jodylee8310@aol

heres the story, i have a 1987 transam with a L98 350 tpi.I had the motor rebuilt bored 30 over with flat top pistons everything else is as it was before except changing the thermostat to a lower temperature.I kept getting a code for my egr valve when driving it for long distances. i found out i had a vacum leak and have also replaced the egr.We put new seals throughout the fuel rail also on top and bottom of the injectors.I have replaced the tps sensor and have set it to its correct voltage.I have replaced the maf unit.I also have gone through the correct procedures for the iac valve set up.Still i have a idle problem when i start the car it sounds like it has a radical cam. it will idle to about 1000rpm for about 10 seconds then it will drop down to about 600rpm with a lope to it.the car will run like a bat out of hell when you step on the gas but it just want idle correctly at a sit still.The car idled fine before replacing the egr valve and doing the fuel rail,and now the exhaust fumes are killer.I thought i might have another vacum leak but i cant hear one, or maybe the iac valve is not working correctly.I have also considered replacing all the vacum lines,and checking the fuel injectors.Maybe someone else has had the same problems and can give me a little insight.I also need a vacum diaghram so i can check to see if all the lines were put back as they were we had the car painted and of course all the stickers are gone.Also can anyone give me the correct proceedure to checking the fuel injectores?

Vader

What temperature thermostat did you install? If it is under 180°F you'll have problems unless you reprogram the ECM.

jodylee8310@aol

vader i believe the thermostat was a 160 or 170,how does this affect the running of the car.it use to run about 220 all the time but now it takes a while of driving to get it there,it runs about 160 most of the time unless you drive it for long distances then it gets to about 220,we usually only drive the car about 15 miles at the most around town.

Vader

The ECM references the coolant temperature sensor for many functions. Unless you reprogram the ECM, you need to reach 176°F before the ECM will allow full closed-loop operation.

These are some of the CTS related parameters in the ECM programming:

AUM/BUA Closed-Loop Operation Parameters
CTS < 14.7°C (58°F) for 75 seconds;
CTS >14.7° (58°F) and < 40.7° (105°F) for 51.4 seconds;
CTS >40.7°C (105°F) for 12.5 seconds;
O2 >0.699V & O2<1.99V for 10 seconds;

Coolant Temperature Sensor Related Parameters
BLM enabled between 50°C (122°F) and 140°C (284°F)
Cold spark advance disabled above 56°C (133°F)
Hot spark retard begins above 116°C (240°F)
Highway Mode spark advance > 59.8°C (140°F)
Knock sensor disabled below 66.5°C (152°F)
Power enrichment at base A/F ratios > 56°C (133°F)
Target IAC idle RPM >80°C (176°F)
IAC multiplier at 1.0 (base) > 32°C (90°F)
Knock Control enabled > 67°C (153°F)
EGR Duty-cycle enabled at 56°C (133°F)
EGR Duty-cycle at MAX >80°C (176°F)
TCC lockup enabled >50°C (122°F)
SHIFT light enabled >50°C (122°F)
Diagnostic communication enabled at 70°C (157°F)
DTC 43 enabled > 90°C (194°F)
Cooling fan #1 enabled at 107°C (226°F)
Cooling fan #1 off at 104.7°C (220.5°F)
Cooling fan #2 enabled at 115.2°C (239.5°F)
Cooling fan #2 off at 110°C (230°F)
Cooling fan duty cycle at 100% at 80°C (176°F)
Acceleration enrichment multiplier at 1.00 below 80° C (176°F)
Acceleration enrichment multiplier at 0.75 above 80° C (176°F)
Acceleration enrichment multiplier at 0.50 above 104°C (220°F)
Acceleration enrichment decay factor at 25% below 80° C (176°F)
Acceleration enrichment decay factor at 40% above 80° C (176°F)
Acceleration enrichment decay factor at 50% above 104° C (220°F)
Acceleration enrichment decay factor at 60% above 128° C (262°F)
Fuel limiting factor timer at 217 counts below 80° C (176°F)
Fuel limiting factor timer at 169 counts above 80° C (176°F)
Code 13 (oxygen sensor fault) enabled above 70°C (157°F)
Code 14 (CTS high fault) enabled above 130°C (266°F)
Code 32 (EGR fault) enabled above 30.5°C (87°F)
EVAP canister purge enabled above 70.3°C (158.5°F)
Hot closed-loop timer enabled above 70.3°C (158.5°F)
Rich/Lean O2 offest at 16 counts between 20°C (68°F) and 92°C (197.5°F)
A/C clutch disabled above 150°C (302°F)

Miscellaneous
25.3° maximum allowable knock retard when not in WOT

jodylee8310@aol

car still runs about 190 to 220 all the time except it just takes a while to get it there.what is open loop compared to closed loop operations how does it affect the running of the motor

Vader

How does the ECM mode affect engine operation?

