what makes the cel come on and then go off right when you put power to the car? is it the ecu, or the main relay??

my fuel pump isnt coming on and im thinking im having main relay issues, im just wondering if this cel issue is related. my cel doesnt light up at all

 

all cars have the CEL come on when you put the key to the "on" position.

same stay on while in on (before starting) some just blink on then off (before starting)

the fuel pump not priming could be the main relay. but the light has nothing to do with it.

 

When you turn the key 'on', it energizes the main relay. When that happens, it's allowed to power up the ECU which in turn does two simultaneous things: allows the ECU to activate a second set of contacts in the main relay which in turn powers the fuel pump on for 2 secs and the second thing it does is activates the CEL for 2 secs as well.

So if you're CEL isn't coming on for 2 secs, and the wire from the ECU to the CEL isn't broken or shorted, then your ECU may not be getting battery voltage...which comes from the main relay.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by EE_Chris &raquo;</TD></TR><TR><TD CLASS="quote">When you turn the key 'on', it energizes the main relay. When that happens, it's allowed to power up the ECU which in turn does two simultaneous things: allows the ECU to activate a second set of contacts in the main relay which in turn powers the fuel pump on for 2 secs and the second thing it does is activates the CEL for 2 secs as well.

So if you're CEL isn't coming on for 2 secs, and the wire from the ECU to the CEL isn't broken or shorted, then your ECU may not be getting battery voltage...which comes from the main relay.</TD></TR></TABLE>

good stuff man.

yeah when i plug a working ecu in it still doesnt do anything. the relay doesnt get/give any power, hence my cel and fuel pump doesnt comee on at all when i turn the key "on".

ii think the previous owner hacked the main relay wiring, ive tried 4 relays and they all do nothing

 

Matt the main relay for the fuel pump might also have cracked solder pts not allowing it to prime. Happened to me on 2 civic hatches already all I did was crack it open and resoldered to the board. so give it a shot. How is she coming along other wise. I just had a long weekend under the front end of mine. New upper controlarm and balljoint, new lower ball jnt, new inner and outer tie rods and boots, new axles, all new es bushings for the rack and lower control arms. Just need to take her to get aligned.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by blackeg &raquo;</TD></TR><TR><TD CLASS="quote">ii think the previous owner hacked the main relay wiring, ive tried 4 relays and they all do nothing</TD></TR></TABLE>

You've probably already checked, but missing thermostat ground?