Puzzling overdrive problem... possible pcm issue

FWC_Bronco

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Will do, Miesk.

558
332
327
628...
(ignore the egr codes for now as I’m in the process of getting those cleared according to your previous instructions).

The weird thing is the truck will drive fine for close to 30-40 min. Will hold lockup fine and then randomly start bucking and revving into neutral.

Speedometer is bouncing like crazy and the other night I had to pull down the gear selector and put it back into park to get it to start.

Is there a way to test the mlps?
 
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FWC_Bronco

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Update: Pulled the tone ring off the carrier and found some broken/smashed teeth. I'm going to replace that and the vss with a motorcraft sensor.

Has anyone had issues with a bouncing speedometer triggering TC lockup problems?
 
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miesk5

96 Bronco 5.0
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Yo FWC,
Yepster! In a way.

In 92 through 96, the rear axle mounted VSS provides a 72,900 to 86,900 pulses per mile signal via the 4WABS module to the Programmable Speedometer/Odometer Module (PSOM) aka Speedometer/Odometer;
PSOM then converts this signal to 8,000 pulses per mile.
The correct PSOM vehicle speed signal to the PCM is an AC square wave that rises to 5 volts positive and drops back to 3 volts negative, with a frequency of about 120 Hz at 60 mph.
The sloping tops and bottoms on the waveform are normal, and don’t indicate a problem in the circuit..."
That signal is sent out to the Powertrain Control Module (PCM) aka Computer or Electronic Engine Control (EEC) that controls the shifting of the Electronic 4-Speed Overdrive Transmission (E4OD) if equipped, and then to:
speed control amplifier, if equipped;
and overhead consoles compass/outside temperature display module, if equipped. Overhead console module uses the PSOM signal to estimate the accuracy of the outside temperature sensor that uses a high-speed counter to monitor vehicle speed to determine whether engine heat is causing erroneous readings.

When I thought my 96sPSOM was bad, I shipped it to DNA SPEEDOMETER, Tampa, FL, but a nasty lady at the UPS store tossed my Well-Wrapped and labeled, "THIS SIDE UP, FRAGILE" shipping box into the a hamper despite my request to handle it as described. I contacted the stores owner, he came over in 10 minutes, saw the box laying at bottom of hamper and relieved the woman permanently. He shipped it for free.
DNA speedometer folks said the odometer section was stained upon receipt.
DNA has Excellent service!
They offer a, "Get a free repair quote"
➡Plus
CALL US AT:
813-875-8226
TOLL FREE
1-888-495-2777

Other Bronco owners love their service too!
 

FWC_Bronco

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Installed the new tone ring and a used PSOM with the tach. While it’s a lot better I’m still getting speedometer waiver... It seems to start right around 65-70mph. The weird thing is the PSOM seems to “lag”. When I start driving it will take the speedometer a second or two to register my speed and it will then jump from 0 to however fast I’m moving.

Could the 4WABS module cause this? I plan to clean up the vss sensor mounting surface to make sure it has a good ground.

On another note I ended up taking the MSD coil I had installed off the truck and I’m no longer having bucking/jerking issues. My guess is that once the coil was hot it would cause a misfire issue at load... No transmission codes and the truck is shifting perfect.

I did install an Eddie Bauer bronco roof console. What’s the next item I should check to solve speedometer waiver?
 

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miesk5

96 Bronco 5.0
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Yo,
4WABS Control Module could be a perp.
Mine caused slam down shifts and PSOM HAPPY DANCE,
4WABS Control Module Bypass for PSOM Operation due to Bad 4WABS Control Module at 4WABS Module Connector; "...jumper 14 (CKT 530, LG/Y)to 21 (CKT 519 (LG/BK) & 39 (CKT 491 (O/LB)to 22 (CKT 523, R/PK)..."


by Turbo Ghost
I did this too by disconnecting the 4WABS Control Module under ws washer fluid/ coolant recovery tank.
Then I unwrapped harness covering to expose the wires and cut the wires 4 inches away from the coonector and spliced wires shown in turboghost's pic.
I used weather resistant in-line (butt) crimp connectors. Covered connector with a surgical glove , leaving small opening facing down.
Tied connector to radiator neck.
 

miesk5

96 Bronco 5.0
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Yo,
Go back to a stock Motorcraft coil
#10 Oct 14, 2014
yo,
High Quality Motorcraft TFI Ignition Coil Attributes
Source: by SeattleFSB (Seattle FSB) @ http://www.fullsizebronco.com/forum/showthread.php?t=199185
Many Bronco owners shop for an ignition coil by looking for the highest voltage available. But I venture to say that there is much more to look for in achieving both a quality ignition system and saving money in the long run.

