How do I test my ECU?
 

I randomly have issues starting, I can crank it but it won't fire. Only telltale sign I've noticed is the CEL staying on. On no start, off no problems. I've tried many different "fixes" including disconnecting the battery, pulling the ECU fuse, etc.. it may work one time but not the next. Lately plugging in a paperclip for ECU codes (no codes ever come up) cranking, pull paperclip, ignition off, crank & fires. I finally found in my Chilton if the CEL stays on, to test the ECU. But how do I besides buying one and waiting for the random occurance (sometimes a month) to happen?

Re: How do I test my ECU?
 

What year/engine/mods?

The only reliable way to test the ECU is to swap in a known good one.

When the engine won't start, do you notice that the fuel pump doesn't prime for 2 seconds when the key is turned to ON(II)? Have you checked for lack of spark?

My first guess is a bad main relay, but this should be confirmed by a failure of the fuel pump to prime when the engine won't start.

Re: How do I test my ECU?
 

--What year/engine/mods?

92/ d15b7/ none except air intake

--When the engine won't start, do you notice that the fuel pump doesn't prime for 2
--seconds when the key is turned to ON(II)? Have you checked for lack of spark?

can the fuel pump be heard? either i haven't heard it or haven't listened for it.. don't think there is lack of spark, when the CEL turns off it runs strong, just won't start when CEL stays on

--My first guess is a bad main relay, but this should be confirmed by a failure of the fuel
--pump to prime when the engine won't start.

where is the main relay? i'll listen for the fuel pump. btw i noticed tonight hearing (my best description) something electrical turning on under the dash drivers side when the CEL finally turned off..

Re: How do I test my ECU?
 

The fuel pump is located at the top of the gas tank in the rear and makes a low humming noise for 2 seconds when the key is turned to ON(II). If you don't hear it, resolder or replace the main relay.


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Re: How do I test my ECU?
 

I hear the fuel pump (now that I know what to listen for) and you're dead on. It doesn't prime when it won't start nor does the relay click. I'm gonna try to replace the main relay this weekend (schedule permitting) and let you know how it goes. I'm certain the relay is the problem, everything points to it.
Thanks for all your help!

Re: How do I test my ECU?
 

I have the same problem.

- cel stays on
- fuel pump doesn't prime
- main relay doesn't click
- tried 2 different main relays, still doesn't work

I dont understand whats going on.

What am I missing? Fuses have been checked repeatedly.

Re: How do I test my ECU?
 

I had similar problem idk how old this thread is but mine was a bad ECU....

Re: How do I test my ECU?
 

Re: How do I test my ECU?
 

Old thread that got bumped, but I thought this would still share this.......I made this video recently after having to chase down my issue and found it

Re: How do I test my ECU?
 

Thank you for that, I have been having this issue for months but after replacing the main relay didn’t work I have just been ignoring it because like you said if I give it 5 or 10 minutes the fuel pump does eventually prime.
I liked and saved your video, now maybe I’ll go and fix it some time

Re: How do I test my ECU?
 

‘hopefully this helps some people, I sent mine off to someone that repaired mine for me....has worked perfectly ever since