Someone please help me......I have a '98 4runner 3.4, 137,000 miles.......trucks been running fine up until about a month ago.......when I'm driving everything is fine and quiet then all of a sudden i hear a tap/knock that corresponds to me pressing the gas.......also I get a nice white/light blue smoke from the exhaust.....after 1-2 minutes the smoke and tap/knock is gone. This only happens maybe every two-three weeks and then only after I have done some serious driving. I would greatly appreciate any assistance you guys could provide........

Also, I don't know if this is related but I found out from calling Toyota that this truck has never had a timing belt well not at an authorised Toyota butcher shop.

 

Symptoms sound like ignition knock. The warm motor provides enough energy to ignite the fuel before the spark plug fires. The smoke concerns me a little though.

Do you ever get smoke without the knock- like starting up after sitting a while?

Auto or manual tranny? Is the knock worse if you're in a higher gear?

Is this truck new to you without service history? If so, I would start with a complete tuneup:
Timing belt (they are due every 90k miles) - should consider water pump while you're in there (due every other timing belt change)
Plugs, wires, dist cap
Check/adjust timing
Air filter
Fuel filter
Oil change
Coolant flush/change
(has nothing to do with above problem) recommend changing fluid in diffs, transfer case, and tranny while you're at it

You don't need to be a super mechanic to do any of the above. There are several writeups on how to do the timing belt.

 

you will need a second pair of hands doing the t/belt. i just did mine the other week (boxing day), we took our time and had several other eyes check to make sure we had it lined up correctly. w/p, t-stat, p/s pump, coolant, upper & lower rad hoses and belts over approx 7 hr time span. lots of referring back to the fsm for torque specs and making certain we understood what it was saying.

once everything was buttoned up, it fired and once things warmed up it ran like a new truck again! be patient, its worth it.

lee

 

Thanks for your responses......To think of it I do recall having it give some well a good amount of pure white smoke a while ago maybe 9 months but it went away. The last time I had the knock/smoke this is what I was doing. Driving on the hwy 75mph exited the highway sharp right turn....then the knock started and then the smoke.....the smoke smelled more like gas or exhaust than oil or water....I revved the engine 2 maybe 3 times.....BIG smoke cloud then jut that fast it was done and over with.....the smoke reminded me of the seafoam treatment but nowhere near as nasty smelling.

TC: I bought the truck 10 months ago from a guy in a divorce proceeding. Previous to that it had sat for 5 months in a field. It's a 4runner limited, auto.
Hope that helps.

 

Helps A LOT. DEFINITELY do the tune up. May have some dry rotted vacuum lines too. Sounds like you aren't getting good combustion and blowing unburned fuel out the tail pipe. What is your gas mileage?

 

My gas mileage is absolutely the worst......I average about 9-10 miles per gallon if that.......So it sounds like a correctable issue right?.....The last thing I want to do is launch the engine......

 

Ooh - forgot to ask earlier - Do you have a Check Engine Light on? If so, take it to Autozone and get the code, post it up here.

I would say that definitely qualifies as bad mileage! (I get 17-20)

I don't see anything from what you've said so far that leads me to believe the motor is in jeopardy. Worst case, maybe you have some scoring on the cylinder walls that is letting a SMALL amount of oil past the rings.

Do the simple tuneup stuff (ie - not the timing belt) and let us know what happens. It is all very easy, a Chilton or Haynes manual can guide you through it no problem if you can work a wrench and a screwdriver.

If you take it to a mechanic to have the timing belt done, ask to have a compression test done - that will tell a lot too.

 

No check engine lights.....TC any recommendations as far as spark plugs......I want to make sure I get the best spark possible to ensure i'm burning all fuel......

 

Denso or NGK for Toyotas - no Bosch. Apparently the Axis powers (Germany and Japan) don't work as well together as they once did...You can search on here - sounds like people have mixed opinions of platinum or iridium plugs. I would use regular ones for now - platinum/iridium plugs are expensive, and there's no guarantee they will fix the problem.

I would, however, spend a little more $$ for good quality wires - IR suppression is what you want, not carbon/graphite core. Eventually the carbon conductor will get little cracks and experience severe voltage drop. (Great writeup in the book "How to Build Horsepower" about plug wires)

 

Thanks TC I'm gonna try what you suggested and post my results here. Thanks.