sean.rostami

Hi, I believe that I need to replace my ECU/ECM (reasoning below; if you think I am mistaken then please let me know! I'm an amateur).

My car is a 1992 Honda Civic DX Sedan with a manual transaxle. My car is originally from California and so is "type" KL5MT rather than KA5MT.

The main question is: does it matter which ECU I buy? I know it's related to emissions, but is there any other incompatibility that can occur? Assume that I will not return to California. The part numbers for the two ECUs are 37820-P06-A01 (for the KA5MT) and 37820-P06-L00 (for the KL5MT). The non-California one is much more common (obviously) and I prefer to buy that one.



As for why I think it's the ECU:

The bottom line is that the car won't start. But:

(1) battery is charged and healthy,

(2) the starter motor works fine and sounds healthy,

(3) all wiring between the battery and the distributor is good,

(4) rotor, cap, ICM, ignition coil, spark plugs are working (all but the coil are new actually) and pass all recommended electrical tests,

(5) there is no spark (using an inline test light)

Additionally, there was no fuel pressure after I released the initial remaining pressure from the release valve on top of the fuel filter. I didn't use a pressure tester (because I don't have one), but I re-tightened the release valve, tried starting a few more times and re-checked the release valve and no fuel came out. Also, I could not hear the fuel pump operating, although it is actually very quiet anyway. This made me highly suspicious, because what are the chances that the fuel pump and the distributor failed at the same exact time, right?

(6) The relevant underhood and underdash fuses (ECU and AGR (?) ) are fine. They look fine, and just to be safe I used a multimeter.

(7) I checked the Main Relay and one of its relay functions did not work (I applied voltage to a particular pair of terminals and checked for continuity on the relevant pair of terminals and a very faint click could be heard only sometimes, and no continuity was registering on my multimeter.

(8) I replaced the Main Relay, but the car still wouldn't start. I suppose that the old relay was not completely dead yet, but was almost dead, so I'm not upset that I replaced it. Just to be safe, the new relay easily passed all the same electrical tests.

(9) the connector that goes into the Main Relay passed all recommended electrical tests

(10) I checked to see if the electrical connector to the fuel pump was receiving electricity when the key was in the ON position, and it was.

(11) I inserted a jumper wire into the appropriate terminals on the Main Relay, turned the key to ON, and now I could hear the fuel pump activate (I pressed my ear against it to be sure). I could also hear fuel flowing through the pipes, and when I opened the fuel filter release valve, fuel came out like it normally does.

(12) When the key is turned to the ON position, the "Check Engine" light comes on and stays on indefinitely rather than turning off after a couple seconds. No error codes are displayed by the Check-Engine light when I put a jumper wire on the diagnostic connector near the ECU.

(13) A friend told me that if the key is in the ON position, the MAP sensor is supposed to receive about 5 volts of electricity, and if it's not then the ECU is probably bad. I checked and it is only receiving maybe 1/3 of a volt.

Thanks in advance for any tips.

fungus mungus

A check engine light that stays on solid after the car is turned on usually means a dead ECU. You should be OK with either ECU, as long as it's for a manual transmission.

fm

sean.rostami

Ok, thanks.

I did hear that the persistent Check-Engine light means a bad ECU, but I wanted to be extra extra sure before I buy an expensive component like that. Besides, it gave me some good experience with all those components.

Does the persistent Check-Engine light and a lack of error codes usually mean a bad ECU regardless of the car? I'd like to know if there is a general principle here.

fungus mungus

I don't think a solid CEL is universally an indicator that the ECU bad, but I know that it is an indicator that a Honda ECU is bad. The only exceptions would be if the ECU had been modified. I have a Hondata in my ECU, so the solid CEL came one once when it started to overheat...that was function of Hondata. But in a stock Honda ECU, it means a problem with the ECU and replacement is in order. Here's more about it.

fm

sean.rostami

Ok, thanks for the link. I'm pretty sure mine is stock since the brand is one of those common Honda stock brands like Mitsuba (I'm not the original owner of the car but I've owned it since 2002).

Last few questions:

(1) What do people think of refurbished ECUs like those made by Cardone?

(2) Is there a typical lifespan of stock Honda Civic ECUs, or is it very random how long it will last?

(3) Finally, since my current ECU is apparently 20 years old, it would not be surprising if it died from old age. However, is it possible that it was killed by some other more secret problem that I do not know about yet? How seriously should I think about this other possibility?