Need Help speedo gone whacky

vettl83 · 08-14-2004, 12:38 PM

My 91 has 37k on the clock and the speedometer just started going nuts. When your going 30 mph it reads 75 mph and when your going 75 mph it's reading 135 mph. No matter what speed you run at it reads faster than your going. Is the processer in the ecm going south? Time for a new ecm? Could the speedo gears be trashed? Any help would be greatly appreciated. All other gauges work fine. Thanks in advance, 84 CF 91 ZR1

ZR1Pete · 08-14-2004, 05:28 PM

Do you have in the Metric setting?
If not then i would say the speed sensor is going bad, it's in the trans tailhousing.

BiZ · 08-15-2004, 10:11 AM

It's the car telling you it wants to go faster.

vettl83 · 08-15-2004, 10:44 PM

Thanks guys, got it working again. On a hunch I disconnected the negative battery cable for 15 minutes and it started working again. Hope it lasts. Again thanks, 84 CF 91 ZR1

VaderVette · 08-16-2004, 10:38 AM

Went on a road trip this last weekend, and on the way back my speedo started acting "funny". The LCD portion of the dash, including the speedo, odometer, trip odo, mpg, etc, areas stopped displaying correctly. I'm not sure how to exactly describe it - some sections of the numbers show faded, and some sections of numbers are showing when they shouldn't.

Does anyone have experience with a similar situation? Thought about disconnecting the battery for a while and then reconnecting, but haven't tried it yet. Could it be that the LCD is just "jammed" and needs reset (by battery disconnect), do I need a new LCD, could it be ECM? I replaced the sensor in the tranny case just last year, so I don't think that's it.

Any help would be appreciated.

90 Corvette ZR-1 · 08-16-2004, 03:00 PM

Vader are you going to carlisle?

Jeffvette · 08-16-2004, 03:23 PM

I have had a similar issue in the past. My speedo would dispolay some funky numbers, had it hit 255 when I was doing 40, it would jump all over the place. Also it wouldn't display certain functions and it would kick into SES mode.

My fix was to replace the ECM after it died. Fixed the problem completely. Try to find a car the same year as yours and swap the ecm. It's a simple 10 minute job for both

VaderVette · 08-16-2004, 08:47 PM

90: I don't think I'm going to Carlisle this year. I'd like to, but I have some pretty hectic deadlines to meet at work, and already have 2 getaways planned for September (including one to watch the NHRA races at Maple Grove in Reading), and also my car is not running quite right (aside from the speedo). I'm lugging in low rpms, before the secondaries kick in, so I thought that it was a clogged injector. Now with these speedo problems, I'm wondering if the ECM is indeed bad, and is perhaps causing all the problems. I don't think I want to go limping into Carlisle and get laughed at...

Then again, it might be a good chance to try to get some info.