Overcharging at startup

BroncoIIJeff

New member
Joined
Feb 22, 2020
Messages
5
Location
Winston-Salem, NC
Hello, I have 1989 Bronco II which is bucking, erratic idle, poor drivability, but only at start up. It runs and drives perfectly after it warms to operating temperature. So I need to wait 2-3 minutes on a warm day, but 7-8 minutes on a cold day. I'm not new to Fords, have a modified '96 Mustang, but this, my first Bronco just acquired Oct. 2019. I replaced the originsl injectors as one was leaking, but that made no change to to bucking start up. Tested the IAC, TP and MAP sensors, oK. Replaced the ECT sensor, but still no change. While working with a mechanic, discovered that unplugging the voltage regulator eliminated the bucking at start up! The B2 fast Idled up to 1,100rpm, then settled down, ran smooth, like every vehicle should, except I was not charging the battery. Thinking my problem was electrical I tested the battery at 11.6-11.8 key off. My battery is a good one. With cold B2 engine running, bucking, got 14.7 volts-too much charge as we want to see 13.25-14.25, right. Replaced alternator with a Driveworks brand. No change, still bucking at start up, then smoothes out after warm up 3-5 minutes. Some said the Driveworks brand was poor, so back to Advance Auto, they Exchange for a Carquest 80 Amp. Still no change. Not wanting to cut and crimp/splice wires again, I pulled the regulator out and replaced with a BWD unit. Still no change. I might add the charging voltage drops to 14.5 after warm up. The motor Smooths out and I can drive it. It is supposed to drop down a bit, thank goodness. But still charging too high. So phone call to bwd resulted in a spec sheet which says their regulator is based on a 14 volt system, with 14.7 nominal voltage. Not a coincidence I read 14.7 charging voltage at cold start up. I have not touched the white sense wire. The green ignition wire is at battery voltage key on eng off. Then the green wire voltage drops to 2.3 volts at start up. The B2 runs great AFTER warm up, 3-5 minutes, and a voltage drop down to 14.25-14-5. I am now thinking the 14.7 nominal charging voltage is not the problem, but the results of another issue. Can anyone help or experienced this anomaly?
 

miesk5

96 Bronco 5.0
Staff member
Moderator
Joined
Oct 18, 2005
Messages
7,685
Location
Coronado, CA
Yo Jeff,
Welcome!
You addressed the fuel managers at cold start & normal operation,
IAC, TPS and ECT sensors, however, testing those sensors may be needed.
For no,w let's look another perpetrator(s).

Have you checked for Diagnostic Trouble Codes《on a cold engine and when at normal operating temperature?
Here are test methods other thanwith a scan tool @ https://www.therangerstation.com/tech_library/OBD_I.shtml

Vacuum Leak in a Cold Engine:
One way to do a quick check is to grab a vacuum gauge. Some parts stores will loan you a gauge with refundable deposit.
The vacuum gauge should read between 15 and 22 in-Hg depending upon the engine condition and the altitude at which the test is performed. SUBTRACT ONE INCH FROM THE SPECIFIED READING FOR EVERY 1,000 FEET OF ELEVATION ABOVE SEA LEVEL.
The reading should be quite steady. .
When engine is rapidly accelerated (dotted needle), needle will drop to a low (not to zero) reading. When throttle is suddenly released, the needle will snap back up to a higher than normal figure.

When vacuum leaks are indicated, search out and correct the condition. Excess air leaking into the system will upset the fuel mixture and cause conditions such as rough idle, missing on acceleration, or burned valves. If the leak exists in an accessory unit, such as the power brake, the unit will not function correctly. Or Air Conditioning when in MAX mode may switch to Defrost.

A friend had same issue, he. noticed a crack in the Y-pipe adjacent to the O2 sensor. When the exhaust warmed up it then sealed the minor air leak. So the sensors vacuum hoses could have an issue when colf
•○¤
Oxygen Sensor Testing, Bronco & Ford; "...three wire O2 sensors; two gray wires and one black. The black should read ground. One gray wire should read 12V with the ignition on, and the other gray wire is the one we are after. Probe this wire with the engine warm, and running with a voltmeter’s (+) probe, and ground the negative probe. While the vehicle is running, the reading should be approximately 0.5V. A reading below this indicates a lean air fuel mixture; a reading above this indicates a rich mixture. If no reading is present, and all connections are good, the sensor is probably in need of replacement.." by Ford
⊙●⊙
Next Up to Bat is the Diode Leakage Test; "...To check alternator diode leakage, connect the multimeter in series with the alternator output terminal when the car is not running. Leakage current should be a couple of milliamps at most; more often, it will be on the order of 0.5 milliamps. Use care when disconnecting the alternator output wire; make sure the battery is disconnected first..." by Fluke

A long shot on an Alernator Bad Bad Waveforn; @

Bad IAC Waveform
This waveform was captured using the lab scope. This is a good example of how an alternator with a bad diode can affect other signals that the ECM looks at. In this case it is an IAC motor.
When viewing waveforms that have a lot of hash always look at the alternator diode pattern as a possible cause.


