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2005 chevy trailblazer_ls
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Discussion Starter #1 (Edited)
So my 05 Trailblazer began running rough a couple days ago.It was slightly choppy sounding with a misfire also.I bought a scanner and pulled codes earlier tonight.Two map sensor codes were present,but Im almost 100% sure they're from 3 months ago when I had Autozone pull codes which lead me too replacing the map sensor at that time?? I never cleared those codes out because I didn't have a scanner and I didn't wanna disconnect the battery cable because the throttle body was dirty & I was afraid the PCM would relearn the idle to a dirty tb.So the following codes are the ones I got tonight,including those two map codes.
P0106
P0107
P0128
P0303
P0014

P0106/P0107 are map sensor codes,but I believe they're from months ago,so they may/may not be valid for my current issues.
P0128 is a ect code,but I ran the code scan
only a couple minutes after the vehicle was started,so the engine not being at operating temp may be the cause of this code??
P0303 is a misfire in cylinder #3.This is a valid for sure with the symptoms Im having.
P0014 is the cam position sensor,but from my research this may be caused by dirty/ clogged oil passages/screens on the cam
actuator solenoid valve.

I pulled the spark plug for the #3 cylinder and it had electrode wear and the insulater had some rust on.The coil on plug had some whitish/grey crusty material on the top of the spring & on the rubber boot.I don't believe replacement of just the spark plug is gonna rid the issue,so would it be worth swapping the #3 & #2 coil on plugs out with each other,then clear the codes with the scanner and start it up and let it run for a few minutes and shut it off then pull codes and see if the misfire moved to cylinder #2?? Im gonna clean that spring off also_Or is it gonna take me driving the vehicle first before I can get the pcm to pick up any codes?? Can the cam position actuator solenoid valve being dirty cause my symptoms?? BTW - I was slightly overdue on an oil change and wondered if that could have been a partial cause for the symptoms too,so I done an oil/filter change last night but a few minutes of runtime didnt help clear any symptoms.Suggestions/ Recommendations

The Trailblazer is used so Im unsure about its service/parts replacement history.The coil on plugs are Delphi so I assume theyve been replaced before,otherwise AC Delco cop's would have been in place and they wouldve looked rough from being factory or newer looking from replacement previous owners had done.AC Delco is the GM brand cop,correct?? 160,000 miles.
 

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2005 chevy trailblazer_ls
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Discussion Starter #2
Update:

So I removed the spark plug & coil on plug for cylinder #3,installed a new spark plug,reinstalled everything and started the engine.The symptoms were still present.So
I removed the cop for cylinder #3 again then I removed the spark plug & cop for cylinder #2,installed a new spark plug then I moved cylinder #2's cop to cylinder #3's location and moved cylinder #3's cop to cylinder #2's location.I cleared the codes out,started the engine and let it run for a few minutes,then I shut the engine off and ran a code scan again.This time,the p0303 misfire code changed to p0302.So the misfire code followed the cop that I moved from cylinder #3 to cylinder #2.I cleared codes again and ran the test one more time after letting it run for a few minutes & p0300 came up this time. So Im gonna try replacing the cop tomorrow and hope it works.If it doesn't,my next move will be removing/cleaning the camshaft position actuator solenoid valve,since it was a code I originally had.If anyone else knows of any other tricks I should do,feel free to comment.
 

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2003 chevy trailblazer_lt_ext
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sounds like you have it well looked after.
I have replaced all my coils after similar issues with misfires. In fact I can change a coil in less than 8 minutes with a flat screwdriver and a 10mm socket wrench. I gave up on the "off shore" coils and forked out major dollars for a full set of Delphi coils only to have them start dropping like flies. Now I carry a spare coil and tools to change roadside when needed.

Knock wood.....its been almost 2 years since last one failed...I still carry the spare
 

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Discussion Starter #4 (Edited)
Will one bad cop really cause it to idle that bad?? I thought I would try starting it and disconnecting the cop harness to see if it continues running rough or gets worse.If it doesn't make any noticeable difference,then that would 100% verify it as bad.Any idea why it showed up as p0300 vs p0302 on my last scan?? Or is it possible I just didn't let it run long enough to set p0302 again instead of p0300?? Have you had issues with the cam actuator solenoid valve being dirty or missing screens,etc?? Was wondering if I should pull it out and clean/inspect it then reinstall and run it before I replace the cop??
 

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You are on the correct path. Disconnecting the coil wire one at a time will locate the offending coil pack. Remove wire....idle worsens = good coil. Remove wire...no change in idle= misfire found.

The codes will sometimes be as you described. The P0300 is a generic code indicating the computer has sensed a misfire. After some time the code may become P0301, 0302, etc showing which cylinder


Frustrating but seems to be a common problem with triggers ranging from water running under back of hood and soaking the wiring harness to a total mystery cause.

