found solution for late auto shift (2-3), and hitting rev limiter

[John_D.]

Not sure if this is a question for General Tech, Advanced, Suspension/Trans, Exhaust, or what...

Ok, I put the CIA headers and the Borla 3" exhaust on this weekend. And now the car is consistently hitting the rev limiter on the 2-3 shift and it's driving me nutty.

Here's what I'm doing.
1. Cruising at 50-55 behind another car.
2. Put it down in drive, to get ready to pass.
3. An opening comes up, mash the gas to pass.
4. Transmission kicks down to 2nd.
5. Speed is building up good, then the engine starts uh,uh,uh,uh,uh,uh for what seems like forever.
6. Let off the gas, it shifts up to 3rd, mash it down again and go on...

7. Hope the other driver is not laughing too hard at me for pulling up beside him and then stuttering along side for a bit before finishing the pass. [img]smile.gif[/img]

It used to do this once in a great while, and now it's every time.

Is the shift point really that close to the limiter? If so, it seems that with the improved exhaust the engine can now push just a little higher, and do it quicker, in that window of time while the pcm and trans are trying to get around to getting the 2-3 shift taken care of.

I guess I need to find a way to bring the shift point down a little lower, or raise the rev limiter a little.

Any similar experiences or ideas?

[ May 30, 2002: Message edited by: John_D. ]</p>

[mike malloy]

reset the computer. mine did the same thing.. your vss is probably out of wack.
get with dom, he is very knowlegable is this area..

[strange_trp]

agreed. reset pcm so it can learn new adaptive strategy due to mods.

[John_D.]

I'm still not clear on how a new exhaust can foul up shift points, but I gave it a try anyway (resetting the pcm).

It's a little better, it only bounces 2 or 3 times now on the 2-3 shift, instead of a bunch of times. But it's still hitting it, and then shifting slow as a result.

If I am taking off from a stop, it does not do this, it shifts clean and quick. Only a problem if it downshifts from 3-2 first. Pretty weird...

[John_D.]

The pcm reset didn't fix it.

But, I did find a way around it. After the car automatically downshifts to 2nd for the pass, put it back in overdrive (before the 2-3 shift occurs). Then it will shift normally, at 5800 or so.

The problem only occurs if the shifter is still down in drive, and then only if the trans has auto shifted down to 2nd.

Not the ideal solution, but hey it works, and I'm happy about that!!!! [img]smile.gif[/img]

[Magnus]

Ya know, I'm going to move this to drivetrain. Seems like it fits this post better.

[99Camaro99]

I have the exact same problem. Mine started as soon as I threw my K/N and Lid on...first it was both the 1-2 and the 2-3 shift...now it's just the 2-3 shift.

[TheBeast]

would putting a shift kit on there possibly take care of the problem? i know the kit mainly affects the 1-2 shift, but doesn't it affect the 2-3 just a little?

[P-nut-]

The Transmission shift are based on vehicle speed. If you changed tire size, gears, or anything that would cause your speedometer to be off, then that would cause you to hit the speed limiter.

[John_D.]

Nothing that would change the gear ratio, including tires. Still have even the same brand as the originals, so it wouldn't even be a slight difference due to brand...

Only change was the headers and 3" exhaust.

Well, the SES light is on, because the o2 sim for the post-cat sensor isn't here yet, and there is no post-cat sensor in the new exhaust system. But I wouldn't think that would cause it. Of course I will have to duplicate the conditions when I get the o2 sim, just to make sure, for myself...

Especially since it shifts ok if its up in OD, just not in D. Also if taking off from a standing start, regardless of whether its in D or OD. The pcm is behaving differently depending on the selected gear, after a downshift, which points to something other than gear ratio.

I think the pcm code probably has a bad path somewhere in the coding for the 2-3 shift when the selector is in D and the trans has recently downshifted to second gear. So putting it back up in OD gets it back on the "regular" path through the code and everything works fine then.

[99Camaro99]

OMG John D. I love you man (don't take it the wrong way) but you describe EXACTLY MY SAME FUGGIN PROBLEM. Mine started with a SIMPLE install of a Lid with K/N. I later on did change my tires to 245/50/R16 from stock 235/55/16...don't think that would change much...would it?

[99Camaro99]

oh I sort of found a solution for the 2-3 shift...it's kind of ghetto but here it is...
Leave it in OD from a take off...let it do the 1-2 shift...once it shifts to two...drop the shifter to D...when it hits about 5,000RPMs on the tach throw it back to OD and it SOMETIMES makes a more normal shift instead of it's granny shift it's typical of.

[John_D.]

Here's a good tire size calculator. According to it, your tire size changes the speedometer by 2%. The diameter goes from 26.18 to 25.65, and the rpms are off by about 120 rpms at 6000 rpms.

http://www.venommotorsports.com/libr...calculator.asp

I guess we're stuck with the manual shifting from D to OD to fix the 2-3 shift... Unless HPP3 comes out for our cars and we tweak the shift points.

[John_D.]

Well guess what. I put the o2 simulator on, hooked up the autotap and cleared the dtc's, tried 'er out this morning, and it shifts just fine... So, something about having the check engine light on, in combination with the other sequence of events...

Unfortunately, the light came back on again.

When I cleared the dtc's, not only were they for the o2 sensor, but also for "insufficient flow" through the egr (which, ummm, got bypassed somehow during the header install...) But that's another story for another thread.

[99Camaro99]

get you MAF sensor replaced...that slow shift is GONE! [img]smile.gif[/img] 100% GONE. REPLACE IT OR CLEAN IT. Trust me