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!

[Madswede]

The voltage issue is definitely still there even with the new battery, and I've heard from more than one person that MS is sensitive to voltage fluctuations. The voltage is great for a bit then inexplicably tends to drop to ~12V or lower when the engine is running and warmed up. Since the injectors tend to shut off when the computer is seeing these very high RPMs, I don't want to run it like that, so she sits for now.

I did notice that the computer tach is spiking when I plug in the laptop to it, but the analog tach in the dash - which I've been told gets its signal from the computer - is reading the correct RPM, or at least it was when I was driving it while it was logging. Very strange. I'm wondering if I'm imagining things or if the log is actually showing what I think it's showing... (IMG:style_emoticons/default/confused24.gif)

The car was recently at the shop where they replaced and upgraded a lot of the connections to the battery and computer, so I'm pretty confident it's OK. I can ask them to check them over again since I paid for all the work to be done and it's clearly not working.

For info, I do have a 36-1 toothed wheel and a VR sensor (I believe) that has been replaced from Clewett along with a better mounting bracket ... here's a picture of the old one that became "groovy" ... the shop found that the old one was not seated well in its bracket and had drifted too close to the wheel.
(Sorry about the lack of focus, iPhone camera isn't focusing in on near field objects for some reason. Might be time for a new one.)


The MS gets the signal for the RPMs from the cam sensor input, I just verified. There still might be an issue with the replacement they made so I'm also going to ask them to check over it again. I have been wondering if this might be contributing to the issue of the RPMs going crazy and the injectors closing or remaining closed when they should be squirting fuel, or if they're behaving as programmed and the computer is being fooled somehow into thinking the RPMs are ridiculously high. Then again, with a VR sensor, the voltage irregularity should not be causing or contributing it seems, so perhaps it is a failed repair.

If the second one were the case, I think I should be seeing lost syncs in the log, which isn't there. Then again, maybe it's not being reported (like it was before when the sensor got grooved) in the general log file from the MS ... which seems unlikely. In hindsight, I should have logged the initiation / timing events (so-called "composite log"). Maybe I'll start it up and just idle it to get a composite log. I'll look at the general log again to make sure I'm not crazy, and that the RPMs were really being recorded at Ludicrous Speed.

All of that thinking and logic leads me to conclude that it's one of two things: a failed repair of the old VR sensor causing RPMs to be reading wacky and the computer is fuel cutting in the mistaken belief the engine is way over redline, or some other voltage irregularity from a bad alternator/regulator is causing the major confusion somehow and the VR sensor repair is fine. I'm returning it to the shop, for sure.

Thanks for all of your input folks! Will post in this thread again in a couple weeks when I can get the car to the shop next. I will say that, for the very brief moments when she does run correctly, the thing is a monster!