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How to TEST the ECU/COMPUTER if its fried??

aroncull

NAXJA Forum User
Location
North Denver, CO
OK so the short of it is, i think i may have crossed the wires somewhere and was curious how do i test if i have fried the computer?

97-I6
144K

Turns over just fine, over and over matter of fact.

crossed the ground to the chassis for the battery onto the hot side terminal of my yello top and smoke came out below/behind the engine, at what looked like the firewall.. but in the engine compartment.

Just got it fixed from a previouse no start and it was the camshaft sensor. Worked flawlessly. Till i fubarred it again.

So 1st and 2nd time starting it after the smoke it started and idled super high at 2.5K then 3rd and 4th and on times is just turnes over.. i havnt tested anything. but i cant figure out what would smoke from that area of the engine basically looked to be dead on on the end of the engine but down.. maybe the Crank PS.

So ill fill in more details after a few but i was wondering if there was any was to test if the ECU/Computer is fried? i called my NAPA guys and after they laughed a little they said it could be anything all the way around as far as solenoids and fuses, and he thought the computer was almost for sure fried.

thoughts?
 
BUMP!! Need help guys..

Is there a way to test if the computer is fried?
I thought that there would be big fuses in the lines to the computer.

Also

What do you think would smoke at the back of the engine area.. down below, lower then the valve cover ish area.. yeah well thats a great discription.. lol

Any ideas please..

thanks

Aaron
 
Hook a good quality scan tool up. It's 97, so OBD-2. Whether or not the computer's fried, a dealer level scan tool eliminates all the guessing games since you can see the rpm signal (CPS), fuel synch, all that other good stuff. If the computer's truly bad then you won't be able to get the scanner to talk to it. Once you get that indication, load test the power and ground circuits to the PCM with a headlight bulb and verify the communication circuits from the datalink connector are intact. If power, ground and communication all check out then the PCM is indeed toast.
 
Thank you for the reply,

So i take it there is no Dirty field type test to see if the ECU is toasted?

All of my gauges light up and read the correct values.
lights work and other stuff.
I was hoping for a way to determine if it was fried without taking it to the shop.

thanks

Aaron
 
disconnect your battery completely. first negative, then positive. MAKE SURE THEY CAN NOT COME IN CONTACT WITH THE BATTERY.

turn the key on, and leave it sitting for a few minutes. go have some coffee or something.then when you come back, turn the key off, make sure you hook the cables up right this time and hopefully you'll be ok. when i started working on cars, i had a couple careless accidents that made the car act all kinds of weird. did what i just told you to do, and thank god the cars were fine.

give that a try.
 
I'm guessing here, based on experience with GM ECMs. Turn on ignition key, but don't start engine: 1. should here fuel pump run a couple of seconds. 2. the "check engine" light should be lit.
If "yes" to both questiones, it tells you the PCM is communicating in at least two areas.
The "master reset" for OBD-I computers was to disconnect the battery; not sure about OBD-II, but it wouldn't hurt to try.
If you have a digital volt meter, there are a number of sensor tests that can also help verify the PCMs operational status.
 
My buddy connected the battery reverse-polarity on his YJ and it fried the coil and a fuseable link at the starter solenoid. You may want to check to see if that smoke was the result of a fusable link doing it's job.
 
yeah im thinking its likly fusable link too. ill have to dig. man i am tired of the jeep messing with me [she's mad cause i fucked up and shocked her].
 
Several good suggestions below. I suspect you burned out a fuseable link, fuse, small GROUND wire or ground wire connector.

If ignition switch was off (was it off at the time????), the only items that could have been damaged would be just a few items that would complete a circuit with the ignition off, which are very few! I would bet it was a small ground wire or fuseable link. Basically you completed a circuit from the positive battery cable to the negative battery cable through the ground wires and any equipment that was hot at the time, like an open door dome light, or hood light, I think.

ECU should be fine, especially since it started twice after the short. I'd guess you lost most of an important ground connection in the electronic controls circuit that caused the TPS you run a high idle at start up.
 
Thank you very much!
I will look at it tonight and see what i can find!!!

Thank you!!

Aaron
 
This is all really good help... im gonna comment anyway.

I had a water issue when I went into a swamp 2 years ago. When the computer died.... it behaved really funny.... would turn over sometimes.... run rarely then kill itself.... it would do all sorts of stuff.

I beat my head for 2 days forgetting a had a spare computer in a kit of mine. When I put the new computer everything worked.

oh and ps.... I got squirt in the face with fuel while working on the car... so I think gas moves through the lines pretty quick either way.. ( 88 cher )
 
OK guys thanks for your time..
I had an old CPS laying around from previouse throwing parts at it session a month ago. since the smoke was around that area i thought i would throw the one part i had at it to see.
it works!


now theres a battery drain while the car is off somewhere.. need to find it, luckily i have a yellow top!

i watched the multimeter while on the battery when running to see if i fried the alternator and it kept its charge and even topped itself off some.
i have it trickle charging now.


THANKS!!!
 
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