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Chevy Forum: Wont Start After Wet Compression Test and Throttle Body Cleaning
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  #1  
Old 03-15-2016, 07:09 PM
kernhills kernhills is offline
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Unhappy Wont Start After Wet Compression Test and Throttle Body Cleaning

First off, thanks for helping out a newbie on the forum here... I just bought a 2005 Trailblazer with 155,000 miles. I had trans flushed and mechanic said it needed a tuneup. It was running very well but had a bit of a rough idle. I had to get it smogged for ownership transfer (thanks CA), so I wanted to do the tuneup prior to. When I pulled the plugs I found a small amount of the infamous oil in the plug wells (have since learned from your forum about replacing the valve cover gasket, we'll tackle that one day). I replaced the plugs with AC Delco Iridiums (as also recommended). When I started back up, the idle was exactly the same. A mechanic on a paid site I've used before suggested I do a wet/dry compression test and clean the throttle body. I did the test and posted the numbers for his review (which all looked good). Cleaned the throttle body by removing it completely and using throttle body cleaner and a toothbrush (it was extremely dirty). I had the battery disconnected for about an hour, and also pulled the two PCM fuses during that time. So... Reassemble, and now the thing wont start.... Cranks, runs for 3-4 seconds VERY ROUGH, and dies. I can do that till the battery goes dead... I pulled the plugs and found there was oil on them from the wet test day before. I tried blowing out the plug wells with air, cranking motor without plugs to try and force some oil out, and cleaning the plugs themselves with carb cleaner. I reinserted them and still the same problem. The mechanic that recommended the wet test has no recommendation now, so here I am, HUMBLY asking for some expertise from this site :-) Should I toss out the $60 worth of new plugs and try putting in my old? Any other way to make sure I got all the oil out of the cylinders from the wet test? It was running very well (minus the slightly rough idle) before this mess.... Thanks!!!
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Old 03-16-2016, 10:16 AM
zora zora is offline
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Default Re: Wont Start After Wet Compression Test and Throttle Body Cleaning

Not sure how much oil you put in there but I would think removing all the plugs and cranking the engine over would blow out the excess oil. You sure you didnt damage the throttle body or have a vacuum leak from removing the throttle body? No chance you mixed up the spark plug wire sequence?
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Old 03-16-2016, 12:15 PM
kernhills kernhills is offline
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Quote:
Originally Posted by zora View Post
Not sure how much oil you put in there but I would think removing all the plugs and cranking the engine over would blow out the excess oil. You sure you didnt damage the throttle body or have a vacuum leak from removing the throttle body? No chance you mixed up the spark plug wire sequence?
Thanks for the message. I was fairly careful with the throttle body, other than it was very very dirty, and it took quite a bit of scrubbing with a toothbrush and cleaner to get everything off. I used my fingers to hold the flapper open while doing so, but I didn't disassemble it once it was off the truck. I'm hoping that's not damaged. The 5 and 6 coils are close to each other, but it looks like one wire set is further back in the harness than the other, so I believe those are in order also, the others are pretty clear. I may swap what I think are 5 and 6 for the heck of it and see what happens. Can't run any worse at this point.
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Old 03-16-2016, 03:27 PM
zora zora is offline
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Default Re: Wont Start After Wet Compression Test and Throttle Body Cleaning

you didnt mention which engine you have but i would look up the firing order and visually confirm the wiring before randomly switching 5 and 6. While the engine is running spray some throttle body cleaner around the throttle body to see if the engine runs smoother which would mean a vacuum leak. The mechanic who suggested cleaning the throttle body told you to remove it?
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Old 03-16-2016, 04:44 PM
kernhills kernhills is offline
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Default Re: Wont Start After Wet Compression Test and Throttle Body Cleaning

Quote:
Originally Posted by zora View Post
you didnt mention which engine you have but i would look up the firing order and visually confirm the wiring before randomly switching 5 and 6. While the engine is running spray some throttle body cleaner around the throttle body to see if the engine runs smoother which would mean a vacuum leak. The mechanic who suggested cleaning the throttle body told you to remove it?
Thanks for your help!! I have the 4.2l V6. When I looked closer, the wires only seem to reach to the length for each cylinder, so it seems kind of difficult to get them swapped accidentally. I'm 95% certain they are right based on that. The mechanic told me to unbolt it, remove it, and use throttle body cleaner, which I did. I did have to do some scrubbing with a soft toothbrush, but it all eventually came off. I did manipulate the plate with my fingers (opening/closing) to reach where I needed to for cleaning, I hope that didn't do something.

I did another dry compression test today after getting what seems to be all the oil out of the cylinders. The results were consistent with the dry test I did before any oil was ever added, which leads me to believe they are mostly dry now. I still have a very dark/burnt plug coming from #2 and #6 which were not that way when I pulled the originals. Also checked all my fuses, and those are good. Starting to think its something other than oil in the cylinders at this point.... Maybe a throttle body issue. Going to test spark at the coils next.
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Old 03-16-2016, 05:01 PM
kernhills kernhills is offline
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Default Re: Wont Start After Wet Compression Test and Throttle Body Cleaning

Sorry. Its the 4.2l v6. Yeah I think I have the coils in the right place, only seem to reach one spot nicely. I ran a dry test this morn and the numbers are all the same as the dry test prior to the wet yesterday, which leads me to believe they are dry at this point. Plugs in the #2 and #6 are coming out extremely black and charred (which was not what the originals that I removed looked like). Not sure if something went wrong with the throttle body from removing and cleaning, or possibly something else. I was instructed to remove it before cleaning, and use a soft brush and throttle body cleaner. It was very dirty, had to manipulate the flapper quite a bit to reach spots to clean. Thanks for your help with this :-)

Last edited by kernhills; 03-16-2016 at 05:11 PM.
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Old 03-17-2016, 08:44 AM
zora zora is offline
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Default Re: Wont Start After Wet Compression Test and Throttle Body Cleaning

Has the check engine light come on and if it has what is the code?
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