Fuel gauge misreads

[Smokee]

Ok, reading all the previous posts has answered most of my questions about my 97 Jimmy. But not all....recently my fuel consumption went through the roof. At the same time, my fuel gauge stopped reading full even though it was full to the brim. When I fill up, it reads ¾ full. As far as the gas mileage goes, I suspect the CPI unit is leaking. But I can't figger out the gauge thing. Engine light is always on. PO300 code (random misfire engine cold at 0 mph) and I get a P1870 (tranny slipping). Any help to the above would be greatly appreciated.

[rlith]

For the gauge, it's the sending unit that's bad/not sending right... For the p0300, that could be caused by your fuel injector dumping fuel (You have CSFI, NOT CPI), but it is more likely caused by the need of a tune up (cap, rotor, plugs, wires) or your coil..., the tranny slipping could be because of a bad valve body or a bad ignition switch (look to the ignition switch first)

[BlazerLT]

1997 ignition switch causes many problems from sender problems to tranny codes and engine performance failures.

Tune up the engine completely.
Replace the ignition switch.

[Smokee]

Thanks for the advice. You guys are great. I can't believe how many little problems were solved by simply replacing the ignition switch. And yeah, them little torx screws at the end were real bastages. Thanks again.

[BlazerLT]

Sweet, glad it worked for you.

So everything is perfectly normal now?

[Smokee]

Actually, it fixed everything except the fuel gauge problem. But the rough idle, misfiring and excessive fuel consumption all seem to be gone. Also, my SES light is not on for the first time in months. I am doing a major tune up including fuel filter tomorrow. If that don't fix it, I'll have my fuel pressure checked and go from there.