Hey all.. well on my 04 4.2l. After replacing the ac compressor and running the vehicle through some high water due to flooding in my erea. It just loses power when climbing up to speeds above 60. I practically have to force it to downshift to get it to stay at about 70 if I'm lucky to get it there. Strangely enough with cooler temps outside around 80 it runs like a champ. But when it gets to 90 or higher it's just a dog. Haven't noticed a huge decrease in fuel mileage. There is a leak in the exhaust manifold side. Hasn't thrown any codes whatsoever. Fuel filter, plugs, coils air filter all new. I'm at a loss. Is there a possible sensor that reads temps causing it to run this way? Any input is super appreciated.
NEED HELP Loss of power after....
- Thread starter BigSilver
- Start date
Unplug your MAF, and try driving it again. It will throw a check engine light, but it will go into a base default value in the ECM.
If it drives better, than you have found your problem.
If it drives better, than you have found your problem.
Hmmm... May not be the MAF involved in this particular instance...
But depending upon your Mileage (If VERY High) and your Historical Misfire Counts with any P03XX Codes... (P0300 to P0301-P0306) then You might have a Clogged (Poisoned) CAT causing Back Pressure and Killing Power whenever driving at Higher RPM and under Higher Engine Loads while at Highway Speeds...
One EZ Test for this Issue is... With the Vehicle PARKED AND WHEELS CHOCKED... ENGINE OFF AND PARKING BRAKE SET FOR ANY INCLINES...
(1) Lay Down a Large Piece of Clean Cardboard under the Passenger Side of the SUV.
(2) Recline upon it and after getting comfortable... Take a "Dead Blow" Hammer and VERY GENTLY *Tap-Tap-Tap* on the underside of the S/S CAT CAN and Listen for the sound of "Coins being dropped into a Ceramic Bowl" ...sort of sound.
(3) If you can hear any such *Tinkling Re-Bound Sounds*...then it means that the Rare Earth Impregnated Ceramic Honeycomb Insert might have Fractured and Fallen down inside of the CAT CAN and thus, render an obstruction to any High Flowing Exhaust Stream... causing a Back Pressure event.
Performing Other Tests is the right approach... Such as doing a (Relative) Non-Invasive Compression Test using an Oscilloscope to read the Amperage Draw during the Short 10-15 Seconds of Starter Activation while using an AMP Clamp fitted around the Positive Battery Cable (The Negative Cable will also work by flipping the AMP Clamp Over). This approach can easily reveal LOW Amperage Draw changes on any Cylinders with LOW Compression.
This is the Least Invasive of the Two Compression Test Methods (versus a much more Hands On "In-Cylinder" Compression Test) but it does require an inexpensive Oscilloscope connected to your Laptop Computer using FREE PICO-Scope Automotive Software to view the rising/falling Amperage Draws per Cylinder. LOW Compression always produces LOW Power during Combustion Events.
Having Broken or Worn Out Compression Rings and Ovaled-Out Cylinder Walls or Leaking Valves will also produce LOW Compression Events as well. These issues are caused "Mechanically" and thus "Marvel Mystery Oil" and other such solutions will not make any lasting improvement and so, the corrective action might require extensive internal repairs.
If this turns out to be the case... Swapping in another Low Mileage 4.2L Engine of Like Vintage (As Rare as Hen's Teeth) is preferred to attempting the R&R of the GMT360 Atlas Engine (17) Bolt On Head via frequently *Snapping Off* Head Bolts or any secondary repairs while the Old Motor is still located in the Engine Bay. Instead... Choosing the Low Mileage Replacement Motor Route is a Much Better Long Term Solution.
Even though the VOP (Video Original Poster) below is a "Brit" and thus, may not be working on North American GM Products... Nonetheless ... He absolutely knows his *Stuff* around Automotive Diagnostics... especially when Demonstrating the Inexpensive PICO-Scope Model# 2204A unit married to the Hantek Model# CC-650 AMP Clamp while performing tests like these for Relative Compression.
Note that for a Visual, Identity Reference, he chooses to pick up the Ignition Coil Signal from the #1 Cylinder... but protects the PICO-Scope on the #2 Channel-B by first installing a Hantek Model# HT201 ... a 20:1 Voltage Attenuator BNC Unit ...and he explains WHY this is required for High Voltage Readings during this Test:
For More On Site GMT Nation "Oscilloscope Dope" In-Sight ...Visit THIS Link:
gmtnation.com
But depending upon your Mileage (If VERY High) and your Historical Misfire Counts with any P03XX Codes... (P0300 to P0301-P0306) then You might have a Clogged (Poisoned) CAT causing Back Pressure and Killing Power whenever driving at Higher RPM and under Higher Engine Loads while at Highway Speeds...
One EZ Test for this Issue is... With the Vehicle PARKED AND WHEELS CHOCKED... ENGINE OFF AND PARKING BRAKE SET FOR ANY INCLINES...
(1) Lay Down a Large Piece of Clean Cardboard under the Passenger Side of the SUV.
(2) Recline upon it and after getting comfortable... Take a "Dead Blow" Hammer and VERY GENTLY *Tap-Tap-Tap* on the underside of the S/S CAT CAN and Listen for the sound of "Coins being dropped into a Ceramic Bowl" ...sort of sound.
(3) If you can hear any such *Tinkling Re-Bound Sounds*...then it means that the Rare Earth Impregnated Ceramic Honeycomb Insert might have Fractured and Fallen down inside of the CAT CAN and thus, render an obstruction to any High Flowing Exhaust Stream... causing a Back Pressure event.
