Low Idle Speed + Battery Light

[Dave's95Limited]

Hello all, I have a1996 Explorer Limited. I recently had the engine and transmission changed and haven't had much of a chance to drive it since. I took her out of the garage yesterday, filled her with gas and drove around town a bit. The idle speed seems really slow with the tach sitting at zero both in park and in drive. Also at idle the battery light in the dash flickers on and off, not sure if this is due to the low idle speed or not, I did not notice this while driving at speed, only when stopped or foot off the gas pedal. I did note that the battery they put in after the engine swap is rated at only 450 cca which is below the recommendations for this vehicle, not sure if this would cause the battery light issue. I had this work done in OH and I now live in SD so taking it back to the folks that did the work is not an option. Looking for some ideas, where to start?

 

[fast_dave]

@Dave's95Limited

Just checked my service records - here's the battery that your Explorer should have:
Group 65 1,000CA/850CCA/150AH Reserve

Start there, report back, hope that helps!

 

[J_C]

Welcome to the forum! Which engine?

It is your low idle speed. Alternators produce a tiny fraction of their normal output at low RPM, and generally at the correct idle speed only produce enough to power everything with a tiny reserve to keep the battery charged. Below that correct idle speed, output drops off a cliff.

450CCA is on the low side for areas where it gets much below freezing in winter, but right now you should have no problems with a 450CCA battery in good condition IF the alternator were getting charge into it. If it's some worn out old battery and while rated at 450CCA, it is now down even lower, it would make the vehicle more difficult to start before you'd get a battery light flashing with the engine running IF the engine RPM were high enough.

SO, ignore the battery and light for the moment and attack the low idle issue. - EXCEPT that if your battery is now low, you might want to put it on a charger to start out with a charge for further troubleshooting, and if the battery light goes off that doesn't necessarily mean the battery is bad. Even if your engine installer is far away, I'd still call and ask if they have any ideas or suspicions on what might have gone wrong... can't hurt even if you are told IDK.

Next I might hook up a scan tool and find out what the RPM is and if any readings look off like the fuel trim. Might it be coincidence and you have a more common problem like a bad IAC? When my IAC starts going out, I find the idle tanks more with A/C turned on.

Around here, Walmart has the best price on a group 65, 850CCA Everstart Maxx battery at around $100. Costco was competitive but recently dropped their warranty 3 yrs total while walmart is still 3 replace, 5 pro-rated. Some walmarts still have their service centers closed due to the pandemic so while you may be able to buy the battery there still, may need to DIY to swap it.

Do also check for battery terminal corrosion. I'd hope nothing like that would exist with a recent engine swap but you never know until you check. That also tends to cause more problems starting than running, but who knows if it's shaking around from low RPM AND you have a loose battery terminal.

 

[fast_dave]

@J_C

He's a 1st post newbie and I let him slide; didn't want to put him through the wringer - LOL - 95' has only one engine = the Old Reliable 4.0 OHV

But perhaps he changed to the SOHC - so it's a valid question!

With that said - @Dave's95Limited - it would be good to put that detail in your profile so that when you start asking engine related questions you (hopefully) don't get SOHC related answers.

With that said - welcome to the forum!

 

[rasouth]

Stating that you just had the engine and tranny changed, I would check to see if the ground cable from engine to chassis is connected and clean.

 

[Dave's95Limited]

Thanks to all for the replies! So far I have changed the battery, picked up a new 850 cca from O'Reilly. Oddly enough while driving it for a while this evening the battery light came on and stayed on the entire time idling and driving at various speeds. First thing I did when I got home was leave it running and disconnected the negative battery cable, it did not die, turned on the headlights still ran fine, so I don't think it's a bad alternator. I'm going to check the voltage tomorrow with a multimeter to see what the alternator is putting out. Does anyone know what that voltage should be? Oh, by the way the explorer is a 1996, my mistake, now I'm stuck with it as my user name. lol

 

[Dave's95Limited]

Welcome to the forum! Which engine?

It is your low idle speed. Alternators produce a tiny fraction of their normal output at low RPM, and generally at the correct idle speed only produce enough to power everything with a tiny reserve to keep the battery charged. Below that correct idle speed, output drops off a cliff.

450CCA is on the low side for areas where it gets much below freezing in winter, but right now you should have no problems with a 450CCA battery in good condition IF the alternator were getting charge into it. If it's some worn out old battery and while rated at 450CCA, it is now down even lower, it would make the vehicle more difficult to start before you'd get a battery light flashing with the engine running IF the engine RPM were high enough.

SO, ignore the battery and light for the moment and attack the low idle issue. - EXCEPT that if your battery is now low, you might want to put it on a charger to start out with a charge for further troubleshooting, and if the battery light goes off that doesn't necessarily mean the battery is bad. Even if your engine installer is far away, I'd still call and ask if they have any ideas or suspicions on what might have gone wrong... can't hurt even if you are told IDK.

