I have a '97 ford f-150 and it will not pass emissions.the emission guy said it was the evap.told us to replace the gas cap.we took the truck to another emission place and it read ready.we replaced the gas cap and directly after we got the truck tested again and it failed the readiness test.the truck is a 4.2 v6.
We have already driven over 300 miles.we have tried to get it tested and it will not read any codes.also it failed the o2 sensor and o2 sensor heater testing.could that be what is stopping it from passing?any suggestions?

 

If the code reader won't work, check the cig lighter fuse.

Need code numbers to help.

 

For the evap I think the system will only self test between 3/4 and 1/4 of a tank of gas, so if the 300 miles is at $20 of gas at a time, it won't test.

Like glc said we need codes (P0xxx) to help zero it in.

Plus if you are having evap issues then check all the hoses hooked to the gas tank.

 

Time to go get an "inspection" from a shady guy that'll pass you for a slipped bill! If the truck runs fine, and the emissions is really the only problem it has, you'd might as well. No sense is fixing stuff that doesn't really need to be fixed. I don't like to suggest to pass emissions like that, but you do what ya gotta do sometimes

 

If the readiness indicators wre read, then the scan tool was able to connect at the inspection station.

You're going to have to produce actual fault codes, if any, in order for us to assist in any diagnosis.

FWIW, it takes TIME for the readiness monitors to run. The EVAP is the toughest as it has the narrowest set of entry parameters. Sometimes it takes days or weeks for it to run. A drive from the auto parts store back to the testing facility isn't likely to cut it.

Also, if you're resetting the computer before any testing, knock it off. You'd only be extending the process.

Most jurisdictions allow one or two readiness monitor to be incomplete and will still pass e-test as long as there are no faults. Check the rules in YOUR area so you now what is going on.