hi guys, i'm trying to repair my electricals problems, but need knows the causes of the ECU's makes start the FAN on. No SES engline light on, its runing normal, but engines stumbles and just start the fan, without SES engine light. Can be the cause? I disconnect knock sensor, start engine, SES engine light goes ON, the car runs as normal, but after various minutes engine stumbles (like a misfire), and just start the fan. What causes makes de ECU to start the fan? Thanks very much pd: I have new fuel pump, filter, coil pack, spark wires, spark, all sensors (ICV, TPS, CTS...)...

Which ECM? Fan control varies over the years and induction systems.

RBob.

Thanks for your reply!

My car is a Firebird V6 3.1 MFI '90 and have a ECU with 1227730

I know my ECU can make start the for the next reasons: (have only 1 fan, and the car have A/C system).

- High temp, controlled by ECU using the Cold Temp Sensor
- Very high temp
- A/C high preassure sensor broken, disconnect (y disconnect it, start the engine but my fan don't goes on).

Need to know more reason to make the ecu start the fan, because I have a problem, and have new this part:

- Fuel pump & fuel filter
- Sparks wires
- Sparks
- Coil Pack
- HEI module into DELCO
- Throttle Pos. Sensor
- Idle Valve Control
- MAF
- MAP
- Cold Temp Sensor
- Fuel Pump Relay
- Knock Sensor desactivate (I was thinking my knock sensor its sending a false signal to my ECU and it was retarding the timing to solvent the 'false' knock. Car don't knock anytime!)

I'm thinking my ECU it's starting the FAN because it detect a problem, but no SES engine light and without this light on its difficult to found the problem.

I only need to change the delco, rotor, and rotor cap to make a complete rebuild of the injection system.

I buy a new ECU case 1227730 without chip, and put my chip into this ECU case and put the key in ignition, and fan start before engine start , start the engine and fan stills on, and the car stumbles.

Thanks and sorry for my language!

Sounds like either the MEMCAL or the ECM is bad.

At key-on, engine-off the SES light should: turn on, blink off, then turn on solid. Can repeat test after key-off for 10 seconds or more.

If the SES doesn't do the blink off then the ECM isn't running from the PROM. It is in limp mode which also turns on the fan.

With the fan turning on that means that the ECM driver, fan relay, and fan & wiring is all OK. But that there is still something wrong with either the MEMCAL or the ECM.

When operating properly the fan is always turned on by the ECM. With the engine running unplugging the A/C pressure switch connector will tell the ECM to turn the fan on.

A high engine temperature will also turn on the fan. This is via the ECM. The temperature is rather high at about 108 C.

RBob.

Thanks for your replies RBob.

Yesterday, I put key-on & engine off, SES goes on for a little time, goes off and goes on. Start the engine, and the light goes off permantly.

Only when put the new ECU case (buying from rockauto without PROM) and put my PROM, the car its on "limp mode".

Was probing the car and unmount delco, loking to this I can see any corrosion into the delco, but I don't know if this can be the cause of the problem.

Thanks very much... I am looking into ebay and see there is a full ecu (with memcal) for about 45$ with shipping to my country, this is really god for me!

Hi again!,

Last week I bought trought eBay an ECM with Memcal (7730, identic from my car), and must arrived this week.

I think this is the final problem from the car, I'm crazy to replace and probe it!

Thanks very much RBob!

Hello!

Last week install the used ECU from eBay, for 7730, but surprise!, when it arrive, I can see this ECU was originally from a Sunbird 3.1 V6 from 95, and the memcal was different from my numeration.

I install it, put the battery, try to start, the engine start but was horrible!.

I put my old and original memcal into the used eBay ECM, install it, put the battery, start the engine and run normal

There is no problem when hot, cold, nothing!, always running very good!

I hope the problem never happens again

Thanks you very much!

POST RESUME: Engine stumbles and fan start without SES (service engine system) light, change a lot of parts, but the problem persist. Buy a used ECM from eBay, change it, and solved the problem. The car appears run great again!

Glad to hear that it worked out and the Firebird is back to running good again.

Note that the Sunbird is probably running a DIS setup. This is in place of a distributor. So the spark timing was way off with that MEMCAL.

However, the MEMCAL can be used. The PROM would need to be replaced with the proper one for your Firebird (AZTY if auto, BAWX if stick). So if you ever get into tuning or need a spare MEMCAL the Sunbird one can be used with a PROM change.

RBob.