First, some basic info on the vehicle:
It's a 95 w/o ABS. It has a coldside MP62, MSPnP, 460s, no MAF, DIY water injection (not MS controlled). Driven solely at high elevation (5,500' - 9,000'). Boosting at 14psig peak.
Over the weekend, I reflashed to the latest high-res firmware (from 029y4), performed the cap/filter mod, and installed an LC-1 wideband. I thought everything was going fine and dandy, until I noticed that I had no speedo on the way to work this morning (it is reading zero). I fired up MegaTune, and noticed that the MPH was reading at a constant 24.7mph regardless.
I know the speedo was functioning correctly when I arrived home on Wednesday evening from work, because I have been closely monitoring the trip counter playing the 'how many miles can I go on one tank' game. That was the last time I drove the car prior to the modifications outlined above.
Here are the steps that I performed:
1. On Wednesday evening I cracked open the MS and performed the 0.1uF cap/filter mod, in anticipation of the high-res firmware reflash. I figured it wouldn't hurt to perform the mod even if I did not need it (hope that doesn't come back to bite me).
2. I reinstalled the MS and started the car. It fired right up. I did not take it for a test drive.
3. On Thursday I installed the LC-1. I tapped the ECU +12v for the controller power supply. I grounded the gauge and LC-1 controller at the ECU ground point. However, I tapped the gauge power off the auxilliary/cigarette socket (in hindsight, I am going to move this to the ECU +12v). I grounded the O2 sensor heater in a different location. I reprogrammed the LC-1 analog output 1 per the common 10:1 - 20:1 range, and configured MegaTune and the MS accordingly). I cut the wire in the main harness for pin 2N, and spliced (soldered) it in to the appropriate LC-1 analog output.
4. Exported my fuel and timing maps in MegaTune.
5. I downloaded the 10g firmware, then copied over my modified matfactor plus the two additional therm files from the original MSPnP (029y4) source code distribution.
6. Successfully compiled the firmware. Disconnected my coils, reflashed the firmware, reloaded and burned my MSQ, re-imported the fuel and timing maps, then re-connected the coils, etc.
The car fired right up. I spent a couple of hours over the next two days logging and tuning my fuel map, and the car has been running much better on the high-res firmware. However, for some stupid reason I didn't even once glance at my speedo. Based on where the trip counter is currently stuck at, I am pretty confident that it has not functioned since Wednesday evening.
So, before I go poking around with the DMM do you have any thoughts on what I might have screwed up?
Also, can somebody give me a high-level overview of how the speed-sensor circuit functions? I mean, do the speedo and ECU read independently from the speed sensor? Or does the ECU read the signal and then output it to the gauges (my assumption), or vice-versa? What ECU pinouts are in play? Sorry if these are dumb questions, but the answers might give me a better idea of the likely failure point.
The possibilities as I see them, in no particular order:
1. I screwed up something on the MS mainboard when I made the cap mod.
2. I knocked a wire loose when I was groping under the dash, wiring in the LC-1 gauge.
3. I inadvertently damaged something when I cut and spliced 2N near the ECU connector.
4. Something in the high-res firmware and/or MegaTune needs to be re-configured to get my speedo working.
5. Something in the speedo circuit happened to fail this weekend by complete coincidence, unrelated to the modifications I made (seems unlikely).
I am kicking myself for not taking the car for a drive after making the cap mod, but I am comfortable with a soldering iron and I figured that if I screwed anything up then it would manifest as the car not firing or something equally profound.
Cheers for any help.
p.s All this aside, the high-res firmware rocks!
[Edit] Incidentally, I am open to the possibility that I just have a broken speedo cable and will be checking that tonight. It just seems like too much of a coincidence that it would fail at the same time I did this other stuff. I'll feel pretty foolish if that's the case, though.