That's why I started carrying spares :cry:

AND yes, one coil will affect the power and smoothness of the engine in a massive way. The Check Engine Light will flash indicating "shut down now !" or risk damage to emissions systems (Cat)


Otherwise, great truck.
 

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Discussion Starter #6
I followed your advice and disconnected #2,3 & 4 coil on plug harness and cylinder #2,which is the coil on plug I moved from #3 cylinder to #2 cylinder,didn't trigger any change in how the engine was running.So
I ordered a new Delphi cop from RockAuto and it should be here by Wed hopefully.I also
removed the vvt solenoid and cleaned it out thoroughly with carb cleaner.Im gonna remove the throttle body tomorrow and clean it too because of how dirty it is,since Ive gotta wait on the cop to get here.When I connected the code scanner to it & ran live data on it,the tp was reading 25-30% at idle.
Does that sound right or is that too high??
Well I'll get off here for now and I'll clean the throttle body tomorrow then update after the cop gets here and I get it installed.Thanks for the info.
 

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If the check engine light is on it’ll spit out a code. After you clear them you still gotta drive a bit to allow the Trailblazer to run it’s own diagnostic. Could be 50 miles?? If it catches anything the check engine light will turn on.

Once you find the misfire & the truck at least runs better might be a good idea to clear the codes. It might be like starting over however you’d mostly likely nail the problem accurately from here.
 

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I followed your advice and disconnected #2,3 & 4 coil on plug harness and cylinder #2,which is the coil on plug I moved from #3 cylinder to #2 cylinder,didn't trigger any change in how the engine was running.So
I ordered a new Delphi cop from RockAuto and it should be here by Wed hopefully.I also
removed the vvt solenoid and cleaned it out thoroughly with carb cleaner.Im gonna remove the throttle body tomorrow and clean it too because of how dirty it is,since Ive gotta wait on the cop to get here.When I connected the code scanner to it & ran live data on it,the tp was reading 25-30% at idle.
Does that sound right or is that too high??
Well I'll get off here for now and I'll clean the throttle body tomorrow then update after the cop gets here and I get it installed.Thanks for the info.
Sounds good.
Have you cleaned the throttle body before? Make sure you follow the correct procedures to prevent any issues with the computer.

Hope it all goes well.
 

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Discussion Starter #9 (Edited)
Sounds good.
Have you cleaned the throttle body before? Make sure you follow the correct procedures to prevent any issues with the computer.

Hope it all goes well.

My plans are to install the coil on plug tomorrow or Wed when it arrives from RockAuto,then start it up and see if the idle/
misfire issues are gone.If they are,I'll remove the two fuses #10 & #28 that do the same thing as pulling the battery cable,then I'Il remove the throttle body and clean it, reinstall it then reinsert the fuses then start it up.Im worried that if I clean the TB now and it causes any issues,I won't know if the cleaning of the TB was the cause of it or something that was already present before I cleaned it.Its definitely nasty though so I'll for sure be cleaning it.Is it possible to remove the throttle plate for easier access to the entire bore or should it not be removed at all?? Ive read a few threads that stated you should never open the throttle plate by hand because it could damage the tb motor??If this is the case,could I remove it & clean everything accessible with the throttle plate closed,then reinstall it,lay something against the gas pedal to keep the throttle plate in the fully open position & reach in with a carb cleaner soaked rag to get any remaining buildup out??
Another question I have is how do you release the vacuum hose from the throttle body??
When I ran the code scanner in the "view freeze frame data" it showed the tp sensor
being between 26-31%.Is that a normal value/position at idle??
 

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I agree with your plan. Clean the TB after you switch out the coil.
You can fire up the engine without all the airbox etc so if all goes well then you are ready to remove fuses and go after the TB cleaning.
I'm not familiar with the numbers you are getting on the scanner so I cant assist with that.
As for moving the butterfly on the TB, once you kill the voltage and unplug the TB I believe you are good to move the butterfly for cleaning. From what I know it is only when the TB is part of the live system that moving it manually causes problems, BIG problems. I have cleaned mine many times and have always manually moved the plate once removed for cleaning.

I hope you have success after Rockauto comes thru tomorrow.
 

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Discussion Starter #11 (Edited)
Thats good to hear about being able to manually opening the throttle plate without any damage.For the last 6 months,the mil would come on & remain on for between 5-10 drive cycles & it would trigger a drastic increase in fuel usage.Once the mil turned off,it would remain off for about 5 drive cycles and fuel usage would go back to normal.That was when I had a map sensor code only.The pcm was either richening the fuel trim because the o2 was reading a lean condition or it was simply richening it for some other reason.I replaced the map sensor,but never cleared the code.Im hoping the throttle body cleaning clears that issue up because its pretty dirty and Ive read a bunch of threads where cleaning it solved many driveability issues,so we'll see.
Well I can't believe it.My girlfriend just hollared up the stairs & said Fedex just arrived.I can't believe how fast the part arrived.I didn't order it til Sunday night & its Tuesday morning and its already here.Guess its time to jump into my get dirty outfit and go drop that cop in.Thanks so much for your help so far & I'll update shortly.Oh yeah,whats the trick to getting that vacuum hose to release from the throttle body?? Do I just squeeze the sides in or is there a clip on it that has to be removed?? Talk to ya again after awhile.
 

