rmdl51

iTrader: (4)

Hello everybody, a few weeks ago I post here about engine swap and tranny rebuilt, well finally after a looong month I'll have the car back today but mechanic told me there's a delay on the shifting points that are not normal, another guy (electrician) checked the car and said there's something wrong with the transmission control unit, so the shop who rebuilt the tranny took it out again and re-check everything and they said everything was fine with the rebuilt.

Mechanic is convinced by the electrician advice that the TCU is bad, but before trying to get this part replaced I come here to listen to your advice, if TCU is really bad, do you have any idea how much they run right now? not willing to get from stealership so maybe online or local junkyard, but, how to test? and how can I know certainly if they are telling the truth?

I'll be testdriving the car this evening so I'll update later with how do i feel the car now, mechanic said is much better than before but it should be better because there's a delay on the shifting points where the TCU is not working properly.

Thanks in advance for your input.

mikekantor

iTrader: (5)

The used ones are cheap, I found a used TCU and ECU together for about $60. There is a sticky link to do a diagnostic on it, I would try that.

CapedCadaver

iTrader: (8)

i have a TCU that i don't need anymore.

rmdl51

iTrader: (4)

Oh! yeah! I remember you have your spare parts car how much for it shipped to 92835, but just let me be 100% sure I need it ok, I let you know today later or maybe tomorrow, oh! BTW please remember mine is a VG I don't remember which one you have, actually I don't know if that matters or not but I believe VG - VE ECU/TCU are different, I might be wrong I can't remember right now.

CapedCadaver

iTrader: (8)

Well it's actually the TCU from my main car, a 90GXE (all GXEs are VGs yadda yadda), which i don't need anymore as my GXE is a 5spd now. $30 shipped ground, or will you need it rush-shipped?

sonicii

What do you mean 'delay'? Does it just shift late (higher RPM), or is it slow to shift? (slipping / pause during the shift)

If it is shifting late, then your TPS probably needs to be adjusted.
If it is shifting slowly, then it could be a bad connector, or a bad ground point on the Transmission (or no ground point!!). Or a fault within the transmission.
I think it is unlikely to be the TCU. But if you can get one cheap, then it is worth a try!

Greeny

iTrader: (43)

Send a pm...Please

rmdl51

iTrader: (4)

nah! ground will be fine, just give me a couple of hours till i get home and talk to the mechanic and test drive my car to check everything this guy told me on the phone.

But I'm wondering, GXE and SE don't have any differences pre-programmed on the TCU? I ask because I keep thinking if the MODE switch (power/auto/confort) or any of the shifts will be affected if I put a TCU from a GXE into an SE, I'm not sure either but I think GXE don't have a MODE switch right?

gapboi210

GXE has the switch too.

rmdl51

iTrader: (4)

Ok, I just test drive my car and is in much better condition, it's finally picking up speed, I reach 60MPH pretty good but the take off is still taking forever, maybe I need to try it on the freeway

Mechanic said, the TCU is not sending any signal, so sometimes it shifts at some point and sometimes it shifts at a different one, even the Mode switch is not changing that.

I also have a steering wheel vibration which he told me is because my idle speed is wrong, that is not getting the correct information from the TCU, I told him about the idle speed controller but he said that's for the base idle speed, after putting on D the RPM drop to 500rpm and my steering wheel shakes, if I press the gas to raise the RPM to 800 the vibration is gone but then he said that is controlled by the TCU and not by the idle speed controller, is he right?

The way he explained to me convinced me that there's a high chance the TCU might be bad, so the question here would be:

Is it very hard to replace the TCU? I think that job could be easy for me maybe because I know my dashboard and I've installed a sound system and check the codes on the ECU but I don't know if this would be more difficult.

mikekantor

iTrader: (5)

You just need to remove the panels by the feet, and undo some screws. The most difficult thing about it is that it puts you in an awkward position in order to actually be down there. I like to just lie down and put my feet on the seat.

LvR

So you wanna replace the TCU eh? - lots of speculation eh? - what results do you see with the proper diagnostic procedure

sonicii

If the TCU was not sending any signals, the transmission would not be shifting at all, it would stay in one gear. All gear changes (excluding R) and fluid pressure are electronically controlled.

The idle speed is controlled only by the ECU (using the IACV), but the ECU will have a signal from the TCU to say when a gear is selected, the ECU will then adjust the idle speed to maintain the correct RPM. The idle speed is NOT directly controlled by the TCU.

