As of recently, possibly immediately after doing full oil change service on my 88S4 auto, I have heard some valve chatter when I step on it from a dead stop.

The noise sounds as if it is coming from the valves, but I am uncertain.
It only really happens when starting from a dead stop and I floor it while the auto transmission is in D. Just as I step on it, the sound is as if for a second it is not getting power, the valves chatter, and then Varoom it goes and no more noise.

I am running Mobil 1 15w 50, and it has less than 100 miles on the oil.

I also have a RRFPR 24lb injectors and fuel pressure set to 44PSI. Is it possible that I am not running the correct mixture, and prior to the O2 getting going, something is haywire?




That sounds more like detonation than valve chatter.



I am running 91 octane Chevron and have Autothority custom header exhaust chips in.

If it is detonation, should I try and up the Fuel Pressure or try another tank of gas? Or alternatively, I could add some 104Octane boost for right now and try and tune it on a dyno for the correct Fuel Pressure.

If I am going ot tune it on a dyno, will octane boost mess up the A/F ratio measured from the dyno?

What about just upping the FP and then trying to tune it down on the dyno?



The fact that the car has upgraded chips and exhaust means it needs 92+ Octane. 91 octane will NOT cut it! YMMV.

Here in northern VA, every gas station owned by a major brand (Amoco, BP, Exxon, Chevron, Hess, Mobil, Shell, Texaco) sells 93 octane as their premium grade. Even the non-major company stations sell 92 octane. Also, Sunoco sells 94 octane as their higher-grade premium.

If the major stations near you don't sell 92+ octane, go to the local automotive supply store and buy several bottles of 106+ octane boost.
Read the back labels and use as needed. YMMV.

~ Merry motoring ~  Ed Ruiz


The chips up the ignition advance slightly - just enough to cause your detonation on 91 (R+M)/2.

It is not very likely that you can get rid of the detonation by richening the mixture.

You need to be aware of a marketing scam. If you read the octane booster labels, you will see that they promise to increase the octane rating of a
tank of fuel by three points, or five points, or some such number. That is probably a factual statement.

What they hope that you don't know is that an "octane point" is 0.1 octane numbers. In other words, a five-point boost is 0.5 octane numbers. If you
start with 91, you get 91.5 (R+M)/2. Not much help.

Looks like your choices are to find better fuel (tough to do in California) or to change back to stock chips, or to come up with some other answer.

Wally Plumley
928 Specialists


With all disclaimers that this is a really nasty chemical, I have had great luck with Toulene, which is available at paint stores in San Diego. With an
approx. "octane" of 114, the mix you want is up to you. Try it. Use gloves, and a very windy day.

It comes in five gallon bails.



From: Jerry McMurry []

Brendan, it is spelled "TOLUENE" and is pronounced TAHL-YOU-WEEN. And I have me doubts about it being able to bring up the octane. This sounds like the old moth-balls in the gas tank myth again. But OK, maybe you are right. CONVINCE me.

...Jeez Jer. First you get me on "Hydo-lick", and now Toll-you-Weeny.

Here are a few reading stops:

The brits always want to "list" things:

And as we know, Xylophone-Leen is pretty much the same, and is Benz-EEN

I have used toluene to thin epoxy resin so it would penetrate dry-rotted sailboat wood before it hardens. Works great. You end up with a better material than the original wood.

...I didn't see much water in La Mesa.