At the track yesterday this happened several times only on really hard launches. After a good burnout, I would launch the car hard (in OD as always)and it would pull hard in 1 st for about 30-40 ft out and jump to second gear with the rpms barely @ 4200-4500 and this would carry the car 3/4 track and then it wouldn't shift to 3rd. It would bounce off the rev. limiter if I let it.If the car cool comletely, I could get one run in before it did it again.It drove home fine.It was as if it went into "limp home mode" just off the line. The fluid appeared to have increased it's level a bit from where it was before heading to the track. I haven't Ataped it yet , but will be shortly. Any thoughts on this? TIA. (YST3500 with 1.57-1.60 60 fts) <img src="images/icons/confused.gif" border="0">

 

James, it could be that your WOT is too rich. Check your o2's on A-Tap and adjust your MAFT one or two clicks lean. Also talk to Steve about this. He has had some experience with something similar to this.

 

Well , I have a little more data to help diagnose. The Ltrms (cruise) are 0-2 and O2s@ .875-.880 which has shown to be my lean mean sweet spot. The car doesn't "lay-down" , it just jumps strait into limp home mode right off the line. Atap showed code PO502-Vehicle speed sensor low input. What is this sensor and where is it located? I hope this info helps to make more sense. Thanks.

 

I'm going to go out on a limb , and I am hoping I'm wrong. Is it possible that the vehicle speed sensor(assuming it's in the trans) is detecting the proper speed to shift at based on trans output speed and is shifting to 2nd properly? If that is the case then the clutches would be slipping allowing it to see that shaft speed.It only does this on real hard launches.Anybody?

 

Hello Veterans.......HELP!ttt

 

is the fluid burnt?
smell it, if its got the ol rotten eggs smell, its slipping. if its bumping the limiter i think its the tranny starting to slip, fluid gets hot and is killing the tranny maybe...hard to say at this point

steve frank

 

ATAP & watch the temp. Check the trans fluid. Could be bad electronics inside the trans, or slipping, as suggested above. So many things it could be. I have heard of this problem before, on one of the boards, so some extensive searching may be in order. Are you loosing fluid? I did at one time, & it turned out to be a $5 seal on the back on the trans. I would watch the trans temp close & use that to rule out slipping.

 

Well, I am definitely not losing fluid , it doesn't smell burnt and I checked the trans cooler lines to ensure nothing was bent/crimped causing a fluid restriction. The problem is that I have only experienced this at the track on rock hard launches.Also-on the last pass that it did this,I had to let off the gas because it wouldn't shift to third so I coasted to the turn around and when I tried to accelerate, the engine free wheeled while in D or OD. I had to pull it back to 1st and it finally engaged. after it cooled everything was fine. I am not sure which item to select on Atap to monitor the line pressure solinoid volts. Which points will give that info? Thanks. <img src="images/icons/confused.gif" border="0">

[ February 19, 2002: Message edited by: TXCAMSS ]</p>

 

Yeah it's still under warranty.I guess it's a good news bad news deal. I am sure the ETs weren't spinning much since the front tires were in the air at the launch. Warlock- did you get yours covered under warranty? I think I got jinxed. MMiller asked me that night at the track what I would do if I fried my transmission. I guess we'll find out now. Thanks for all the input. Is this a common A4 problem? I've got about 75 passes on it and most were with the stock converter.

[ February 19, 2002: Message edited by: TXCAMSS ]</p>

 

I sometimes get early 1-2 shifts if I'm spinning hard. The pcm perceived mph will be at the shift point but the rpms will be lower than it should be for the speed. For example, Autotap shows 48 mph but the rpms will be in the 5K range.This may be where your getting the code from? I've never set any trans codes, FWIW.

 

Sorry to be the bearer of bad news but your 3rd gear drum is about gone. I just had mine rebuilt less than a month ago. Had the EXACT same experience at the track. drove ok under normal driving but under hard acceleration no 3rd gear. Hope it is still under warrenty. Good luck!

 

UPDATE- After reviewing some GM documents , it appears that this code PO502 is set when several conditions are met. A few of them are: Hi trans fluid temp , the TPS is greater than 12% while in gear,and the engine speed is greater than 3000 rpm in gear with the output speed of trans less than 150 rpm for more than 3 seconds. These conditions could have been met at the launch considering the high rpm launch style I use. I will track test it again to verify the integrity of the transmission.I just thought I'd pass this info on for those that might encounter the same problem code and symptoms.

 

I'm running a A-4 in my '94 Z-28 with a big stall Yank 3700. I have the same problem as you. My buddy JS found out that the computer can't handle the RPM's that the big stall is putting out. I was losing 3rd gear and it would come back and work perfect when you don't wack it. Had to purchase a TCI Trans Control Unit from Jegs for $741.00. This unit has its own computer and you would by-pass the car computer. If you need anymore info on this, contact "JS" on this board. BTW/ I have OBD1.

Steve <img src="graemlins/camaro.gif" border="0" alt="[Chevrolet]" />

 

[quote]Originally posted by TXCAMSS:
<strong>Yeah it's still under warranty.I guess it's a good news bad news deal. I am sure the ETs weren't spinning much since the front tires were in the air at the launch. Warlock- did you get yours covered under warranty? I think I got jinxed. MMiller asked me that night at the track what I would do if I fried my transmission. I guess we'll find out now. Thanks for all the input. Is this a common A4 problem? I've got about 75 passes on it and most were with the stock converter.

[ February 19, 2002: Message edited by: TXCAMSS ]</strong><hr></blockquote>

Sorry so long in responding. Yes I did get it covered under warrenty but I had to put my stock stall back in and basically make sure it was back to stock. Find a mod friendly dealer and make sure your wheel wells are clean (no rubber) <img src="gr_grin.gif" border="0">

Good Luck <img src="graemlins/gr_cheers.gif" border="0" alt="[cheers]" />

 

[quote]Originally posted by PHATKOP:
<strong>I'm running a A-4 in my '94 Z-28 with a big stall Yank 3700. I have the same problem as you. My buddy JS found out that the computer can't handle the RPM's that the big stall is putting out. I was losing 3rd gear and it would come back and work perfect when you don't wack it. Had to purchase a TCI Trans Control Unit from Jegs for $741.00. This unit has its own computer and you would by-pass the car computer. If you need anymore info on this, contact "JS" on this board. BTW/ I have OBD1.

Steve <img src="graemlins/camaro.gif" border="0" alt="[Chevrolet]" /> </strong><hr></blockquote>

Could you give a more detailed explanation on this? I'm confused about the PCM not being able to handle RPM's that the converter is putting out. I've run as big as a Vig 4000 in my '98 T/A (flashed over 5,300), and there are quite a few people just on this board running 4,400+ stalls with no problem. My Vig 3200 in my SS flashes 3,800, and I've never seen the problem due to the PCM not being able to "handle the RPM's". It sounds like James' problem stems from the code that he mentioned above.

James - Hopefully that's the problem. With only 75 passes on the trans (much less w/ the stock converter for most of them), you should have quite a bit of life left in that trans! Good luck w/ it.

 

I'm pretty sure the tranny is ok. I believe I met the condtions for the code which set the limp home mode by stalling over 3000rpms for more than 3 seconds and the drive shaft not exceeding 150 rpms. The night this happened I was experimenting with the higher stall launch and it was instant green night at HRP. The guy at the tree was a tad slower than normal. It just seemed that the higher the stall , the better the 60 ft (1.57s so far). So basically you can stall as high as you want, but you have 3 seconds to do it. Also , you need to be sure not to exceed the 12% open on the throttle position sensor as that will cause the same problems. I sure hope this helps.Take care.

James