Kazza Posted September 1, 2022 Share Posted September 1, 2022 (edited) Hi guys, Bit of an odd one but recently I have noticed my QX4 seems to be struggling a bit. I find the auto transmission is always in a higher gear than normal when accelerating. It still cruises at highway around 2k rpm but it will drop a gear at the slightest gradient (even flat ground sometimes) when I apply even light acceleration, and too easily drops 2 gears and starts screaming above 3k rpm sometimes when it just really shouldn't be. I noticed this change around the same time my muffler broke away from the midpipe and my fuel lines took some serious heat from the exhaust fumes (even melted the carpet in the trunk) for a few days before I bandaided it back together. I was just running with the problem for a few weeks but yesterday my car almost overheated for the first time climbing a hill.. and now I'm faced with both issues and can't ignore it. Could the exhaust heat have kinked my fuel lines and affecting fuel delivery/pressure? I'm a bit at a loss as to what else could have caused this, no codes throwing. All maintenance done (apart from spark plugs slightly overdue). Edited September 1, 2022 by Kazza Link to comment Share on other sites More sharing options...
XPLORx4 Posted September 1, 2022 Share Posted September 1, 2022 Replace your fuel filter, check the air filter and if it's dirty, replace it. Spray off the radiator from the engine side to the grille. Check that your brakes aren't dragging by shifting into N on a flat surface and verify that it coasts as expected. Check and if needed, replace the fluid in the transmission, transfer case, and differentials. Check the condition of your spark plugs and replace if needed. Link to comment Share on other sites More sharing options...
XPLORx4 Posted September 1, 2022 Share Posted September 1, 2022 One last thing- Do you have a check engine light? If so, repair the cause of it. Link to comment Share on other sites More sharing options...
Kazza Posted September 2, 2022 Author Share Posted September 2, 2022 On 9/1/2022 at 1:46 PM, XPLORx4 said: Replace your fuel filter, check the air filter and if it's dirty, replace it. Spray off the radiator from the engine side to the grille. Check that your brakes aren't dragging by shifting into N on a flat surface and verify that it coasts as expected. Check and if needed, replace the fluid in the transmission, transfer case, and differentials. Check the condition of your spark plugs and replace if needed. Today I changed the fuel filter, spark plugs and I also pulled and cleaned the drivers side upstream (precat) o2 sensor (couldn't get to the passenger side) and cleaned the throttle body butterfly valve. I also checked all 4 corners and wheels all spin without much effort. Car also coasts in neutral no problem. I'm still experience this issue of the truck generally hesitating to go into a higher gear/driving at higher revs. I've also got a ses light since doing the work today.. don't have a code reader will see if it dissapears after a few drives. I'm thinking perhaps this is transmission related. I have never changed the fluid on it and it'd 170kms.. is it advisable? I've heard mixed stories about changing fluid on a tranny that's higher mileage Link to comment Share on other sites More sharing options...
Nix Posted September 5, 2022 Share Posted September 5, 2022 (edited) Once of these 3 might fix the issue: This can be because of clogged injectors Trying adding the STP complete fuel system cleaner. Do this 2 times. Add one complete bottle 12oz when the fuel is 3/4th empty or quarter to empty. Drive around (in between rev it to 3K-4K RPM) till its time to fill fuel again. Repeat it on another bottle. If this doesn't work. Check your catalytic convertor, even these can be clogged. Replacing it will be expensive, try getting it cleaned. This is for the heating issue: Even get 2 of the thermostats checked. Or rather replace if its older than 10 years. Remember when replacing the thermostat behind the engine CONSIDER replacing the PCV valve, ICT sensor and injectors seals. Edited September 5, 2022 by Nix Link to comment Share on other sites More sharing options...
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