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Old 10-31-2007, 08:41 AM   #51
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Great Info

Great thread. Keep us updated on the progress

If I ever take the plunge into hacking the TCU, the voltage drop and wire gauge considerations are good tips. So far, I haven't had to consider this aspect -- just supplying juice to various applications has been easy.

I too, look forward to the progress. (I'm also envious of the single-wire lockup command).

RH77
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Old 10-31-2007, 09:06 AM   #52
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Bruce: thorough work. The suspense is killing me.
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Old 10-31-2007, 09:27 AM   #53
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The scary part will be the current draw from the solenoid when breaking the circuit -- it should easily be several amps.
Is it Hallowe'en scary? What is your concern there?
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Old 11-06-2007, 12:37 PM   #54
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Good to go

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Is it Hallowe'en scary? What is your concern there?
Frying switches, maybe burning fingers. I found a couple of 12V relays in my parts bins, so I should be able to use those for breaking the circuit instead. I should be able to use these for a crude but safe logical "or" of the PCM and external switch signals by putting the switch ends of the relays in parallel between a 12V source and the TCC solenoid.

I finally "listened in" on the converter lockup signal this morning. (I've been biking quite a bit more lately, so it can be a while between experiments.) I took an old earphone, soldered a 1KOhm resistor in series and hooked it up to TCC and ground. A pop at engagement and faint, noisy whine while engaged. The noise sounds exactly like the noise you get on the AM band -- it rises and falls with engine RPM -- so I have to assume it's just plain old noisy 12-15V from the alternator, nothing fancy. So, it appears okay to feed it straight 12 Volts.

Next will be finding a line to tap for 12V, ~1.5A. The cigarette lighter should be a good candidate if I can get at the back of it, since it's already pretty close to the shifter.

I need to find a cleaner way of routing the wire to the interior. Quite a bit of it is exposed along the hinge area of the driver's door when the door is open.
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Old 11-07-2007, 04:57 AM   #55
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A blinding flash of the obvious

Duh! How about plugging into the lighter socket instead of tapping 12V permanently? Hmmm....

I could connectorize the TCC cable and run it up through the ashtray. Put the relays, switch and some LEDs (for power, PCM lock signal and manual lock signal) into a small project box with a couple of pigtails for the TCC cable and 12V lighter plug. Velcro the box anywhere it's convenient to use.

If I make up a jumper for the TCC connector, I could then just unplug and remove the box, plug in the jumper and tuck in the connector end whenever I need to lend the car to somebody else (usually my wife). Voila, the car is stock again with no mystery buttons.

I like it. It's a solution I can visualize, and it should be relatively easy to implement.
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Old 11-08-2007, 04:48 AM   #56
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A minor setback

I didn't have time to wire up a couple of relays, so I wired up a simpler circuit last night: a Schottky diode (.525V forward drop) between the PCM lead and the TCC lead, and a heavy-duty switch between the positive on a cigarette lighter plug and the TCC lead. I also left the LED and pullup resistor between the PCM lead and ground.

Just to make sure everything had power, I measured the current of the solenoid with ignition on across the switch leads. 1 Amp, as it should be, and the coil inductance made nice sparks when disconnecting.

I drove to work this morning; I never used the switch. I coasted down to the end of the street, as usual, fired up the engine and the CEL stayed on.

After coasting to a stop, I restored the wiring to its previous configuration, and went for another burn. The CEL stayed on, so I pulled into a parking lot to check and clear codes. The code was for Transmission Shift Solenoid E, of course.

I drove to work without further incident. Everything still works fine.

My best guess is that the PCM is checking for opens/shorts on the TCC solenoid by using a voltage divider. It probably leaves a high-value resistance between the TCC output and +12V; if the TCC output is greater than a certain threshold (say, 0.1V), then it throws a code. Apparently, the 0.525V added by the diode isn't low enough.

I can probably get around this by using a big, low-value resistor to ground in series with a relay coil for switching the TCC. Unfortunately, that means drawing an additional 12 Watts from the alternator over the stock configuration when the PCM normally switches the coil, e.g. above 45 MPH. I'm not sure how much impact this would have on FE, but it certainly won't help.

I guess the first step will be to find out how much resistance (how little power) I can use between the PCM output and ground without throwing a code. With any luck, I may be able to keep it down to a Watt or two.

I'm hoping the PCM will throw codes without starting the engine so I don't have to idle while trying different resistance values.
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Old 11-08-2007, 06:20 PM   #57
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I'm hoping the PCM will throw codes without starting the engine so I don't have to idle while trying different resistance values.
No such luck, unfortunately. After work, I pulled apart the PCM output and TCC lead, turned to IG-II and put it in drive. No codes without starting the engine.

I'll hook the relays up this weekend and put a 12 Volt, 11 Watt lamp between the PCM output and ground to spoof the PCM. If that works, I also have 7 Watt and 4 Watt bulbs for the same fixture that I can try.

A resistor will have better long-term reliability, but the bulbs are easier for testing.
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Old 11-10-2007, 03:49 PM   #58
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It works!

I wired up a circuit today with a couple of relays, a couple of resistors, an indicator LED, the 12V light, a momentary-contact pushbutton switch, a cigarette lighter plug and some leads for the PCM input and TCC output. I tested everything on the bench before hooking it up.

It appears to work properly. It definitely lowers the engine speed in second and third at lower speeds and applying more gas doesn't raise it immediately. The TCC locks up normally at ~44 MPH as usual, and the light comes on.

The only problem is that I'm not sure it's gaining me any FE. I think it's a matter of using it judiciously and learning the speed ranges where it'll help. There's a large speed band in the 35-45 MPH range where it's probably better to leave it unlocked in 4th than locked in 3rd as long as I'm not going uphill.

I only got 33 MPG on a short drive this evening (8.3 miles), but it's only around 40?F or so. The car didn't have much of a chance to warm up.

I need to move the pushbutton to the shifter so it's more convenient to use.
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Old 11-12-2007, 05:57 AM   #59
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More tests

I unplugged the lamp on the way home Sunday morning. No codes. The PCM appears to be happy with a 450 Ohm resistor and the relay coil in parallel.

Surprisingly, it's looking like I'm better off not using the switch during warmup. The couple of times I've tried it, overall FE seems to be worse and I've watched the instantaneous MPG go down when the TCC is locked up. I guess the engine gets slightly better FE at higher RPMs when it's cold.

It is nice for cruising, though. I can keep it locked at 35 MPH in 4th at low throttle, which is great for most roads around here. If I need to accelerate up a hill at 30-35 MPH, I can throw it in third and lock it up. It's also nice for accelerating in 4th, since I can lock it up right away and not need to back off to get the PCM to engage the TCC.

Acceleration with it locked feels much stronger, although there's a fine line between strong acceleration and lugging the engine at low RPMs. I've learned to not lock it up unless the engine is turning at least 1500 RPM under light load; otherwise, I'll lug the engine.

But, hey, it's possible to lug the engine -- what more could a FE nut want with an auto besides bump starting?
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Old 11-13-2007, 06:55 PM   #60
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I can't access it right now, but the Australia Hilu Surf Owner's site has alot of info about lockup switches for the 3.0L diesels and trans.
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