Just a simple, quick question. I posted a nice long thread in the 3rd gen section ( https://www.rx7club.com/3rd-generation-specific-1993-2002-16/bad-idle-stalling-when-hot-555142/ ) and did a search but didn't come up with any info.

I'm trying to troubleshoot a possible bad alternator and I wanted to know what battery voltages you guys see on the commander. The car is relatively stock, no crazy gel cell batteries in the storage compartment or anything.

The workshop manual says 14.1-14.17v while operating, and I'm usually seeing 13.5v driving around, sometimes as low as 13.2 and high as 13.8 and I want to get an idea of what others are seeing.

 

I've seen low voltages like this during idle with cars that have underdrive pullies idling below 1k rpm. Driving around the revs are higher and these same cars indicate high 13 to low 14 volts. These cars are getting old and the electrical systems have issues with grounding, alternators are getting old too. Check the voltage at the battery and confirm what the PFC is reporting. I usually clean the metal at all the accessible ground points, install a separate ground lead between the battery negative and the engine block, relocate the block ground from the bracket by the spark plugs to the block, etc. etc.

Don't assume the alternator is healthy, I looked at a car recently that had the battery dying prematurely and found the alternator was running hot as fire and making a slight squeeling sound. This unit tested perfect at Hi-Lo auto parts store but we replaced it anyway because of the aforementioned, replacing the alternator fixed the problem with the battery dying and the new unit was problem free. A few months later the battery would be dead after a week or so of downtime and it appears there is a drain somewhere in the electrical system. Morale of the story, these cars are getting old and it takes alot of work at times to get them back to health.

 

My PFC shows 13.8 while my very good digital volt meter shows 14.1.

 

My pfc says 13.8 also. For 3 years now. I have an optima red in my drivers side bin but it was the same before also.

 

Thanks for the replies, especially for your input twokrx7. I have a little more perspective on the issue now.

The only reason my battery died (at least how I see it) is because I like to run the fans until it's cooled down and that really puts some stress on the battery. I'd bet the alternator is having to work extra hard when I start the car on 11.5v as well.

At this point it looks like a complete crapshoot as to what I should replace next. Thanks again for the input.

 

Damn.... my battery voltage as of late when idling at 800 RPMs is barely 13.6 and at a cruise it is around 13.9

Maybe it's time for a new alternator?

I'm going to be sending mine out to Gotham Racing for polishing and supposedly they check and overhaul the alternator while it's there.

 

Worshop Manual Spec is 14.1 - 14.7 V with temperature gradient characteristics. Notice your typo Eric (pr0k . My Commander voltages above idle are usually 13.3 - 14 V this time of year. At idle my voltages can drop down a little more. Note that this is with underdriven eccentric shaft and alternator pulleys as well as an AGM (Miata) battery. Your alternator is likely ok. My voltage at the battery using a digital multimeter is .2 - .3 V higher than what the PFC Commander was displaying as Chuck (cewrx7r1) was saying. I guess the rest of the difference from the spec must be the "temperature gradient". I'll second the adding another ground wire or 2 suggestion.

 

First off, check all your electrical connections. Bad grounds and bad power leads can cause a MAJOR voltage drop - as much as half a volt. Put your meter on the two battery posts and see what voltage you get, then see what you get from the main post on the alternator. If there's a difference, time to work on those cables and connections.

Dale

 

im gettin 14.1-14.4...optima red top. my Apexi S-AFC reads it jus if you were wonderin

 

so Dale if I check the battery voltage at the battery post and at the altenator...and they read the same, then I'm good? Because my stupid apexi turbo timer reads 12.8 when crusing and drops to 12.3/12.4 when I full throttle it.