&

Ford Idle Air Control
This is a typically good ford idle air control (IAC) motor waveform. The Ford IAC waveform has its own unique "sawtooth" signature. The IAC valve is being pulsed and the duty cycle determines the volume of air through the valve.
A 100% duty cycle is fully open and a 0% duty cycle is fully closed. When checking this solenoid look for dropouts or spikes in the waveform that could indicate a problem

□■□
Also fyi, Loose or Weak Contact at Generator Harness Connector TSB 96-21-4 for 86-93 Bronco & F Series, etc.includes your BII
ISSUE: When a generator fails, there are a few failure modes that may cause heat to be produced at the wiring harness-to-generator connector. This excess heat may damage the female terminals on the wiring harness, resulting in increased resistance. The increased resistance produces more heat. When the generator is replaced, the resistance produced by a damaged connector may damage the new generator and could result in a repeat repair, including installation of another generator. High resistance (caused by a damaged connector) will not go away until the damaged connector is replaced.
ACTION: Visually inspect the harness-to-generator connector for damage (heat, corrosion, distortion and cracking) before installing a new generator. Install the Generator Wiring Harness Connector Kit (E5AZ-14305-AA) if the harness-to-generator connector is damaged.
The Generator Wiring Harness Connector Kit (E5AZ-14305-AA) contains the following:
One (1) Red Wire Butt Connector
Two (2) Yellow Wire Butt Connectors
One (1) Wire Connector Assembly
One (1) Instruction Sheet (I.S. 6849)
PART NUMBER PART NAME
E5AZ-14305-AA Generator Wiring Harness Connector Kit
◇⊙◇
Al
 

BroncoIIJeff

New member
Joined
Feb 22, 2020
Messages
5
Location
Winston-Salem, NC
Yo Jeff,
Welcome!
You addressed the fuel managers at cold start & normal operation,
IAC, TPS and ECT sensors, however, testing those sensors may be needed.
For no,w let's look another perpetrator(s).

Have you checked for Diagnostic Trouble Codes《on a cold engine and when at normal operating temperature?
Here are test methods other thanwith a scan tool @ https://www.therangerstation.com/tech_library/OBD_I.shtml

Vacuum Leak in a Cold Engine:
One way to do a quick check is to grab a vacuum gauge. Some parts stores will loan you a gauge with refundable deposit.
The vacuum gauge should read between 15 and 22 in-Hg depending upon the engine condition and the altitude at which the test is performed. SUBTRACT ONE INCH FROM THE SPECIFIED READING FOR EVERY 1,000 FEET OF ELEVATION ABOVE SEA LEVEL.
The reading should be quite steady. .
When engine is rapidly accelerated (dotted needle), needle will drop to a low (not to zero) reading. When throttle is suddenly released, the needle will snap back up to a higher than normal figure.

When vacuum leaks are indicated, search out and correct the condition. Excess air leaking into the system will upset the fuel mixture and cause conditions such as rough idle, missing on acceleration, or burned valves. If the leak exists in an accessory unit, such as the power brake, the unit will not function correctly. Or Air Conditioning when in MAX mode may switch to Defrost.

A friend had same issue, he. noticed a crack in the Y-pipe adjacent to the O2 sensor. When the exhaust warmed up it then sealed the minor air leak. So the sensors vacuum hoses could have an issue when colf
•○¤
Oxygen Sensor Testing, Bronco & Ford; "...three wire O2 sensors; two gray wires and one black. The black should read ground. One gray wire should read 12V with the ignition on, and the other gray wire is the one we are after. Probe this wire with the engine warm, and running with a voltmeter’s (+) probe, and ground the negative probe. While the vehicle is running, the reading should be approximately 0.5V. A reading below this indicates a lean air fuel mixture; a reading above this indicates a rich mixture. If no reading is present, and all connections are good, the sensor is probably in need of replacement.." by Ford
⊙●⊙
Next Up to Bat is the Diode Leakage Test; "...To check alternator diode leakage, connect the multimeter in series with the alternator output terminal when the car is not running. Leakage current should be a couple of milliamps at most; more often, it will be on the order of 0.5 milliamps. Use care when disconnecting the alternator output wire; make sure the battery is disconnected first..." by Fluke

A long shot on an Alernator Bad Bad Waveforn; @

Bad IAC Waveform
This waveform was captured using the lab scope. This is a good example of how an alternator with a bad diode can affect other signals that the ECM looks at. In this case it is an IAC motor.
When viewing waveforms that have a lot of hash always look at the alternator diode pattern as a possible cause.


