Will not start after throttle body cleaning and wet combustion check

Kernhills

Original poster
Member
Mar 15, 2016
5
Phelan, CA
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 :smile: Should I toss out the $60 worth of new plugs and try putting in my old? Is this more than likely a problem with the throttle body now that I cleaned it? It was running very well (minus the slightly rough idle) before this mess.... Thanks!!!
frown.gif
 

Mounce

Member
Mar 29, 2014
13,667
Tuscaloosa, AL
I would say it's from the oil in the cylinders from your wet compression test before I'd point fingers at the throttle body cleaning or plug change which many of us have done without such issues. Smoke from the exhaust while it runs?
 

Kernhills

Original poster
Member
Mar 15, 2016
5
Phelan, CA
Yes, lots of smoke from when it runs. It will start and run rough for 3-5 seconds if I hold the accelerator all the way down. Lots of smoke... I just pulled the plugs again. 1,3,4,5 are a little oily (still mostly clean) but 2 and 6 are burnt black. Should I put the old plugs back in maybe and see if I can get it to start and burn up that oil?
 

Kernhills

Original poster
Member
Mar 15, 2016
5
Phelan, CA
Won't hurt to try. Gotta get all of the oil burnt out so it'll quit fouling the plugs somehow.

Copy that... What a mess... Shopvac didn't seem too effective lol... SOmeone suggested putting some carb cleaner in those two cylinders but that seems like a risky idea to me...
 

Mounce

Member
Mar 29, 2014
13,667
Tuscaloosa, AL
I honestly have no idea how to get it out other than getting it to burn out by running it.

Seems that you might have been a little too liberal with the oil dosage, doesn't seem that a test as such would be recommended if it normally has such outcomes.
 

Kernhills

Original poster
Member
Mar 15, 2016
5
Phelan, CA
I honestly have no idea how to get it out other than getting it to burn out by running it.

Seems that you might have been a little too liberal with the oil dosage, doesn't seem that a test as such would be recommended if it normally has such outcomes.

I'm sure I was in hindsight... tried to pour a few drops but I'm sure it was most likely too much. I'll keep on it then and see how it goes. Wondering if a heat gun would be any help either... just thinking out loud here. I appreciate your input immensely!!!!!!!
 

gmcman

Member
Dec 12, 2011
4,656
I guess you could clean the plugs and try to let it idle until you burn off all the oil residue. I wouldn't keep adding liquids to the chamber to reduce the risk of accidental hydroscopic lock.

Maybe crank the engine over a dozen times with the plugs out first,

Once it fires let it idle, don't rev the engine until it smoothes out. Maybe even use the old plugs to get it back to normal so you don't risk permanently fouling the new plugs.

If one plug doesn't fire for an extended period you may fuel foul it and then you're better off just replacing it at that point.

If that were mine, I would use the old plugs to get it running and install a fresh set of plugs.
 

Kernhills

Original poster
Member
Mar 15, 2016
5
Phelan, CA
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. Thanks for your help with this :smile:
 

mrrsm

Lifetime VIP Donor
Supporting Donor
Member
Oct 22, 2015
7,639
Tampa Bay Area
Without knowing exactly how much oil was deposited inside each cylinder and realizing that Oil and Water share the dangerous feature of being incompressible... the safest approach to take is to remove ALL the spark plugs... then spray a very light amount of WD-40 with a long nozzle tube in a sort of semi-circle around inside each cylinder and with the plugs all still out... lightly pack some rolled up paper towels by poking them carefully down inside each spark plug well...but NOT far enough down to block the spark plug holes.

Now...with either a brand new battery...or two for swapping out if needed...or a well-charged one... Crank the motor over for 30 seconds over five intervals... separated by a few minutes in between each one to avoid damaging the starter...and change the paper towels in the spark plug wells after each interval so you can see what is being ejected or blown out and stuck to them and not all over the engine and you during each 30 seconds of turn over time. Afterwards ...leave things rest for about 5 -10 minutes... then clean out the spark plugs wells with fresh absorbent towels one last time and re-install all of the spark plugs....sprayed out on the tips with brake cleaner and bone dry B4 you re-install them.

Turn the Ignition Key to the First Start Position so you can listen for the Fuel Pump Prime... and then start the engine AT IDLE... You need to give the engine a chance to allow the atmospheric Fuel-Air conditions to normalize while the PCM tries to sort out what is happening. If the engine sputters..but keeps running...let it...Don't press on the gas pedal just yet. If it keeps running at idle...albeit rough as a cobb...give the engine a chance to warm up and burn off the residual oil and WD-40 still lingering inside. If it keeps going after that...while still parked... elevate the RPM to 1,000, then 1,500 and finally keep it purring at around 2gs for just a minute or so. Then shut the motor down and wait 5 Minutes. After that...see if your ordinary Start-Up procedure works as before.

It is not a hard thing to do to hydro-lock an engine in this fashion and either bend connecting rods or do serious damage to the bottom end... so by getting whatever is left inside all those cylinders removed... the spark plugs will have a better chance of burning vaporized gasoline and air... instead of the fuel designed for an Oil Burning Diesel Locomotive.

You have a fairly High-Mileage Engine...which means that a fair amount of residual carbon has accumulated inside each cylinder head combustion chamber and covering the piston tops. When exposed to oil.... as the carbon deposits soften...they can fall down inside the cylinder and as the pistons cycle up and down... the pieces of carbon (which to some degree ARE compressible) can get wedged into the Spark Plugs and foul or short them out and around the Valve Seats, too. This is what the inside of my GM 4.2L Engine looks like after 240,000 Miles... The amount of carbon deposits in there is NOT trivial:
DSC05485.jpg




DSC05446.jpg



http://s557.photobucket.com/user/60...INEREPAIR/TRAILBLAZEREPAIRTOOLS?sort=3&page=1
 
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