What voltage should I have at the battery terminals with engine running?

[The Shape]

Last couple of days my GT has been kinda hard to start. The starter sounds the same as usual, but the engine turns over longer before it will fire. A couple of times I have had to crank it twice to get the engine started. I always let the fuel pump prime before I try to crank the engine before anyone suggest that. I believe this all started about a week ago after trying to jump start my '93 4 popper coupe I just bought as a beater. I am wondering if I damaged my battery. The beater didn't have a battery on it when I bought it and I just ran jumper cables from my car to the other cars battery cables so I could pull codes on the 2.3. I also cranked the engine over a few times on the 2.3 with the cables hooked up like that to make sure the engine wasn't locked up. The battery on my car is just some no-name cheap battery it was on there when I bought it 2 1/2 years ago. I was wondering if I could use my multi-meter across the battery terminals with the engine running to see if it was bad, and if so what voltage should I see?

 

[BlackFox5.0]

about 13.5v

 

[The Shape]

Thanks

 

[Michael Yount]

Depends on how many accessories are working while it's running - but I'd say anywhere from 13.5-14V. Output of the alternator may be as high as 14.4V. But if you're trying to test the battery, take the car to Autozone or PepBoys and have them load test the battery - that's really the best way to test it. Voltage across the terminals may not tell you much of anything.

 

[90mustangGT]

Depends on how many accessories are working while it's running - but I'd say anywhere from 13.5-14V. Output of the alternator may be as high as 14.4V. But if you're trying to test the battery, take the car to Autozone or PepBoys and have them load test the battery - that's really the best way to test it. Voltage across the terminals may not tell you much of anything.

What he said.

Also you have to look at other factors. To properly test the alternator the battery has to be good. The voltage should be steady. A alt with a bad diod will read proper voltage most of the time, but won't be good, and will kill a battery quick. A scope is the best way. One way to test a battery is to run a few accesories for a minute or two (erasing surface charge) and then testing it, then turn the key on, engine off and run the highbeams and HVAC blower and see what it reads then, it should stay in the 11V range. Crank it and see what happens, it should not drop below 9.6V durring cranking.

 

[89MustangGX]

Depends on how many accessories are working while it's running - but I'd say anywhere from 13.5-14V. Output of the alternator may be as high as 14.4V. But if you're trying to test the battery, take the car to Autozone or PepBoys and have them load test the battery - that's really the best way to test it. Voltage across the terminals may not tell you much of anything.

It's true -- it's almost not worth the hassle of doing much more than going to one of these places as a first step. In my experience, their equipment is usually dead accurate and gives a real good indication of problems. They can check the entire charging system in a matter of minutes, and their machines tell them what to say, so they don't even have to know much more than how to connect it to the battery.

I don't necessarily buy my parts from the same place (junkyard is a favorite store of mine), but as long as they offer to do free troubleshooting with their fancy machines, I'll keep taking them up on it.

 

[HISSIN50]

so your car cranks longer before starting? it still turns over fine?

you are gonna hate to hear it, but have you tried priming the FP a couple times before trying to start? if your pump is on the outs (or the check valve or regulator is/are bad), you might not have enough static pressure to start (the heat of summer where you are is hard on diaphrams).

just a lame idea (only easy thing i could think of to check).

oh yeah, while i like doing as Adam et al, do - you can check the battery's cells specific gravity - if you have a dead cell, you will know. a static voltage reading under 12 volts can indicate that as well.

some ramblings. good luck, big J.

 

[Michael Yount]

I even have a battery specific gravity tester in my tool box - unused for MANY years due to so few batterys being sold anymore that aren't sealed.

 

[QDRHRSE]

Mike its ok.....we know you break into your neighbors cars and test their batteries once in while. You've got issues but we can work through them together......I remember the time you drove around late at night with a thermometer under the hood (and in the fenderwell) to prove that fenderwell air intakes are a good idea. Yeah....we've been moving in the right direction but still have miles to go.

 

[Michael Yount]

Oh no, I've been discovered....

