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2005 gmc envoy_sle
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22 Posts
Discussion Starter #1
Happy turkey day everyone , I'm having an issue with our envoy ,. I had a problem with miss fires , replaced the coil packs and spark plugs , cleared it up for a couple of weeks , now she would start like having another miss fire but clear up after warming up , scanned it and found out that the coolant temperature sensor is going , yesterday it was giving us trouble starting and was acting like it was miss firing again , well now she's running like she's in lump mode , so if anyone could give me advice on what they think is causing this it would be greatly appreciated , I have a hunch it could be the crankshaft position sensor. Thank you all in advance , and again Happy turkey day..
 

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Catalyst efficiency bank 2 , miss fire cylinder 4 , too lean bank 1 , thermostat code .
conveter code prob 0421 for bank 2 can be weak converter but prob just because you have a miss and it is not burning fuel up... 0304 for 4 misfire is probably moisture or coolant down in the plug well, recheck number 4 and I'd go ahead and put another new plug in there. A simple drop can damage a plug and it can mess up in a few 1000 miles.
Not sure what therm code is off top of head but could be an temp sensor to tell ecm the temp.
Some cars will go into limp mode or cyl cancellation if they overheat but I don't think the 4.2 does this.
Start with the #4 misfire and get that to go away.
 

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2005 gmc envoy_sle
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22 Posts
Discussion Starter #6
Happy turkey day everyone , I'm having an issue with our envoy ,. I had a problem with miss fires , replaced the coil packs and spark plugs , cleared it up for a couple of weeks , now she would start like having another miss fire but clear up after warming up , scanned it and found out that the coolant temperature sensor is going , yesterday it was giving us trouble starting and was acting like it was miss firing again , well now she's running like she's in lump mode , so if anyone could give me advice on what they think is causing this it would be greatly appreciated , I have a hunch it could be the crankshaft position sensor. Thank you all in advance , and again Happy turkey day..
Hey all I replaced the engine coolant temperature sensor and the MAP sensor and throttle body , it still running like it's miss firing , now there are 2 new codes P502 and P0622 , and the light that looks like the cel but has the arrow pointing down to the oil pan comes on and feels like it goes into limp mode , I spent 7 hrs trying to fix these issues , any help would be greatly appreciated thank you all.
 

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2004 chevy trailblazer_lt_ext
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33 Posts
One lesson i learned was putting in coil packs that weren't ac/delco. I initially used some cheaper brands, changed all six, and i thought i would never get it right again. Somehow, that is an engineers secret, the cheaper coil packs act on the engine computer causing all sorts of problems. I bit the dollar bill and bought the real ac/delco packs, (got them off amazon), changed them out, and the engine ran great. Then, I took the cheap packs and swapped them out one at a time in an attempt to find the fault, and sure enough, 5 out of the 6 caused wierd problems. I threw them in the trash after smashing. Sounds like you may have multiple problems though, with the coolant thing going on too. Hope this helps.
 

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2003 chevy trailblazer_ltz
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Did you clear codes, after scanning? I've had similar issues with our '04 Trailblazer, I bought a new MAP, and thermostat, which includes the lower housing it's located in, behind the alternator. I'll update after I swap it, to see if that ends the incorrect temp code. It's possible that your #4 coil connector is dirty causing a bad connection, though more likely that coil is defective. One way to narrow it down, is clear codes, swap coil with another cylinder, then see if the misfire moves with it. If it stays on #4, clean the connector, and replace the spark plug. You did not say, but are you using Delco coils, or cheaper replacements? I'd also clean all ground connections, paying particular attention to the block to body connection, as that can cause odd malfunctions, given the computer is mounted to the engine... Also it wouldn't hurt check the added grounds to the negative battery cable... I replaced the cam variable timing solenoid, which eliminated periodic code and limp mode, the oil filter screens in it were dirty, and one had a hole in it...
 
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