&

Ford Idle Air Control
This is a typically good ford idle air control (IAC) motor waveform. The Ford IAC waveform has its own unique "sawtooth" signature. The IAC valve is being pulsed and the duty cycle determines the volume of air through the valve.
A 100% duty cycle is fully open and a 0% duty cycle is fully closed. When checking this solenoid look for dropouts or spikes in the waveform that could indicate a problem

□■□
Also fyi, Loose or Weak Contact at Generator Harness Connector TSB 96-21-4 for 86-93 Bronco & F Series, etc.includes your BII
ISSUE: When a generator fails, there are a few failure modes that may cause heat to be produced at the wiring harness-to-generator connector. This excess heat may damage the female terminals on the wiring harness, resulting in increased resistance. The increased resistance produces more heat. When the generator is replaced, the resistance produced by a damaged connector may damage the new generator and could result in a repeat repair, including installation of another generator. High resistance (caused by a damaged connector) will not go away until the damaged connector is replaced.
ACTION: Visually inspect the harness-to-generator connector for damage (heat, corrosion, distortion and cracking) before installing a new generator. Install the Generator Wiring Harness Connector Kit (E5AZ-14305-AA) if the harness-to-generator connector is damaged.
The Generator Wiring Harness Connector Kit (E5AZ-14305-AA) contains the following:
One (1) Red Wire Butt Connector
Two (2) Yellow Wire Butt Connectors
One (1) Wire Connector Assembly
One (1) Instruction Sheet (I.S. 6849)
PART NUMBER PART NAME
E5AZ-14305-AA Generator Wiring Harness Connector Kit
◇⊙◇
Al
Thanks. I'll check those.
 

BroncoIIJeff

New member
Joined
Feb 22, 2020
Messages
5
Location
Winston-Salem, NC
My CEL stays off. The OBD1 scan tool shows no codes. Remember, I unplug my voltage regulator, and the B2 runs perfectly, even in the first minute at cold start! My alternator charges at 14.7. I think it is detecting a load. When the B2 warms up, the load goes away and the voltage drops to 14.25 and albus well.
 

miesk5

96 Bronco 5.0
Staff member
Moderator
Joined
Oct 18, 2005
Messages
7,685
Location
Coronado, CA
Yo Jeff,
Yes I recall about the regulator.
"The case of the alternator must provide a solid ground to the voltage regulator & the stator, so its mounting points must be clean, and the engine block & intake manifold must be well-grounded to the battery (-) post.

Have you tested the vacuum?

emmisions-label2.jpg
Source: by Seattle FSB
 

Buschman

New member
Joined
Feb 19, 2020
Messages
10
Location
Ohio
I had a 89 with a 2.9 that did the same thing. Every thing miesk5 said makes perfect sense. My bronco2 had vacuum leaks and pore grounds. The ground between the intake and fire wall was very bad. I then found out the former owner tried to fix the problem by messing with the timing so I adjusted that and fixed it. I hope u find it is some thing simple as a bad ground or leaky vac hose.
 

BroncoIIJeff

New member
Joined
Feb 22, 2020
Messages
5
Location
Winston-Salem, NC
I tested the IAC, TPS and ECT sensors, OK, traced black signal return wire back to ECM, OK, no breaks. Got 5 volt reference to these sensors, as well as the MAP.
I read good charging voltage at battery positive and alt bracket, chassis, body, everywhere. Can not find any vacum leaks under the hood. B2 starts fine and runs fine AFTER WARM UP. But bucking, erratic idle, can not drive it for 2-7 minutes, depending on the outside air temperature. It is like there is no "open loop" condition or ECM is stuck in 'closed loop." The Cardone tech I phoned said that was impossible. He said the ECM can NOT be stuck in closed loop.
What do you think?
 

BroncoIIJeff

New member
Joined
Feb 22, 2020
Messages
5
Location
Winston-Salem, NC
I will check the potential crack in the exhaust pipe before the O2...but I learned the O2 does not send a signal until it warms up to, say, 650 degrees. The B2 runs horribly before that. Thanks for your help, Miesk5.
 

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