Question-------------------------
Followup To
Question -
I have a 1994 Chevelet corcica, milage 158**** there has been a tapping in the head since i moved with it some three thousand miles hauling a trailer, I'm, supposing it's the valves, it didn't pass emissions test here in Arizona last year and I got the sparkplugs changed and it passed, it didn't pass this year and I've scheduled for a valve job, what's the chance that it has other internal damages, the motor runs smooth as glass, and I haven't notice any steam or smoke coming from the tail pipe, the oil is clean of any other fluids.
Answer -
Hi Linda,
Why the valve job?
The tapping may just be a lifter. Possible an adjustment nut backed off a little.
Could also have carbon deposits on the valves and pistons. But if it runs that good, I would at least want a compression test before doing the valve job.
May just want another set of plugs.
Of course, if you have a mechanic there that is good, he has at least seen it, so may have some info I don't see.
A bad knock sensor could allow a noise like a tap.
Van
Why Value Job? It's really loud when engine is cold, but it get's quite ofter it warms up, could that be pressure in the cylinder building up? and it is really loud on exceleration and going up hill. I guess the expression "tapping" was kinda mild, more like knocking, but then again it starts real easy, anyway I'll ask the mechanic when I take it in if he would check the rocker arm and Hmmm! Never heard of such a thing as a knock sensor. Linda
AnswerHi Linda,
A knock sensor screws into the block and when the engine clatters,(used to be called low octane knock), it sends a signal to the ecm, which in turn retards the timing to eliminate the knock.
If it is bad, or unhooked, it can't do its job, and you will hear the knock.
Of course, you could have a knock that the timing cannot correct.
Van
