96 Shifting Early, No Power Mode?

[burnsvl]

Need some advise for my 96 LSi with 74k miles. Purchased it about 5k miles ago knowing it needed a little work, and have managed to fix most things with a lot of help from this site. Really enjoy the car but have one problem I haven't been able to solve and haven't been able to find an answer to:

No matter how quickly I floor the gas taking off from a stop and keep it floored, the trans will up-shift just before 4500 rpm. If shifted manually, it will pull all the way to redline. It does this in first and second (and probably third, but trying not to get another ticket). When up and rolling, you really have to floor it quicky to (sometimes) get a downshift, but it will pull past 4500 if it does downshift. Basically it seems like it is really, really hard to get into power mode, but since my 96 doesn't have the power light, can't be 100% sure that is the problem. Just installed a brand new TPS after trying to clean and adjust the old one (it was not reading as suggested in the how-to between fully-opened and fully-closed, and the first time I checked the ODB-II codes, there was a TPS error), so I assumed this was the problem. Car does seem to run a little smoother, but it didn't fix the shifting problem. It is set right on 0.50V. The A/T Temp light does not flash at start-up but I tried checking the trans codes anyway, but did not read any existing or previous codes (A/T Temp light just constantly flashes when in diagnostic mode which I think means no codes, correct?). No other shifting or trans problems that I can tell, and I enjoy shifting the car manually, but would really like to figure this out. Sorry for the long post, but wanted to get all the details out up front.

Any thoughts?

Thanks, Vern

[burnsvl]

Any ideas at all?

[SVeXy96]

That sucks...I'm clueless I also have a 96 LSi, but never had this problem...then again I bought my car when it had 98k on it and the only tranny problem I've had was replacing the whole thing! Anyways I'm sure someone will have an idea just give it a while. All the old geezers are still in bed (just kidding)

[UPnorth362]

This could be a long shot. But it could possably be the TPS sensor on the throttle body is off calibration, or defictive. There are posts on yhis site on how to check and adjust it.
good luck.

[SVeXy96]

I don't think it should be the TPS only because I was throwing a code for a bad TPS and waited several months before I fixed it. The whole time it was bad there was no change in the way my car drove, shifted or accelerated. I replaced with the TPS from my other SVX and it drives the same as it did before but without throwing anymore codes for it. Whatever the problem i hope you figure it out and that its not serious. Honestly though if your tranny has never been rebuilt (which it shouldn't need to with only 70k) I would start saving for a rebuild or a manual swap. My tranny went out at 113k. I used the tranny from my other 96SVX that had 148k. Though the tranny was still good in the other SVX I rebuilt it anyways so I wouldn't have to worry about it in the future. Car drives AWESOME!

[Trevor]

Originally Posted by UPnorth362

This could be a long shot. But it could possably be the TPS sensor on the throttle body is off calibration, or defictive. There are posts on yhis site on how to check and adjust it.
good luck.

See above. --- Did tou check the applied voltage and adjustment, when you changed the TPS units?

[burnsvl]

I did adjust it to the 0.50V after installation with a quality multi-meter, but I did not check the resistance across the range before installing. I will pull it off this weekend and check. Brand new so I would hope it is good, but never know. Took 3 "new" distrubutors on a Probe GT I once had before I got a good one. I'll update after I check it.

Vern

[Trevor]

Originally Posted by burnsvl

I did adjust it to the 0.50V after installation with a quality multi-meter, but I did not check the resistance across the range before installing. I will pull it off this weekend and check. Brand new so I would hope it is good, but never know. Took 3 "new" distrubutors on a Probe GT I once had before I got a good one. I'll update after I check it.

Vern

Refer to the simple tests shown in the how to stuff. The complicated system is not valid. That said, I would think that if the TPS was new out of a sealed package, you are involved in a very long shot.

[burnsvl]

Finally got a chance to check the new TPS. Assuming I did this correctly (mechanical engineer, not electrical the resistance between the middle and bottom pin (as mounted on the car) is approx. 4,860 ohms fully-closed and 56 ohms full-opened. That sounds about right, doesn't it? All readings were taken with the TPS off the car. I re-checked my old one as well, and got 5,620 ohms and 90 ohms, though it was jumping around a bit, especially on the fully-opened end.

I'm at a loss. I also have a knock sensor and O2 sensor trouble codes, but wouldn't think those would have anything to do with it, would it?

Any suggestions would be welcome. Thanks, again.

Vern

[thumper_svx]

After having suffered dual knock sensor failures on my 96 LSi lately, I have to say that part of your problem could easily be that.

