so that fuel trims are applied to the proper bank of cylinders. If the injection bank assignments are wrong, fuel trims are extreme and the engine runs poorly and may even stall.
Although the PCMs are the same, the ignition systems are different. Gen I Vortec V-8 engines use a fourpulse, low-resolution, crankshaft signal for single coil and distributor ignition. LS-series engines use a 24-pulse (24x), high-resolution, crankshaft signal for coil-percylinder ignition. However, the same logic applies here if using a Gen I small-block engine with the LS-series engine’s 24x crankshaft signal. The wire harness requires that ignition coil assignments for cylinders 4 and 7, and 3 and 2 be swapped.
DTCs are assigned to ignition coil control circuits. The calibration table for the assignment of these DTCs is not available within most tuning software packages. A changed firing order may result in an incorrect DTC notification.
For instance, let’s say you have a PCM from a 2001 Camaro with the LS1 engine. You installed a 24x conversion on the Gen I small-block and made the necessary wire harness and injection bank assignment updates. During engine operation, the PCM determines that the ignition coil 4 control circuit has shorted to a voltage. The DTC P0357 for cylinder 7 is set. Because the firing order has changed, and the ignition coil control circuit firing order diagnostics table has not been updated, this DTC actually represents cylinder 4 because of the firing order difference between a Gen I small-block and LS1 engine.
To begin, open your previously saved calibration file or read the current calibration stored in your PCM (press Ctrl+ Pg+ Up). Once your calibration file is open in EFILive, access the Injection Bank Assignments table by expanding Engine Calibration, expanding Fuel, expanding Injectors, and then selecting the Injection Bank Assignments table.
For each fuel injector (labeled A through H in no particular order), the table indicates which bank of cylinders (bank 1 or 2) the fuel injector is located in. Bank 1 represents cylinders 1-3-5-7, and bank 2 represents cylinders 2-4-6-8. Notice all odd injectors are assigned to bank 1 and all even injectors are assigned to bank 2.
Let’s first look at the injection bank assignments for an LS1 engine. (See Figure 7.1.) The firing order for Gen III engines is 1-8-7-2-6-5-4-3. Because the engine firing order begins with cylinder 1, the injection bank assignments table uses Injector A to represent the fuel injector located at cylinder 1.
Moving along with the firing order, the fuel injector located at cylinder 8 is represented as Injector B, the fuel injector at cylinder 7 is represented as Injector C, the fuel injector at cylinder 2 is represented as Injector D, the fuel injector at cylinder 6 is represented as Injector E, the fuel injector at cylinder 5 is represented as Injector F, the fuel injector at cylinder 4 is represented as Injector G, and the fuel injector at cylinder 3 is represented as Injector H.
Now let’s look at an engine with a different firing order, the Gen I small-block. This firing order is 1-8-4-3-6- 5-7-2. Just as with the LS1 example above, you see that the fuel injector at cylinder 1 is represented as Injector A and along the engine firing order through cylinder 8 represented by Injector H. Once again, all odd injectors are assigned to bank 1, and all even injectors are assigned to bank 2.
Six-cylinder engines do not use this entire table. If you were to open a calibration file from a 2001 S10 4.3L PCM (see Figure 7.1), you would see values for the last two injectors, G and H. (See Figure 7.2.) This is because the “LS1 PCM” is simply an ECM that is calibrated for the engine in which it is being used.
For the injection bank assignments table to exist in the PCM’s memory space, it must be dimensioned. A programmer must define the size (memory space) that an object (such as a table or constant) requires. In this case, General Motors intended for this injection bank assignments table to be used with an engine that contains no more than eight cylinders. This is why the table displays eight injectors for a calibration file written for an engine with only six cylinders. (Had General Motors written a calibration file for a PCM for an engine with four cylinders, the table would also display eight injectors.)
This is simply a lookup table as the PCM knows (from elsewhere) that this engine has six cylinders, is using a low-resolution 3x crankshaft signal to know engine position, and to fire injectors once every 60 degrees of crankshaft rotation. The last two injectors represented in this table are simply ignored when the PCM looks for injection bank assignments. The firing order for this 4.3L V-6 engine is 1-6-5-4-3-2.
Again, begin with the fuel injector at cylinder 1 being represented as Injector A and move along the engine firing order through cylinder 6 represented by Injector F. Here also, all odd injectors are assigned to bank 1, and all even injectors are assigned to bank 2. The value of Injector G and Injector H are ignored.
Written by Mike Noonan and Posted with Permission of CarTechBooks
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