Dodge Caravan transmission lock-up
 

I have been watching the SG in my 2003 Caravan 3.3 and noticing the increase in mileage when the transmission locks up. This happens about 42 MPH. This is a little fast for around town driving. Does anyone know what parameters the computer looks at when it locks up and if any of these parameters can be affected by altering sensor inputs without affecting driveability or mileage? This aproach seems to have the potential for significant improvements in city mileage.
Mike

I am not too up on Chrysler. But for my cars, it looks for the following.

-Needs to be in 3rd or 4th gear (there are 3rd and 4th gear switches in the trans). That also dictates the speed to a point, mine is about 33 mph lower limit for 3rd gear.
-Engine needs to be out of warmup mode.
-Throttle position needs to be in a certain middle range, foot off the gas or pushing hard will disable the TCC, it likely reads the TPS.
-Foot needs to be off the brake, there is a switch for this at the brake pedal.

IIRC, if you want to lock the TC, you can just find the TCL solenoid and put a switch on the wires. It shouldn't cause a MIL, but on the 2003 models it might.

Your transmission is electronically controlled, not hydraulically. With a little work and a switch box, you can openly control how your transmission shifts.

Also, if you leave your transmission in L or 1, it will automatically shift at or around 5-5.5k RPM, just so you know. It's a safety feature.

Any mods would have to leave the van driveable by anyone so I am not enthusiastic about a manual lockup switch (but I wouldn't rule it out). I had been thinking about a TPS tweak but am wondering about driveability issues from an altered signal.

A manual lockup switch is a two-way setup... you can just tap the lockup solenoid while leaving it attached to the ECU, so that when the ECU thinks it should be locked, it will still send the signal, even if you've already got it locked w/ the manual switch.

On the other hand, if you engage the manual switch, it will be locked, even if the ECU says "no".

Basically, when someone else is driving, the switch is utterly useless, and they probably won't ever touch it/know what it does. When you're driving, you can impress us all with your extra 2-3 MPG b/c you can lock it manually, without affecting anything. (Except you may get a CEL.. not sure.)

I think I would need to put relays in the circuit to isolate the ECU form the TCL so the ECU wouldn't know about the manual switch. This would avoid the CEL. This would also allow me to wire the relay to either unlock on brake application or maybe on the 4-3 downshift.

Brake application, I can see, but there is an advantage to having the converter locked in any gear - 1:1 operation with the engine and transmission. There are lots of manual valve body options which allow (for race applications, granted) you to have lockup in every gear, without a manual switch. Those applications are for manual lockup though, where the lockup solenoid is controlled by fluid pressure and a valve.

Regardless of the control method, having lockup on demand will allow you to engine-brake (although not in DFCO) in any gear except 1st, which is a sprag-type gear.

If it were me, I'd probably try to find a way to de-activate it with the speed sensor (when it gets below a certain speed), so that I could have engine braking when I actually wanted to slow down, but after it gets into 2nd gear, below, say 22 MPH (where it usually shifts out of first), it would unlock before going into first (b/c it wouldn't make a diff if it was locked in first or not.)

I started thinking about a 3-2 unlock but then it occurred to me that coasting would probably be better for MPG.

the drawback with Autotransmission-"coasting" (not sure if that is the case any more...) is that the hydraulic pumps only work with the car in drive. Coasting in neutral, the tranny fluid isn't being circulated/cooled and the tranny overheats/burns up.

This has never been true, to my knowledge. Back in the day, you could "pop start" an engine w/ an automatic transmission because they still used rear (tailshaft) fluid pumps, but not so much anymore, unless they're designed with that purpose in mind (industrial apps, "other" designs).

When you're coasting in neutral, the engine is still running. Since the pump is driven off the engine's output (transmission input shaft), the pump is still being driven as long as the engine is turning. Putting the transmission in neutral does nothing more than bypass the valve that allows fluid pressure to build up enough to engage the clutches in the gear set, but the fluid is still flowing very much so.

Where the problem comes in is when attempting EOC with an automatic, because then the engine isn't turning, so the transmission fluid isn't being pumped, except in circumstances where the transmission is designed to be towed for long distances in neutral w/ the engine off (most or all Saturns are built this way.)

I was not referring to coasting in neutral, only to having the converter unlocked and allowing the motor RPMs to drop with the resulting reduction in fuel feed to the motor. I am not a fan of coasting in neutral, I think it can increase reaction time in some emergency situatons and poses a safety hazard.

why would it ruin your reaction time? The average driver's first reaction is to hit the brakes and steer, not hit the gas or gear down.

(I know, you're not average... no one is.)

No offense, but I think the "neutral isn't safe because you can't accelerate on demand" argument is the most bogus thing I've ever heard. I've been in plenty of dangerous situations to know that even if you try to think about it, you'll almost definitely hit the brakes and/or steer first.

I agree that the first (and correct) impulse would be to steer and brake (Mine too) My thought is if the next need turns out to be acceleration, in the heat of the emergency with the adrenaline flowing, the next impulse will be to hit the throttle and THEN to remember you are in neutral and shift with your foot on the gas, not a smart move.

1 million to 1 chance that you'll ever need to accelerate from an accident (that you didn't cause, and you're not trying to run from).

Horsepower will inevitably get you into more trouble than it will ever get you out of.

How do you think people get away with not dying when they're driving those 30 HP sub-sub-sub compact clown cars? They're certainly not trying to accelerate, that's for sure! :P

If you don't like to coast in neutral, that's your own thing, I just don't see anything dangerous about it. (Even though it's illegal in most states, AFAIK).

OK I guess we can agree to disagree on that subject
As to the original subject I think your suggestion of a manual lock-up is probably the way to go. I am getting a dealer service manual for the van and that should tell me a lot more than my Haynes does about how it works. On a slightly different subject, have you had any experience with Synthetic ATF-4? My van is approaching 100K and will be due for fresh transmission fluid by fall.

