my vote is the sparkplugs............

 

I'm ready to cut my losses and trade this damn thing in. Today we replaced the front O2 sensor, the plugs, and the plug wires. Rebooted the computer, and it runs exactly the same. Idling at 500 rpm with no Check Engine light. One thing we figured out is that if you rev the engine in Park, the timing advances. If you shift into Drive and power-brake it, the timing retards.

 

Replacing the A/F and O2 is spensive just to do it for kicks without determining they are bad. I am fighting through some issues and more and more getting pointed to my injectors. I would get teh final diagnosis before just changing out $1000 in parts.

 

What if he didn't use Denso plugs? My girlfriend had her truck in the shop and they replaced her plugs with Champion or something.

 

What do you know about the history of the truck? Was it abused at all? Have you done anything like a leak-down test or compression test?

http://www.type2.com/library/engineg/leaktst.htm
http://autos.yahoo.com/maintain/repa...ques057_1.html

You can also do a simply test with a tissue or paper towel... Start it up, let it idle, take a tissue and hold it about an inch from the tailpipe. it should only be blown away from the pipe. If it looks like it's getting sucked in, you've got a stuck/burned valve.

 

I'm working with 2 excellent mechanics, we aren't doing this "for kicks", and I haven't spent nearly $1000. Believe me, I have better things to do with my money. Most of the parts we've replaced have been maintenance items anyway.

 

Hi Mark. I assume you've actually seen this occur with the tissue test? I'd trust that, but I must admit that it is hard to believe a non-functioning exhaust valve would actually create a negative pressure strong enough to overcome the other 5... strong enough to reverse the flow in the entire exhaust.

Of course I'm speaking only "theory" here. Maybe you'd get a momentary reduction in the postive pressure, enough to make the tissue pull back from the positive pressure appearing as kind of vibration in the exhaust pressure.

Anyway, a cute idea. And easy enough to try.

 

Glad to hear that!

 

Have you tested the fuel injectors? It a pretty easy test. What do you have to lose? Take an Ohm meter and see that the injectors are around 13-16 Ohms.

 

Break down...go to Toyota Dealership...pay 70 bucks and let them diagnose the problem with their computers. Then take it somewhere else to get it fixed.

 

I don't know if that was done or not, but I'll ask.

 

Oh yeah... DD showed it to me on my truck before we tore it down. It's pretty clear - much more than you would think.

But in the end, a leak-down will be a much better indicator.

 

time for a compression test and as stated leak down test.

your gonna have to start narrowing down the field

If compression is fine and leak down are within specs, then check fuel delivery system. Are the injectors working properly. If those are ok next check for proper spark. etc etc

My biggest concern is the history of the vehicle. Especially the engine what it went through. I currently have a 3.4L engine sitting my garage that is toast because of a lean out condition from having a supercharger on it.

 

Well, I finally got my 4Runner fixed! I took it to another mechanic on a friend's recommendation (mine had given up), and he diagnosed the problem immediately. He said he could tell what it was as soon as he drove off in it. The problem was with the lower timing belt sprocket. The keyway had "walked" as he put it, and was gradually widening the slot. Because of this, the timing read OK at idle, but jumped all over the place when you put any load on the engine. He said he'd only seen this a couple of times, and those were with Camry 4-cylinders. So dusty98 was on the right track, even though the belt was OK and had not slipped. The first mechanic said he thought it was a timing issue, but he would have never suspected the sprocket, and that he had never seen that happen.

Anyway, as soon as I turned the key, I got a big smile on my face. It runs great now! Gobs of power, smooth as silk, and MPG went from 9 to 18. He also found that the rear brakes were hanging because of gear oil leaking due to bad axle seals. He went over the whole truck, lubing and adjusting everything in sight. The thing drives like a completely different vehicle. I'm a happy boy. Thanks to all for the suggestions!

 

sweet

 

I love when a plan comes together

 

That was probably a leftover from a timing belt that wasn't done properly (ie improperly torqued).
You're very lucky you caught that early because it could have been ALOT worse!

https://www.yotatech.com/forums/f2/help-my-crankshaft-pulley-wobbelin-79429/ (this is probably what yours looked like)
https://www.yotatech.com/forums/f116/lesson-learned-pics-76293/
https://www.yotatech.com/forums/f2/crank-pulley-wobble-88872/
https://www.yotatech.com/forums/f2/crankshaft-bolt-felt-out-bye-bye-crankshaft-89038/
https://www.yotatech.com/forums/f2/crankshaft-pulley-came-off-help-65946/
https://www.yotatech.com/forums/f2/3-4l-engine-problems-37150/
https://www.yotatech.com/forums/f2/help-harmonic-balancer-16920/

 

MTL, that's exactly what mine looked like.

 

That's the first time I've heard of that problem. I never would have guessed. Glad that someone finally found a resolution.

Ed

 

Cool thread... I wonder if there is anyway to catch this "in the driveway" as opposed to have an ace mechanic in your pocket.

Hmmm.... maybe not.