Gas pressure drop between Tranny Shifts

[Trevor]

Originally Posted by sd2649

Good lord, I messed up something. It now has multiple CEL's and shifts hard at 3500 all the time under WOT. The details are in this thread:

http://www.subaru-svx.net/forum/showthread.php?t=41036

Someone please help!!! what to do??!!?!??

Starting a second thread I must venture to say only adds to the confusion.

You will find a reply there, but here take the opportunity of suggesting that you should get hold of a set of manuals, so that you do not continue groping in the dark. The cost will be offset many times for sure. Please do not confuse this comment as inferring in any way, that all are not pleased to continue to offer assistance.

[sd2649]

I did have the cables loose, I didn't use them to set anything. This is what I noticed..... When I pulled the Throttle body, the butterfly valves appeared completely closed however after cleaning them , I could see daylight through a small crack around the butterfly valves. The only thing limiting them from completely closing was a small adjustable screw that was holding the throttle slightly opened. I also noticed that it had been tampered with before (remember this engine was completely rebuilt by the previous owner, maybe they used it to get the car idling right for them but had something else screwed up all along).

So.... When I started it with the clean throttle body (now having thin passages for air) it idled high. I pulled the stopped screw back to what looks like factory and it idled a little slower.

sorry, got the series of events out of order on the first post

THEN I set the TPS to the .5 volts as best I could. And like I said, it runs much better than EVER before, I thank you for that wonderful write-up. It would hesitate before when i pushed the throttle and would downshift for no reason sometimes on the highway, all this is now gone and I love it. I am fully confident that the TPS is set correctly, because it was throwing a CEL and idling stupid before I set it, and after, it idled nice and smooth and there was no CEL present.

Still wonder why I have no CEL but 6 codes when I read it though

[sd2649]

ok, this thread is now dead, sorry, on to this one!

http://www.subaru-svx.net/forum/showthread.php?t=41036

again

[Nomake Wan]

The fact that you have two Crank Angle Sensor codes at the same time yet your Tach and, more importantly, engine both still run just fine gives me fresh hope that the Code 11 I have is a total fluke that just won't go away.

[sd2649]

On top of all of this, the SVX still does the same weird shifting thing.

ONLY when I hold the car to WOT does it hesitate for a long time between gear, on the magnitude of 2-3 seconds. The transmission was completely replaced by the previous owner, and it has done this for as long as I have owned it.

If I pull back just a little on the throttle right before the shift, it will shift perfect, however I have to wait 2 full seconds before I can floor it again. If I floor it before a set period of time, the engine cuts gas and slows the car down until the time limit has expired.

What I do now, is just pull off a little before the shift and then wait for the tach to reach 4000 and then floor it again, works great, but is annoying not to mention if I ever sell it the next guy will be flipping out at the huge pause between shifts.

any ideas?? maybe the tranny has an incompatible TCU? the engine seems to be cutting the fuel, so how are the ECU and TCU communicating?

[Nomake Wan]

The engine is meant to cut fuel. It's part of the "luxury" or perhaps "transmission-saving" measure in place in the computers. Right when the transmission shifts, it momentarily cuts fuel to reduce shift shock. I read that somewhere, forget where though. In any event it's normal...but shouldn't be noticeable. If it's noticeable, then something's wrong (but we already know that!)

[sd2649]

definitely noticedable, the engine "brakes" for a full 2 seconds, like it's at half throttle stuck manually in second gear. I've heard of the cut off of fuel, but was wondering what sensor or device was used in figuring when to do it. The fact that my tranny has been replaced makes me think something electrical might have been installed incorrectly.

Also, I have heard that a code 11 doesn't ever throw a CEL because the ECU just picks up the signal from your other properly functioning sensor.

[Trevor]

Originally Posted by sd2649

I did have the cables loose, I didn't use them to set anything. This is what I noticed..... When I pulled the Throttle body, the butterfly valves appeared completely closed however after cleaning them , I could see daylight through a small crack around the butterfly valves. The only thing limiting them from completely closing was a small adjustable screw that was holding the throttle slightly opened. I also noticed that it had been tampered with before (remember this engine was completely rebuilt by the previous owner, maybe they used it to get the car idling right for them but had something else screwed up all along).

So.... When I started it with the clean throttle body (now having thin passages for air) it idled high. I pulled the stopped screw back to what looks like factory and it idled a little slower.

I have never seen this screw mentioned here, and neither the screw nor the adjustment of same is mentioned in the manuals.

------------ Possibly someone may be able to throw more light on this item.-------------

Could the screw by any chance comprise a modification, added to overcome an idling problem?

[svxistentialist]

Originally Posted by sd2649

WEIRD!!

So, now the car runs PERFECT! it is better than ever. The only weird thing is that even though it doesn't show a CEL anymore, it still throws codes at me when I read them, AND they're the same codes!

11 - Crank Angle Sensor/Circuit
21 - Coolant Temperature Sensor/Circuit (PS my temp sens works in dash!)
31 - TPS (It is installed as it should be!)
24 - Air control valve
29 - Crank Angle Sensor #2
56 - EGR system

If I'm not mistaken, it would be running POORLEY if all this were true, soooo..... why can't I get the codes to clear???? any ideas???

