car: 1993 Maxima GXE

ok, i know exactly what my problem is (for the most part).

the ECU does not power up 3/4ths of the time. i know this because the light on the dashboard for the ECU only kicks on when it powers up.

not powered up:



powered up:




i should also note, i have exposed the ECU so i could visually look at it from the passenger side. when the key is put to ON, you can see and hear it kick on for a second or so.


i went through this crap all last year and it has just gotten worse. yesturday i started it up, drove it around for a couple hours and no problems. now i go to try to start it, and no dice.


id like to just hardwire the ECU and be done with it. i have zero cash to be throwing at this thing. i understand though you cant give the ECU a direct 12v source.


any and all advice welcome! thanks!

-Roo

 

The problem is most likely not with the ecu...My engine light hardly ever comes on when i cycle the key,but my car runs fine....I would start checking all wiring and wiring connectors under the hood, cabin for corrosion{green crap} or broken,loose connections. If you dont find any then check the computer for any stored codes....

 

That is engine check light = Error Message.

It also means ECU is well and alive... its telling u have some engine problems; who knows if its true or not....

Check sensors, do the mentioned DIY cleanup, run self diag after that. clic read: http://www.cardomain.com/ride/748507/1 ...pages 9,14,15

 

cant check the ECU for codes when it wont power up and stay powered...

when the 'engine light' does NOT come on, the car will just sit and turn over.

when the 'engline light' comes on, you can here the a couple relays and the fuel pump kick on, and it will turn over AND start.

is there a relay for the ECU i am over looking?

-Roo

 

Have you tried to check the codes???

 

again, I CANNOT CHECK FOR CODES because the ECU will not power-up.

 

I was referring to the other 1/4 times when it is powering up....Don't get pissy with us man were only tring to help!!

 

my bad dude, my bad.

unfort. that 1/4th of the time is powers up has gone bye bye

back to messin' with it more.

-Roo

 

If you haven't already...Try checking the harness on the ecu for looseness..Then if it is alright then go though the engine bay and check all the connections.wiring,relays,etc[Some of the relays are interchangable under the hood,try to switch them out]

If it turns out the ecu is fried...I have a good ecu if you need it....

 

ok, so check this out. i will try to be as thorough as possible in detail so i hope i dont loose anyone.

for ****s and giggles i looked under the car today to find ALL but the exhaust hanger at the muffler broken. so basically it was being held up by the motor and the one hanger by the muffler, leaving the whole middle of the exhaust sagging.

well, when all the hangers gave out, it also broke the copper braided ground wire the goes from the body of the car to the exhaust. let me also add that 'sometimes' a peice of the braided ground wire would touch the exhaust from what i could see.

so... i ran a wire from the ground terminal of the battery directly to the O2 Sensor (just wrapping it around the bare metal/sensor), then went to turn the key to ON and cha-ching ECU powers right up and car starts.

so....im thinking one of two things. might be silly but im not ruling them out.

me theorys:

1.) the O2 uses that 2nd ground (braided cable) to complete some sort of circut...

or the more realistic one

2.) the main ground for the O2 has been disconnected/badly corroded somewhere therefore it was using the brainded ground line as its ground.

now, i thought i read a diagram/chart some where that the starting circut first checks to make sure the O2 Sensor is there/working and if it is, allows the ECU to power up.

call me crazy, but its working now with a peice of wire going from the O2 Sensor to the ground terminal on the battery. any input on my madness is appreciated.

btw, i checked my ECU for codes... nada.

-Roo

 

ok completely ignore that last post... just went out again to try to start the car and NO DICE... back at ground zero.

 

.. did u ever disconnect the plug that plugs into the ECU? i swapped ECUs a couple of times due to increasing gas prices, and the last time i did it, the car won't start, i took the plug out and checked if a pin was bent, nope... so i pluged it back in, and it would start, and idle at over 2000rpm...

so i took it back out again and tried again, this time making sure the plug was evenly seated into the socket and the screw tightly secured.. then the car ran fine..