On a lighter note, just get the stuff from Wally World. ATF+4 is ATF+4 is ATF+4, regardless of who's name is on the bottle. It's not made any cheaper or easier, it's not a byproduct, it's not "crap oil" like some would say, it's just a cheaper bottle of OEM Mopar-approved ATF+4. Save yourself some money, get it from Wally World. (SuperTech brand).

Taken from Allpar.com:Chrysler transmission fluids: 7176, ATF+3, ATF+4

More information on Base oil grouping: Amsoil - Motor Oil Base Stock Groups

ATF+4 (legally licensed) uses a Group 3 base oil, which, by legal definition, is a base oil used in full- and part-synthetic oils.

By definition, legally licensed ATF+4 is synthetic. Don't waste your money on the Mobil1 or Pennzoil version of ATF+4, it's the same stuff.

SuperTech ATF+4 is legally licensed, and has passed Chrysler's quality testing to assure that it meets the Type9602 Testing Requirements.

Licensed ATF+4® Brands

Third column, 6th listing down.

If it's not in that list, don't use it.

very interesting and good to know!

Does this mean that if you coast with the motor off that the transmission is then in danger of running dry?

In the case where you have a pump on the output of the transmission, no.

In the case with almost every automatic transmission since the 60's or so, yes.

Try it for 1/2 a mile or so... you'll either smell fluid burning, or you'll just kill your transmission with no warning.

If the engine is still running, then both ends of the tranny are still turning, so whichever side the lube pump is on, it's still getting the job done.

Some autos you don't dare EOC, but I do engine-on neutral coasting all the time, in every vehicle I drive from a Subie Forester all the way up to a 16ft Fuso cargo van. No worries.

-edit- (reads further in thread) Okay, somebody else said it too. Uh, ditto!

I'm thinking about installing a TC lockup switch in my Previa. Were would one find the solenoid (It's not in the wiring diagram or Haynes manual I have)

Since I may forget to switch it off, what is the effect of having the TC locked up in gears lower than 3+4? Does it stall out if you try to stop? Why not lock up at lower speeds?

I live in hilly country with a low speed limit and I am hoping that TC lockup will help FE on those steep hills and the flats we do have. I'm always in 2+3 and it rarely locks up.

If it's not in the wiring diagram, and you don't have an electronically controlled transmission, it's a fluid circuit inside the transmission. For more information on that, you'd have to contact the mfr of a shift kit for your transmission, who would know a bit more about it than I would.

I just found out the other day that mine isn't controlled by the PCM like I thought it was, so I can't use this idea anyway, unless I modify my valve body to allow for an external valve.

I can't imagine there being a problem with lockup at lower speeds, except if you stop, it will stall you out. (or break/slip the lockup clutch in the TC).

Basically, if you can wire in a switch, you'll have to remember to wire in a circuit so that it's unlocked when you're using the brakes, or after you're below a certain speed, if you were so inclined.

The repair guide says it's an ECT and there is a an ECT solenoid in the diagram but not specifically a TC lock solenoid. I should look online at another site for a different wiring diagram or ask at a Toyota site. Why don't they set TC lockup at lower speeds and higher loads? My guess is engine knock under high load/low speed.

Thanks for the info. A brake switch is within my current skill set as opposed to a speed sensitive switch.I had also thought of a pressure sensitive throttle switch so it would lock up only under a certain load.

Now that I think about it , my fantastic digital vacuum gauge from Vtec-e, has two output signals which can be set to any vac number. I could set it for on at say, 18 inches so it would be off at idle.

One reason I want to do this is that it would make P+G much more do-able the other reason is the hill climbing issue.

Thanks Christ

Selective lockup helps you with engine braking. You probably won't want it on the throttle, as it would then unlock as soon as you let off the accelerator.

I'm not sure why they don't allow it to lock sooner, as other manufacturers more recently have allowed lockup in all gears for faster/smoother acceleration and better economy. I can't see it having anything to do with damage to the clutch, since lower speed = less load on the clutch.

Add this to my tinfoil hat theory that cars are built as oil consuming machines.

Loosen the neck tie... your hat will fit better :P

At times, I agree... at other times, not so much. It depends on my mood.

I agree that you should check for a better wiring diagram. I have the two volume factory set for my Caravan and most of the second book is wiring diagrams. I my case the lockup is accomplished by grounding a lead from the transmission and I will have to wire it so the computer still sees voltage or it will think the solenoid is burnt out and set a code. In Mass I can't pass inspection with the check engine light on. The brake light switch sounds like the best option for unlock but I would suggest a bright RED light as a visual reminder. It shouldn't take long for you to get into the habit of unlocking, when was the last time you forgot to put in the clutch while driving a standard?

I have now installed an on demand TC lock up switch on my Toyota Previa.:thumbup:

It was simple. For now I have a momentary switch and I will install a parallel toggle and a big red light. In my case, in order to trick the ecu, a 15 ohm, 25w resistor needs to be installed from the ECU TC wire to the ground. I have not done this yet but I don't have to worry about codes.

My thread is here: Freezing the Slushbox. Torque Converter on-demand lockup switch.

Thanks for the thread.

I don't have an electronically controlled transaxle. It's all hydraulic, and the only electronics on it are the neutral/park start switch and the reverse indicator switch.

I haven't seen any other wires anywhere on it that would be related to a lockup solenoid, so I have to assume that it's governor controlled, like my shifting.

This link shows how to make a manual torque converter lockup switch for a dodge/cummins 48re transmission. The details will be different, but concept is the same. Beware, there are warnings about possible input shaft damage on stock components. I haven't done it yet, but am thinking about doing it in the future.

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