The TCU controls the shifts based on the signals it receives, this includes the TPS, engine RPM, Vehicle speed, transmission fluid temperature, and gear selector position, therefore the fault could be a bad TCU, or a bad sensor input.

If you don't have a spare TCU handy, I would be starting at the TPS.
Does the engine RPM also drop when the air conditioner is turned on? If it does, then the RPM problem is most likely a clogged IACV.

But first run the TCU diagnositcs as shown above.

Wiking

Definitely. Its dangerous and waste of resources staying around mechanics who do not ctrl the basic issues...

gapboi210

Starting to sound like they messed something up or didn't connect something when they worked on your car. Why did they give it back to you in this condition?

Wiking

If TCU main connector is disconnecter, gearbox still 'works' hydraulically. At least gears do engage while stationary... From TPS the controller gets info for shifting points - driving electronically controlled valves (4pcs).

When multiple problems are stacked, they tend to mask each other. Unfamiliar mechanics will be lost...

My guess: TPS is bad, IACV sticking, Cap-Wires-Distr.GND ...are bad.

Issues on these pages have to be checked:
http://www.cardomain.com/ride/748507/4
http://www.cardomain.com/ride/748507/6
http://www.cardomain.com/ride/748507/9
http://www.cardomain.com/ride/748507/10
http://www.cardomain.com/ride/748507/12
http://www.cardomain.com/ride/748507/15
http://www.cardomain.com/ride/748507/21

rmdl51

iTrader: (4)

Thanks a lot for all the input everybody!

Well, Mechanic and electrician guys said the problem seems that the self diagnostic test is not running, they said they couldn't run the diagnose, so I'm gonna try it myself to find out if it's true or not, in case that's true what's next? I mean if I got not blinks at all, BTW which light is supposed to blink? the P on the mode switch? or what is the "power indicator lamp"?

Awesome writeup and pictures Wiking! Thanks a lot man! that helps a lot!

EDIT: I just read another thread about this and I guess is that Power led on the mode switch for sure,

and the last line on the writeup says if the lamp does not come on: inhibitor switch, OD switch & TPS circuit

That's what I have to check if I have no blinks at all then. Thanks again

Wiking

My guess is that if temp sensor is not working, diag will not run (?). For sensor to give 'reading', the box/oil has to be warm =20min drive minimum.

All these (circuits that the self diag tests) can be also directly measured with dmm from the TCU connector [PITA].

...Check p.15 -table; pin33 for temp sensor...

------------------------------------------------------
edit:

1. First thing is to test charge voltage at batt -> min 13.8V
2. Run Self diag.
3. Check charge voltage/gnd at TCU -> min 12.5V
4. Test the TCU pin voltages with DMM (see table)
5. Open solenoid connectors under hood, on tranny, measure solenoid etc. resistances

sonicii

I would expect a bad fluid temp sensor would not prevent the diag procedure working. after all there is a code for a bad temp sensor, which you could not extract if the diag procedure doesn't work. The sensor will still give a 'reading' at low temp, it will just reflect the current temp. The FSM states the fluid temp sensor should have a resistance of 2.5Kohms at 20C or 68F, it's resistance will decrese as the temperature rises. The FSM does recommend running the engine for 20 mins prior to the diag to ensure everything is up to operating temperature, but I am fairly sure I have run the TCU diag with a cold engine and transmission, the diags do work, and it does not throw a temp sensor code.

One other thing to check, when you first start the engine, does the 'P' light flash a few times before going out? (assuming you don't have the switch set to 'Power')

rmdl51

iTrader: (4)

Well I just start the car this morning and a few hours ago on my lunch time and nope, the P light doesn't blink at all. And I confirmed that after the procedure I get no blinks, nothing...

I repeat the procedure for the self diagnose after warming the car for about 30 minutes and still nothing, no blinks, is there a chance that I might be doing something wrong? the P light should blink right after the release of the gas pedal right? anybody has a video doing the TCU self diagnose test?

Wiking, I will test my voltages when I get home and get my DMM but so far at the stereo (it has a voltage meter) shows 13.9v I don't know how accurate is that meter so I will check again when I get home, and I will also try again the procedure after driving 10 miles a 25-30 minute trip (lots of traffic at 5:30pm ) and see if this time blinks

internetautomar

iTrader: (30)

does the "P" light up when you initially start the car or when you push the switch forward into power?
you may need a bulb

sonicii

Good point!!

