What do I have to do to make my speedo accurate with my 17 wheels and 275/40/17's ? Also SES light comes on when I am cruising at 60 then coast a while How can I figure it out cheap? Or should I just buy a code reader? WHich one?

 

275/40/17s should have the same diameter as the stock wheels. so there is no need to fix the speedo.

since you have an obd1 computer you can get a cable and connect it to a laptop or desktop (if you can get it close enough) and use free software to read the codes and sensor info.

some parts stores use to scan for free. call around

 

they are off by about a half inch. you need to correct the speedometer

 

Depends. The outside diameter of a 275/40-17 tire is 25.65", IDENTICAL to a stock (Z-rated) 245/50-16. That assumes that the car was originally equipped with the optional Z-rated tires. If it came with 235/55-16 (base V8 models without Z-rated option), it will be "off" - 25.65" vs the original 26.17".

 

A Hypertech Power Programmer will let you adjust for tire diameter .25" at a time but is limited for engine programming for the price ($325). The cable/laptop/software option is the best for adjustability of engine parameters. The cables are around $70 last time I checked and if you have a laptop or can borrow one would be great. Search for LT1Edit for more info.

Advance Auto Parts and Auto Zone are two chains that will scan codes for you for free, though there's no guarentee the scanner will work. . . I had my 2000 Zr2 Blazer scanned one day and the code cleared. When the SES light came back on 4 days later, I replaced a simple part that may have been the cause (gas cap) and asked them to scan and clear the code. The guy couldn't get the reader to work and blamed it on the truck.

Z28Nut

 

Is there an easier way to adjust your speedo, can dealerships do it? Going to be moving from the 235/55/16s to 275/40/17s in a few weeks and I have no other use for any of the programmer things.

 

nothing......i'd just see how far it's off first.....i bet you will be pretty close if not right on. Like Injuneer said you just have to know the tire diameter