93 TCU in 90 Q

[brucepelletier]

I'm quoting here from a posting by bondofca on the old Yahoo group:

Q Trans Computer

"I discussed this issue with JWT. The problem with using a 93+ factory controller (first gear start) on a 92 or earlier trans is that the the first and second gear is lower on the earlier trans, and the controller looks at driveshaft speed to shift, so it would shift according to the ratios in the 93+ trans -

93+ trans 1 & 2 gear ratios are 2.57, 1.4892 or earlier is 2.7 8, 1.54

With a 93+ controller looking for a driveshaft spped of 2645 RPM (6800/2.57), it would allow an engine speed of 7350 before the first gear shift (7350/2.78 = 2645).

My question is, I've heard about people swapping 93 TCUs into earlier Q's but does it work? I would like a 1st gear start but don't want to spend a lot of money for nothing or conflicts with the original design.

Members, your experiences please.

[Q451990]

The TCU from the 1993 model year Q should work fine in the 90-92 models. Maybe the old post from JWT was talkiing about build dates instead of modely year?

The transmission gearing didn't change until 1994. The TCU will have one of these part numbers:

31036-64U2031036-64U75

The U75 is an updated version, but either one will work just fine. You should find them in cars built between 7/92-2/93 according to an old yahoo post by Tom Novak (former Infinti of Lisle parts manager)

There are some reports of quacky behavior at redline in that the rev limter of the 90-92 ECU and 93 TCU may not match exactly, causing it to top out for a few seconds before shifting into second. I haven't noticed this problem, but I don't see redline that often. I had the 64U20 for a couple of years now and have used it with both the updated 90 ECU (swapped with transmission) and a 93 ECU I purchased on eBay. I can't really tell much difference, but I think the 93 ECU did seem to smooth out the 1->2 shift slightly. Maybe not, but when I spend $$ or time on the Q my mind will find improvment to justify it! All in all the 93 TCU is the best bang for the buck for a reliability/performance modification!

Heath

[Q45tech]

It depends on the internal condition of the transmission: The tcu knows how long [in fractional seconds] a good transmission takes to shift so the start of shift is backed off that amount so that the rev limiter is not engaged. If the transmission can't shift fast enough you hit the limiter...........a function of internal line pressure

A faster reving engine due to tire slip [hard tires] or a more powerful engine [chain stretch] can throw this timing off.

Even a hundred pounds of load [empty 90 low gas] vs heavier 93 [sound deading] can be 0.1-0.2 secs.

The JWT ecu's extra 400 rpm [rev limit raised] covers up lots of AT sins/problems.

Use a Consult to log when the TCU commands the shift and when the shift actually occurs.......you can monitor things in 5/100 of second increments.......as you know some over 70k trannies take 1.5 seconds vs oem spec of 1.0 second.

New vs used ATF varies in viscosity so the actual slip/engagement time will vary.........new ATF should shift faster than old friction modifier depleted ATF.How fast does the Q engine rev per second -greater than 1200 rpm per second in 1st gear..........see how the 400 extra rpm [JWT ecu] gains a 1/3 of a second in time for 1st shift completion.

Once te shift command is sent the ecu backs off the power by reducing ignition advance by 20 degrees so that the clutches won't fry! During the shift the acceleration essentially STOPS.

[Q45tech]

If you add up the missed acceleration: 0.5 + 0.5 sec [1>2>3] you see why the AT is a full second slower in the quarter than a fast shifted manual transmission with exactly the same gear ratios.

Obviously the manual/clutch has less losses than a torque convertor but this amounts to only 12% at launch and 5% at 4,000 rpm 3% at 6,000 rpm.

[greg_atlanta]

'93 TCU isn't perfect but still a good bang for the buck. I find the 1>2 shift to be very smooth at high rpms but a little bit rough at low rpms. I switch back to '92 TCU for winter since I don't like the way '93 TCU wants to shift from 1>2 at higher rpms (when engine & trans is cold).

With stock TCU the transmission never shifts from 1>2 EXCEPT at high rpms so I think that might explain the rough shifts at lower rpms... something the trans has never done before???

[DougQ45]

Buy one you will really enjoy it, especially around town. Best purchase I have made for my 1990 Q. Have bumped into the rev limiter a couple of times at around 6,800 RPM's but will not do it again---I PROMISE!!

[landtodd]

Greg and I have the opposite experience. My '93 TCU (in a '92) gives me buttery smooth part-throttle shifts, increasing in firmness with more throttle and rpm. (Probably just higher line pressures as rpm increases.)

I've had my '93 TCU over a year now. Overall, the 1>2 shift has become noticably smoother as (I suppose) the hypothetical "edges" wear off a first gear that was rarely if ever used. Maybe I'm just getting used to it.

Great bang-for-the-buck! Transforms the around-town experience. As someone said, it makes the car feel 700 lbs lighter.

Since my next car will be a '91 Q, I *will* take this TCU with me if I ever trade this car away -- I wouldn't go back to the '92 TCU voluntarily.

There are many different combinations of ECU and TCU, some happier than others. For example, if I recall Dennis correctly, for '92 there were 3 different ECU firmware revisions, and there are two different TCU revisions for '93. So, in my case, I got one of 6 possible combinations by luck of the draw.

I'm quite pleased with the outcome.

[greg_atlanta]

Since my next car will be a '91 Q, I *will* take this TCU with me if I ever trade this car away

oh? got one lined up already?

[landtodd]

Tee hee. Jeff and I bought one already.

[1qckser]

Who has a good deal on the trans ECU? Thanks