Valve Clearance and Engine Knock

[blk95lumina]

Hello.

My girlfriend has a 1998 Toyota Camry 2.2L w/ ~190K mi.
The engine knocks under medium to hard acceleration, and I have replaced the spark plugs (w/ the correct dual ground plugs) and wires but the knocking still remains.

There are no engine trouble codes and gas mileage still averages ~28mpg.
Using mid-grade gas seems to slightly help the knocking but does not eliminate it.

Can improper valve clearance cause the timing to be off enough to cause engine knock?

How often should the valves be checked for clearance and adjusted as needed?

Any other ideas on the cause of the engine knock?

Thanks.

[Mike Gerber]

Carbon in the EGR valve and the tube leading to the valve are the most likely causes of pinging in an engine with 190,000 miles on it. The valve and the tube need to be removed from the engine and cleaned of carbon. The pinging will then most likely be eliminated.

Mike

[blk95lumina]

I removed the EGR yesterday and there was minimal carbon build up on the EGR, intake manifold, and tube. I cleaned off what was there and sprayed a little injector cleaner in the EGR. I did not remove the entire tube, since I figured there was a pretty small chance it was clogged at the exhaust pipe since nothing else was clogged. Unless the diameter gets significatly smaller at the exhaust pipe than what it is at the EGR, then I think it should be OK. If my assumption is way off, then let me know.

If the EGR was malfunctioning, I figured it would be throwing a code.

Any other ideas to try?

Thanks.

[Brian R.]

Try running some Seafoam or GM Top Engine Cleaner through the intake to decarbonize the combustion chambers. Maybe the engine has too much carbon on the piston and around the valves.

[Brian R.]

Originally Posted by blk95lumina

Hello.
Can improper valve clearance cause the timing to be off enough to cause engine knock?

How often should the valves be checked for clearance and adjusted as needed?

I have not seen an engine knock from improper valve clearance. It seems unlikely. However, you can get really loud tapping if they are adjusted really loose.

The valve clearance in that engine should never need to be adjusted. The only time you need to adjust the clearance is if you do a valve job or replace a valvetrain component.

[csaxon]

Mike and Brian are right on, but I'd go with Brians suggestion. "Try running some Seafoam or GM Top Engine Cleaner through the intake to decarbonize the combustion chambers. Maybe the engine has too much carbon on the piston and around the valves." 190,000 miles and 11 years of service tend to carbon up injectors, valves, etc.

I prefer pure Chevron Techron (not a techron mix) or Toyota Techroline (techron in a Toyota bottle) or Seafoam in the gas tank before I try the heavy guns. Follow the instructions, it may take a few tanks full before you notice results. If you have Chevron Texaco stations in your area, they have Techron in the fuel.

I won't go into knock sensors and how they compensate for fuel and combustion chamber pressures.

I use Seafoam also, but wait to see if the Techron does its job.

[blk95lumina]

Thanks for the suggestions.
I have been using Lucas fuel treatment for about the last 5 tank fulls or so. It helps but does not seem to eliminate the knock when under a load.

Is the recommendation to still try the Techron treatment even though I am using Lucas?

In regard to the knock sensors, what should the impedance be for a "good" knock sensor on this engine? How about the AC voltage?

I replaced the ones on my Silverado and to verify they work there was an ideal impedance and they put out an AC voltage. I could never find any info. on what the ideal AC voltage is supposed to be though at various RPM ranges. Not sure if the knock sensors on this Toyota engine operate any different.

Thanks.

[Brian R.]

The knock sensor should have no continuity from the terminal to the body of the sensor. They don't normally malfunction: More likely it is the wiring if your knock sensor system is not functioning. Check the wiring and the connections.

[csaxon]

I'd drop the Lucas, it emphasizes lubrication with mild cleaners.
Techron (Porsche factory recommended) and Seafoam put the emphasis on de-carbonizing and upper cylinder cleaning.

Good cleaners use the main active cleaning ingredient PEA (polyether amine) in various proportions. The rest of them may use PEA with fillers such as naptha or kerosene. Gumout Regain comes to mind. Independents may use BG44 (a good product) since it's heavily pushed by its salesforce.

You may have other problems but I's start with the simplest. Techron or Seafoam or alternate and see if you prefer one to the other. Good Luck!