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P0446,emissions;a perpetual problem. no one can fix. is it a guessing game?

(2006 Isuzu i280 Pickup)
in Hillsborough, NC on November 30, 2011
have spent $1000.00 two different mechanics in two weeks and the light is back on again. replaced the evap purge valve hose and electric harness. light came back on after 50 miles. Took it to Authorized service center, they said it is the evap purge valve. No just replaced it, oh ok then it is the canister. ok so they changed the canister, two days later check engine light on again. Seems you could test the parts before replacing all one peice at a time. please help, running out of money.
Displaying 2 answers & 2 comments
Popular Answer
of Contra Costa Smog and Repair on November 30, 2011
Ask for your money back as they did not fix the problem you payed them to fix. You need a smog machine/evap presure guage and a lot of pinch pliers, it may take a while but eventually the smoke will appear, or while pinching the hoses you will see the smoke machine indicate no leak, this would mean the leak is downstream of that hose/plier, keep moving your pliers down stream untill you find the leak
on November 30, 2011
Thank you for your fast response, sorry to burden you with a long reply; I am in need of good advise.

Should I ask the Authorized Serv. Center (David Wescott) how they determined the canister was the fault. First they said it was the evap vent valve, I told them it had just been replaced by Tire King($440.00). Then they said, I had to many miles on the truck since the check engine light came on. They reset it and told me to come back when the light comes back on, which I did. Then they replaced the Charcoal Canister ($500.00). Two days later, light back on. They said bring it back next week and we'll do another diagnostic evaluation. ($70.00). I think it would be best to stick with one person until they get it right, but I'm not sure they will not charge me again. Should I ask them if they know how to test it to find the problem opposed to trial and error?

This truck has had the check engine light on eight times in one & a half years. 1. O2 sensor (mechanic fixed) had to take it back twice, 2. I changed the plugs, 3. I changed the plug coil and 4. Gas Cap 5. I changed the Thermostat 6. Evap vent valve, Tire King worked on it. 7. Evap vent valve, David Wescott worked on it. 8. Evap vent valve, needs to be checked again. David Wescott, Serv. Center said the computer showed that someone has been into the engine of the truck. Not while I've had it (since 2008). Is all this typical for this vehicle with 87k miles? or is this an indication of on going problems for the life of the truck?
Thank you,
of Contra Costa Smog and Repair on December 01, 2011
If there is no leak and you have an intermittent electrical proplem, that shows eroneos codes, at this point all one can say is good luck. I would have them check all the ecm connectors and grounds.
on May 20, 2014
Don't know the right answer without diagnostics, but you are dealing with the wrong service provider! There is no code or computer symptom that informs them that " someone has been in the engine since we were working on it".....he is trying to avoid you. Make sure that is a dealer gas cap, not aftermarket. It concerns me that it took three tries to get an o2 sensor installed correctly....I suspect stripped threads and an air leak in your header (probably too late to help you, but stay away from this shop!). Replacing an O2 sensor is like changing a light bulb- screw the old one out, screw a new one in- it's that simple. You didn't say, but was the O2 sensor done first?
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