 

yep, unplugged and plugged the ECU back in again... no luck.

-Roo

 

I'm going to hazard a guess that you do in fact have a bad ground issue with the ECU.
the question remains where is the missing ground.
I'd start by fixing the ground strap that you now is busted, and then find which pin on the ECU, if any, is ground. some ECUs ground through the ECU chassis.

 

it would be awesome if someone had an ECU pin layout or diagram somewhere

even the circutry for the ECU... id still like to know if there is a relay somewhere that may also be acting up.

-Roo

 

There is.

Info. As already said.

The relay.

The pin schema.

Waiting.

For u to click on.

And read.

Go to my first post & click on to surf my CDomain pages.

try at least...

 

i'd be highly doubtful of our maxima's ECU being grounded through chasis, because i've been running a remapped ecu with it just pluged in and tucked under the passenger side carpets.. so that's one less possibility there..

 

I guess the cover is grounded. The pcb should not be grounded to chassis, only as depicted below. When grounding has loops, and does not form a TREE, problems start. Loops form an antenna, this creates I/O signal fluctuations, causing all kind wrong output put puts... car-bage in, car-bage out.

Alas, Nissan engineers have not the faintest idea of basic grounding principals: here and there grounding is ok, often not, forming loops.

Note that the box grounding is NOT drawn into the pic; this is the way it should go, dunno excatly how it is installed.
clic on http://www.cardomain.com/ride/748507/10

 

i greatly apologize for looking over your post... everytime i see a link to a cardomain page or dont think much of it... looks like you have all the info i need.

from the pic you just posted and one i just found on your site, it looks like there is 2 relays for the ECU? one in the trunk and one in the engine bay?

whats the best methodology to bypassing a relay for testing purposes? (jumping it)

-Roo

 

On that pic its jumperin pin 3 to pin 5 = wrap bare wire around those relay pins, plug in. At the moment cannot say which is which... NOT the ones u can measure coil resistance.

The rear relay is safety relay for wrong polarity ECU accidental connection.

Cardomain = no costs. I know what u mean, stupid to gather info on such place... Well, I am stupid.

 

The green relay is a b1tch. Those who have been hanging around here long enought know, that I have been having exact same sympthoms as your until I changed it. It's only like $20 at the dealer.

 

which relay, the engine bay or trunk one?

-Roo

 

well boys its workin'... (for now)

i just don't get it (well i do, just kinda scratching my head wondering if i really did solve the problem)

so check this out... but first id like to thank Wiking for the Relay and electrical information. you are my hero and cardomain rules! ok moving...


first i jumped the 3/5 Relay in the trunk, tried to start, no dice... then i jumped 3/5 Relay in engine bay, tried to start, no dice (both Relays are being jumped here).

then for whatever reason, i took out the Relay in the trunk, and the jumper out of the one in the engine bay and SAWEETNESS, starts right up. so i turn the car off and on multiple times, flip the key back and forth, ECU light always comes on, flawless...

so, the reason im scratching my head 'what the ****', i thought the circut NEEDED the Relay in the trunk because it acted as some sort of fail safe for an accident or something along these lines.

again, its working now with NO Relay in the trunk, and ONLY the Relay in the Engine Bay...

so it looks like the Gremlin has been found. but maybe the grounding issue in the exhaust could have had something to do with it to, hense two problems at the same time.

who knows, i just thank all of you for your wizdom! i will report back if there are any new developments.

-Roo

 

Happy to hear, thank you. (I Would like to see smtg else than cdomain; it limits the site arrangements to very mini mum, currnetly juts a pileup... but then, not possible for me to $ink any $)

Guesswork: There has to be some kinda short somewhere: now if u turn ign on, pushing the safety relay in, you must hear it click? =gives fault -signal to ECU.

But as long as it works w/o the relay, just keep batt polarity (!?) this way