Early shifting into OD. Strange readings on TunerPro RT

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FourEightZero

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Well.. Here's an update. I'd appreciate any feedback or ideas.

DRAC module came in today. I set the DIP switches for my tire size and gear ratio.

Didn't make a difference. Still getting a high speed signal and early shifting at the ecu.

Could it be the wiring from the VSS to the DRAC?
 

FourEightZero

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I'm just oing to throw this out there.... check the tps
Already replaced TPS. Values look normal to me.

So here's a screencap of the "dashboard" view when I have the transmission .adx file loaded up in TunerPro RT.

This is the point right before I start braking to turn the corner at the end of my street. Dash speedo was maybe at 20 at most. Computer thinks I'm doing 46 and already has me in 4th gear.
 

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yevgenievich

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Need to look at the signals and wiring of the drac.
Edit: it might actually be a faulty 4low signal, but not sure if it goes to drac or ecu
 
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tayto

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have you tried another .adx file, sometimes they aren't complete or there are errors in them. is your dakota dash wired to the drac still (2000 ppm signal) or directly to the speed sensor? have you checked the wires from the drac to the PCM by eye and with a meter? what does the PCM say for speed when you are not moving? have you tried unplugging the dakota gauges and seeing if that changes anything?
 

FourEightZero

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Well... after solving a host of issues with the engine (misfire due to exposed wires on the 4-pin connector going to ignition control module, subsequent fouled plugs and plug wire arcing), I got the engine running well and now I'm back to this issue.

Upshifts are coming way too early and when the converter locks up, engine lugs.

I'll have some time this weekend and will pick up a multimeter and start taking readings on all the relevant wiring (I have the wiring/troubleshooting PDF for this truck). I'll also start going through all the grounds, cleaning them up, and perhaps adding some.

So, speed does read zero when I am at a complete stop, but when moving, it reads much faster than I'm actually going (just as I mentioned earlier). New VSS & connector, new DRAC, tried a different 16168625 PCM, made no difference.

Attached is a data log and and the trans .adx file for TunerProRT. If any of you guys wouldn't mind taking a look and throwing some ideas my way.. that'd be greatly appreciated.

At ~00:01:30 I pull out onto the 45 MPH street (I think I only got up to 30MPH) manually shifting to get to residential side street.

At ~00:02:00 I turn down the side street

At ~00:02:14 I take off in OD start driving thru residential area and dash speedo never goes over 23 MPH. PCM is reading vehicle speed super high.
 

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FourEightZero

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Need to look at the signals and wiring of the drac.
Edit: it might actually be a faulty 4low signal, but not sure if it goes to drac or ecu
This is the wiring diagram for the 4WD system. The dark blue wire on the right side of the page is going to the PCM. This would be where the 4 low signal would be sent, correct?

Any idea what the voltage should be if I'm in 2HI?

(BTW, I have noticed that the lights on the transfer case shifter (floor display) are constantly on. I am not in 4WD though.
 

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Schurkey

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Already replaced TPS. Values look normal to me.

So here's a screencap of the "dashboard" view when I have the transmission .adx file loaded up in TunerPro RT.

This is the point right before I start braking to turn the corner at the end of my street. Dash speedo was maybe at 20 at most. Computer thinks I'm doing 46 and already has me in 4th gear.
Tach shows 1461 RPM, in 4th gear. Seems like 46 mph is more likely than ~20 mph.

What gear ratio do you have in that truck? Is the tach screwed-up, too?
 

FourEightZero

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Tach shows 1461 RPM, in 4th gear. Seems like 46 mph is more likely than ~20 mph.

What gear ratio do you have in that truck? Is the tach screwed-up, too
3.73 ratio. I set the drac to that and tire size.

I was on icy streets in a neighborhood. I know for sure I wasn't doing 46. Plus I compared dash speedo to GPS. It's almost dead on accurate.
 

FourEightZero

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I think I found a possible solution:

DATE: 1996

TECHNICAL BULLETIN # 343

TRANSMISSION: 4L60E, 4L80E

SUBJECT: Lack of Power, Early, Late or Erratic

APPLICATION: GM

1993-96 4L6OE and 1994-96 4L8OE Lack of Power, Early Shifts, Late Shifts or Erratic Shifting

Some 1993-96 4L6OE or 1994-96 4L8OE equipped pickups, sport utility vehicles, motorhomes or vans may exhibit one or more of the following concerns or symptoms:

^ Lack of power especially when carrying loads or during heavy acceleration.

