Loss of Power and MPG
03-20-2019, 07:34 PM
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Loss of Power and MPG
I've got a 2000 4Runner Limited 3.4 2WD with 267k miles. I bought it new in January 2000. This has been a super low maintenance vehicle. Oil, tires, batteries, struts & shocks over the years, U-Joints at 135k, front brakes at 180k and rear brakes at 265k. I'm in the Dallas area so we have to pass a safety and emissions check every year. Plugs & wires (NGK) were replaced 4/2016 when I replaced the valve cover gaskets because I was there so why not. Coils were replaced 7/2016 because it had an occasional miss I couldn't figure out. It didn't help.
In late December 2016, a week after I passed inspection, it suffered a sudden loss of power and mpg dropped from 19 to 16.5. No CEL. When the symptoms started I replaced the O2 sensors and MAF. I did have to replace the O2 sensors (Denso) again in 12/2017 to pass the inspection. Nothing special in 12/2018 when I passed inspection. Still low power and mpg though.
A vacuum test rules out plugged exhaust. The entire exhaust was replaced (with Toyota parts) in 2012 because someone thought they needed the catalytic converter more than I did.
At idle, in park, and at 2000 RPM, the vacuum needle is steady at 21-23. Accelerating on the highway or trying (and failing) to maintain speed going up a hill (because of low power) it dives down to between 1 & 5. On level highway at 65 mph vacuum is about 12.
The timing belt is due for a change. Supposed do that every 265,000 miles, right?
I hope I've given all the data needed. It always starts and never stalls. It runs good but it's weak. What could be the cause of the low performance?
In late December 2016, a week after I passed inspection, it suffered a sudden loss of power and mpg dropped from 19 to 16.5. No CEL. When the symptoms started I replaced the O2 sensors and MAF. I did have to replace the O2 sensors (Denso) again in 12/2017 to pass the inspection. Nothing special in 12/2018 when I passed inspection. Still low power and mpg though.
A vacuum test rules out plugged exhaust. The entire exhaust was replaced (with Toyota parts) in 2012 because someone thought they needed the catalytic converter more than I did.
At idle, in park, and at 2000 RPM, the vacuum needle is steady at 21-23. Accelerating on the highway or trying (and failing) to maintain speed going up a hill (because of low power) it dives down to between 1 & 5. On level highway at 65 mph vacuum is about 12.
The timing belt is due for a change. Supposed do that every 265,000 miles, right?
I hope I've given all the data needed. It always starts and never stalls. It runs good but it's weak. What could be the cause of the low performance?
03-21-2019, 05:50 AM
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Fuel injector is my guess, are you getting any misfire codes, any pending codes. Fuel injectors on 99+ 3rd gens have been showing there weak spot, surprisingly the earlier models are fine.
Timing belt is listed as 100,000mi change interval,.. but this is not necessary as the belt is good for 250,000mi or more IMO,.. but age is also something 1 should consider as well as water pump after that amount of miles.
Also have heard a few reports that not all OBD readers are connecting properly, either due to OBD code reader or OBD ground fault on vehicle.
Timing belt is listed as 100,000mi change interval,.. but this is not necessary as the belt is good for 250,000mi or more IMO,.. but age is also something 1 should consider as well as water pump after that amount of miles.
Also have heard a few reports that not all OBD readers are connecting properly, either due to OBD code reader or OBD ground fault on vehicle.
Last edited by Malcolm99; 03-21-2019 at 07:24 AM.
03-21-2019, 06:14 PM
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Fuel injector is my guess, are you getting any misfire codes, any pending codes. Fuel injectors on 99+ 3rd gens have been showing there weak spot, surprisingly the earlier models are fine.
Timing belt is listed as 100,000mi change interval,.. but this is not necessary as the belt is good for 250,000mi or more IMO,.. but age is also something 1 should consider as well as water pump after that amount of miles.
Also have heard a few reports that not all OBD readers are connecting properly, either due to OBD code reader or OBD ground fault on vehicle.
Timing belt is listed as 100,000mi change interval,.. but this is not necessary as the belt is good for 250,000mi or more IMO,.. but age is also something 1 should consider as well as water pump after that amount of miles.
Also have heard a few reports that not all OBD readers are connecting properly, either due to OBD code reader or OBD ground fault on vehicle.
03-21-2019, 06:33 PM
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Automatic and the OBD doesn't give me a clue. That's the real bugger on this. The engine seems to run great but it lacks power. Diagnostic tools have failed. So I think back to my 66 Belair and 69 Lemans and it was carburetor, timing, points, distributor cap, rotor, coil, plugs or plug wires. There wasn't much else.
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