350TBI Battery Change... Vehicle Won't Run!

[Austin40]

I've done a few searches on this, but haven't found what I'm looking for...

I put a Yellow Top Optima in my FJ40/TBI350 today. After swapping out the battery, I started it up and everything seemed normal. I let it idle for a few minutes while I went inside and washed my hands and changed my t-shirt to drive down to my local watering hole for a beer. About a mile or two from the house, the truck started to feel like it was misfiring, so I turned around. It quickly got worse, and started backfiring VERY loudly if I put my foot in it at all. Finally, it died altogether and I had to tow it back to the house. I can't get it to start at all at this point.

I've had the vehicle for about a year and have never had a single problem with it. Given that the problems started after changing the battery, it seems it must be an electrical problem, and most likely an ECM issue. I'm at a loss at this point... any help would be greatly appreciated!

[UNO_RACING]

Sounds like a grounding issue, but I'm no expert. Optima batteries are very sensitive to grounding. Personally I'm not a big fan of Optima, I had optimas that wouldn't hold a charge and I dumped them for Interstate. Haven't had a problem since.

Try getting another battery and make sure your block is grounded to your chassie.

Best,

UNO

[73fj]

I've had very good experience with Optima. When you say it won't start, is it turning over or completely dead?

[Austin40]

It turns over just fine. It ran fine for a few miles after changing the battery, then suddenly whenever I gave it more than just a little throttle it would misfire. As long as I took it easy, it was OK though. Then it got to where I couldn't accelerate at all. Then it died at a stop sign and wouldn't start back up. It turns over, but makes some pretty sickly sounding coughs through the exhaust rather than try to start.

[peesalot]

timing. fuel delivery. Did you have any acc. or po added wires at the battery ?
check voltage going to fuel pump and you will probably need to get a scanner and see what is the timing doing and look for any codes.

[Austin40]

No accessories connected directly to the battery except a winch. Nothing else about the vehicle was changed other than the battery when it started running poorly.

I've read that on TBI small block Chevys, the ECM "learns" over time based on data it receives from the O2 sensor, etc and adjusts itself to run properly. If you disconnect the battery cables, the ECM "forgets" the data it previously learned and starts from scratch. I can't help but think that my problem must be related to this. But that doesn't explain why it ran just fine for 10-15 minutes before gradually running worse and worse and finally dying. I don't know... I guess I need to get my hands on a scanner.

[Austin40]

I bought a scanner from Auto Zone, but it just flashes code 12 indicating that there are no problems. After the trouble started, I disconnected the battery and reconnected it to make sure all connections were tight. I assume that this reset the ECM and erased any codes that might have been stored. Turning the engine over doesn't make any codes appear either.

I'm pretty sure I'm getting fuel. When I turn the engine over for 5 seconds or so, I can smell fresh gasoline.

I've got spark. I spot checked two plugs on the drivers side of the block, and both had good spark. Whether the spark is happening at the right time, I have no idea.

[DGAphlyer]

I would be wondering how long that battery had been on the shelf before you got it. The symptoms suggest that the voltage to the coil starting getting to low. So, first, the misfiring, then ultimately not enough juice to give a good spark.

So, it could be a combination of a low battery and a failure to charge (grounding issue).

You were on your way to the watering hole. Were you using the lights? That would explain the voltage drop, and the subsequent loss of fire, and therefore the missed opportunity for that tasty brew...

[DGAphlyer]

OK. Disregard all that I said...

I had some coffee and reread the posts.

If anybody needs me, I will be over here finger-painting!

[Austin40]

I had a few doubts about the battery as well, but I don't think that's the problem. It wouldn't run when I put the old battery back in either (not that I really expected that to work, but when things go wrong, I always try to go back to the last thing I f$*ked with).

I appreciate the concern about missing the cold beer... but I was OK. After towing the 40 back to the house, I decided it was better to think on it overnight rather than tear into it while I was pissed off about it. So I just took the pickup to the bar instead!

[Doug_S]

If you have a way of checking the coil, that might also be worth looking at. Sometime, when coils get hot, and the internal windings have broken down, they'll begin to get fussy. According to my FSM, the primary coil resistance (when measured between the two "small" terminals) should be between 2.6 and 4.0 ohms w/o resistor and 1.3 to 1.6 ohms w/resistor.

Secondary coil resistance, when measured between the center high tension socket and one of the "small" terminals should be between 6.0K and 9.0K Ohms w/out resistor and between 9.5K and 14.5K Ohms w/resistor.

I'd make the measurements when the coil is hot to try to replicate running conditions.

Hope this helps!


Doug

[Austin40]

Problem solved. I checked the coil, and it was bad. I am a little confused about that since I was getting a good spark before I replaced it. And it is an odd coincidence that the coil would go out right after changing the battery. But whatever, it's running like a top once again, and I learned something new! Thanks for everyone's help!

Now about that beer...