bad ECM???

[nalgman]

hello guys

how can i test a ECM??
is for a 1990 TBI 4.3L Z

there's a method??

thanks..

[rlith]

Jumper pins a & b if it gives code 12 then it's fine... Why, what are your problems?

[wolfox]

Remember too, that you want to do the jumper trick with the truck's ignition turned to the "RUN" position (Where it lights up all of your idiots lights and zeroes the gages), but do NOT start the engine. DO NOT perform the "jumper trick" on a running engine either. Put the jumper into your test port under the driver's side knee bolster and merely turn the key to "RUN" and watch your "Check Engine Soon" light. As Rlith said, code 12 means all is fine.

You determine the codes by counting the blink cycles. For example, code 12 will look like:

<blink> pause <blink> <blink> 3 second pause <blink> pause <blink> <blink> 3 second pause <blink> pause <blink> <blink> (repeats sequence)

Each code, even if it is a "good one" like code 12 will be repeated 3x before it moves onto the next code. If there is a problem, it is going to look like this:

<blink> pause <blink> <blink> 3 second pause <blink> pause <blink> <blink> 3 second pause <blink> pause <blink> <blink> 3 second pause <blink> <blink> <blink> <blink> pause <blink> <blink> <blink> 3 second pause <blink> <blink> <blink> <blink> pause <blink> <blink> <blink> 3 second pause <blink> <blink> <blink> <blink> pause <blink> <blink> <blink> long pause (repeats this sequence from the beginning)

This is an example of a trouble code "43". Code 12 tells you that the "brains" in your computer/ECM are fine, but then any other codes will follow the "Code 12" and repeat three times just like the code 12. Man, after all of that blinking, I need Visene... Good luck and happy tinkering.

[tom3]

Don't know anyone who can actually test the computer itself. They almost never fail, always something else. Real common on the older vehicles to have a bad connector, really drive you crazy trying to find the problem. Replace sensors, test wires all day. Anyway, a rebuilt ECM is about $100 with trade in, beat taking to dealer and paying several hundred to have them screw with it. What problems are you having?

[nalgman]

this is my problem..

my truck... has a rebuilt engine with all sensors brand new(MAP,TPS,COOLANT SENSOR, OXYGEN SENSOR,SPEED SENSOR,CAP,ROTOR,WIRES,COIL,POWER STEERING,REBUILT ENGINE,PLUGS,ALTERNOR,BATTERY,MASTER CYLINDER,STARTER,EGR(CLEANED) ...but not the knock sensor .
my engine stalls in a stop or trafic light.
i replaced wires , and that stuff..
my fuel pressure is fine.. all is fine ,
but stalls , the RPM goes down and the engine goes rough.
the mechanics dont know what it is...the 3 mechanics says that this is weird..
one says that maybe is an electrical failure..

when i disconnect(electrical conection) the MAP.. the engine normalizes.. and dont stalls fast.. but when i conect the map the engine goes crazy and other sensors...

i have no error codes..in A & B pins. only code 12 (normal)

so i already make Voodoo and santeria to this truck , and nothing changes!

so they says maybe is the ECM...
or some wire gets hot.. i dont know..

please help..

Nalgman

[rlith]

Ok, 1st, see if there are any codes as outlined above... Next check all vac hoses... Is it a CPI or TBI motor? Either way, check your injectors.... How's your fuel pressure?

[nalgman]

Originally Posted by rlith

Ok, 1st, see if there are any codes as outlined above... Next check all vac hoses... Is it a CPI or TBI motor? Either way, check your injectors.... How's your fuel pressure?

is a TBI system the pressure is 11psi they say that is a barely good.

but some sensors fails, and the're new! :S

thank you..

Nalgman

[rlith]

TBI runs at 9-11 PSI, your pressure is good...Are your injectors dripping?

[nalgman]

Originally Posted by rlith

TBI runs at 9-11 PSI, your pressure is good...Are your injectors dripping?

the truck is in the shop.. and my booster has a failure.
so they will repair that and then check the engine cables and stuff .
(the electrical system )

my injectors are fine..i just cleaned out .
so.. i'll wait a call from the tech.

thanks again..

Nalgman

[dreamweaverzink]

Here is how I test my ECM:
First follow outlined steps above to get codes (jumper between pins A&B)
If all you get is a code 12, turn the switch OFF.
Unplug any one or more of your sensors.
Check codes again.
If your ECM is working properly it should pick up any of the sensors that you unplugged.
IE: if you unplug the TPS, you should get the code for the TPS indicating it is faulty.
Next you need to reset the trouble codes.
To do this Turn the switch OFF.
Reconnect any connections you may have unplugged.
Unplug the NEG battery cable for a minute.
Reconnect the Battery cable and recheck the codes. They should reset to a code 12. If it does not or you get another code that wasn't there before recheck it a second time. If you get the same results it is likely that you have found the problem (whatever code it shows) and you can replace the faulty part then re-test it. You can also do this test even with a fault code showing. All you would do differently is you will have to pick a sensor that is NOT showing a trouble code for the TEST component.
IE: if your test shows that your MAP sensor is faulty then unplug something else such as the IAC, TPS or any other sensor that is NOT showing as faulty. When you re-test it a GOOD ECM should find the problem when you test it the second time.

Now, I can't promise that this will completey eliminate the ECM, however it seems to be a logical test to perform.
Maybe some of you more experienced guys can comment on this???
Hopefully this test will save folks money that will otherwise replace the ECM thinking it faulty only to find they wasted that $100. ECM failure happens, but it is RARE.

[dreamweaverzink]

Almost forgot...
If you get different results other than what you would expect (such as the ECM showing a WRONG fault code, or erradic results such as a different result each time you perform the test) THEN it would be more likely that the ECM is FAULTY.
Therefore it would be a good idea to perform the TEST at least twice, using TWO or more DIFFERENT components for your "Test Part" each time. IE: Unplug the TPS for Test #1> perform the first test; then Unplug the MAP for Test #2. (make sure to RESET the codes after each test. Otherwise when you go to Test #2, the first code stored will still be there)