If the P light turns out to be ok, then you should look at the items the FSM shows could prevent the diag test working. the inhibitor switch can be tested by trying to start the engine with the gear selector in something other that P or N. The overdrive switch should show a 'OD off' lamp on the cluster in one position, so that is also easy to test. The TPS is a bit harder but if you have the FSM and a DMM, you should be right!

rmdl51

iTrader: (4)

My mode switch was dead a couple of weeks ago so I order it from the dealer and install it and now it turns ok perfectly, if I put it on C green led comes on, if on P amber light comes on.

When I start the car in Auto the P light comes on for two seconds, the car doesn't start if not in N or P, the OD light comes on/off normally.... also check my voltages and is 12.2v when is off and 13.4 when is on....

Well... I guess next is the TPS, I will look on the information wiking provide to see if I can figure it out how to test that sensor,

1992maximase30

you said they did a engine/tranny swap.
odd are they probably swapped the parts off your old car.
or the "new" engine had a bad tps or unadjusted tps/idle switch.

thats what was going on with mines.
once adjusted all was good.

500 rpms does seem low.

my ve did it (even when i adjusted the idle).
my gxe idles at this speed.
another member here idles around that too.

Wiking

Can be so. The temp sensor may fail by cutoff or short or resistance being out of the range. Who would test all and report how test behaves...

The FSM says: "Start the engine and warm it up to normal operating temp..."

The question hangs on the word [it] ... is [it] the engine ... or the object to be tested [tranny]???
IF [it] is the [tranny], then only minimum 20 minute drive satisfies [it] ... e.g. the diagnostic flow requirements...

I have tested my working tranny with cold engine and it passes. In problem solving this knowledge does not validate a pass - tester needs diligently to do as the designer (?) wants... especially in this case where 'ten cooks' are boiling the pots charred. As/if one wants desperately to shoot the trouble down, only exact testing (what you are also after) will give results.

LvR

Totally agreed ................... and I would even go so far as to say that if you test a tranny when cold and it reacts different to when its warm ito the posted testing procedure EVEN THOUGH THE WARM TEST MAY PASS AND THE COLD TEST DOESN'T, then there is something not right with that tranny/environment imo

internetautomar

iTrader: (30)

Both my Grey VEs idled around 500

rmdl51

iTrader: (4)

Actually the shaking is not so bad when is a little bit over 500rpm, the shake is terrible at 600-700rpm which happens sometimes, I've noticed while driving the shifting is erratic, sometimes pickup speed ok shifting correctly and sometimes the rpm neddle stays at 2k even I floor the gas pedal and it's slowly going up delaying the shifting a lot.

Well, back to the TPS testing I was checking on it last night with the link Wiking provide and I'm such a noob taking measures really but when I disconnect both connectors from the TPS one of them (top one) was very rusted (well it was with that greeny stuff) so I try to clean it and then measure the resistance between all 3 pins and like I said I must be very unexperienced with the measures on the DMM but on the range of Kohm on top and middle I get 2.014 but eventually drops to 0.142-0.138, middle and bottom has no reading, after getting this numbers I don't actually know what they mean.

somehow I think the TPS from this car doesn't work, but I don't want to keep buying stuff if I can't be sure which parts are definitely bad, I still can't get the self diagnose to run...

What should be next?

Wiking

TPS contains two separate entities in one box, thus two 3pin connectors:

1. One is the zero position switch = blk 3-pin connector attached to 'TPS box' ... Check only the mid an top pins. Has to be closed, opens as throttle is opened/turned by hand.
2. Second is slider potentiometer giving throttle axle angle information to ECU. It is gray 3-pin -connector, separate, in the end of the wire coming from TPS. Check only the mid an left pins, while rotate throttle with hand....

Check again the TPS -page, I just re-edited it and now txt is muchas more clearer...

Ask 'your neighbor' to help with the dmm.

rmdl51

iTrader: (4)

Well today tried the A/C and if I turned on while in P the RPM drop from 1100 to 700-750making the car shaking a lot! but if on D it makes a drop from 600 to 400-450.

What does that mean? normal operation of AC shouldn't drop the RPM? is that a clogged IACV as sonicii said?

One more thing I don't understant, where is the adjust on the TPS? the screws on each side are only to secure the TPS right? do I have to loose them in order to adjust the slider?

Oh Man! so many questions! thank you for your time and patience with my ignorance!

Greeny

iTrader: (43)

I'm thinking there is something wrong with your tranny rebuild, not the tps.

I have no idea what it could be, i just think are looking in the wrong place for answers.

If the car didn't do this before the tranny failed, then take your car back to the shop, make them fix your car right.

Btw, you may have to get a little nasty with them.

