AEM ecu runs 3 to 4 minutes and dies cuts off

[Halsupramk3]

i have run a aem in my 90 for years and tuned well. i rebuilt my engine, wired in 2 5 volt sensors, and reinstalled aem. I put my cal file back in and the car crancked. it ran for about 3 to 4 minutes and died. the ecu was dead and disconnected.
The engine wont crank again for 15 minutes to hours later. when the key is turned on the circuit opening relay (cor) will not engage to prime the pump. the check engine light will not come on. later if the engine light comes on the car will crank again. if the engine is cold it will run for about 3 to 4 minutes and dead again. if still somewhat hot it may run for 30 to 90 seconds and die.

when the car/ecu dies i can take it out of my 90 and put the ecu in my 89 and the check engine light comes on and the cor primes the pump. i cant crank the car because the 89 has a 1uz in it. it runs on a modified aem.

i have tried two 89+ecus and both do the same thing. i have tried an older cal file and same thing. i reinstalled my aem program on my computer and same problem. i think my cal file is corrupted or virus but i did try an older cal file.

the power batt, B+, B1+, main relay pin, and fc pin for the cor all have 12 volts even when the ecu dies. i shorted the main relay and same thing.

may be in wiring harness or a contact is intermittent somewhere.
i did install a small braille battery but i think it is working fine.

what to do?
hal

 

[hvyman]

Fuse box getting good power?

Main power for the Ecu comes out of there.

 

[Halsupramk3]

as mentioned

the power batt, B+, B1+, main relay pin, and fc pin for the cor all have 12 volts even when the ecu dies. i shorted the main relay and same thing.

the power is still on the pins it needs to be.

i called a tuner out in CA and he had a similar problem when his map sensor was wired in backwards. when he disconnected the map sensor the ecu woke up. he had wired in the 5 volt to ground and the ground to the 5 volt pin on map. it will read but it must overheat a resisitor or something in the ecu and it shuts off.

i had wired in a new 5 volt oil temp sensor and when i pulled the plug the ecu woke up.

IT RUNS NOW.

i did not have the pin out for the sensor and guessed on color. 50/50 chance so that means it is wrong. so now it runs and the new ffim idles too high and now i can tune.

thanks
hal

 

[jetjock]

As I've said in the past no Vc = no workie...

 

[3p141592654]

The ECU internal 5V power supply will 'crow-bar' if the load on the 5V supply is too large.

 

[IBoughtASupra]

So 3P, since the main sensors such as IAT, MAP, TPS all use a 5V reference and so do oil pressure/temp along with other sensors, how can you prevent an overload or know when you are getting to it's limit?

 

[3p141592654]

Any additional load on the 5V bus would is risky. There seems to be about another 250mA or so of extra capacity, but it likely varies with ECU.

 

[Nick M]

So 3P, since the main sensors such as IAT, MAP, TPS all use a 5V reference and so do oil pressure/temp along with other sensors, how can you prevent an overload or know when you are getting to it's limit?

Don't add to the circuit, or any circuit for that matter.

 

[Halsupramk3]

The air temp sensor and the stock oli pressure sensor and the oem temp gauge (not the ecu coolant temp) are resistor 2 wire sensors. I bought a 5 volt temp sensor foil my oil as there are no extra reaisitor inputs only 5 volts.
In this problem I wired the 5 volts to the sensors ground wire and this heats up the ecu board causing it to shut down dead in 1 to 3 minutes.
I will check my 5 volt sources. I think the map uses the 5 volt avail on the AEM plug C. And I have a 5v oil pressure and a 5v oil temp as mentioned on the same 5v source from another plug. Probly the 5 volt source that would be the oem 5v. I will check. If I have the two oil 5v on the same 5v as the tps oem source it may be that I am drawing too much 5 volts from one output and the ecu shuts down. That is a guess. But I may move the 5 volt douce for the two oil sensors.