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03 trailblazer wont accelerate
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superdave
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May 24, 2010, 7:13 PM
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03 trailblazer wont accelerate
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I have a 2003 Chev Trailblazer LTZ with 4.2L I6 and its running poorly. Low power and cant get above 55 mph. It bogs down and doesnt shift smootly. I got 4 codes, P0107 (MAP circuit low input), P0172 (bank 1 too rich) and P1120/1220 (TPS circuit 1 low/TPS circuit 2). I have changed the fuel filter, spark plugs, and tested fuel pressure. After researching and testing these circuits i found the all to check out OK, including the wiring to the PCM. While its running, I depress the accelerator and it barely revs, also the opening on the throttle body barely opens. I dont know if I should just replace the throttle body (built in TPS) or go with something else. What would cause all of these symptoms?
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Hammer Time
Ultimate Carjunky
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May 24, 2010, 7:27 PM
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Re: 03 trailblazer wont accelerate
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I think the first thing you should check is do a pressure test on the exhaust through the 0/2 hole looking for a plugged up converter. You can also take a manifold vacuum reading looking for low vacuum and even lower if you bring the RPMs up to about 1500.
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superdave
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May 25, 2010, 5:14 AM
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Re: 03 trailblazer wont accelerate
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I had thought of a converter, but I dont know how to eliminate it. How do I test the exhaust pressure, and what should it be? For the vacuum, I assumed it to be good after the MAP sensor test. The signal voltage was steadily rising and falling with RPMs, but i didnt test the actual pressure...should I?
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Hammer Time
Ultimate Carjunky
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May 25, 2010, 7:41 AM
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Re: 03 trailblazer wont accelerate
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Don't assume anything. On the vacuum test you should see 16 to 20" of vacuum at idle. Bring it up top 1500RPM and it shouldn't drop more than 3" of vacuum.
For the pressure test you remove the upstream O/2 sensor and thread a pressure gauge in there. You should see about 1 PSI there. 3 or more is a problem. Be sure to test both sides.
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superdave
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May 29, 2010, 4:59 PM
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Re: 03 trailblazer wont accelerate
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Exhaust Pressure is good..1 PSI at idle, and only went up to 4 at 1500 RPM. The vacuum was also good 19" at idle and 16 at 1500 RPM. Im baffled. The throttle body valve will open all the way (100%) with ignition on, engine off, but will barely open with the engine running. The accelerator is sending a full 100% signal to the computer, but the throttle angle only goes up to 30% . Im thinking PCM or throttle body, but i dont know.
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Hammer Time
Ultimate Carjunky
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May 29, 2010, 5:14 PM
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Re: 03 trailblazer wont accelerate
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Do you have a "Reduced Power" light on?
I just realized this is a "drive by wire". It has dual TPS's and if there is a problem with one of them it goes into a failsafe mode of half throttle. You'll need a tech2 to diagnose it properly but your probably going to need a new throttle body.
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superdave
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May 29, 2010, 6:09 PM
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Re: 03 trailblazer wont accelerate
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I have had a reduced power light a few times, but not solid. I have been trying to get a voltage measurement off of the sens 1 and sens 2 circuit and every time i touch the wire for the sens 2 circuit, (key on, eng off) the throttle stops moving fully, my guess is, like you say that one TPS is bad and causing half power. Does that make sense? Did I mention that I hate drive by wire? First time working on one for me.
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Hammer Time
Ultimate Carjunky
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May 29, 2010, 6:24 PM
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Re: 03 trailblazer wont accelerate
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Yes, it makes total sense. It's also programmed to stop working altogether if it loses the second sensor also.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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superdave
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Jun 9, 2010, 3:11 PM
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Re: 03 trailblazer wont accelerate
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I put on a new throttle body today and i have the exact same problem, any other suggestions?
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Hammer Time
Ultimate Carjunky
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Jun 9, 2010, 3:13 PM
Post #10 of 10
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Re: 03 trailblazer wont accelerate
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My previous advice was to diagnose it properly with a Tech2 scan tool, not throw parts at it.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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