For clarification, it takes approximately 10-14,000 volts to initiate the spark across the OEM spark plug gap. After the initial arc, the voltage required to sustain the arc is much less and drops off significantly. So while you may have a 48,000v coil you can't actually get that across the plug. The extra power becomes reserve voltage which compensates for worn plugs, increasing resistance in wires and carbon fouling. This increased stress can require an additional 1-5000 volts.
Fact is a higher voltage coil does not work any better, it just lasts longer due to having a higher reserve reducing heat. You cannot push more than 20,000 volts across a spark plug without bad things happening. If you were to try you would see arcing down the side of the plug, across carbon buildups at the electrode end and out any weak points in the wire insulation and connections.

The bottom line is the ideal coil output required for normal applications is about 30,000 volts. So no, your coil does not need to be 48,000v for proper ignition. The benefit would be in having enough reserve to compensate for high resistance due to a worn or altered ignition system.

This is why the Sixlitre Tune recommends a 48,000v coil and larger spark plug wires – to compensate for a substantial increase in resistance from larger than specified spark plug gaps. You are adding resistance as the spark attempts to reach ground. This in turn causes the plug wires to break down and decreases the service life of the rotor, distributor cap, spark plugs and increases the chance of spark scatter within the Distributor Cap.

Think about it, you are setting your spark plugs at a maximum gap even before wear. The higher voltage coil does not reduce stress and wear on your ignition system; it only compensates within a larger margin and then ultimately becomes dependent upon the quality of construction for survival. When opening up your spark plug gap from factory specifications you must be prepared to check your secondary ignition system annually, as opposed to about 40,000 miles with a stock vehicle, or risk performance decreases down the road.


With that being said, IMHO the Motorcraft DG470 TFI Coil is one of the most dependable 48,000v TFI Coils on the market. This is largely due to the quality in design, testing and construction. I have personally had many dependability issues with other imported TFI Coils, such as MSD. Where a Motorcraft Coil has lasted 15 years, I have went through three MSD coils in five years. Your purchase of a TFI Coil should not be totally dependent upon the voltage, but strong consideration should also be made regarding the contruction attributes listed below:


Motorcraft TFI Ignition Coil Attributes
Insulation - Multiple coats on the primary and secondary windings to ensure no internal arcing
Radio-Frequency Interference (RFI) Suppression - Minimize electronic noise
Magnets - Hold strength for the coil to maintain proper energy output
Steel - Used in the lamination stack to ensure a consistent magnetic field needed to develop the required voltage
Coil Housing - Engineered to withstand extremes in temperature without cracking


Low Quality TFI Ignition Coil Potential Issues
Rough Running Engine or Misfires - Causing Check Engine Light
Fuel Economy and Power Decrease – Costs money and performance
Radio Frequency Interference – Affects radio, EEC, sensors, cell phone
Pre-Ignition and Detonation – Can cause engine damage
Weak Voltage Output – Can cause increase tailpipe emissions..."
 

FWC_Bronco

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Feb 18, 2020
Messages
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Location
North Florida
I’m at my wits’ end with this.

I disconnected the abs connector and followed the procedure but the truck actually ran worse. The shift points were really crazy. Speedometer waiver was still present.

After reconnecting the abs connector it’s still acting similar to when I disconnected it. No ABS light.

The bucking/jerking has also returned. It came back after a 1 hour drive.

I tested the tps and found the ohms were out of spec. Replaced it but bucking/rough shifting still present.

Replaced plugs with motorcraft platinums and gapped them to .054. No change.

Replaced spark plug wires and routed them to prevent crossfire. No change.

Replaced the coil thinking another one might have failed. No change.

Somehow the truck is actually running worse.

The only codes I’m throwing are:

558
332

The egr vacuum line isn’t connected so unless the egr valve is leaking or stuck open I don’t see how it could be related.

I’m out of ideas.

Edit: I have an intermittent battery light that will sometimes flash rapidly. I’ve tested it at the parts store several times and it always tests good. I wonder if something internal in the alternator could affect the sensors on the truck and cause problems for the computer...
 
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Skitter302

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Here is a test for ya, block off the egr using Foil tape. (If you don't want a whole roll your local HVAC place can sell you a foot over the counter) install the egr with the vacuum line attached. and take it on another test drive.
 

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