3.0 Intermittent Power Issues

[needlecg]

For years I have had intermittent power issues on my OBD1 3.0. It idles ok but sometimes when I am at partial throttle I can feel the engine dragging, so I floor it and it revs but acceleration is half of what it should be. then next thing you know it feels fine.

I will gain and loose power multiple times through a single drive without turning it off and on. About 25,000 miles ago the head was pulled and re-done due to a burned exhaust valve but it didn't cure the intermittent power loss issue. O2 sensor and fuel filter replaced not long ago using OEM parts, they didn't help.

I am now guessing the cat may be clogged, would that make sense? I never replaced the catalytic converter and I've had the truck since 80,000 miles, now have 253,000. I recently took temperature readings on the exhaust when these symptoms occurred and readings were 600 degrees immediately before the catalytic converter and 500 degrees immediately after the catalytic converter.

I am set to do a 3.4 swap shortly so I don't want to put any more money into the 3.0. I also don't want to needlessly buy an expensive new cat. I was thinking about putting in a test pipe for a while and see what happens. Thoughts or ideas? Thanks in advance.

 

[toyotafan]

Hey, welcome to the site. Let me read though this.

 

[toyotafan]

How your fuel economy? Any known electrical issues? Does the engine miss at all when it's losing power?

 

[needlecg]

How your fuel economy? Any known electrical issues? Does the engine miss at all when it's losing power?

Fuel economy is what I would expect from a thirsty 3.0 with 32" tires and 4.88's. No electrical issues. Engine doesn't miss when loosing power, sounds fine when it revs, it just feels like I'm dragging a tractor trailer behind me with regard to speed of acceleration.

 

[69FJ-2.4LTRTDIESEL]

Have you put the truck on an engine analyzer? I heard that a faulty alternator filter/diode can send static signals into the electrical system of the vehicle which in turn the ECM reads as a signal from control sensors like the O2. You will see this on the analyzer in real time if it exists and also other issues. Snapon's unit is expensive but works well for diagnosis of injectors, sensors and the like. Another issue is electrical connectors on sending units, the blades inside the connector become loose from vibration or wiring entering at an angle other than straight in. I use a very small needle to insert into each terminal (needle thickness to match the male side blade thickness) and you can feel if the terminal is loose fitting or tight on the blade when inserted , this is a common cause for injector malfunction too.Just some thoughts.

 

[needlecg]

Have you put the truck on an engine analyzer? I heard that a faulty alternator filter/diode can send static signals into the electrical system of the vehicle which in turn the ECM reads as a signal from control sensors like the O2. You will see this on the analyzer in real time if it exists and also other issues. Snapon's unit is expensive but works well for diagnosis of injectors, sensors and the like. Another issue is electrical connectors on sending units, the blades inside the connector become loose from vibration or wiring entering at an angle other than straight in. I use a very small needle to insert into each terminal (needle thickness to match the male side blade thickness) and you can feel if the terminal is loose fitting or tight on the blade when inserted , this is a common cause for injector malfunction too.Just some thoughts.

Um, wow, that sounds intense. I have not put the truck on an engine analyzer. I'll have to check into that, thanks for the advice!

 

[69FJ-2.4LTRTDIESEL]

Um, wow, that sounds intense. I have not put the truck on an engine analyzer. I'll have to check into that, thanks for the advice!

Not really, most good shops have one it's like a laptop, you can see the SiN wave which is supposed to be distinct/crisp (like a heart monitor in a hospital) whereas if there is static (electrical interference) it will be a wide band (wide & blurry) not crisp and clear. The diode pack on the back of the alternator can be R&R'ed and stops that. Testing is simple you just take the output from the alternator off the system and if it is bad it will clear the signal up but you need an analyzer to see it. Good luck hope you have a shop in your area. I was having intermittent engin power issues and found it was the left bank rear connector at the injector, fixed the connector and solved my problem. 2 years now no issues, knock on wood.