cousinit99

Has anyone else experienced this? It'd sure be nice to know what's going on here.. The voltage display on my digital dash will read 13.2v or something similar, but then my scan tool, which has a live feed from the ALDL connector, will show a voltage reading of 12.6v or something like that. The voltage on the dash is always higher than it is on the scan tool. It's usually something like 0.5v higher.

My alternator is causing a 300+mA parasitic drain and the voltage regulator is starting to crap out. It's also making this high frequency buzzing sound (resonance from the capacitor inside?) when the car is completely turned off, which coincidentally, stops when I pull the 5A Cluster fuse. Maybe this has something to do with it?

HlhnEast

I think the 93 gauges are known for inaccuracies. Cliff Harris will probly chime in with some answers. Hes pretty good on the electronics.

cousinit99

Are they now??? Well, I certainly hope he does. I'd really like to hear about that... Thanks for the input!

vetteoz

All my datalogs have shown exactly the same as yours ; ditto the fuel pump volts always lower than battery V shown on dash

Cliff Harris

Well… The problem is that I have an '86 and the dash changed completely in 1990, so I really don't know much about it.

That said, on my car the ECM measures the fuel pump voltage. That goes through several connectors and the fuel pump relay and oil pressure switch before it gets to the ECM (PCM on later cars), so it will generally be a little lower than the battery voltage.

The dash measures the voltage from the ignition switch. That's pretty much direct from the battery.

Keep in mind that there are tolerances and inaccuracies in both the ECM and the dash voltmeter circuit, so you can't expect them to be exactly the same.

captainkawasaki

I've found that my gauges are pretty inaccurate when compared to my ALDL datastream. Especially the tach in my 1990, it is pegged aboved 6K rpm when the engine is turning 3100 rpm.

cousinit99

Well, maybe I can help with that. The schematics for the '93 instrument cluster and ALDL connector are below. It seems to me that the dash voltage is displayed as measured from either the PNK/BLK wire coming from the Cluster fuse on circuit 139, or the ORN/BLK wire coming from the LCD fuse on circuit 840.

The ALDL connector, unfortunately, is not nearly as apparent (to me anyway ). Maybe you'll have a better idea where that signal comes from by looking at these. If I had to take a guess, I'd say it's coming from the tan serial wire on 800, but even if it's not, it sure doesn't look like it's coming from the fuel sender (which the fuel pump is connected to, by proxy, on the '93). It looks like the ECM sends that signal to the ALDL connector somehow.. Yes? No? Bueller?

Aghh! Photo hosting sites are pissing me off royally. You can look at higher quality versions of these at:

https://docs.google.com/file/d/0B2jU...Faa1dLbDA/edit

https://drive.google.com/file/d/0B2j...o1V2x0Rms/edit

https://drive.google.com/file/d/0B2j...ZxdGNDYzg/edit

cousinit99

Wow, I definitely don't have that problem. You sure there isn't something wrong with your tach input circuit?

cousinit99

Wow, I officially hate photobucket now..

vetteoz

90 - 92 tachos have well documented problems

http://forums.corvetteforum.com/c4-g...ch-repair.html

http://www.thirdgen.org/techboard/el...meter-fix.html

cousinit99

Ick, I see. Sorry to hear that...