This is on a b18c1 with a p28 obd 1 ecu. When measuring the charging voltage at the battery with the car at idle the voltage is 12.6 volts, even when bringing the rpms above 2000 rpm. The battery is new and this is the 2nd alternator, the previous alternator was putting out between 12.6 and 12.4 volts and with a load put on by autozone it went down to 11.5 volts, they said the alternator tested good. As of right now the car seems to be running ok, but every now and then when idling I will catch the tach and it will kinda figit real quick and start to get more pops in my exhaust than normal. From what I have read the alternator should be putting out between 13.5 and 14.5 volts. I was real surprised when I put my new alternator in and I was pretty much getting the same voltage as before. I am concerned because I have run into this similar problem before where it seems to get to the point where the idle will seem to get real low and start stalling the car out, I assume it's not doing that now cause my battery is still fresh but I could see it happening again in the future. Ok guys, what should I check first, grounds, ecu?? Btw not getting any codes what's so ever, I am chipped and tuned with ectune if that would make any difference.

 

test the voltage regulator, do some volt drop tests on your cables, check grounds

prolly some old shitty connections causing you grief.

 

Checked the voltage at the alt and it is still 12.6 volts. I also checked the the white/green wire on the 4 pin connector at the alternator with the car running it is putting out about 12.6 volts (take note this is the wire that runs directly from the ecu and looks like it should only be putting 1 volt or less, it's a signal wire. I checked this wire for a short, now the book isn't real clear on this test. When I do this test with the 4 pin connector still plugged into the alternator it shows a short, when I unplug it and check for a short (just the wire itself being tested now) there is no short in the wire run. The book doesn't actually say to unplug the connector or not. I don't know if it should still be showing a short with the alt being plugged in or not, (granted the alt itself is grounded). I am scratching my head on this one. I would love to test the ecu with my stock p72 ecu, but my p28 is tuned for 550cc injectors and I would imagine that probably wouldn't work with the idle too well, unless someone knows otherwise?

 

What do you mean "shows a short"? If you unplug something and check for voltage at a connector, you should get whatever that circuit specifies. Now if you backprobe a connection, you won't get any voltage to show up because whatever circuit you are checking is using all available voltage. Its called a voltage drop test.
I think your ELD(electronic load detector) needs investigating, as that is really what tells the alternator how much juice to put out, and if its not running the car at full power, all kinds of weird **** can happen, or a major ground point needs adjustment,

 

I mean when touch the positive probe to the white/green wire and then the negative probe to the chassis while I have the connector plugged in I show close to 0 resistance, when I unplug the connector from the alternator and do the same test I have a perfect 1 for resistance checking the ohms, meaning that the wire run is not "shorting out" (touching the chassis due to a break in the wire). As far as the voltage drop test, shouldn't I at least see 13.5 volts at the alternator itself, because when I check it, it says 12.6 right at the alternator and 12.6 at the battery, so the voltage is consistent. As far as the ELD, I am thinking or should say hoping that is the case the case as opposed to the ecu being bad. Thanks

 

I have been looking at voltages regarding the ELD, I checked the green/red wire which from what I have read the voltage with the key in the on position should be between 4.5 and 5 volts, my voltage is 3.76, when I turn accessories on it reacts but I don't think it leaves the 3 volt range. I tried this test with another ecu and the initial voltage is the same, not the 4.5 to 5 volt range the books says. I tried reseating the connector on the ELD, but that didn't seem to do anything for me. Don't know really what my results are telling me. I went to the junkyard today to try to find another ELD but the latest thing I saw in the junkyard was a 1995 civic, I have a 1999 civic and the fuse boxes are different. Anyone know what my results are telling me other than the fact that I am still screwed. Btw I had 12 volts at the blk/yel wire.

 

problem solved, alternator disable feature in ectune, by default it is set to disable alternator, all better now, charging between 13.5-14.5 volts now, thanks for all your input.