ecu problem

[wikdgsxr]

ok so my car is running good but not as well as it has before i am thinking it has something to do with the code on the ecu. it is a 93 altima with jwt tuned ecu. the code is code 21--ignition signal in the primary circuit is not entered during engine cranking or running...if anyone knows what direction i could go to fix this code let me know i running in circles now. i am running msd ignition box and coil and the car turbo'd but dont think it any of that cuz i checked msd already

[jserrano]

I'm not entirely familiar with MSD ignition but I can tell you about code 21 from the OEM perspective.

The ECU uses a condenser/resistor component to pick up a sampling signal from the primary side of the ignition coil. This feedback signal is called the Ignition Check. You can think of it like an engine "heartbeat" check. When the ECU misses this signal during engine cranking or running, it believes that there is a fault within the primary side of the ignition. If you have access to an oscilloscope you could test pin 3 of the ECU to see if the signal is missing or has the wrong waveshape or amplitude.

Unless you've changed something in the ignition side, I'm more inclined to think that something is wrong with the MSD ignition. Asleep, and a few others, have a good deal of experience with MSD. Perhaps they can throw in a few more words on this...

[wikdgsxr]

i havent changed anything with the ignition side xcept a while back the ignition went out and i had to replace it i wonder if maybe that could be it again. the guy from msd said that maybe i need a feedback signal to the ecu and i have that extra part but he said from his knowledge that the 93 altima didnt need it. so pin 3 on the ecu huh could you explain how i could check that in more detail if you dont mind. r u talkin bout tracing wire and checkin continuity?

[Asleep]

code 21 is a normal code when you run msd since the unit cuts into the ecu's signal.

[khooper]

You will need a high impedance, Minimum 10 Meg (10,000,000) ohm input impedance, Digital Volt Ohm Meter (DVOM) to test the HO2S.

1. Make sure the vehicle is at normal operating temperature. Run the engine at 2,500 rpm for 3 minutes with the transmission in PARK (A/T) or NEUTRAL (M/T).
2. With engine OFF, connect the negative lead of the DVOM to engine ground. Set the DVOM to read DC VOLTS. Disconnect the oxygen sensor (O2S) electrical connector and connect the positive lead of the DVOM to the oxygen sensor signal wire (black/dark green).
3. Start engine. Create a lean condition for 10 seconds . Voltage should decrease to 0.2 volt or less and remain there.
4. Create a rich condition for 10 seconds. Voltage should increase to 0.8 volt or more and remain there.
5. If sensor fails to vary according to the test steps above, the sensor is defective.
6. Connect sensor and clear codes.

If it passes this test then you will have to look at the wiring and a possible bad PCM. There is only one HO2S in the system.

______________________________
Car Tech knows how to Maintain Car

[jserrano]

Every Nissan that triggers a code 21 needs the Ignition Check feedback signal. Perhaps the MSD guy is talking about something else so make sure you both are "on the same page."

The capacitive discharge ignition (CDI), like MSD, uses a big capacitor, and some additional electronics, to store a very high voltage across the primary ignition coil. Discharging this high voltage will cause a larger voltage to be induced across the secondary side of the ignition coil. To get a similar effect from a pure magnetic coil you'd have to increase the coil turn ratios from say 10000:1 to 100000:1 or greater. Combining a bigger coil with a CDI will surely cause the regular spark plugs to wear out more prematurely. Unless you are boosting, have aggressive timing, or something similar like that, then most cylinders won't have a need for such an aggressive spark.

But going back to topic, pin 3 is surely going to have a larger voltage potential going into the ECU. Why? Because remember the primary side is used to pick up the ignition check signal and it will be at a much higher voltage potential. So that original resistor/condenser value will not work since you'd need a larger resistor to bring that signal back to the level that the ECU can safely sense. Do you know how the primary ignition signal is supposed to look? Check out picoscope. That signal is pretty much what needs to go to pin 3. You will need an oscilloscope to see the signal. Only then will you be able to tell if there are any large variations. If so, you will either have to live with code 21 or build a circuit to fix that issue. If that is the "extra part" that MSD provides then go ahead and get it to eliminate code 21. But make sure you know what that part is designed to do.

Good luck.

[wikdgsxr]

cool thank you i will be on the phone with them this week