erratic SES light - Third Generation F-Body Message Boards

devilfish · 06-30-2008, 06:17 PM

Hi guys.

I post here as well...

Need some fresh imputs on a ECM trouble I have.

Its a vette -91.

I get a erratic SES light from time to time. I dont get any codes. The only thing datamaster says when this happens is "lost connection to ECM, reconnecting".
When this happens the idle RPM increase, SES light goes on. Then 2-3 sec later the SES light goes off, and the datamaster scan continues, and the idle goes down to normal RPM again.

This happens more during long idle sessions then when cruising.

I tried 2 diffrent ECMs, 4 diffrent chips includning the stock chip, and also my romulator. I looked for bad groudning, bad censors, but I cant se anything out of the ordinary. Drives my nuts.
1 theorie I have is that I get a powerdip from the battery/alternator. That is next to test. I will hook up a multimeter and se if I get random drops in power.
Other then that Im lost?
Throw me a bone here, anything else you whant me to look for?

Thanks

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Theking · 07-01-2008, 04:41 AM

First guess was a bad ecm, but if you have tried that then its something else, does the car wanna die when the SES lights come on ?

checked all grounds on the car ?.

And as you said, check battery voltage and see if it dimps down below 12 (not good) shall charge around ~14 Volts atleast (14.37 is the spot thou

Theking · 07-01-2008, 04:47 AM

Also what cable is it that you using ?
Some cables may rise rpm and even higher the timing to..
So it could be the cable thats making the problem to.

gta324 · 07-01-2008, 06:40 AM

Hi A.

Try to disconnect the "B" pin on the ALDL cable or connector, not needed.

If you like email me a log file.

/N.

devilfish · 07-02-2008, 06:18 PM

Thanks for taking time

When this happens the SES light goes on, the idle RPM drops.
Datamaster says "lost connection to the ECM", no error codes. Then after 2-3sec the SES light goes off , the RPM goes up high to around 1500rpm. And then starts to drop back to the normal IDLE rpm range. And datamaster starts to log again.

Then over again randomly.

Is whery rare that this happens when the car is cold. Its when the car gets hot and the idle rpm starts to drop this thing starts to happen.
( But it HAS happend once or twice when the car whas cold, but whery seldom ).

Also i checked the grounding. And as far as I can se and mesure I have a good grounding.

I have tried 2 kind of cabels. First is the moates autoprom cabel. Second is the 2 transistors homemade cabel http://www.home.aone.net.au/~techedge/vehicle/2tran.gif

Gta:

I will send you a log.

CHeers..

gta324 · 07-03-2008, 01:00 AM

Maybe "stall saver" activates?

/N.

devilfish · 07-03-2008, 04:04 AM

Quote:

Originally Posted by gta324

Maybe "stall saver" activates?

/N.

Yeah could be, as the rpm drops when the SES light goes on. I do think its strange that I dont get any error codes. Its like the ECM goes "black" for 2 sec, then on again..

devilfish · 07-03-2008, 07:37 PM

I tried to unplug the aldl cabel. But no change. I also noticed that the SES light, when this happens, flicker more then just stays on.