Hi, new member here from over the pond in England, this is a really helpful forum and all the information I've found so far has come from here.. I've recently bought a 1990 Firebird 5.0 TBI auto that has been stood for about a year. The owner fitted a battery and tried to start it, it would crank but not fire, he noticed smoke on the inside so gave up!

After I trailed it home I tried to start it but there was no fuel getting through, the 20A fuse by the battery had blown, I fitted a new one and the pump came on and it ran. It ran far too rich and the Service Engine light is on. I pulled the codes and it was 15 - the temp sensor, when I measured the plug under the hood it's sitting at 12V!

I've pulled the ECM and it's completely burnt out. There was a lot of damp in there which may have caused the problem. I've ordered one from a breakers but don't want to plug it in if it's going to let all the smoke out again!!

Is there any tests that I can do on the wiring to see if there's any faults before I fit the new one? I don't know what could have shorted on the car to make it burn out.

Many thanks in advance

Paul

 

As there are two temperature sensors and a temperature switch, make sure you are measuring the yellow wire that is paired with a black for the ECM's CTS. Can do this with that connector disconnected from the CTS and at key-on, engine-off.

Can you post a detailed picture of the inside of the ECM?

RBob.

 

Thanks for your reply, I was checking the connector with the yellow and black wires, the sensor reads 7500 Ohms and the connector reads 12V across the 2 wires with the ignition on. I've also attached some pics of the ECM.

Paul

 

Yes, that ECM took a voltage hit. The device that fried is for transient voltages. I've seen where that device has failed, but not to that extent. And since there is battery voltage running though the ECM (instead of +5 volts). I'd say the ECM is fried. It may be repairable, I've worked with some with good results. But back to the question.

A jolt of voltage can be caused by various means. Using two batteries in series for a jump start. A bad alternator (can get it tested), or loose/bad alternator/battery cables. An alternator that loses sense can output 70 - 80 volts.

Other then this I'm not sure what to tell you. Maybe someone else has some input.

RBob.

 

With the ECM connected the car will run, albeit roughly, battery voltage is normal and everything else works on the car (except the headlight motors!). I think the previous owner tried it with a jump pack, noticed the smoke and gave up. I've ordered an ECM from Ebay it's the same part Number and has an ANTT EPROM so I'm hoping I can just connect it up and all will be well, the last thing I want to do is fry a replacement straight away. It'll take a couple of weeks to get the UK though.