KYL98

Im just wondering what starting the engine with the "A" and "B" terminals on the ALDL does.... I remember doing that back in the summer accidentally while adjusting my IAC for minimum air, and my car hasnt been "right" since. Ive replaced almost everything, minus the ecm. Ive checked the timing, checked injectors, etc. I know my injectors need to be replaced but Im wondering if I screwed it up by doing that. It ran FINE before I did that that day. Basically its like this....The car runs FINE when you first start it until it warms up, or depending on outside temp. Then, it idles HORRIBLY and stumbles off idle sometimes....almost like the timing is off. But, I know its not, its been checked/set 3 times and I have checked to make sure the balancer hasnt rotated or anything funny like that. I checked the injector's resistance and only two of the eight were in "spec", leaving me to believe thats the culprit. But now Im starting to think I might have messed up the ecm by grounding the diagnostic terminals and then starting the engine.........anyway to check the EST to make sure I didnt short it out???? Ive had the car hooked up to a scan tool twice, and neither time did it show anything wrong....but Im running out of ideas here....HELP!!!!

CaptPicardsZ28

(Im just wondering what starting the engine with the "A" and "B" terminals on the ALDL does....)



It damages the ECM. I can't give you a proper diagnosis. Hopefully someone esle can.

dans82bird

AFAIK it you put something in the diagnostic terminals while the engine is running it will reset your timing ?

Virtualdemo

To my best understanding it only sets the ECM into Diagnostic mode. Depending on the series of flashes depends on what the ECM is sending you. I grounded and started mine as well... No problems. It did "act" funny for awhile till I shut it down and reset the ECM. I forget the specifics of the flashes but it has to do with you car being in open/closed loop or stuff like that...

KYL98 have you reset (disconnect the battery and clear codes) the ECM? When you do this the car "learns" all over again. I have three vehicles with the ECMs and have done this with all of em....

Damon

Won't hurt a thing. Virtualdemo is right. you're just starting in "diagnostic mode" which will, among other things, remove all ECM-supplied timing advance allowing you to set your ignition advance at the distributor to factory spec.

Do NOT shove the jumper in or out while running. Shut it off, remove the key and insert or remove the jumper and then restart.

Vader

Actually, the jumper (or any resistance below 500 ohms) can be inserted after the engine is running to invoke the Diagnostic / Field Service Mode. Attempting to start an engine while in Diagnostic Mode (diagnostic request terminal 'B' grounded, engine off) can damage the firmware (not always does, but can).

Diagnostic mode will will display malfunctions stored in nonvolatile memory and perform other functions as described below when the diagnostic display mode is enabled. This mode requires that the diagnostic request line be grounded and that the engine not be running (see EST).

Solenoid Energization
When the diagnostic display mode is enabled and the battery voltage is less than 16.9V, the diagnostic control logic will energize the AIR control, AIR select, TCC, EGR solenoid, A/C and EVAP canister purge solenoids. In addition, the idle air control motor will be continuously pulsed to retract while in diagnostic display mode.

The solenoid energization function is capable of operating without a calibration PROM installed in the ECM. The purpose of this function is to allow a means to force the ECM to energize its outputs for troubleshooting purposes, and to provide a means for exercising the ECM output devices during burn-in at the factory.

Malfunction Code Suppression
While the diagnostic display mode is enabled, the diagnostic control logic will force the diagnostic control counter to zero. This action has the effect of preventing new malfunctions from being logged into nonvolatile memory while the diagnostic display mode is enabled.

Malfunction Code Display
Each malfunction condition is associated with a two digit code number. When the diagnostic display mode is enabled, the diagnostic control logic will flash the check engine lamp in a logical sequence to depict the two digit code associated with each malfunction stored in nonvolatile memory.

Each code displayed will consist of a number of flashes representing the first digit followed by a short pause, followed by a number of flashes representing the second digit, followed by a long pause indicating the end of the code.

Each stored code is displayed three times before proceeding to the next code. After all malfunction codes stored in nonvolatile memory have been thus displayed, the entire flashing sequence is repeated.

Field Service Mode will display some basic ECM information via the SES lamp. 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.

Inserting a 3.9K ohm resistance in the diagnostic request pin to ground will invoke Factory Test Mode or Backup Fuel and Spark Mode ("Limp Home Mode"), which forces the ECM to use predetermined fuel calculations in the ECM PROM instead of the learned inputs in active RAM. Backup fuel is usually around 12:1 or richer from the factory. Tthe ECM will turn on the check engine lamp in this mode.

A 10K ohm resistance in the diagnostic terminal to ground will invoke the factory End of Line Test Mode, or ALDL Mode. When the assembly line diagnostic mode is detected, the fuel logic will bypass the closed loop time criteria. The fuel logic will enter closed loop mode as soon as the coolant temperature and oxygen sensor thresholds are met. There will be no reset of the integrator function. The IAC will use the calibration memory table value corresponding to a battery voltage of 8 volts, bypass certain criteria for RPM closed loop enable, and bypass coolant restrictions for enabling IAC kick-down mode. The EST system will disable the Burst Knock logic and bypass the RPM and coolant temperature criteria for ESC retard enable. That will force the engine into a condition where spark knock should occur if the throttle is suddenly opened (Burst Knock). Additionally, if ALDL mode has been enabled longer than a PROM timer value, the timer will be removed from the spark advance calculation. The TCC logic will allow the TCC to be enabled sooner and without regard to the CTS input.

89 Iroc Z

Vader, are you saying that when you are data logging through the ALDL with scanning software (for example Craig Moates software) the ECM is functioning differently then when you have an ALDL scanner disconnected? Could you explain this more? I learn something new everyday on this board.

Vader

Yes.

92 zzz28

Vader,
Can you explain that a little?

pvt num 11

Doesn't Limp-Home Mode get invoked whenever the ECM detects a Really Big Problem? I didn't know you could MAKE it do that...

MasterEvilAce

AFAIK, there are some "main" sensors... if any of them go off, or arn't responding for any reason, the ECM will have a hardtime calculating things, and it might go into limp mode

jpk91rs

I started my car, 91 RS, with the code reader on the plug and it made my car run like crap. I bought 2 used ecm's and installed 1 and my car runs like a champ now. When the car was at idle the Check Engine Light flickered. The motor idled really rough and was hard to start.