 

[The Shape]

so your car cranks longer before starting? it still turns over fine?

you are gonna hate to hear it, but have you tried priming the FP a couple times before trying to start? if your pump is on the outs (or the check valve or regulator is/are bad), you might not have enough static pressure to start (the heat of summer where you are is hard on diaphrams).

just a lame idea (only easy thing i could think of to check).

oh yeah, while i like doing as Adam et al, do - you can check the battery's cells specific gravity - if you have a dead cell, you will know. a static voltage reading under 12 volts can indicate that as well.

some ramblings. good luck, big J.

Yeah HISSIN I have definently thought of the fuel pump. When I first bought the car it was very hard to start and the pump made ALOT of noise so I replaced it and it started fine afterwards. I did check my battery with my meter this morning I had 14 volts with the engine running, but I see from Michael, Qdrhse and 89's post that isn't a very accurate way to test it. I need to take it to the local Auto Zone and have them test my charging system. Also since it could be the fuel pump and I need to have one around anyway, how much does a fuel pressure tester normally go for? Any places you guys suggest buying one or a certain brand to buy?

 

[mustangsquared]

Fuel pressure gause will run you $40-50 at autozone or other parts stores...they ar egreat for setting your fuel pressure if you have a AFPR or checking for bleed down. They have the adaptors to connect to the shrader valve(SP?) for easy use.

 

[HISSIN50]

mustang^2 is right on. i paid about 40 at CSK - it screws right on (ive read of some of them needing an adapter to work - im not sure on that). i agree that it is a nice tool to have. ive been meaning to get a fixed gauge and install it, but the braided line and fittings are $$.

good luck, TS.

the cheap batteries i run are not sealed (i like it, as the AZ heat dries the cells out). but most good ones like you all run, are sealed. oh well.

 

[mustangsquared]

HISSIN50... accell make a gauge that screws on the shrader valve OR on the side of your AFPR (the BBK model has a place). No braided line to install. Works great and makes adjustments fast and easy. Costs around $50. I think 50 restoration sells them.

 

[HISSIN50]

HISSIN50... accell make a gauge that screws on the shrader valve OR on the side of your AFPR (the BBK model has a place). No braided line to install. Works great and makes adjustments fast and easy. Costs around $50. I think 50 restoration sells them.

thank you for the info! unfortunately, the line would be a necessary evil - i would want to mount the gauge on the cowl, so i know what's up as i drive [under load].

the accel gauge would really be a permanent version of the quick connect gauge i have now (for testing). i might end up getting a Jegs gauge for 20 bucks and sticking it on the schrader - for side of the road probs. plus i can pay a kid 5 bucks to sit on the motor while i drive, if i have problems and need to have the gauge read. LOL J/K.

thank you very much for the idea. im much obliged.

 

[Michael Yount]

Yeah - having fuel pressure available while driving can really help trouble shoot things sometimes. Even though I hate the thought of that gauge outside - gotta find a way to put it inside without having the fuel in the cockpit.

 

[Mavrick]

Without any lights/blower motor/any accessories on, my car puts out 14.6v at idle.

 

[HISSIN50]

nice one Mav we forgot to give him #'s. i would preface it with knowing what RPM's the motor is at with what #'s (and even if the motor is warm or cold). little stuff makes a big difference (heat can lessen electrical efficiency, and an idle of 650 vs 900 RPM makes a difference in what the regulator is doing).

(im trying to say it is hard to compare one car's alt output at idle with another, w/o knowing more info on the characteristics of the car).

 

[The Shape]

Your are right HISSIN I had about 14.2 at 650 RPM idle wich is about right on with maverick's voltage. As I reved the engine it would climb a bit though. It was hard to tell how much since I had no help, and it is a bit hard to hold the leads from the meter on the battery post with one hand and lean over and rev the throttle with the other . I am leaning twoards it being a fuel problem now though. We have been getting alot of bad gas around here lately so the first thing I am gonna do before anything else is swap my fuel filter out. Right now my main quest is trying to find a rivet gun large enough to install my new door handles. I bought the handles from 5.0 resto for my 2.3 beater , but I broke the drivers side handle on my GT last night . I am catching hell trying to find a rivet gun large enough to pop them on!

 

[Mavrick]

My car idles around 700rpm and puts out 14.6v at idle. I'm not sure on the amperage because i never thought to test amps.

You want over 14v at idle.