Spark knock. Any ideas?

99 with a 3.4 engine, 221000 miles. The past couple of years I have been noticing it. Started out only randomly. Now it does it when the engine gets warm and is especialy noticeable between 1750-3000 rpms. Mainly from half throttle and higher or going up hill. Have tried all grades of fuel and still the same. I ease off the gas and it stops. So I have been driving alot easier now.

 

I can throw a few basic ideas your way. do you know what is the state of the tune on the truck? you know we can go through the whole list, plugs every 30,000 miles and use the org. ones also. also check the wires and coil plugs. if i think of something else i will post it

 

Do you have a check engine light on?

 

Had my plugs and wires replaced at about 150,000 miles. No check engine light. Had the cat and o2 sensor replaced last fall. Might just take it in for diagnostics. Hoping for something simple.

 

A possible failing knock sensor maybe.

 

How steep are the hills? And what kid of speed and rpm are you running when you take these hills?

With my 3.4 and a manual trans, I NEVER have to go above half throttle when driving up hills in the correct gear. And believe me, there are crazy hills where I live. Very steep, high speed, you name it.

 

i have the same issue, some days it is noticeable and others it's not so much. i haven't found the cure just yet. 197k on the clock

 

Does it happen more on warmer days by any chance? A higher cylinder head temp will cause more knock.

 

CRC Mass Airflow cleaner, reset the ECU.

 

Thanks for the replies everyone! Knock seems worse on warmer days. I just back off the trottle when it occurs. Seems like once the rpms are over 3000 it eases up on the knock. My Toyota guy must be out of town, he has not returned my call yet. Maybe this weekend I will clean the MAF and take off the negative to the battery. Will this reset the ECU?

 

First of all, do you have a manual trans, or auto trans? If an auto, ignore this.

Try never going above 1/4 throttle when going uphill.

What i'm suggesting is that you're lugging the engine. For example, when going up a steep hill at around 40mph, you should be doing around 3000 rpm climbing easily while being nowhere near half throttle. Yea, 3000 rpm is noisy on these engines, but it's actually a lot less stress on the engine and better all around.

 

one thing i just thought about, your should be changing plugs every 30,000 miles max. if you went 150,000 miles on one set, I am surprised it would crank. that could be why your cat failed. I would not push a set of wires past 100,000 miles and the coils no more than 150,000,(for me no more than 100,000) those things wear out and loose efficiency. the 3.4 has only 3 coils so they sort of pull double duty, but still, exposed to heat wet cold, it takes its toil.

 

Talked to my Toyota mechanic friend this morning. He will be back in town next week some time. He didn't sound real optimistic. He says if it did not throw a CEL it probably is not a sensor. Also thought maybe a piston slapping or a rod knocking. When I told him it only happens when the truck is hot, he said it should be the opposite. Sould happen when the truck is cold and if the piston is slapping, when it warms up the metal expands a little and no more knock. He also sugested to maybe think about getting another truck. He does know my truck since he has done most of the work on it.Hate to let go of my Taco. Had it since new. Has original clutch. Probably sould have done more mantiance through the years but I can't change that now. He says he will check it out. Still hoping for something simple.

Begining to second guess myself. Maybe it is not spark knock. Sure sounds like it though. Did own cars from the sixtys and when premium was not used it would knock. But with more throttle than I am experiencing.

 

piston slap is at startup and usually last about 2 seconds, more so when it's really cold outside, using the wrong oil filter, or it has sat for an extended amount of time. Piston slap is considered normal under certain conditions.

 

Might be long-term carbon build up significant enough to cause predetonation.

Like Ben said, Seafoam could be the cure here. Into the intake plenum.

Have you babied this thing all its life, or do you ever run it wide open throttle and flog it to help burn out deposits?

 

This also.

Carbon buildups can act like hot spots or glow plugs and cause predetonation.

 

i hate to harp on this but if you were going that long between spark plug changes thats not good. i had to seafoam the ever living @%#@ out of my truck, and she could still use more.... don't do it to heavy at first, go slowly.
you have to keep motors well tuned to get the max life out of the emission components. and modern engines for the most part are lower compression, which helpd the the longevity of the rings, seals, ect. but with E10 if its not tuned good you get carbon buildup, and less mpg and it feeds on its self.

hell i say lets bring back the good o days with leaded gas! there was nothing like a little lead in the gas to keep those rings and valve guides slick.

 

I miss those days.
I clean my MAF every 6000 miles. Has yours ever been cleaned?

 

Is cleaning the MAF a difficult task? Been contemplating it, just don't know what it entails.