The 1985½-1988 TPI system utilizes the following sensors and devices to control the engine: Mass Air Flow Sensor, Manifold Air Temperature, Coolant Temperature, Oxygen Sensor, Throttle Position Sensor, Cold Start Switch, Cold Start Injector, Fuel Injectors, Idle Air Control Valve, Exhaust Gas Recirculation valves, Distributor Electric Spark Timing, (Module in distributor TPI) Electric Spark Control, Module and Knock Sensor.

When the ignition power is first applied to etheECM, the ECM performs a Power-On Self Test (P.O.S.T.) routine.

ECM P.O.S.T. Routine

* RAM Error Detection and Corrective Action;
* NV-RAM Diagnostic Checksum;
* High Voltage Disable of ECM Outputs;
* All A/D inputs read;
* All discrete inputs read;
* All pulse accumulator/pulse period/pulse integrator inputs read;
* PWM outputs energized individually;
* Discrete outputs energized individually each 50-100 mSec;
* Check engine light turned off;
* EST mode disabled;
* Synchronous fuel delivery disabled;
* All discrete outputs de-energized;
* All PWM outputs de-energized (0% duty cycle);
* Asynchronous fuel output fixed at 3 msec every 6.25 msec;
* Checksum of nonvolatile RAM calculated;
* One second ECM turn off delay;
* IAC outputs on, but not changing state;
* EPROM Checksum;
* Check engine light turned on.

That all takes about 1.0 seconds.

When the starter is engaged and the coolant temperature is less than 100 deg F. The cold start injector provides a spray of fuel, of 8 seconds duration max, to each cylinder via a air distribution system built into the intake manifold. If the engine temperature is greater than 100 deg F, the cold start injector is disabled by the cold start switch. Upon startup the ECM utilizes information in the calibrator to establish the initial pulse rate for the injectors and the engine starts. At this time the engine is operating in open loop mode and will continue to do so until the engine warms up. After the warm up period the ECM scans the sensors, if all sensors are operating and within their proper range, the engine then goes into closed loop operation. This means that the sensors are dynamically controlling the engine. In the event the information received is higher or lower than the normal range, a code will set in the ECM, and the Check Engine or Service Engine Soon light will come "on". The ECM receives information on air flow, engine temperature, air temperature, exhaust gas oxygen content and throttle position. This information is used to calculate the proper pulse width for the injectors and fires the injectors for the calculated period. This procedure is repeated continuously in very rapid sequence to maintain the optimum fuel air ratio. The electronic spark control components provide maximum advance, if engine knock is detected the spark is automatically retarded. This too, is a continuous process. It should be noted that the following components are MATCHED for optimum performance; Distributor - EST module, ESC module, knock sensor and ECM calibrator. These components are not interchangeable between 5.0L - 5.7L engines.

GM OBD I System Operation

This generation of engine control systems is a refinement of the first engine control computers and systems. First generation engine controls have some control over spark timing, a few output devices like the EFE system and EGR, and a minor role in fuel mixture adjustment. The OBD I system is designed to control and sense a wider range of functions than the earlier systems, including complete control of fuel delivery, and has proven to be much more reliable and effective.

The system has two basic modes of operation when the engine is running - Open Loop Mode and Closed Loop Mode. In a nutshell, Open Loop mode means the ECM is controlling the engine with essentially no feedback from the engine sensors - the control loop is said to be "open". Closed Loop mode means that the ECM sends control signals to the engine, scans the sensors for feedback to determine further corrections, then adjusts accordingly. The process is continuous, and the control loop is said to be "closed" since the sensors effectively communicate back to the ECM regarding the effectiveness of any adjustments made.

