Popping, stuttering, PW and Batt Voltage dropping, bad battery or bad generator? Options

[Madswede]

Well, I have been wondering why my car will not run well under load. I'm beginning to think, after all, that the latest issue has to do with a bad generator and/or small race battery.

Info: engine is a customized 3.2L, twin plug, Dougherty racing cam with high overlap, JE pistons with high compression (10.5:1), and PMO ITBs. It is EFI via EDIS, controlled by a Megasquirt system. It has been tuned using TPS (alpha-N I believe it's called) instead of MAP due to the difficulties with ITBs and a good MAP signal.

The guys at PMCI (I do believe them) said it was working fantastic when they had it, albeit a bit rich. I took it home two weeks ago and had these issues immediately. Called them, they are quite busy, but suggested that the battery might be a problem - they used an Optima temporarily to tune it, and since that's the only difference between when they had it running and my problems, I'm thinking that might be the source of the problem. More evidence: before they had it for tuning, the Generator light would come on after starting and not go away without a briefly sustained rev to about 1200-2000 rpm.

After logging and looking at the logs, I've noticed that the pulse width (PW) bounces (dropping to 0 (IMG:style_emoticons/default/blink.gif) very briefly) under load and the AFR can spike super lean when this happens. The car bucks, pops, and shows all the signs of having a messed up fuel mixture under any more than 10% load, so I can putter around but cannot accelerate or even go up a steep hill without making a helluva racket and being bucked around in my seat. I noticed on the log that my battery voltage drops at these times ... from 13.5V to around 12 V ... not much, but shouldn't this not be happening at all? Isn't the generator (if it were working properly) capable of keeping up with the minor load the injectors are putting on it under throttle? (IMG:style_emoticons/default/confused24.gif)

Anyone have any experience with this?? I'm thinking of a new battery anyway, since the shop's Optima worked out well, but I don't want to mask the problem by buying an expensive new battery if the generator is the problem. If I do get a new battery, I'll probably go a bit larger than the Braille B2015, so any suggestions there are welcome. It will have to have a lay down bracket available so I can keep it basically where the Braille is now ... I'm thinking a bigger Braille or an Odyssey model will avoid the issues I've heard about Optima's.

So I'm pinging the World here, looking for experiences you may have had ...

Tack!

[Dtjaden]

I had a very similar event with my Megasquirt system. I was on a local PCA drive and I noticed that my power seemed down. Then my engine started to ping under load. I finally looked at my volt meter and noticed that I was at about 11 volts so clearly I was not charging the battery.

I turned around at that point and nursed the car home - over an hour away. I was down to about 10 volts bt the time I got home. When I got home I noticed that my generator light was on even though the car was turned off but not when the car was running! Fortunately I had another alternator that I swapped in (not fun on a 914/4). Problem solved. I haven't seriously looked at this failure mode for Megasquirt but clearly there is a voltage sensitivity.