There are two methods of reading codes on the TCU. One is for existing codes, and the other is for old codes. The old codes are retained in memory so that the history of problems can be accessed when troubleshooting.

Is it possible that the ECU also has a function to retain codes for the same reason?

Or else could it be your ECU is faulty?

Joe

[Trevor]

Originally Posted by sd2649

On top of all of this, the SVX still does the same weird shifting thing.

ONLY when I hold the car to WOT does it hesitate for a long time between gear, on the magnitude of 2-3 seconds.

any ideas?? maybe the tranny has an incompatible TCU? the engine seems to be cutting the fuel, so how are the ECU and TCU communicating?

There is direct electrical connection between the ECU and TCU and engine speed is transmitted via a single yellow wire within the loom. The TPS also forms part of the equation in respect of the smooth shifting arrangements.

As I understand it and as as I have seen reported, engine torque is reduced during shifting by cutting the ignition to some cylinders. However I can find no exact confirmation within the manuals.
------------If someone can provide confirmed information, this would comprise a valuable contribution.----------

[Trevor]

Originally Posted by svxistentialist

There are two methods of reading codes on the TCU. One is for existing codes, and the other is for old codes. The old codes are retained in memory so that the history of problems can be accessed when troubleshooting.

Is it possible that the ECU also has a function to retain codes for the same reason?

Or else could it be your ECU is faulty?

Joe

To clear codes held in the ECU memory. Deciphered from the manuals.:-

Start and warm up Engine. Turn off ignition. Connect test mode terminal.
Connect read memory terminal.

Turn ignition on but do nor start engine. Check engine light should turn on.

Fully depress accelerator pedal, then back off to half throttle and hold for two seconds, then release fully.

Start engine. Check engine light should go out. (N.B. provided no code remains existing.)

Drive at a speed of in excess of 7 MPH for more than one minute and warm up engine.

Engine light should blink. (If a trouble code is indicated, such must remain in existence.)
If the light does not blink, further warm engine and try again.

Warm up engine and run at above 2,000 RPM for 40 seconds.
Turn off engine and remove terminal connections.

All rather tedious, but it is the real oil.

[svxistentialist]

Trevor is correct what he is saying here about the gear change control.

The yellow wire speed signal input is actually sent to the TCU first, then outputted to the ECU.

One of the control functions the TCU performs is called "Engine torque control signal"

This is a single wire from the TCU to the ECU. It is a Black/Yellow wire connecting pin 16 of the black TCU connector to pin 20 of the yellow ECU connector.

The stated function for this wire is "Reduces engine torque at gear change"

Now I have seen it reported that it cuts fuel from 3 of the six injectors during gear change. From memory this may have been in the '91 Road and Track road test, but I can't remember.

For sure nowhere in the WSM does it ever explain exactly how engine torque is reduced, as Trevor mentions above.

However, as your symptoms above indicate this torque control is lingering for a while after a gearchange, this is obviously faulty. As the function is controlled by the TCU I would suspect your TCU is outputting the "control" signal for too long, and you may need to replace the TCU.

It is of course possible the ECU is receiving and imposing the torque control signal for too long either after the TCU has switched off the signal.

My uneducated guess is the fault lies with your TCU.

Check you have clean signal passing through the Black/Yellow wire above.

Joe

[sd2649]

Based on your info, I decided to check transmission codes. I never thought a transmission problem being it seemed to be linked to the engine (through the position of the throttle and all). What I found was that the transmission still has a code for the VSS2 stored. I have paperwork from the previous owner stating that the VSS2 is what he had the transmission replaced for before. In the paperwork for that replacement, the previous owner describes the fault VSS2 as completely disabling the vehicles ability to shift properly at any speed. So.... is it possible that the VSS2 was installed improperly but still working to some degree? or being it is a stored code, is the problem over? also a faulty VSS2 would show itself somewhere other than just at WOT, correct???????????????

Also, did I mention that my speedo works fine. wouldn't it be affected? I also understand the need for two speed sensors on an AWD svx, but mine is FWD, is there a difference in the AWD and FWD TCU's? maybe I have the wrong one installed?????????

THanks in advance for any light on this subject

[Nomake Wan]

Originally Posted by Trevor

To clear codes held in the ECU memory. Deciphered from the manuals.:-

Start and warm up Engine. Turn off ignition. Connect test mode terminal.
Connect read memory terminal.

Turn ignition on but do nor start engine. Check engine light should turn on.

Fully depress accelerator pedal, then back off to half throttle and hold for two seconds, then release fully.

Start engine. Check engine light should go out. (N.B. provided no code remains existing.)

Drive at a speed of in excess of 7 MPH for more than one minute and warm up engine.

Engine light should blink. (If a trouble code is indicated, such must remain in existence.)
If the light does not blink, further warm engine and try again.

Warm up engine and run at above 2,000 RPM for 40 seconds.
Turn off engine and remove terminal connections.

All rather tedious, but it is the real oil.

Wow, I totally didn't see that in the how-tos! Time to go try that procedure out and see if it doesn't clear these codes.

[sd2649]

any luck with that revised method to clearing your codes? It still didn't work for me.