1992maximase30

yes u have to...wait is this a veggie motor??
if so i belive you can adjust the tps too.

and greeny if it is a tranny failure could it be possible that the t/c is stuck on??

sonicii

The IACV is the only device the ECU can use to maintain your idle speed, when you turn on the AC or shift to D, the ECU opens the IACV further to allow more air into the engine and maintain the correct idle speed. If this valve is clogged or faulty, the engine cannot control your idle speed, and you will see significant idle RPM fluctuations as you change the load on the engine. The IACV has a manual base setting using a screw on the top of the unit, there is a procedure to set this. Once this is set, you use the diagnostic screw on the side of the ECU to set the correct idle speed.

The TPS is adjusted by loosening the mounting screws and turning the TPS itself, the mounting has elongated holes to allow this. The potentiometer section of the TPS is what the TCU uses to determine your throttle position, if it is faulty, your TCU may believe you are only at part throttle when you are actually at full throttle, thus it will not shift up like expected, or supply the correct line pressure to your Transmission which may cause slipping.

Although it is difficult to diagnose electronic problems over the internet, my suspicion is you have a clogged or faulty IACV, or associated cabling causing your idle speed problems, and a faulty TPS or associated connectors and cabling, causing your erratic shifting problem.

If you feel you are able to test these items properly, then go for it. and feel free to ask any further questions. If you don't feel you are up to it, then I suggest you take it to a mechanic or auto tech.

rmdl51

iTrader: (4)

The problem is last time I send the car back was on feb 2 and they return the car this monday march 10, you see what I mean! they have no idea! I took my car maybe to the worst place in the area but taking it back to them is giving my car to some people who don't know/care about it.

It just makes me waste more time! I already lost money here and they are obstinated that the problem is the TCU and I have to replace that in order for my car to run ok again, they said that part is not under the job warranty because they rebuilt the tranny and the tranny is good all tests and electrical parts according to them are good (which of course I don't believe) they told me if I replace the TCU and still have the same problem then I take it back to them and they will take care, how do that sound??

they keep giving excuses like getting the mode switch from the dealer took a week, and then the appointment with the electrician, and he said he can't find the problem because self diagnose is not running because a bad TCU and that was it! over a month for that!

I could get nasty with them, but no papers were given, paid cash, what are the odds if in an extreme case I want to sue them? honestly I don't wanna go back there, I just want to figure out the problem and fix it myself, won't be paying a single dollar more to an ignorant shop, if I can't do it myself then my car is gone, but I trust myself, the engine is 80k (i hope is true) and the tranny was rebuild, everything else shouldn't be that hard, but of course that's because all of you if it wasn't because of the org I'll be lost, completely!

Thanks again!

Greeny

iTrader: (43)

I'm sorry to say, but it sounds like you got ripped off mang.

You also kinda screwed yourself by not getting paperwork with this job.I suggest you consult an attorney about this just to make sure, but without paperwork, you still may be screwed.

BenStoked

iTrader: (7)

kinda reminds me of the scene from "the mask", with Jim Carrey, where he goes into the shop to pick up his car, the mechanic says "The brake drums are shot and you need a new transmission."
Carry's character retorts, "What? All I wanted was an oil change!"
fckn weasels.

gapboi210

why did u pay cash without paperwork?!

rmdl51

iTrader: (4)

mechanic is a friend of a coworker... he's not a tranny guy so he pick a "reputable" shop to do the tranny

Wiking

Adjustin TPS zero position is the easiest job on earth, 2 screws on a platter... Your mechanic is not but a clown... I am sorry. If you need to talk to these folks, do it via your lawyer.

Measuring TPS resistance is the next easiest: find a mechanic who is willing to do these twho 3minute operations - with you present - and charge only for the 3minutes.

If this new mech can do that, then ask him to spray some cleaner into the IACV, another 3minute operation. If he can do that but it wont help the idle, ask him to open ONLY the three screws: clean the IACV valve /stepper motor 'screw', see pic items 2&3... Make sure (with a hammer in your hand?) that he opens only the three (valve body, item 4 can stay).

Print the TPS & IACV pics, pages, and go askin... do pay only for '15 minutes work.'

Wiking

Note that the probable TPS and IACV problems are not directly connected to the tranny repair. Faulty TPS, IACV cant be tranny repair shops responsibility. As these features, oxidation etc may start to 'fail anytime', one cannot really find out whose fault is what... Still theyre responsible to deliver a functional vehicle.


Issue no.2: What is the charge voltage? ... this affects all of Maxima.

Bad idle remedy is typically new plugs, cap, wires, oxidized distr ground wire connector (see page10)