High rev chatter?
 

I have an 86 with the L98 motor. At higher RPM the motor really starts to chatter. I would say it starts at 4500 rpm and on.I thought it might be timing, butI am having trouble setting it right.
Might it be because I am using cheap gas? Are those early cars set up for 93 octane?
It sounds like the top of the motor is floating for lack of a better word. I have ad have had LS1, LT1's and the likes. none have this problem. is it normal for L98 motors?

RE: High rev chatter?
 

Floating the valves? What kind of "Higher RPM'S"?

RE: High rev chatter?
 

Mechanic thinks it might be lifters because of spark advance module malfucnction. Don't know exact RPM. Tach is inop, becauseI have an HEI distrubutor I think.I would guess 3500-4500 RPM. this sucks!!

RE: High rev chatter?
 

If you think it's in the lifters or heads, put a compression gauge on, and measure the squeeze in all 8 holes. Check to see how long each will hold pressure too, like each one at 15 minutes, an hour, etc., ...

RE: High rev chatter?
 

I have a '90 with same engine and similar problem. Had good tune-up put on it few months ago and still get valve clatter under hard accelleration. Have been burning Premium gas but
also add a bottle of STP Octane Booster every 3rd or 4th fillup. Seems to help but I have
been advised here in past that I am only putting band-aid on problem. ????

RE: High rev chatter?
 

Did the person who referenced the band aid suggest anything else we could be doing?

RE: High rev chatter?
 

I went back and checked my previous posts. After tune up was recommended a timing check and new EGR valve was recommended here at this forum. Both accomplished but still have
that valve clatter/knock on occasion.


(Always gotta be something ya know.)

RE: High rev chatter?
 

Sounds like the ESC (Electronic Spark Control) is not working or either EGR system is not working. Both will cause detonation. The EGR uses a solenoid usually right behind the thermostat housing that controls vacuum to the EGR valve. Usually, ESC will set a code if not working properly. Does your 85 have a tube off the right hand exhaust manifold that goes to the intake and also has a temp switch in the tube? [8D]

RE: High rev chatter?
 

I don't know, I will check about the tube. I seemed to have fixed most of my problem filling with 93 octane gas. My mechanic said myEGRis stuck open and that might cause it too. He also said I need a new MAF... he said alot!

RE: High rev chatter?
 

If the EGR is stuck open you would have idle problems as that is a big vacuum leak @ idle. MAF would most likely cause stumble or poor idle conditions,