Alt light, misfire, battery issues?

[timford]

A few weeks ago my 96 came up with an alternator light. I checked the output and I'm getting ~14.5 volts.Per the specs in my Chiltons book this is functioning OK. Took it out to have it tested at the local KRAGEN. They didt have the right connector to test it. When I told them what I had found. They said it sounded OK. (not that I normally take my auto repair advice from the parts guy) Re installed it with the intention of taking it to an alternator shop. This may be pertinent: A few weeks earlier I had drained the battery by letting it sit too long without starting. I had to jump the car to start it.Also, when I took the Alt out, I disconnected the battery


So having said all that: Is it possible to get an ALT light because of a bad battery? Is the charging diagnostic system intelligent enough to identify a bad battery?

OK on to problem # 2.
When I first got the car (30 K miles)it had a misfire. I replaced the wires. Still had the misfire. A friends OBD II reader said Cyl 2. Replaced the plugs, misfire gone. OK, I was happy with that. Now 30K miles later I'm getting an occasional miss at low RPM so I decide to change plugs and wires again. After a very careful plug and wire job I have a misfire on cyl 5. I'v tried swapping plugs, wires and even a new coil pack. Misfire still there. I've read some things here that imply (not quite confirming) that battery/alternator issues can cause some peculiar problems.

SAVE ME FROM THE DEALERSHIP PEOPLE!!!!!!!!!
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[Frankie X]

RE: Alt light, misfire, battery issues?

Save you from the dealership people? I am the dealership people! Bwahahahaha!

I'll give you what information I can, but I am unsure of a couple of things: Did you replace the battery? Is the light still on?

First of all, no, the OBDII system cannot directly detect a bad battery, but if one is sulphated from sitting or a cell has gone bad, the alternator may go into an overload type condition trying to charge it. If this happens, the battery light may come on and you most certainly could see "ghost symptoms" anywhere in the OBDII subsystems. Keep in mind, EVERYTHING is designed to function with some form of stable voltage baseline.

A fairly common problem with these alternators is a single diode in the rectifier going bad. The system may charge at the right voltage and amperage, but the battery light will be on (Delco alternators used to be notorious for this). If this is the case, a lot of "electrical noise" is created and could affect other systems.

I think you need an alternator.
If you want to be 100% sure, visit a shop with a proper charging system tester. Any decent unit will be capable of showing you battery condition, charging voltage, amperage output, and will have a display to show the rectifier's diode pattern.

On to problem #2:
There's a very, very, old school phrase about misses: "fire, fuel, and squeeze".

You've gone over the ignition system, so I'm going to assume you're sure you've got fire.

Have you got fuel? Possibilities could include dirty injector(s), an electrically defective injector, or loose or corroded wiring. There seems to be some confusion on these forums as to cylinder location; #5 is driver's front. Did you knock #5 injector connector by accident when removing the alternator?
A localized vacuum leak near that cylinder could affect fuel mixture (I doubt that's your problem).
Again, to be 100% sure, see any decent shop that has a scanner capable of relative injector flow tests and perhaps a high pressure injector cleaning tool.

What about squeeze? Let's leave that alone for now.

Before we start worrying about compression and valvetrain issues, get your charging problem repaired, let the PCM go through a relearn with the system working correctly, and if the misfire persists, re-evaluate the simple stuff first.

 

[XLRVIII]

RE: Alt light, misfire, battery issues?

Frankie is right about Fuel Fire and Squeeze!

I had the same type of misfire happen in the breif moments before my alternator quit "carrying the car" and it died.

If he's got bad charging stuff, then very likely his fuel pump and ignition aren't getting the volts then need to operate properly.

AND as frankie mentioned.. all the sensors are getting screwy reference voltage values isn't helping.

Battery first.. then Alternator IMHO.

"your mileage may vary"