AllGoNoShow Posted September 26, 2006 Report Share Posted September 26, 2006 Well I am at my wit's end with my 1990 Pontiac Grand Prix-4 speed 3.1. The speedo for the past 6 years has exhibited these traits: it will work fine in the winter when it is cold out (like under 50 degrees it always works fine), and then during days when it is over 50 degrees to like 70 sometimes it will work fine (rarely), sometimes it will wander (move 25MPH up and down even when cruising steady-or work for a split second and return to zero), and sometimes it won't work at all. On very hot days (like 75+) the speedo will never work and always reads zero. I have changed the gauge cluster, same problem, and just recently changed the VSS and still the same problem. Where the heck else should I look? It is really making me mad because when the speedo does not work the TCC will not engage (leading me to believe it is not just some wiring problem on the guage or something-but a problem between the VSS and ECU)-and when the speedo "wanders" while i am on the highway the TCC will engage/disengage and really make it annoying. And without the TCC engaged i don't get very good highway MPG. What else could possible be wrong? On another note-when it rains i always get like 3 gallons of water sitting in the floor pans (mostly in rear)-i looked under the car the floor pans are not rusted or anything-anyone have any quick ideas of where it could be leaking in from? Thanks for any tips you can provide! Nick Quote Link to comment Share on other sites More sharing options...
Robby1870 Posted September 26, 2006 Report Share Posted September 26, 2006 I would try a new ECM. I guess new is the wrong word. Get on off ebay for cheap or from a junkyard and see if that fixes the problem. Actually, first look at the 4 connectors attached to the ECM. Take each one off and look for any broken prongs or stuff out of the ordinary. As for the leaking, is it a 4 door or 2 door? I would check around the door seals (weatherstripping) and sunroff seal if you have one. See if there are any cracks or anything that looks wrong. You can always test these with a large cup of water. Just poor it around the top of the door and see if any leaks in. Quote Link to comment Share on other sites More sharing options...
RJansen658 Posted September 27, 2006 Report Share Posted September 27, 2006 If it effecting the TCC then is has to be between the VSS and ECM, if you can tell a different change in climate it is most likely a corroded connection or a chafed wire..... trace it from one end to the other, start by checking the connectors first, then take apart the harness if you dont find anything.... disconnect both ends of the wiring for the VSS to ECM.... check for continuity, and check for continuity to ground.....if ok, check resistance, if ok check ECM ground and powers circuits, if ok replace ECM Quote Link to comment Share on other sites More sharing options...
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