DIAGNOSIS USING ALDL FUEL FLOW ERRORS-INTEGRATOR/BLOCK LEARN

VEHICLES AFFECTED: All 1982, 1983 1989 And 1985 Models Equipped With EFI, MPFI, SFI, MFI, And PFI Engines

The information contained herein explains an ECM produced function called integrator and block learn. When analyzed with the use of an ALDL scan tool the information can be extremely important in analyzing fuel delivery on a vehicle. Integrator/Block Learn can serve the same purpose on EFI and PFI engines as does mixture control solenoid dwell (duty cycle) on CLOC carbureted engines.

INTEGRATOR

'Integrator' is a term applied to a means of temporary change in the amount of fuel delivered to the engine during Closed Loop operation. It has no effect in Open Loop. It is displayed on an ALCL tool as a number between 0 and 255. The average value is 128. The farther the number is from 128, the more correction the integrator is making. The integrator monitors the oxygen sensor output voltage and either adds or subtracts fuel from the system depending on whether it sees a lean or rich signal from the oxygen sensor. As an example when the number 128 is displayed, it indicates that the integrator is neutral; neither adding or subtracting fuel. It means that the oxygen sensor is seeing the results of a 14.7 to 1 air/fuel mixture burned in the cylinders. If the system were caused to go lean by introducing an air leak, the oxygen sensor voltage would decrease and the integrator would add fuel to correct for it. This would be indicated by an increasing integrator number. The higher the number, the more correction the integrator is making. This is accomplished by keeping the injectors energized a little longer. Correction for a lean mixture is indicated by a number above 128, correction for rich mixture is shown as a number below 128.

BLOCK LEARN

Although the integrator can correct the fuel delivery over a wide range, it is only for a temporary correction. Therefore, another control called Block Learn was added. Although it cannot make as much correction an the integrator, it does so for a longer period of time. It gets its name from the fact that the operating range of the engine for any given combination of RPM and load is divided into 16 cells of blocks. When the engine is operating at any given combination of RPM and load, the system would be operating in one of these blocks. The computer has a given fuel delivery stored in each block. As the operating range gets into a given block, the fuel delivery will be based on what value is stored in memory in that block. Again, like the integrator, the number represents the 'ON' time of the injector; therefore, the higher the number the more fuel would be delivered. Also, just like the integrator, the number 128 represents no correction to the value that is stored in that cell or block. When the integrator increases or decreases, block learn which is also watching the integrator will make a correction in the same direction. As the block learn makes the correction, the integrator correction will be reduced until finally the integrator will return to 128 if the block learn has corrected the fuel delivery.

Block learn will use one of two memory designs:

One is called Nonvolatile Memory and this simply means that the value in block learn is retained even when the ignition switch is turned 'OFF'. Therefore, when the engine is restarted, the fuel delivery for a given block will be based on what is stored in memory.

The other type is called Volatile Memory and means that the memory will be lost as soon as the ignition switch is turned 'OFF'. In this case, each time the engine is started the block learn would begin at 128 in every block and would correct from there as necessary to make the oxygen sensor see the results of a 14.7 to 1 air/fuel mixture in the cylinders.

If an engine were operating at a theoretically average condition for which the computer is calibrated, both integrator and block would read 128. If the engine were running slightly rich, the block learn would be a little lower, for example 124, and the integrator would be 128. The farther the integrator and block learn numbers are from 128, the greater the change is in the mixture from the design intent. This means that block learn can be used to get an idea as to whether the system is running lean or rich.

Both the integrator and block learn have limits which will vary with each engine design. If the mixture is off enough so that block learn reaches the limit of its control and still cannot correct the condition, the integrator would also go to its limit of control in the same direction and the engine would then begin to run poorly. If the integrators and block learn are close to or at their limits of control, the engine hardware should be checked to determine the cause of the limits being reached, such as vacuum leaks, sticking injectors, etc.

If the integrator is lied to, for example, if the oxygen sensor lead were grounded (lean signal), the integrator and block learn would add fuel to the engine and cause it to run rich. However, with the oxygen sensor lead grounded the ECM would continue seeing a lean condition eventually setting a code 44 and the fuel control system would change to open loop operation (as long as the check engine light is on).

Should an engine with Block Learn reading of (example) 120 be seen on an engine with a limit 113, no repairs are required. The engine with this example reading is still in control of fuel delivery and unless the high or low limits are displayed the system is making necessary adjustments. The rich or lean readings displayed will indicate what fuel delivery is required for that particular engine to operate at design intent of 14.7 to 1 fuel air ratios.

DIAGNOSTIC NOTE

Block learn and integrator numbers displayed on a Scan tool can be used to diagnose the fuel control system on fuel injected engines.

If the lower limits of Block Learn are reached (example: 113 on 3.8L MFI) the engine is running rich for some reason and would be compared to a 'fixed above 50 degree' dwell reading on a (CCC) carbureted engine.

If the high limits (example: 150 on 3.8L MFI) are displayed the engine is running lean an can be compared to a 'fixed below 10 degree' dwell for (CCC) carbureted engines.

A Block Learn reading of 128 would be compared to a "30 degree dwell" on (CCC) carbureted engines.

As with the carbureted dwell checking procedures, the block learn should be checked at idle and 3,000 rpms.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.