Weird Diagosis Need Help figuring this one out.

[Rex2342]

Okay so heres the whole story, for the last week or so my car has been acting kinda funny. Last month I was having voltage troubles like 12.8v while driving but sometimes it would be 14.2. I installed a new alternator and everything was cool again (14.2v while driving) for a few days. Now it's around 13.4v while driving. Maybe I need a battery?
The car runs good and all but in the last week Its been stalling at stop signs and red lights. It's been very humid here so I attributed it to the weather but it's still doing it now that the weather is cooler. Two days ago my brake master cylinder went bad. It was going bad for a while but I didn't realize it at first. I couldn't get the one for my car so I swapped one out from a 91 TSI auto. Napa claims there are different part numbers from 90-91 but they look identical so I went ahead and used it anyway. Brakes are normal and everything is fine at first. On the way home that day I kept getting random CELs that would come on and go out .
They aren't storing in the ECU so i can't read them with the logger and they won't stay on so I don't what the code is. No idea why this is happening but it seems to go away the longer I drive?
Once I did get an odd backfire when the CEL came on but other than that the car was running normal. Today the car seemed fine going to work. No CELs and no stalling. On the way home from work however it came back but this time when it stalled it was like someone just ripped my battery out for a second. The radio, dash, AFC, everything, just went dead for a second and just came back.The car fired right back up but I kept getting the random CELs for the next few miles then it all stopped again. is going on with this thing? Is this all just coincidence or is something seriously wrong with my car? PLEASE HELP!!!

 

[Rex2342]

I also just noticed that my heater control lights, and switches are all out? Everything else is light up fine, Guage cluster, ashtray, and lighter are all lit up? I'm going to start hunting down fuses tomorrow but I could use more ideas if anybody has them.

 

[schoffs4]

just for the hell of it try to wiggile your ignition switch alittle while driving had the same symtoms on a VW at my shop today and the switch was the prob.. it a long shot but check it anyway

 

[Rex2342]

It doesn't seem to be ignition related. I didn't find any blown fuses or relays today either. Anyone else have any ideas?

 

[toybreaker]

Loose battery connections or a bad/corroded ground can cause some pretty funky issues.

 

[schoffs4]

You can look at the ecu compacitors

 

[Rex2342]

The terminals are newer. Only about a year old and are tight. Same for the grounds. I was going to check the ECU too. I changed the caps when I bought the car and that was maybe 3 years ago now. I started suspecting the ECU after all my voltage issues but haven't opened it up yet. The car ran perfectly fine today. I even took her out on the parkway to stretch her legs a bit and no problems surfaced. These kinds of problems are such a PITA!! At least when it's fully broke I can find the problem and fix but this is driving me nuts. I've got a gremlin somewhere.

 

[Defiant]

Last month I was having voltage troubles like 12.8v while driving but sometimes it would be 14.2. I installed a new alternator and everything was cool again (14.2v while driving) for a few days. Now it's around 13.4v while driving. Maybe I need a battery?

Your "new" alternator has taken what the French call "La merde tres grande".

 

[Rex2342]

Your "new" alternator has taken what the French call "La merde tres grande".

I thought about that too. I might call mitsu in the morning and find out about a warranty. I used my discount through the garage I work for to get a factory new alternator so I wouldn't have these troubles.

 

[Rex2342]

So this has taken another odd turn. 2 days ago while driving home after no problems for a few days my car just shuts off. It's doesn't stall, or anything like that it just go dead. no lights, nothing! it was like someone yanked my battery while I was driving. So i got it pulled over and turned the key off and back on and it was back up and running again? It did this 3 times on my way home and hasn't done it since.Also a few times my radio flashed on and off while the car was still running? Yesterday I pulled my ECU and it looked fine. No fishy smells, no black spots or anything out of the ordinary. I also let it run while I went around the car and messed with the wiring and fuse boxes and the radio and AFC. I couldn't get it to die. I pulled my battery and that checked out good too. Tonight while I was driving I noticed all my heater control lights are back on? So something I did yesterday must have fixed something but I still can't find what it was to permanently fix it.