ECM Vulnerable When Connecting Battery?

[Scottacus]

Hello all. I have a 1990 GMC Jimmy with a 5.7L/ 22o TBI. I'm restoring it completely from engine to interior. I've so far spent at least $11k on just the restoration. Having a blast.

I read an article years ago that the ECM can get fried when connecting the battery while the keys are in the ignition rotated to the ON position. Is this true? My memory isn't perfect on this though...

My truck was running about 100% perfect. But, while working on the windows I was going back and forth connecting the battery in order to make window height adjustments. When I was done, I reconnected the battery but forgot that the key was in the ignition and rotated to ON still... I heard sever relay clicks and pops that aren't' typical when connecting the battery normally. The fuse was not blown but after this moment, the car slowly ran worse and worse over the course of about 20 miles. Now, it barely idles and seems to like to run on only 4 cylinders.

My hunch is that the ECM is compromised and/or possible is some kind of "get me home" mode. Every sensor is new. The only thing I've replace after this incident was the ICM. But, as far as I know, there's not an original sensor under the hood with the exception of the knock sensor. New MAP, O2, EGR solenoid, distributor, cables, etc...

Any thoughts would be SOOO very much appreciated.

Best,

 

[Bent77]

Hello all. I have a 1990 GMC Jimmy with a 5.7L/ 22o TBI. I'm restoring it completely from engine to interior. I've so far spent at least $11k on just the restoration. Having a blast.

I read an article years ago that the ECM can get fried when connecting the battery while the keys are in the ignition rotated to the ON position. Is this true? My memory isn't perfect on this though...

My truck was running about 100% perfect. But, while working on the windows I was going back and forth connecting the battery in order to make window height adjustments. When I was done, I reconnected the battery but forgot that the key was in the ignition and rotated to ON still... I heard sever relay clicks and pops that aren't' typical when connecting the battery normally. The fuse was not blown but after this moment, the car slowly ran worse and worse over the course of about 20 miles. Now, it barely idles and seems to like to run on only 4 cylinders.

My hunch is that the ECM is compromised and/or possible is some kind of "get me home" mode. Every sensor is new. The only thing I've replace after this incident was the ICM. But, as far as I know, there's not an original sensor under the hood with the exception of the knock sensor. New MAP, O2, EGR solenoid, distributor, cables, etc...

Any thoughts would be SOOO very much appreciated.

Best,

I havent heard that, but other than really bad gas or an electrical failure of some other kind, it seems suspect

 

[ryoken]

check codes.....

 

[ChrisPerry]

Yes, you can do damage hooking up battery with the key on. Can also happen jump starting it. Usually though the damage is instant, doesn't happen miles down the road, unless you fried the alternator, then it runs worse as the voltage drops.

 

[Scottacus]

Thanks for the replies. I don't have the ability to check codes on my own. Is there a decently priced tool available?

I'll have to limp it to GM for a check up I guess. It surprises me that a voltage surge with enough strength to do damage wouldn't fry the fuse first.

I've checked and double checked everything related to the ignition system. I've even borrowed a "good" ESC module to verify and that didn't improve anything. What's also weird is that the Check Engine light has yet to illuminate, but I know the bulb has access to correct volts.

 

[ryoken]

all you need is a paper clip....



http://www.troublecodes.net/gm/

 

[Scottacus]

Love it... thanks ryoken!

 

[1-ton]

It is just my opinion, but the ECM is protected by fuses, which will blow-out before the ECM is damaged. I am guessing you have power windows you where working on when your problem began. You should look to see if you grounded out a hot wire on the power windows while you where working on them. This could cause a serious degradation in the performance of the ignition and alternator, thus causing your truck to run crappy.

 

[diesel4me]

Many vehicles with aftermarket alarm systems need the key "on" when you connect the battery cables or else they will set off the "yelper"siren, and not shut off,until you re-set it with the remote..
My friend has to do this at his shop almost daily on customers cars,when they forget to leave the remote for the alarm with him,and far as I know it hasn't resulted in any ECM failures..but you never know,all it takes is one "flash" to fry some sensor or diode sometimes..and the fuse wont pop fast enough..

 

[Scottacus]

Hmmm... I'll check that out. All the windows work now so I don't think I have a + lead grounded... but to your point, perhaps there's something more specifically related to the window job. At the same time, I'm not sure that squares with the slow degradation of performance...

It is just my opinion, but the ECM is protected by fuses, which will blow-out before the ECM is damaged. I am guessing you have power windows you where working on when your problem began. You should look to see if you grounded out a hot wire on the power windows while you where working on them. This could cause a serious degradation in the performance of the ignition and alternator, thus causing your truck to run crappy.