^ Early upshifts, no matter
what the throttle opening.

^ Late shifts in the 4WD-low range only.

^ Erratic shifts (shifts which are early during one upshift sequence and normal during the next sequence or some of the upshifts during a shift sequence are early, while others are normal).

^ Incorrect forced downshift shiftpoints or no forced downshifts at normal road speeds.


These conditions may occur on either 2WD or 4WD vehicles, but are most prevalent on 4WD applications. In addition, these conditions will most likely be intermittent and will occur without any trouble codes being set.

NOTE :1996 applications will set a code P1875 if a short to ground or an open in the 4WD circuit occurs. These conditions may occur on 2WD applications due to the fact that the PCM harness usually contains circuit 1694, even though it is not a 4WD vehicle.

System operation and diagnosis

All 4L6OE, non passenger car applications and all 1994-96 4L80E applications use a discrete input to the PCM, TCCM or VCM to change the shift points of the transmission.

Manually shifted T trucks (1993-95) signal the PCM of the 4WD-low position by grounding circuit 1694. This ground is provided by the shift selector quadrant switch. When the shifter is placed in the 4WD-low range, the PCM will note that the voltage on circuit 1694 has dropped to near zero (figure 1, 1A, 1B).

Electronically shifted T truck transfer cases indicate 4WD-low range position via the transfer case control module (TCCM). The customer selects 4WD-low by pressing the appropriate selector button (figure 2). This signals the TCCM of the drivers desire to engage the 4WD-low range. The TCCM engages the transfer case in 4WD-low, and also signals the PCM or VCM of its intentions by grounding pin C-1 of the TCCM. Grounding this pin drops the voltage on circuit 1694 to near zero volts at the 4WD-low input to the PCM (or VCM) (figures 1B, 2A).

Unlike the T trucks, K trucks indicate the 4WD-low range position using the same method, regardless of which type of transfer case the vehicle is equipped with. All K truck applications use a three position switch (figure 3A) which is wired to circuit 1694 or 1493 of the PCM, TCCM or VCM. When the 4WD-low range is selected, the transfer case switch will be moved to the 4WD-low position. In this position, the switch provides a ground for circuit 1694 or 1493, at the PCM or VCM (figure 3, 3A).

All K truck and T truck applications ground circuit 1694 or 1493 to provide input to the PCM or VCM when the 4WD-low range has been requested. Any range other than 4WD-low, results in circuit 1694 or 1493 remaining ungrounded and the pin voltage at the 4WD-low input to the PCM staying high at source voltage (battery voltage).

Diagnosis:

When the PCM or VCM 4WD-low input signal (circuit 1694 or 1493) is high (approximately 12 volts) the computer will assume the truck is in a range other than 4WD-low and will command the shift points based on the truck being in 4WD-high or 2WD-high. If the truck is really in four-low, the upshifts will be late for the given throttle opening. In addition, the truck will exhibit overly sensitive forced throttle downshifts.

In each case the truck will exhibit conditions which will be objectionable to the customer, but will not set any trouble codes (1993-1995 models). Most 1996 models will set code P1 875 if the circuit develops a problem. Code P1 875 will set if:

^ No TPS, VSS shift solenoid or TCC codes are set.

^ IPS angle is 17-50%.

^ Overdrive range (fourth gear) commanded.

^ Transmission temp 69-248°f

^ Engine temperature below 400°F.

^ The front axle position feedback circuit (new for '96) indicates to the VCM that the front axle is in 4WD, and the VCM calculates the speed ratio (engine speed transfer case output speed) is between .8 and 1.2 (indicating the truck is not in 4WD-low) for five seconds.

OR


The front axle position feedback circuit indicates the front axle is not in 4WD, and the VCM calculates the speed ratio (engine speed + transfer case output speed) is between 2.5 and 2.9 (indicating the truck is in four-low) for ten seconds.

If code P1875 is set the VCM will respond by commanding the transmission to:

^ Increase line pressure to maximum.

^ Inhibit TCC.

^ Shift to third gear only.

^ Turn on the check engine light (MIL).
 
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