Hard Shifts

Abaddon wrote:

manofmany wrote:

Took the car this morning and it was still shifting pretty firm. Shut it off and came back out and now it's back to shifting smooth as ever.

If it is a sticky solenoid, is this a sign it's going to completely go out soon or just that this could keep happening

That's kinda why I said to wait for "different" symptoms. The TCC Solenoid on this trans has a habit of getting clogged/sticky. It causes a couple different issues. I wouldn't worry about it until then.......you may spend too much time trying to find a ghost.

Also, I was thinking about it. A skewed MAF sensor can cause less then desired shifting performance too. But, if it only happens from 1-2, then the MAF wouldn't make any sense. Again, I'd wait.

Abaddon,
Can you explain to me and others how the MAF sensor could possibly affect the shifting of the trans.
Does it cause delayed or rough shifts and how.?
Thanks for any explanation that ties the trans problem to the MAF. I'm interested in the long answer.

Rickw wrote:

Abaddon,
Can you explain to me and others how the MAF sensor could possibly affect the shifting of the trans.
Does it cause delayed or rough shifts and how.?
Thanks for any explanation that ties the trans problem to the MAF. I'm interested in the long answer.

I would be absolutely happy to Rick. If AA would point to the proper post for an explanation......no more hijacking!!!!

Since we're discussing hard shifts in this thread, if you explain how MAFF would be a cause, I can't see how that would be a hijack. It could be the answer we're looking for.

As we all (should) know, the MAF measures the amount of incoming air to the engine. Based on this number, the PCM controls the fuel delivery. Those of you who have tuned a N* throttle body know this system. The first thing you do is change the MAF table, which is programmed into the PCM. This table never changes nor adapts. The PCM uses this table to control just about everything. Based on TP, MAF frequency, BARO, and RPM (no 's for Eldo), the PCM supplies the proper amount of fuel needed for the conditions present.

As for the transmission....our cars have a nice little thing called TAP (Transmission Adaptive Shifting). The PCM has cells, much like the MAF table, that it uses to control trans line pressure, which in turn lengthens or shortens the shift times based on sensor inputs. Like the MAF, the PCM compares these pre-determined values to the actual shift times and adjusts line pressures accordingly.....just like the PCM adds/subtracts fuel, it adds/subtracts fluid pressure.
You guys remember that solenoid I replaced in my trans a while back? That's the exact solenoid that controls the line pressures for TAP. Turning the adjusting screw 1/4 turn clockwise puts the line pressures on the max end of the table without setting a code, resulting in permanent "firmer" shifting.

That being said....If you monitor shift times at low throttle and high throttle, they will be less under high throttle/load conditions, meaning the trans shifts faster (firmer) under heavy load. If the PCM detects more incoming air, regardless of TP, BARO, and RPM, it thinks you want to go faster. Let's say at 30% throttle, the g/sec the PCM expects to see from the MAF is around 40g/s. If it were skewed, and read 55g/s, the PCM will add more fuel at that point and more than likely shift firmer because it's reading a higher value indicating "faster". This explains manofmany's car shifting good after shutting the car off and back on again. The PCM will revert back to "normal" mode until it reads that funky reading again.

Now you're going to ask "why isn't the SES light on"? The MAF will not set a code unless it's shorted to power, shorted to ground, or an improper g/s is given for more than 12 seconds consecutively. There is also a window of error of about 6g/s that the MAF can produce without setting a code. At idle, the MAF may read anywhere between 4g/s to 10g/s "safely". So let's say the MAF reads a constant 10g/s at idle, and is always 6g/s higher than "normal" across the entire range. The PCM sees this as ok. Now add another intermittent 10g/s to this equation. As long as it's not for more than 12 seconds, no code will set. If the PCM see's 16g/s more than "normal", and it happens to be at your shift point, you'll get a firmer-than-desired shift.

I hope it makes sense. I tried to make it understandable.

Is that why a vacuum leak would cause a firmer shift?

AA wrote:

Is that why a vacuum leak would cause a firmer shift?

A vacuum leak, depending on where it's located, can cause harsh or soft shifting.
On a vacuum controlled Transmission, a vacuum leak will cause the line pressures to go low or high. By GM definition (on a 4T60E), harsh or soft 1-2 shifting is caused by

--high/low line pressures
--damaged 1-2 Accumulator piston seals or springs
--improperly tightened Accumulator cover bolts
--misaligned gaskets
--Accumulator valve stuck
--incorrect #2 check ball location
--damaged seals on the support sprocket

So yes, a vacuum leak can cause firmer shifts.

When the vacuum line to my shift modulator was accidentally disconnected i had a very very harsh 1-2 shift. Also I can confirm the MAF shift issue as my trans was slamming in and out of overdrive today while running with the P0102 MAF code.

The guy I bought my Riv from had a 1996 and he had an issue with a 1-2 shift too I think. Turned out to be a bad wire connection in the harness that sits over the case I think? I'd have to ask him again.

Are there any specific vac lines that are involved in tranny shifting in the 97's? Replaced my lines and have a pretty firm 1-2 shift. Not a hard shift. but very crisp and firm.

manofmany wrote:

Are there any specific vac lines that are involved in tranny shifting in the 97's? Replaced my lines and have a pretty firm 1-2 shift. Not a hard shift. but very crisp and firm.

There was a TSB on the 1-2 shift, maybe someone can point to it, I kinda think a synopsis or copy was posted on this site way back when.

Albertj

I've been searching and have yet to come across that. I'll keep looking. Thanks as usual!

Problem fixed itself this morning about half way through my commute. Back to perfection

manofmany wrote:

Problem fixed itself this morning about half way through my commute. Back to perfection

do you think it might be time for a fluid & filter change?

albertj wrote:

manofmany wrote:

Problem fixed itself this morning about half way through my commute. Back to perfection

do you think it might be time for a fluid & filter change?

That's actually first on my to-do list along with oil pan gasket. My thinking is that maybe the solenoid is sticking after the car sits for awhile. May not be, but it's definitely overdue for new fluid.