horseyj18

I have a 95 honda civic dx coupe that I just replaced the engine in. The original engine went bad and it is in the process of being replaced with an identical engine. The car died last November and it sat in the driveway until the beginning of May. The engine ran before storing it (although not well), and it was somewhat winterized with the old engine in it. It would not start when we tried to move it into the garage, but we didn't really think much of it and didn't spend anytime seing why it wouldn't start. The newer engine went in with no problem, it ran strong from the guy we bought it from (saw/heard it running).

Now with the new engine in the car its showing signs of what I believe is a bad ECM. It cranks, but is not getting any spark or fuel. We had a brand new relay so we replaced the old one, still no improvement. We also know that the distributor is good. I did the K-test, and the ECM failed that along with an ECM we borrowed from a friend who said that his ECM was in good shape. The CEL stays on at all times, and the fuel pump only runs when we jump the #5 and #7 in the main relay. I tried to jump the 2 prong harness from the ECM to get some error codes, but the CEL stays on still, and the SRS light flashes continuously.

I downloaded the honda manual for that car, and followed the troubleshooting tree for checking the ECM, all the steps lead us to it being a bad ECM except for the last step. When we tested the voltage between terminal A26(-) and the following B1(+) and A25(+) the manual says we should have battery voltage, does this mean 12 volts? We were only reading again fractions of a volt. So my question is, do you think its the ECM or could it be the wires in the dash that connect the relay to the ECM. I still think its the ECM, but I would like to have a more positive answer before spending another $100 or so.

Former User

Have you tested installed 15A hood fuse 31 for voltage? If you jump #1 to #7 in the main relay connector, does the fuel pump prime?

Have you cleaned and tightened the G101 ground wire attached to the thermostat housing?

Does the TPS connector have 5 reference volts but neither hot wire in the MAP sensor connector does?

horseyj18

Yes every fuse has been checked multiple times, both the main fuse box, and the fuses under the dash on the driver side. We did not jump #1 to #7, we jumped #5 to #7 in the main relay and when we did that the fuel pump primed.

All the engine grounds were cleaned on both ends, and we even cleaned the ground for the fuel pump.

I'm not sure what you mean by "Does the TPS connector have 5 reference volts but neither hot wire in the MAP sensor connector does?" but during the K-test no wires in the MAP sensor had 5 volts with either our ECM, or one we were given that we were told was good, although I'm not sure about it based on the test.

Former User

Do this^ to see whether the fuel pump primes.

The TPS receives 5 reference volts from the ECU on one of the connector terminals. Check that with the key in ON(II).

Was the key in ON(II) for the K-test? What did you use for ground to measure voltage from terminals in the MAP sensor connector?

technic05

Test that again and make sure it's correct. If it still reads less than 12 volts there's a wiring issue which is more common than an ECU going bad in that situation, granted the ECU hasn't been exposed to any elements.

Obviously if something isn't getting source voltage, aka battery voltage, it's not receiving the power it needs to do it's job.

horseyj18

The ignition was on for the K-test, and we used the thermostat ground during the test.

Is the TPS the same as the Throttle Angle Sensor? We did not check that for voltage, only the MAP sensor.

I will check that along with trying to jump #1 to #7. Unfortunatly I won't be able to work on the car till Saturday. If you have any other tips I'm all ears, I'm just running down the troubleshooting guide in the manual along with the information on the forum. Thanks for you quick response.

Former User

Redo the voltage test using the battery ground post as ground. Do you now measure 5 reference volts from two of the three MAP sensor connector terminals?

Yes. Post the result.

Post the result.

horseyj18

That was our thoughts today about a possible wiring issue, but with our limited knowledge we didn't know if it was wiring to the ECU, or the ECU itself. We'll try testing the volts and connectors again to make sure we had everything right, but we did give it a couple of attempts along with making sure we were in the right plugs.

The ECU hasn't been exposed to anything, the car remained dry and sealed, the car did sit through the winter though with no use.

horseyj18

OK we did the rest of the tests that you guys suggested.

Jumping the #1 to #7 relay the fuel pump did not kick on.

We redid the K-test using the battery ground post as ground, and only recorded fractions of a volt with two of the three MAP sensor connector terminals.

And finally the TPS was checked and was also recieving fractions of a volt.

We were also able to obtain a known working ECU and plugged it into our car and that is not the issue as it did not help things at all. So I guess it must be a wiring issue. Any help at this point would be greatful as I can't find any other suggestions online.

Former User

^This is the problem. In post #2, I asked:

You said that you checked it. How did you check it? Is there voltage to body ground at both top test tabs of fuse 31?

The low voltage at these sensors is simply due to the fact that the ECU does not get voltage from fuse 31.

horseyj18

Well problem solved thanks to your help. To check the fuse we used a continuity checking devise with the ground attached to either the battery ground, or thermostat ground, and device always lit up.

Since you said the ECU was not getting power from fuse 31, we removed the fuse box and checked the wires leaving it. Somehow, only the yellow/white wire was corroded, and when moved, it actually broke, so we soldered it, and the car started right up. Pretty random only one bad wire, and the most important one, but its fixed now.

Thanks for your help and now on to the fine tuning.

DJohn916

ECU p06 civic dx
pin D1 memory back-up constant 12v
A25 and B1 they are interconnected inside the ECU and you should find 12 positive volts wen you open the key,
and some of these pins A23,A24 and A26 logic ground are interconnected inside the ECU
B2 is a logic ground and isn't interconnected with any other pin inside the ECU,
ECU chassis do not supply ground to the circuit board and is not connected on any way to it,
All four ground wires A23,A24,A26 and B2 run from the ECU to the junction ground bolt at the thermostat housing and individually they maybe supply ground to some other components of the engine management system you shouldn't have a lot of resistance between the battery negative and these pins,
make sure the pins are making good contact with the plug connectors,
Use common sense...
If you're testing for positive voltage your ground is the negative terminal of the battery and if you're testing for negative voltage your power is gonna be the positive of the battery...
You can check for continuity between a23 a24 a26 and b2 or if you checking for resistance clamp one probe to the battery negative and use the other probe with a23 a24 a26 b2

Former User

Old thread closed.