Next I might hook up a scan tool and find out what the RPM is and if any readings look off like the fuel trim. Might it be coincidence and you have a more common problem like a bad IAC? When my IAC starts going out, I find the idle tanks more with A/C turned on.

Around here, Walmart has the best price on a group 65, 850CCA Everstart Maxx battery at around $100. Costco was competitive but recently dropped their warranty 3 yrs total while walmart is still 3 replace, 5 pro-rated. Some walmarts still have their service centers closed due to the pandemic so while you may be able to buy the battery there still, may need to DIY to swap it.

Do also check for battery terminal corrosion. I'd hope nothing like that would exist with a recent engine swap but you never know until you check. That also tends to cause more problems starting than running, but who knows if it's shaking around from low RPM AND you have a loose battery terminal.

Could you recommend a decent scan tool, not too pricey but not cheap junk? I'm wondering now about my tachometer would be nice to know the actual RPM. The idle is actually quite smooth not stumbling like the engine wants to die.

 

[fast_dave]

@Dave's95Limited

Battery Light after a new battery is a sign you alternator (or regulator) is bad.

Drive your Ex back to O'Reilly, take off your alternator in the parking lot (10 minutes at MOST), bring it inside, and have them speed test it on their computerized tester.

Their alternator tester tests for many parameters that a hand held tester can't replicate, including a load test and relay test, and it's FREE.

Hope that helps -

 

[J_C]

Do not disconnect the battery with the engine running. Some people get away with it but it is a bad idea for vehicles modern enough to have electronics that depend on the battery to buffer the spikes from the alternator.

You are fixating on the battery again when I think you should focus on why it idles low. With a new battery at good charge, it wouldn't be the battery causing low idle so there is an underlying problem and once that is fixed, maybe the battery issue is too.

My preference for a scan tool (given only this isolated case) is a BAFX from Amazon linked to an Android phone running Forscan app. If you have other non-Ford vehicles with other manufacturer specific subsystem codes outside the OBD2 code set then more research will be needed on your part to decide what product best covers all bases for all your vehicles, but the BAFX with Torque app would cover all codes within the OBD2 range from any manufacturer. Both of these apps have a freeware version, BTW.

If your battery has drained due to a bad alternator or too low RPM, the "Okay" voltage is hard to predict when it could be slowly (trying to) charge the battery, but when everything is right, good battery w/charge, good alternator, good cables and clamps, it should be around 14.4V with engine running or at least near that and rising towards that.

 

[Dave's95Limited]

Ok, the only thing I have done so far this morning is check voltages with a multimeter. 12.5 V battery, 14.5V with engine running. It was actually idling at around 1,000 RPM as it was 40 degrees here this morning. I'm gonna go warm it up and see if the idle drops back as soon as I get a few spare minutes. Could it be that I just need to run it longer to let the PCM sort things out after the engine swap?

 

[J_C]

As long as it has oil pressure and isn't misfiring, I'd do that, let it run but watch the battery voltage. If the RPM drops too low and it stops charging the battery, that could deep discharge the battery and at a low voltage, make all sorts of odd lights bells trouble codes just due to low voltage.

At 12.5V the battery is near but not at full charge yet. Not necessarily a bad sign, could be expected if it had sat a little while and the engine hasn't ran long yet.

 

[Dave's95Limited]

The more I mess with it the more I'm starting to think the tachometer is just being weird. The idle is very smooth yet the tach sits at zero after it warms up and the idle slows down. After I warmed the engine idle sitting at zero RPM the voltage dropped to 14.25. Turned on radio, headlights, and A/C it read 14.20 V. I've double checked connections at the battery, and the alternator, all were good and tight. Unplugged the 4 pin connector from the alternator and re-seated it, battery light was off when I started it back up. Going to drive my son to school in a few and see if it comes back on.

 

[Dave's95Limited]

Just wanted to update the thread. I simply unplugged and put back the wiring connector on the alternator and the battery light issue went away, been driving for a couple of weeks now and all is good. I purchased a scan tool to monitor the rpm and the idle is good, my tachometer is not working correctly. Any thoughts about the tach? Where would I start to try to get it fixed?

 

[410Fortune]

did the tach work correctly before the new engine?

Tachometer is really pretty simple on these trucks
One wire leaves the pcm and goes all the way to the instrument cluster
It is possible the tachometer itself is worn out
Was the needle ever messed with? instrument cluster ever taken apart?

If you hook up a scan tool you should be able to see tachometer reading from the pcm, I bet it reads differently then what your tach is showing.

Also the brake light can come on whenyou are low on brake fluid or if the E brake is depressed, so anytime you have an intermittent brake light on the dash always a good time to check brake fluid and check the little switch on top of your e brake make sure its clean and working