Inconsistant times

**Jeff400w** · 06-10-2012, 06:52 PM

My 96 used to be very consistant but lately it will make 2 consistant runs then it might slow down 4 or 5 tenths. No change in the weather.
Yesterday it slowed down a full second and 10 mph in the 1/8th. Later it usually picks back up.
The whole run is slower, 60ft,330',660' and mph.
I have a Pcm for less tune with just bolt ons.
Anyone have any ideas?

***popo8*** · 06-10-2012, 08:48 PM

What kind of weather changes are you seeing between those runs?

**Jeff400w** · 06-11-2012, 10:12 AM

No change in the weather at all.

**96LT1355Z28** · 06-11-2012, 08:56 PM

If the 60' is slower then the entire run will also be slower. What's the difference in 60' from a "good" pass to a "bad" pass? .4-5 tenths/ 1 second and 10mph difference at the 1/8th is alot. If it's not spinning or bogging my shot in the dark guess is a trans slipping issue. Do you know what temps you trans fluid is seeing, what's the trans fluid look like?

**Jeff400w** · 06-12-2012, 12:59 PM

On the 1 sec. slower pass the 60' went from 1.77 to 1.90. I don't have a trans. temp guage so I don't know about the trans. temps. It does have a trans. cooler and the fluid looks good. It could be getting hot, but it doesn't feel like it's slipping.
The weird thing is the next run it picked back up. Maybe it didn't get cooled down enough before that run?
I was thinking maybe a sensor giving the pcm a false reading? I have also been thinking about converting to OBD1 so I can use a data logger. Any thoughts on that?

**96LT1355Z28** · 06-12-2012, 03:59 PM

You would not be the first one to convert to OBD1 for that reason! When it picked back up was the 60' improved as well? I have a spread sheet I made to layout all my runs from a day side by side. This way I can see if a pass is slower where it started to occur. It's kinda like long distance shooting, the more difference you have at the start of a pass the more pronounced it is as you get further down the track. Almost 1.5 tenths at the 60' would make quite a difference at the 1/4 but I wouldn't think 1 full second.

**Jeff400w** · 06-12-2012, 08:49 PM

It ran a 1.78 60ft on the next run. The more I think about it, it had a lot less time to cool down before the run that it slowed down. It had a while before the next run when it picked back up. Maybe I need to make more effort to cool it down more on the back to back runs. It never seemed to effect it before. I remember making back to back to back runs on a test and tune night and making 5 runs within 4 hundredths.

**Jeff400w** · 06-16-2012, 09:12 AM

I think it's fixed. I installed 2 new AC Delco O2 sensors, cleaned the MAF sensor and reinstalled the original TB (It had a 52mm). It ran a new best et-speed and ran pretty consistant all nite except for traction issues because of track prep.