rotory86

Ok, I have a 1992 DX D15B7 P06 A00 ECU that has been plagued with an electrical problem for the past 3 months or so. It started when i disconnected the battery one day to replace a coolant hose and then when it was reconnected the car would not start.Problem ended up being no fuel no spark, still cranks. Eventually after leaving it for a week i went back to it and with the key in the ignition while checking fuse 18, 31, and 24 both tabs to ground with a multi meter, all checked good. But then the fuel pump randomly kicked on while i was just standing there. I could have sworn I saw the check engine light flicker when I turned the key to position 2 initially. I drove it another 2 weeks before it would not start again. This time I checked ground G101 and at the trany, battery to body, and valve cover all looked good and had no change in car starting. I bench tested the main relay, it tested good. let the car sit for a week. bench tested the relay again to be sure, it tested good again. threw it back in and the car started. So i drove it another 3 weeks before it dies again, this time I checked power to the ECU harness at A25 and B1 ( yellow/black) and they had 12V. I jumper the Main relay pin 1 to 7 and pin 5 to 7 and the fuel pumped primed. I grounded ECU harness pin A7 and A8 ( Green/yellow) and fuel pump primed. At this point i figured it had to be the ECU. Got a re-manufactured one, plugged it in and the car fired right up. Fast forward a month. and the EACV ( IAC ) ( not the fast idle solenoid) started acting up, If I hit it with a wrench car would run fine, for a while then begin to idle erratically after a while again. So I replaced it two days ago. Drove it to work, and left my lights on draining the battery. Now same situation, no spark no fuel still cranks. Help????

Summary of testing:
Main relay bench tested per Haynes Manual: Results Good, replaced anyways
Fuse 18, 31, 24 tested both top tabs with multi meter to body ground: Results 12V
G101 Checked and cleaned: Results checked and good
ECU A23 and A24 tested to body ground continuity: Results Good Continuity
ECU A25 and B1 ( yellow/black) test to body ground Results 12V
Main relay Pin 1 to 7 and Pin 5 to 7 jumper with key at position 2 Results Fuel pump primes
ECU Pin A7 and A8 ( Green/Yellow) grounded to body with key at position 2: Results Fuel pump primes
Checked CEL codes: Reads code 0
CEL Stays on

Should I be checking the crank sensor? why would the car not prime the fuel pump post battery dieing? Obviously I am out of logical ideas and am grasping at straws and hoping some of you with more knowledge than I can point me in the right direction.

Former User

Nice troubleshooting.

Do you measure continuity to body ground at pins A26 and B2 in the unplugged ECU connector with the key off?

rotory86

Hi RonJ,

Thanks for your reply and compliment. I did not want to waste anyone's time on a topic that has been beaten to death over the years so I did my best to do some homework and study the service manual. To answer your question, I had not previously tested those two pins. However I ran out of the office and checked them just now,

Tested ECU pin A26 ( Black/red) continuity to ground: Result good continuity
Tested ECU pin B2 (Brn/Black) continuity to ground: Result good continuity

The car is stuck at work for now sadly.

Former User

The replacement ECU seems to be blown. What voltages do you read at the two hot pins in the unplugged MAP sensor connector?

The ECU can be blown if sensor connectors are swapped. Check for that too.

Open up the ECU and also check for any blown or burned components, such as a capacitor.

rotory86

Checked MAP power wires at the sensor itself as follows

Key at position 2 voltage check to ground
D19 (Yellow/green): Result 5V
D21 (Green/Blue): Result 0V

Ill bring the ECU home tonight and crack it open and let you know what I see, if anything. Thanks again for the help to this point.

Former User

Grn/Blu is ground.

Measure voltage at the Wht wire with MAP sensor unplugged.

rotory86

Thanks for the clarification. I'll retest that right away in the morning when I get to work where the car is sitting. Sorry for the delay, had to go home and do my fatherly duties. Now that the kid is asleed it's time to crack into the ECU.

What is it that the voltage and ground checks at the MAP are telling me other than the ECU is sending power to the sensor and the ground is continuous thus the ECU ostensibly can receive signal from the sensor. Am I missing anything else regarding these tests?

Former User

The Wht wire should read ~5V. If the voltage is much lower, then it would indicate a bad ECU if the wire is fine.

rotory86

Ok, So back at work this morning and I tested the continuity on the Grn/Blue D21 MAP sensor at the sensor plug with the key at position 2 with good continuity, Checked White D17 wire for voltage and got ~3.5V. Checked Continuity of white wire from ECU harness and sensor plug with good continuity. ECU cap C18 and C19 look like they have some discoloration on the board next to the solder joint. Trying ot see if my I&E guy at work has a fluke with a REL capacitance setting to test those. anything else on the car I should check? Why would the car be blowing ECUs?