Performing Other Tests is the right approach... Such as doing a (Relative) Non-Invasive Compression Test using an Oscilloscope to read the Amperage Draw during the Short 10-15 Seconds of Starter Activation while using an AMP Clamp fitted around the Positive Battery Cable (The Negative Cable will also work by flipping the AMP Clamp Over). This approach can easily reveal LOW Amperage Draw changes on any Cylinders with LOW Compression.
This is the Least Invasive of the Two Compression Test Methods (versus a much more Hands On "In-Cylinder" Compression Test) but it does require an inexpensive Oscilloscope connected to your Laptop Computer using FREE PICO-Scope Automotive Software to view the rising/falling Amperage Draws per Cylinder. LOW Compression always produces LOW Power during Combustion Events.
Having Broken or Worn Out Compression Rings and Ovaled-Out Cylinder Walls or Leaking Valves will also produce LOW Compression Events as well. These issues are caused "Mechanically" and thus "Marvel Mystery Oil" and other such solutions will not make any lasting improvement and so, the corrective action might require extensive internal repairs.
If this turns out to be the case... Swapping in another Low Mileage 4.2L Engine of Like Vintage (As Rare as Hen's Teeth) is preferred to attempting the R&R of the GMT360 Atlas Engine (17) Bolt On Head via frequently *Snapping Off* Head Bolts or any secondary repairs while the Old Motor is still located in the Engine Bay. Instead... Choosing the Low Mileage Replacement Motor Route is a Much Better Long Term Solution.
Even though the VOP (Video Original Poster) below is a "Brit" and thus, may not be working on North American GM Products... Nonetheless ... He absolutely knows his *Stuff* around Automotive Diagnostics... especially when Demonstrating the Inexpensive PICO-Scope Model# 2204A unit married to the Hantek Model# CC-650 AMP Clamp while performing tests like these for Relative Compression.
Note that for a Visual, Identity Reference, he chooses to pick up the Ignition Coil Signal from the #1 Cylinder... but protects the PICO-Scope on the #2 Channel-B by first installing a Hantek Model# HT201 ... a 20:1 Voltage Attenuator BNC Unit ...and he explains WHY this is required for High Voltage Readings during this Test:
For More On Site GMT Nation "Oscilloscope Dope" In-Sight ...Visit THIS Link:
How To Use PICO #2204A & HANTEK #1008C Oscilloscopes
You don't need a Huge Bag of Coins in order to obtain and use an Oscilloscope for performing In-Depth Wave Form Analysis in Automotive Applications on everything from Problematic Electronic Fuel Injection to obtaining accurate Compression Tests to Diagnose Internal Engine Conditions. HANTEK...
gmtnation.com
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"IF" the Relative Compression Test reveals the Culprit On Screen... Perform the "Hands-On" Method of checking out the "Suspect Cylinder" by pulling that particular Spark Plug and replacing it with a Compression Test 14mm Adapter. Then attach a Low Pressure Air line onto the Adapter to provide a constant supply of low pressure air into the Cylinder. This requires ensuring that the Overhead Intake and Exhaust Valve Lobes are sitting LOW on their Base Circles with both the Intake & Exhaust Valves...ARE ALL CLOSED while nearing TDC (Top Dead Center)....Then...
(1) Listening at the Exhaust Pipe for the "Hiss* sound of Escaping Air will confirm Bad Exhaust Valves.
(2) Removing the Air Plenum-Resonator and GENTLY opening the Throttle Body Plate and hearing the out rush or *Hiss* of escaping Air will confirm Bad Intake Valves.
(3) Removing the Oil Filler Cap and Listening for that familiar *Hiss* of air escaping from within the Crankcase-Oil Pan...will confirm the presence of either having Gas-Gum Trapped, Low Tension Compression Rings ****...or a Worn Cylinder with Badly Worn Compression Rings.
**** Try using the ACDelco TEC (Top Engine Cleaner) Foam Can Method for Soaking the Cylinders with this POWERFUL Solvent to dissolve the Carbon Mung- Gas-Gum Trapped Low Tension Compression Rings and allow them to "Spring" Outwards again and aid with Improving Their SEALING Abilities during the Compression Stroke of the (4) Cycle Events.
Visit THESE GMT Nation Thread Links for More Information on How to Use ACDelco TEC:
(1) Listening at the Exhaust Pipe for the "Hiss* sound of Escaping Air will confirm Bad Exhaust Valves.
(2) Removing the Air Plenum-Resonator and GENTLY opening the Throttle Body Plate and hearing the out rush or *Hiss* of escaping Air will confirm Bad Intake Valves.
(3) Removing the Oil Filler Cap and Listening for that familiar *Hiss* of air escaping from within the Crankcase-Oil Pan...will confirm the presence of either having Gas-Gum Trapped, Low Tension Compression Rings ****...or a Worn Cylinder with Badly Worn Compression Rings.
Amazon.com : engine compression test kit
www.amazon.com
**** Try using the ACDelco TEC (Top Engine Cleaner) Foam Can Method for Soaking the Cylinders with this POWERFUL Solvent to dissolve the Carbon Mung- Gas-Gum Trapped Low Tension Compression Rings and allow them to "Spring" Outwards again and aid with Improving Their SEALING Abilities during the Compression Stroke of the (4) Cycle Events.
Visit THESE GMT Nation Thread Links for More Information on How to Use ACDelco TEC:
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