Issues starting, coolant gauge not reading.

[Mothman]

Hi again.

After my last post back in February, I no longer had issues with my brother's 2005 4.2L I6 Trailblazer. It didn't last long.

About three weeks ago, it started really acting up. It would just crank and crank, but not turn over. That was unless you floored the gas pedal, then it would reluctantly start up, but run like garbage, spluttering and not running smoothly. On the second try, it would almost do the same thing but keeping the pedal to the floor, the engine would rev up, whereas it wouldn't do that on the first try. This was an issue every other start up. There would also be a decent amount of smoke pouring out of the exhaust and a fairly strong gas smell. (I hope that makes sense)

It hit a high just this past Monday when I went to start it up. I followed the same procedure of starting it twice with the gas pedal pressed to the floor. It started and ran ok. It was idling around 1500 RPMs which is a little high for this trailblazer. When I put it into drive, it almost shot off versus just slowly moving when the gas pedal isn't pressed. The trailblazer started accelerating high enough that it was shifting into 2nd gear without the gas pedal being pressed. When I shifted into neutral, it would rev up to almost 3000 RPMs. It would stop when I pressed the brake pedal in all the way, but I could feel it fighting against it. It only did this for about 2 or so minutes before it went back to normal. Since then, the trailblazer has started up first try with no issues.

Along side all this, the coolant gauge stopped working and the "check gauge" light came on. Coolant was still making its way through the engine thankfully. It was however reading that the coolant was -40 degrees F. I replaced the coolant temp gauge with an Echlin one from Napa. It worked once on the first start up, but stopped reading on every start up afterwards. I haven't checked any electrical connections or for voltage anywhere.

I can still occasionally smell gas or exhaust when I'm driving with windows down.

Any help would be appreciated. Thanks.

 

[Mooseman]

When starting it with the pedal down, it's basically in flood clearing mode which turns off the injectors and fully opens the throttle body. That tells me that too much fuel is getting into the engine along with the exhaust smoke and rough running. Two ways this can happen; the injectors are leaking or the fuel pump's pressure regulator is faulty and not regulating the pressure.

Check the fuel pressure and see what it does when you turn the key to RUN but not start it. The pump will prime for a few seconds and stop. If the pressure is too high (over 60 PSI) and doesn't drop or drops to a lower pressure, then the pump will need to be replaced as the pressure regulator is integrated in the pump module in this returnless system. If the pressure drops from a normal pressure (50~60 PSI) to 0, I would suspect the injectors are leaking. The only way to further confirm this would be to do an injector balance test sung a Tech 2 or other advanced scan tool.

One word of warning, be careful hooking up the pressure gauge to the fuel rail's test port. It's in an awkward position and the gauge's hose can put some pressure on the rail tubing and crack it. Ask me how I know.

 

[mrrsm]

The Symptom of Over-Revving you describe sounds like the Butterfly Plate inside the Throttle Body might have gotten --Stuck Solid-- by a Ridge or Ring of Dirt and Inhaled Blow-By- passing through with Un-Burned Gasoline and Partially Combusted Exhaust Fumes getting past the Pistons' Upper Compression Rings. This causes a Brown "Gas-Gum MUNG" Lacquer to collect and form a Durable Gummy Dirt Ring. Thus, this condition can serve to Prevent the Plate from Returning to its ordinarily Spring-Loaded CLOSED Position:




The GM 4.2L Engine is a motor that is controlled by the Regulation of --AIR--. So, regardless of WHAT it was that was holding that Butter-Fly Baffle OPEN...as long as MORE AIR was allowed to become ingested... the PCM would respond by allowing in --MORE FUEL --in an effort to allow for a Stoichiometric AIR to FUEL Ratio to maintain itself in Balance.

The Reason the Engine failed to over-rev to the Redline at around 6,500 RPM is that whenever the Park Neutral Safety Switch is engaged and Shifted into either Park or Neutral... the PCM places an UPPER LIMIT on Engine Rotations to 3,000 RPM via its programmed Rev-Limiter.

Pull the Throttle Body completely off of the Intake Manifold and Bench Clean it with a Proper Carburetor or Throttle Body Cleaner...NOT Brake-KLEEN. @MAY03LT 's Classic TB Cleaning Video shows how this work is done RIGHT:

*Click On" "Watch On YouTube" to View this:

And Kenny from "GRIME TIME" Shows us all... Just How BAD This Condition Can REALLY Get...

 

[Mothman]

I had checked the gas psi back in February and it stayed consistently at 57psi, plus or minus 1, regardless of key position. I checked it again earlier today and I had the same results. I let it sit under pressure and it still stayed at about 57 psi. When the engine was running, it hit 60psi, but never gained more pressure nor did it lose any.

I have done a less intrusive cleaning of the throttle body before, but when I get the chance, I will definitely remove it and do a thorough cleaning of it.

Any thoughts on the coolant gauge not reading?

 

[mrrsm]

Look around the position(s) where the Coolant Temp Sensor is located (At the Upper Left Side of the Early Model GMT360s and in the Upper Right Rear of the Later Models LL8 Motors) ...seeking any signs of the Sensor Harness Connector being loose, damaged... or EATEN away by Rodent Depredation.

Do likewise around the Throttle Body Harness for the same reasons. PLEASE... If you see ANY Signs like these depicted below... Wear Eye Protection, M11 Nitrile Gloves, and an N-95 Face Mask and AVOID USING COMPRESSED AIR DURING CLEAN-UP. Use Wet Wipes soaked in 5% Liquid Bleach or Calcium Hypo-Chorate in Water.

The Airborne HANTA Virus gets into the Lungs and Open Mouth, Eyes and Nose after the Desiccated Feces, Urine and Saliva of Rodents becomes disturbed, either by sweeping or from agitated dusting.

The North American Deer Mouse is the dominant Vector up North and is carried as "The Black Creek Canal Fever" by Hispid Cotton Rats down here in the southern USA (and in particular, Arkansas as covered in the Linked Article below). Be Thoughtful and Cautious here.. This Infection KILLS 40% of its Victims and destroys the Quality of Life for its Survivors!

Images Courtesy @christo829:

Novel Ozark Orthohantavirus in Hispid Cotton Rats (<em>Sigmodon hispidus</em>), Arkansas, USA

Novel Ozark Orthohantavirus in Hispid Cotton Rats (<em>Sigmodon hispidus</em>), Arkansas, USA

wwwnc.cdc.gov

Cotton Rat

 

[Mooseman]

Another thing about the throttle cleaning, don't forget to disconnect the battery for 30 minutes while cleaning it. This will reset the PCM for the idle settings.