idle/electrical issue

[john112deere]

This is my '97 Ranger 4-cyl.

Lately, sometimes when I come to a stop sign, just as I'm rolling up to the stop, the engine idle will drop (no tach, but rough guess would be 4-500 rpm) for a second then come back up. Manual trans, and I'm in neutral when it happens. When the idle drops, the battery gauge will also drop, and then come back up slightly behind the idle coming back up. This seems to happen only within the first couple stops of starting the engine, and each time I remember, I've had the heater fan on, and the headlights. Doesn't happen every time, or necessarily on the VERY first stop. But usually within the first 1/2 mile or so of driving.

The truck starts OK down to 5* (coldest I've had occasion to try this year), it did crank a little slow, but that seemed pretty normal given the temps; the alternator is an Autozone one about 35k miles old, and the battery is also Autozone, maybe 5 years old.

It seems to me that there could be three issues here: battery is old and takes a while to recharge after starting the engine, alternator is crapping out and has trouble charging the battery after starting the engine, or the idle is dropping for some other reason, and the battery/alternator aren't getting enough juice when that happens.

What would be a good first troubleshooting step (limited tools, but I do have a multimeter)? It's happened enough that I know it's not just a fluke, but I can't make it happen every time, either.

 

[F150]

There's more qualified personnel on here than me, but it sounds like this needs to be more broke to find out what the problem is......... if that makes any sense.

 

[john112deere]

Well, yeah, but I've always thought of that as a last-resort diagnostic technique.

Forgot to mention it idles rough most of the time. Never dies, but it shakes the truck a bit. It's not awful, but it's not exactly smooth, either.

I don't mind replacing the battery, and the alternator's not a bad job to replace on that truck. I just don't want to throw parts at it until it works right, though.

 

[Fellro]

Best thing to do would be to get a volt meter hooked up. You can get some that simply plug in to the cigarette lighter and read the voltage. Then you can validate what is happening with that and confirm or deny those thoughts.

 

[blacksnapon]

At first thought, I would look at the idle speed control motor. Fuel injected motors use the isc to adjust air flow for engine speed adjustments. Anything that changes the amount of air into the engine, will change idle speed (isc motor, vacuum leaks, egr valve) And low idle means the alternator isn't turning fast enough either.

 

[john112deere]

So you think the idle is dropping, and as a result, my alternator can't keep my battery charged.

Makes a lot of sense, but it's not the answer I wanted. Alternators, batteries- easy to change. Diagnosing anything else intermittent, not so easy.

 

[Bob Ayers]

The first thing I would try is cleaning the IAC valve. If it changes things, it might have to be replaced. To make the system less senstive to low battery voltages, the PCM has a 5V linear regulator (12V to 5V) that will maintain 5V
with the battery voltage as low as 7V (but the coil pack & injectors will not
operate with the battery voltage that low).

 

[Fellro]

I was thinking IAC as well, the troubles can be interelated. Possibly a simple cleanup would make a difference, always a possibility. WD-40 does pretty good on dissolvong the deposits, or carb cleaner in this location.

 

[john112deere]

I can clean the IAC, that's no big deal.

Not that I think it's related, but if one of my coil packs failed (dual-plug ignition on this truck), what would the symptoms be? My buddy and I were talking about it, and we got to wondering- with dual plugs, it seems like you could lose a coil pack, and it would still run on all 4 cylinders. But I don't know for sure.

 

[Fellro]

I'm personally not familiar with dual plug setups, most I have dealt with have multiple coil packs fire multiple cylinders, meaning a waste spark setup. One would have the exhaust open, the other would have the compression stroke, both get fired by the same coil. Basically, if the coil dropped, it should have a missfire and likely lose some fuel efficiency as well. Perhaps I am off on this since I haven't worked with that new of a truck though.

 

[Bob Ayers]

Each coil fires all 4 cylinders, so you won't get a misfire if you loose one of the coilpacks.

 

[john112deere]

That's what I thought. But does that mean that, in theory, I could have had one go bad 10,000 miles ago and not noticed, because it's still firing on all four?

Or would a bad coilpack throw a CEL?

Like I said, I have no reason to suspect a bad CP, I'm just curious how the ignition on this truck works.

 

[blacksnapon]

hope this helps

Ignition Coils
Two ignition coil packs are used for the 2.3L twin-plug engine (6007). The two ignition coil packs are triggered and timed by the powertrain control module (PCM) (12A650). Each coil pack contains two separate ignition coils (12029) for a total of four ignition coils. Each ignition coil fires two spark plugs (12405) simultaneously, one spark plug on the compression stroke and one on the exhaust stroke. The spark plug fired on the exhaust stroke uses very little of the ignition coil's stored energy. The majority of the energy is used by the spark plug on the compression stroke. Since these two spark plugs are connected in series, the firing voltage of one spark plug will be negative with respect to ground, while the other will be positive with respect to ground. Refer to the Powertrain Control/Emissions Diagnosis Manual for additional information on spark plug polarity.

Plug Inhibit
Dual Plug Inhibit (DPI) is a function of the powertrain control module (PCM) (12A650) that is used when the vehicle is being started. During engine cranking, the powertrain control module will only fire the spark plugs (12405) on the right-hand side of the engine (6007). When the engine has started, the powertrain control module will start normal twin-plug operation.

Additional information on the EI-High Data Rate theory of operation is contained in the Powertrain Control/Emissions Diagnosis Manual.

 

[Bob Ayers]

That's what I thought. But does that mean that, in theory, I could have had one go bad 10,000 miles ago and not noticed, because it's still firing on all four?

Or would a bad coilpack throw a CEL?

Like I said, I have no reason to suspect a bad CP, I'm just curious how the ignition on this truck works.

Not 100% sure, but I think it will throw a CEL if a coilpack goes bad.