Recluse

Mine does. My car didnt seem to pull very hard at WOT so I bypassed the Knock sensor to see if it was getting false knock but now I cant even get WOT without SEVERE knocking (think -shaking a can of marbles). Ive searched the posts and everyone who has bypassed theirs said thier cars ran better (or the same) but no posts saying they got excessive knock after the bypass. Is my ride that sick? Or does disconnecting the sensor and bypassing it mess with the computer causing it to advance my timing up to 50degrees or something? If I cant get full advance with no knock Im seriously losing out on performance. The best I could get at the track was 14.79.

Ed Maher

If you bypass the KS and you get a bunch of audible knock, then yes there is something seriously wrong with the engine or EFI. What is making it knock. Likely causes would include dirty injectors or too much timing. Could also be crosstalk between the wires that can have the effect of prematurely firing #5 for example. Could also be something really goofy like the MAF on it's way out reporting less air then is passing, leaving you reallylean.

But in short, yes you have a problem that you need to find. Bypassing the KS doesn't magically advance timing.

Recluse

my timing is set at 8 degrees advanced with the brown wire disconnected. I have new 8.5mm taylor wires and I cleaned the injectors recently which seemed to help out with cold starting and all around gas mileage. I also have an A/F gauge and my car runs around the bottom of the green area between stoich(yellow) and rich(green) at WOT -Ive heard this may be too lean. Perhaps too much base timing? Crappy gas? Im running 89 octane. Thanks for the reply.

89BlueTA

Try better gas, I only run 92 octane or better.

Nicholas

Ed Maher

First off, that A/F guage is absolutely useless. Just a decoration, the stock O2 sensor is completely inaccurate for WOT AFRs. The onky thing you can kinda glean from it is if you're way rich or way lean, but unless you know what voltage corresponds to which light, kinda hard to say where you even are.

Second, yeah, could be as simple as running 89 octane gas putting you over the edge. Esp. with even a little bit of extra timing. Could also be the injectors too, home cleaning kits are no match for true professionally cleaned and flow matched injectors. Even relatively minor imbalances in flow can be enough to get you all out of wack, my car had that problem when i first got it.

And then there's always carbon deposits in the chamber, or ECM / sensor problems, etc, etc.

bigals87z28

dude, drop teh extra 20c and get 93 man but in NJ, gas is pretty low

Recluse

better gas definately helped along with reducing the timing a few degrees. 93 Gas is 1.65 here in TX. Kinda steep for the area.

formul8!!

The extra $1.00 or so you spend on a tank of 93 octane is much cheaper than rebuilding your motor.

I DO NOT recommend running without the knock sensor because if you happen to get a bad batch of fuel, then the computer can at least try to keep things in check at WOT. If it cannot hear the knock, then the last thing you may hear is KABOOM!

Good luck.

bigals87z28

wow, i would think texas would have the cheapest gas... 93 in NJ is 1.61.. in Mass. where i go to college its $1,420,430,498,304 for 87... thats cause all of new england blows....

formul8!!

Sheeeeeit....I paid $1.87 for 93 here in the Chicago 'burbs yesterday!!

And that is average!!!

Damon

It can also be that you have alot of carbon buildup on the backs of the intake valves and especially in the combustion chamber. There are cleaners you can buy and run through the system (do it with multiple tanks of gas at double the recommended strength).

Also, you can quickly clean it out by running stright water through the intake at an elevated idle speed (2000 RPMs) on a fully warmed up engine. I had good success doing this recently with an old gunked up 85 TPI Vette. Pulled off one of the small full manifold vacuum vacuum lines from the TB and running the line over into a quart bottle of spring water. The manifold vacuum pulled the water through the vacuum line like a straw at just the right rate to draw in enough water to clean out the carbon but not drown the engine out. Made a HUGE difference afterwords in terms of knock. But the motor was badly carboned up to begin with.

Breadfan

first off carbon on the back of the intake valve wil not cause pre-det . Cause its not in the combustion chamber . Also gm had problem a few years ago with deposits from those reform fuels . So they have this fogger cleaner they run through the cars . I know this because i was a tech for saab... who is owned by gm .
oh and i pay 1.45 for 93 chevron . Thats the only gas i run . Speacking of gas did you reply what octane you are running .And have you tryed a different gas , such as a different gas station . Also has it only been doing it on this tank . if so have you been running the same gas since you started experiancing pre-det?

Recluse

I was running 89 at the time I was expereincing the severe knock. From what I gathered the place where I got it has notoriously bad gas. My g/f gassed up there recently in her jeep and it rattled like a beast too which is uncommon. And aboout the carbon thing, the only thing that I hear helps against knocking is polishing the chambers in the heads to remove hot spots. Just my $.02

Tremo

Sheet mon, here in California all we can get is 91, and that costs like $1.75 at the cheap stations.

Damon

Carbon on the back of the intakes CAN cause knock. It acts like a fuel "sponge" and leans out the mixture even if it's only for a fraction of a second after going to WOT. This starts the detonation process. It is much more difficult to stop detonation once it has started than if it never started in the first place.

Breadfan

actually that would be called a lean misfire . Not a pre-det condition . Pre-det is caused when the air fuel mix is ignited before tdc . a lean misfire woulded be ignited , not the word misfire .