Battery light on constantly car runs fine

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marklindholm

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1994 SHO MTX
Last week the battery light just came on while driving.
Started troubleshooting today.
Resting battery voltage is 12.7 Volts (battery was replaced about 3 months ago)
Engine running is 14.7 Volts. I believe this is all normal.

I pulled trouble codes and got
542 (O,M) Fuel pump open, bad ground or always on – Power/ Fuel Pump Circuits
551 Problem in Intake Manifold Runner Control (IMRC) solenoid/circuit - Solenoids

When I turn the key on I can hear the fuel pump run for about 2 seconds and shut off (as usual).

Could the 551 trouble code be related to the battery light being illuminated?

Any other ideas as to what may be going wrong.
 

BaySHO Performance

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You may have generated the 542 simply by stalling the car.
The Intake Manifold Runner Control actually refers to the solenoid on the back of the intake that controls the secondaries. 551 refers to the Idle Air Control, the silver cylinder just inboard of the throttle body. Neither would cause the battery light to come on.

A brand new or just fully recharged battery will be at 12.3 volts. The alternator is therefore putting an extra 2.4 volts into the battery engine running. Shouldn't be more than 2 volts. I suspect that the alternator is overcharging the battery because the internal voltage regulator is bad. I suggest replacing it before it fries the battery.
 

marklindholm

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You may have generated the 542 simply by stalling the car.
The Intake Manifold Runner Control actually refers to the solenoid on the back of the intake that controls the secondaries. 551 refers to the Idle Air Control, the silver cylinder just inboard of the throttle body. Neither would cause the battery light to come on.

A brand new or just fully recharged battery will be at 12.3 volts. The alternator is therefore putting an extra 2.4 volts into the battery engine running. Shouldn't be more than 2 volts. I suspect that the alternator is overcharging the battery because the internal voltage regulator is bad. I suggest replacing it before it fries the battery.
I got the 551 code from here:
And it refers to the IMRC.
I checked my IMRC and it is indeed bad. My secondaries do not open at idle, and no vacuum is passing through the IMRC. I will replace it.
I do beleive this has nothing to do with the battery light.
Will too high a voltage on the battery cause the light to illuminate?
 

marklindholm

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I got the 551 code from here:
And it refers to the IMRC.
I checked my IMRC and it is indeed bad. My secondaries do not open at idle, and no vacuum is passing through the IMRC. I will replace it.
I do beleive this has nothing to do with the battery light.
Will too high a voltage on the battery cause the light to illuminate?
Oh and I cleared the codes by disconnecting the battery and the 542 code disappeared, but the 551 came back.
 

BaySHO Performance

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Interesting that those Ford codes say that a 551 is the IMRC, which you have found to be bad. These codes say it's the Idle Air Control: http://wiki.wikisho.com/wiki/Three-digit_EEC_codes

A google search found a person with the same code that also couldn't figure out whether it means IMRC or IAC. That was on a 94 Ford explorer that only has an IAC. No secondaries.

The secondaries are open engine off, but then close when the engine is started. Have you observed that the tabs on the secondary butterfly valves don't change position when you start the car? What happens to them when you rev above 4,000?

One of the things that can cause the battery light to come on is a bad voltage regulator in the alternator. As stated, I believe that it's charging the battery at too high a rate.
 

marklindholm

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I replaced the IMRC which was definitely bad. Now I see the secondaries open when the car idles. The 551 code is gone. Now I get 3 codes 114, 10, 111 and the battery light is still on. I let the battery drain down for a few hours with the headlights on then measured 12.2 Volts idle and 14.0 Volts chargeing. Battery light still on. I have ordered an IAT/ACT to get rid of the 114.
1644904470086
 

luigisho

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Some places on the interwebs say 14.7 is the upper limit of normal but I have never had a reading that high in any of my cars. Nick is probably on to something with the charging. I hope a replacement IAC fixes the code. Does it run normally with the 114? When a few of mine went bad I could tell the difference for sure.
 

black92

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Make sure the indicator light wire has a good connection. Single wire connector at alternator. If this connection is weak or bad, battery light will illuminate, but alternator will still be charging.
 

FastCAD

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I got the 551 code from here:
And it refers to the IMRC.
I checked my IMRC and it is indeed bad. My secondaries do not open at idle, and no vacuum is passing through the IMRC. I will replace it.
I do beleive this has nothing to do with the battery light.
Will too high a voltage on the battery cause the light to illuminate?
"The battery Light" my '91 mtx did the same thing. It was the starter relay on the driver's side fender.
If u replace the IAB get a quality unit 'Delphi' summit racing (SHO specific).
Hope this helps
 

SHOMON

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Make sure the indicator light wire has a good connection. Single wire connector at alternator. If this connection is weak or bad, battery light will illuminate, but alternator will still be charging.
Just had this happen on my 95...Was going to suggest it too!!
 

marklindholm

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I unplugged the single wire and started the car, the battery lite was still on.
I replaced the single wire. Started the car lite still on.
I removed the multiwire connector and started the car. The battery lite went out.
I replaced the multiwire connector and started the car. The battery lite is out. Success.

Conclusions:
My IMRC and Air Intake / Charge Temperature Sensor were both bad and replaced and had nothing to do with the battery lite. Also note that with the 2 bad sensors I never had a check engine lite.

The battery lite on was a result of a poor connection in the multiwire connector on the alternator.

I do not believe there is anything wrong with my alternator or voltage regulator. The charging voltage will vary depending on the "state of charge" of the battery. When I recorded the 14.7 the battery was only a few months old and had a battery charger on it just prior to me starting the car and measuring the running voltage. In other words the battery was very fully charged. According to the chart above a fully charged battery, with the alternator charging can see up to 14.8V. For the past few weeks the car has been sitting idle without the battery charger on it. Before I started messing with the alternator wires this morning I measured the resting voltage at 12.56 and the charging voltage at 14.01. I am concluding the resting voltage and the charging voltage are related. If your resting voltage is high your charging voltage will also be high, which yes is counter intuitive. I have noticed the same phenomenon on my motorcycle, which has a voltage meter on it. Just after I start it the charging voltage will be relatively low and will creep up as I ride, because the battery is getting charged up, the chargeing voltage goes up.
 
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