I notice after replacing my knock sensors that power delivery was much better than it had been before. Back to how it had been when I bought the car... maybe a little better. I had done a lot of other work (crank and cam sensors as well), so I can't say for definite that the knock sensor replacement really made a huge difference... but particularly at WOT the car seems a lot "spryer"

Also bear in mind I replace the muffler the same week; it had a collapsed baffle and so was actually blocking the exhaust slightly. This could've made a difference, too...

HTH.

[svxistentialist]

Originally Posted by burnsvl

Finally got a chance to check the new TPS. Assuming I did this correctly (mechanical engineer, not electrical the resistance between the middle and bottom pin (as mounted on the car) is approx. 4,860 ohms fully-closed and 56 ohms full-opened. That sounds about right, doesn't it? All readings were taken with the TPS off the car. I re-checked my old one as well, and got 5,620 ohms and 90 ohms, though it was jumping around a bit, especially on the fully-opened end.

I'm at a loss. I also have a knock sensor and O2 sensor trouble codes, but wouldn't think those would have anything to do with it, would it?

Any suggestions would be welcome. Thanks, again.

Vern

Vern, it is my opinion that the knock sensors being bad is not directly the cause where getting Power mode to light up is concerned. I am willing to be corrected on this if any of the other old geezers have better ideas.

Your knock sensors being bad will cause the ECU to run the fuelling in fail-safe mode, and that will mean retarded ignition and lack of power. If both sensors being gone also causes a lack of Power Mode, then this is something I have never seen documented. On the other hand, anything's possible

Either of the knock sensors being out of range causes the fail safe mode described as " Sets regular fuel map and retards ignition by 5 degrees " in the Workshop Manual.

Now if "Sets regular fuel map" has the knock-on effect [no pun intended ] of also holding Normal mode in the TCU, or denying Power mode, if you like, then your symptoms of shifting up too early are understandable.

Power mode on demand is engaged by the TCU depending on two signals, vehicle speed and TPS. The slower the road speed, the easier to engage Power. The TCU looks at the RATE at which the TPS changes voltage; the faster you mash the pedal, the quicker the box will engage the Power shift map.

This in turn implies that if the TCU is not seeing road speed, it will run in failsafe mode. So if you had a code 33, no speed signal from TCU, it might mean your TCU would not allow Power mode to engage.

However it is glaringly obvious you must replace both knock sensors NOW before you do more investigation. With the engine running on failsafe fuelling like it is now, you must rectify this before you do more about the Power mode. You should notice a big difference in how it drives after replacing them. They are transducers, and fail because of age and heat.

One other small thing Vern, and forgive me if you have already eliminated this one. If the Manual switch is on, there is no way under the sun you can engage Power mode. They are mutually exclusive, for different purposes.

If Manual mode is on, the letters MANU in amber should be lit up below the clocks. If it is lit, no way you can get Power shift map. It is always possible that the MANU bulb has blown inside the clocks, in which case you would not know if it was on or off. The MANU light is on the lower bar of lights, positioned between the 1 range indicator and 0 MPH. Bottom line, make sure MANU switch is not on.

When you have replaced the knock sensors and ensured that MANU is not engaged, if your car still shifts too early and won't engage Power mode, then your next places for investigation will be the wiring and connectors to the TCU, and if not a bad connection in this area, you may need a new TCU.

Hope that helps, sorry for being long-winded,

Joe

[Earthworm]

I thought the power light never comes on on the 96/97 models.

[svxistentialist]

True

You need to read the first post again David.

Vern is aware there is no Power light. What he is debating is the fact that in fully auto mode, the box ALWAYS shifts up early, no matter how hard he accelerates. This implies the Power shift map is not engaging in the gearbox TCU.

Joe

[b3lha]

Originally Posted by svxistentialist

True

You need to read the first post again David.

Vern is aware there is no Power light. What he is debating is the fact that in fully auto mode, the box ALWAYS shifts up early, no matter how hard he accelerates. This implies the Power shift map is not engaging in the gearbox TCU.

Joe

I wonder if it can be engaged with a switch or whether his TCU just doesn't have a power mode at all.

[svxistentialist]

Originally Posted by b3lha

I wonder if it can be engaged with a switch or whether his TCU just doesn't have a power mode at all.

I was wondering Phil if maybe his Manu mode was permanently on. If it was, Power mode can't engage. That is where I would look first. It's often the simple things that cause complication. Manu light bulb blown on the clocks??



Joe