Spark Knock randomly comes and goes. If you want a challenge, please read.

My 01 3.4L Manual Trans 4x4 tacoma will spark knock under acceleration at random times. By random I mean, one red light it does it, another red light it won't. I've changed the spark plugs, wires, MAF sensor, air filter, fuel filter, and I have cleaned and applied electronic grease to all of the electronic plugs that I can get to. The CEL is not on. I live in an emissions inspection county, so it has to pass the test where it is hooked up to a computer, and it passes without question. The truck also distinctly runs and accelerates smoother when it doesn't spark knock. It can't be fuel, because it does it so randomly. Help.

 

How many miles are on it?

 

It has 150,00 miles. Keep in mind, when it doeen't act-up it absolutely runs like a champion, very strong and smooth.

 

check your pcv valve and all vacuum lines. if you have a broken vacuum line it could cause this problem, I have also heard that a clogged pcv valve can cause pinging. Take the valve out of the truck and shake it, if it doesn't make a rattle or clunk sound inside of it then replace it. As they are only about 5 bucks if you haven't replaced it in a while you might want to just do it anyway.

 

also check the gasket around the maf sensor. It could be broken or gone and allowing air to enter the intake un-metered.

 

I'll check the EGR valve, sounds like a logical solution. Recently installed the MAF sensor, gasket looks good.

 

I dont think our trucks had an egr at least I know that my 01 3.4 does not. What I was refering to is the pcv valve which looks like a plastic elbow coming out of the passenger side valve cover. it will also have a vacuum line running from it to the underside of the tb.

 

Oh this is a tricky one... Does it sound like a misfire??

 

My bad, was thinking PCV and typed EGR. Replaced the PCV just now and so far it seems to be working. Time will tell though, this problem is a come-and-go problem. Will update after a little more time has passed. Thanks everyone for the help.

 

jr97tacoma

It doesn't sound like a misfire. It doesn't seem to affect the idle/start or anything that isn't under a load for that matter. Sounds just like an older chevy that is having timing advancement issues.

 

This is a long shot, but a year after I had a shop do my timing belt/water pump, my truck would randomly act strangely. After about 6 months of changing out most that you have with no improvement, I gave up and took it to another shop. He finally figured out that my crank pulley was coming loose, and that the crank position sensor would randomly retard the timing. I had to buy a new crank pulley, but at least the nose of the crankshaft was ok.

 

That is very interesting. Wouldn't have thought of that. Sounds like a possibility though. Changed my timing belt about two years ago. I have often thought that it could be some kind of timing issue, just didn't know how that could be, with the timing setup that these tacomas have. Especially with my problem coming and going.

 

Sounds like bad ground wire to engine. Find where is connected to and check the wire itself

 

Should not knock wonder if one of the knock sensors is bad I think that engine had one for each bank.

 

I'm not familiar with a knock sensor. Tell me more.

 

What a knock sensor does it basic listen for a a tapping sound . When it does it gives off a A/C current.

On the 3.4 there are two. Left bank and right bank. They are under the intake in a valley of the of engine. Yes you have to take the whole middle of the engine to get to it.

To test the sensor is hook up a volt meter set it to A/c current. Use a 3/8 extender and a hammer. You you tap the extender on the block with the hammer the sensor should send out a A/c current( it will be a very small about of volts.) If it does sensor is good if it does nothing sensor is bad.

 

What grade of gas are you running?

 

mid grade usually. doesn't seem to change anything when I try a different grade.