Well I am still uncovering oddities on my GN, trying to get it all straightend out. For some reason the MPH does not read right in Turbolink in 1-2-3 gears, but is dead on in 4th. It reads almost half of what it should be in the first 3 gears. The speedo is right on too. Previous owner put a collection of GNX style VDO gauges in the car, but they all seem to function correctly.
What problems could the ECM be having if it's getting a wrong reading for the mph? What could be giving a wrong reading in 1-2-3 but not in 4th? I am using an older T-link cable without the battery connector, on an old Tandy XT laptop. It works great, except for the mph thing. I am almost certain it is not related to the laptop because it worked great on a friends T-type.
The car just isn't performing like it 'should' be and I've got several things to consider. Just want to make sure this isn't a symptom of something and is just an annoyance. It needs to be fixed either way.
Thanks
Paul Campbell
http://www.oldwestracing.com
campbell@oldwestracing.com
Forgot to mention....
It also looks like the gear selection "light" on the T-link isn't exactly right. It seems to be saying i am in a higher gear before it actually happens. I haven't seen this occur all the time, but it has occured and shows up on some runs I jsut did at the track.
Paul Campbell
First, it sounds like your VSS isn't right or lags ...
Second, the light indicates when the ECM sees the pressure switch in the transmission come on. If the transmission "lags" a bit between when it is "supposed to shift" (i.e. the VB opens the passage) and when the actual mechanical shift occurs, then you'll see those symptoms.
I kind of wondered if Turbolink wasn't trying to tell me something
If the VSS is 'lagging', could the computer be confused and cause other problems? Does it use the VSS data for other computations? Is the VSS located in the tranny, ie off the output shaft? Is it adjustable, or should it just be replaced? Finally, why would it be good in OD but lag in the lower gears?
if the computer thinks a shift has occurred, but there is a delay, wouldn't this be a problem in that it takes this into consideration for timing, etc?
I have been seriously considering pulling the tranny and doing a full HP rebuild. It's seeing some age and just doesn't always feel right. It shifts nice and firm, but at WOT feels like it may be slipping too much (though it still feels firm).
Actually, the VSS is mainly used for TCC lockup and some "cruise" type trimming (especially in something like the Thrasher chip's "lean cruise" feature). A lot of times at cruise, the EGR is pumped up, the timing advanced and such to reduce pumping losses and improve fuel economy. Nothing supercritical, but nice if it all works right.
The VSS is located behind the dashboard and is alot of times replaced or replicated with the GNX dash kits. That's why I wonder if something isn't quite kosher with the VSS used with your dash?
As far as the shift ... we're not talking about a significant amount of time here (and add the fact that you get data at about 1 frame/sec, you may be seeing something that is on a "boundary".. i.e. the frame shows the command and the trans shifts in the before the next frame). The ECM doesn't normally do too much fancy with the timing on the shifts (other than back a couple degrees out in the upper gears in several street chips). The slip you are feeling may also account for the difference between the displayed data and the actual shift... the shift is commanded and it s-l-i-i-i-d-e-s into the next gear at WOT.
Anyone have the instructions for the AVC GNX-style dash with the VDO gauges they can scan and send to me?
Or at least the wiring for the VSS and speedo?
Thanks
Paul Campbell
campbell@oldwestracing.com