Dead battery- now a miss?

[mopar250]

Hey everyone- I have an 80 C10 that I did a 5.3 swap in a few years ago that has now has a miss. Last summer we drove it to a cruise night and when I got home, I pulled in to the garage and left the lights on when I shut it off and drained the battery. The next day, I charged the battery and fired it up, and it has had a miss ever since. The truck will drive, but misses pretty badly and I haven't had the time until now to mess with it. It has a 5.3, ls1 intake, headers, aftermarket harness and a GM computer with a "mail order" tune, so nothing wild. I have a set of the Dakota Digital gauges, and it isn't throwing any check engine lights. The swap has been done for about 4 years and I put probably 4000 miles on it since I finished it and never had any other issues so I'm honestly not even sure where to look first? Anyone have any idea's?

[BR3W CITY]

Have you scanned for codes (even if its not showing a CEL)? If you have that drastic of a miss, it should at least be recording a single or multiple misfire code. I'd say pull the battery for a few minutes and try again. There's no real mechanical or tuning correlation to low battery that would directly cause a misfire.

[davepl]

If an OBD2 motor (or a recent one anyway) actually misses, it will flash the CEL light. If it continues to miss for more than a second or so, it will LIGHT the CEL light. So are you certain it's actually a miss? Or is the light on?

[mopar250]

Sorry, I got busy with work and just got back to working on the truck today and tried a couple things. I did unplug the battery, and let the truck sit over night. When I fired it the next morning, it ran the same. I also got two new O2 sensors, put those in, and more of the same. The sensors that came out didn't look terrible, but I thought that would be a good place to start. Not really sure which way to turn now; very strange.

[mopar250]

Forgot, the light is not on. It's for sure a stumbling miss, it will move on its own, but defiantly not derivable this way.

[ls1nova71]

Start with the easy stuff. Pull the plugs and look at them How old are the plugs and wires?

[dec010974]

mopar250 I would check all the connections such as spark plug wires, injector, coil pack etc. its kinda hard to diagnose your truck and we are reading this problem from our computer. Im not trying to be a smart azz, just trying to be helpful to suggest simple stuff. also are you sure the Check engine light is installed correctly and you never said if you checked for codes? that would be helpful. good luck, Clark.

[mopar250]

Worked on the truck today and yesterday and have a little more information. I thought about what Dave had wrote, and that's a great point, I don't know if it is a miss. The truck breaks up when I give it throttle, but i'm not sure if it is actually missing or not. I took out all of the plugs and wires, and everything looks to be in good shape. The plugs and wires were new when I put the engine in. That could be why the CEL light hasn't been on? I did go buy a scanner for codes today, and had a P1637 "Generator L Terminal Circuit". After seeing that, I took off the alternator and had it tested, which was fine. I also found all of the ground connections, took them apart and cleaned them. While I was messing with the ground, it could effect the quality of idle. I extended those wires to run to the battery instead of the frame, but it wasn't any better. Any other idea's for that code?

[homemade87]

Most likely the Alt is not charging . Probably why it is running bad on low voltage . Dead battery is a clue . Put your a meter on the battery while running and see what its doing . The L wire on the Alt could be a bad connection . This is what starts the Alt to charging . Check it close . The L wire on the Alt is the reason for the code . Still could be the Alt .

Let us know what the running volts are at the battery .