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2004 chevy trailblazer_lt_ext
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Discussion Starter #1
OK, My 04 4.2L trailblazer has been stalling at Idle while stopped at a light Occasionally. I recently had it to the local GM Dealer and they recommended a fuel system cleaning, from the Fuel Rail, for which I have ordered parts for but haven’t come in yet. However the tech said that he had some concerns and was watching something with the Fuel Trim. So as I wait for the part to come in I started to look at it as well, I have noticed my Long Term fuel Trim was around a -7% or -8% at Idle when you gas and get the RPMs up it goes + to around 15% and as it comes back to Idle back to -7%. Short Term runs close to 0%. So i guess at Idle it is running Rich. What would be causing it to run Rich. I have dug up some info on dirty Mass Air Flow Sensors causing this same problem and symptoms, " - "at Idle and " + " under load, However the 2004 doesn’t have a Mass Air Flow Sensor, so there goes that Idea. Anyone have any thoughts. Also would a fuel system cleaning at the rail Help correct the issues or help it run richer, from what i have seen my Goal is to get all of my fuel trims as close to 0% as possible.


I don’t know if this would affect it or not, but I have replaced the Catalytic converter with aftermarket one from Flowmaster.


Thank You in Advanced,

Matt
 

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2004 chevy trailblazer_lt_ext
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Discussion Starter #2
Sorry, I have a few more details that I omitted, I recently replace the variable valve timing solenoid, in April. However I did not replace the Camshaft Sensor.

Back in February the dealer told me it was showing a code for it, but the MIL light wasn't on. So I didn't do anything until April, when I was having problems for poor performance, which turned out to be a back-pressure issue, that when I replaced the cat as well.

Also the throttle body gets cleaned twice a year. Once in the spring and before winter.

Thanks Matt
 

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2008 chevy trailblazer_lt
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Your "cat eater" was / is likely your running rich. Have you had your fuel pressure monitored / checked. My guess would be poor fuel regulator. I think normal idle readings should show LTF near zero with some variability to the STF but not much. Maybe check / monitor vacuum along with O2 readings / output.

what kind of gas mileage are you getting?
 

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2004 chevy trailblazer_lt_ext
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Discussion Starter #4
my MPG is around 12 around town, haven't had a any good highway trips to watch lately. I think a vacuum leak would cause the to run in the positive, because it would be pulling in air. I was thinking maybe a MAP Sensor or the camshaft Position sensor.
 

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2004 chevy trailblazer_lt_ext
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Discussion Starter #5
Well I went ahead and did the Fuel Injector Cleaning from the rail, during that service my #2 cyl ignition coil went. Replaced the Coil and the injector cleaning and now it runs great plenty of power. I have a feeling that the coil was going bad for some time causing my cat failure in April. With 165,000 miles it might be time to replace the rest of them.
 

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2003 chevy trailblazer_ls
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I have been fighting a stalling problem when its extremely hot outside under acceleration and sitting at and idle. Power has been down and not running correctly for the last 3 years and i have replaced everything camshaft sensor, throttle body, solenoid for the timing and fuel pressure regulator, all of which helped for a short period of time or it was my mind playing tricks on me. Well it's extremely hot here again and the problem came back worse than ever almost leaving me stranded. finally threw a code that said it may be the crankshaft sensor which I replaced the today and what a world of difference. So if you guys have been chasing a rough idle or stalling condition under acceleration be sure to check the crankshaft sensor it seems to have solved my issues.
 
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