Open Loop Mode

When the starter is engaged, if the coolant temperature indicates less than 100°F and the intake air temperature is within 20°F of the coolant temperature, the cold start injector provides a spray of fuel or the cold enrichment subroutine allows longer fuel injector pulses on the service injectors. The cold start or cold enrichment subroutine is of eight seconds duration at a maximum. On a cold-start injector system the extra fuel is distributed to each cylinder via a air distribution system built into the bottom of the intake manifold. If the engine temperature is greater than 100°F, the cold start injector/subroutine is disabled by the cold start switch or ECM. Upon startup the ECM utilizes information in the PROM to establish the initial pulse rate for the injectors and the engine starts. At this time the engine is operating in Open Loop mode and will continue to do so until the engine warms up sufficiently to enable the oxygen sensor.

Closed Loop Mode

After a warm up period the ECM scans the sensors. If all sensors are operating and within their proper ranges, the ECM will enter Closed Loop operation. This means that the sensors are dynamically controlling the engine fuel and spark. The ECM receives information on intake air flow, coolant temperature, intake air temperature, exhaust gas oxygen content, barometric pressure, manifold pressure or vacuum, air conditioner status, power steering pump load, EGR operation, evaporative canister valve operation, engine RPM, vehicle speed, transmission gear selection, fuel pump status, combustion detonation, and throttle position. This information is used to calculate the proper ignition timing advance and pulse width for the injectors, and fires the injectors for the calculated period. This procedure is repeated continuously in very rapid sequence to maintain the optimum fuel air ratio. The electronic spark control components provide maximum advance, if engine knock is detected the spark is automatically retarded. This too, is a continuous process. It should be noted that the following components are matched for optimum performance - distributor EST module, ESC module, knock sensor and ECM PROM. These components are not interchangeable between 5.0L - 5.7L engines. In the event the information received is higher or lower than the normal range, a code will set in the ECM, and the Check Engine or Service Engine Soon lamp will light.


Block Learn / Integrator

The factory ECM/PCM has a learning capability which allows it to make corrections for minor variations in the fuel system to improve performance and driveability. There are two learning features. The Integrator and Block Learn (INT and BLM) and Block Learn Memory (BLM) cell. The INT and BLM feature is normal with a value of around 128 (the possible range is 0-255). If this value is higher than 128, it indicates that the ECM is adding fuel to the base fuel calculations because the system is running lean. A value lower than 128 indicates that the ECM is taking out fuel because the system is running rich. The integrator is a short term corrective action while the BLM is along term correction. The BLM value will change if the integrator has seen a condition which lasts for a longer period of time. There are from two to sixteen different cells which the ECM modifies, depending on RPM, airflow or manifold air pressure and other conditions such as AC on or off, etc. The ECM learns how much adjustment is required in each cell, retains it in memory, and applies these adjustments when the engine operates in that cell or RPM/Load Range. These features of the ECM allows the system to adjust itself constantly to your engine and assure peak performance for stock and other than stock engines.

NOTE: When the vehicle power is disconnected for repair or to clear diagnostic codes, the learning process has to begin all over again. To reinitialize the ECM, drive the vehicle at operating temperature with moderate acceleration and idle conditions for at least twenty minutes.

Performance PROMs typically change the parameters for fuel flow, fuel cut-off and spark advance-timing and will allow increased fuel flow and modify the spark advance curves during rapid acceleration. They can be programmed to tolerate differences in idle quality and manifold vacuum due to altered cam profiles and fuel systems.

Field Service Mode

On the OBDI ECMs, you can jump 'A' and 'B' terminals on the ALDL while the engine is running.
WARNING! This must be done after the engine is running. This is called "Field Service Mode" and will not harm the ECM.

If the ECM is in Open-Loop mode, the SES light will flash rapidly, about 2½ times per second. If it's in Closed-Loop mode, it will flash about once per second. When in Closed Loop mode, flashing less than once per second indicates the ECM is enriching the mixture above the 128 count base line. Flashing more than once per second indicates the ECM is leaning the mixture below the 128 base line.

Backup Fuel Mode

A 3.9K resistor installed between ALDL terminals 'A' and 'B' forces the ECM into Backup Fuel mode. This mode forces the ECM to use predetermined fuel calculations in the ECM PROM instead of the learned inputs in active RAM. This is more commonly referred to as the "Limp Home" mode of operation. Backup fuel is usually around 12:1 or richer from the factory.