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Discussion Starter #13 (Edited)
Success

@ Wcosh,
Well,finally got everything done.I replaced the spark plugs,one defective COP,cleaned the throttle body & cpas & done a oil change with a switch to synthetic.I haven't done a test drive yet,but the rough/choppy idle,mis-firing,mil,codes & the rich condition are all gone now,thank goodness.The vacuum hose
I asked you about,just required me to grab that little tab on the right side of the hose fitting,pull it towards me then down and pull
the hose fitting towards me while keeping that tab pushed down.
One thing I do have to check tomorrow though is a oil leak.The oil drain plug didn't have a gasket on it and I thought it might have been the cause of the leak because I seen a couple drips from the drain plug,but when I started searching with a flashlight, I saw some oil that had pooled up on that plate, that sits directly under the oil pan,so tomorrow Im gonna remove that plate to see if I can pinpoint the leak.If it happens to be the oil pan gasket thats leaking,I'll check the oil pan bolts first to make sure they're not loose & if not,the oil pan cannot be removed with the engine in place,can it??My luck tells me no. BTW- its a RWD so there aren't any 4wd components that could be the cause of a leak in that area.Im fixing to browse through my 30 day Alldatadiy subscription that I received with my scanner purchase to see if theres anything else in that general area that could leak,but do you know of anything either under the block or on the lower driver side of the block that could leak oil or thats at least what it appears to be is oil??I was wondering if maybe my switch to synthetic oil could be a possible cause of the leak also,but Ive only let the engine run for a total of 5 minutes since I finished the work above,so I doubt it could be related?? Well anyhow,I'll dig into it first thing in the morning & post my findings afterwards.Thanks again for the help & advice.
 

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Oil drain plug

If the oil drain plug doesn't have a gasket, it is going to leak, Duh!!!
Napa has a replacement plug with a gasket or the gasket available separately.
 

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There is an oil sensor above where the oil filter screws on. My TrailBlazer had a leak from that sensor. I replaced the sensor and that fixed the leak. It is hard to see the area around the sensor, but get a flashlight, and look from the top and bottom to see if that is where your oil leak is coming from.
 

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Discussion Starter #17
Well it actually turned out being a coolant leak instead of an oil leak.That plate thats bolted to the underside of the vehicle,under the oil pan,had some old caked on oil/grime sitting on it and coolant was running down from the water pump,then falling onto that grimy plate then dripping off the plate to the ground and also dribbling down the oil pan,which would then drip from the oil drain plug every minute or so.It wasn't doing it too much with the engine running,but once I shut the engine off,thats when it would start dripping the most.I guess once the coolant had sit long enough on that plate,it would mix with the grime and once it began dripping from the oil drain plug,it appeared like an oil leak from the drain plug,especially considering the plug gasket was missing.If the oil would've been black from being old,I instantly would have known it wasn't oil that was dripping,but since the oil was new,it was harder to tell if it was oil or coolant.It was also too thin to be oil once I rubbed it between my finger & thumb.The previous owner had put some teflon tape or sealant on the plug to keep it from leaking and the plug had never leaked since Ive owned it.I had read threads about synthetic oil possibly doing something to any seals & gaskets,so I thought the oil could have been the cause of the leak,eventhough the drain plug had tape/ sealant instead of an actual gasket,which the oil could have affected.So tomorrow Ive gotta get a water pump from the parts store and tackle that problem.Because of the area where the leak was occurring,Im glad it turned out being a coolant leak vs oil leak because an oil leak would have meant the oil pan gasket was likely to blame,if the drain plug was ok.Id much rather replace a water pump vs pan gasket.
 

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Taste test?

Next time you have an unidentified leak, after rubbing it between your fingers, just touch your finger to the tip of your tongue. The taste of antifreeze is very distinct and unforgettable.
 

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Good that you figured that out. I do not remember my drain plug having any gasket on it, but it has never leaked. Anyway if you do get an oil leak you now know something else to check.
 

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Discussion Starter #20
Next time you have an unidentified leak, after rubbing it between your fingers, just touch your finger to the tip of your tongue. The taste of antifreeze is very distinct and unforgettable.

I had too much grease and grime on my hands to distinguish it as coolant or oil,if I would've done the taste test.LOL.
 
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