Knock problems...too much fuel?

[Matt Weiser]

Seems like I read in a recent thread that too much fuel can cause knock. True?

Reason I ask is I'm fighting a battle with part-throttle knock. I'm showing double-digit knock retard at low boost and recently installed a Power Plate to try to deal with it. This helped, but it seemed to just move the problem higher into power band. Now I'm getting over 10 degrees KR at around 8-10 psi. (I also reset IAC and TPS after installing PP.) My O2 readings during all this seem high, between 820-850.

This is on 91 octane California gas (best I can get) with max boost set around 15 psi (though I never see that because I back off with the early knock). I have a stock fuel pressure regulator, 30lb. Tomco green stripe injectors, a hotwired Walbro 307 and a new timing chain. I already did the Top Engine Cleaner. I also know it's not false knock because I can hear it. I have not verified if the fpr is working right (it's original). I do have a 237 regulator I could install, but wouldn't this just make the 02s even richer?

So, could it be TOO MUCH fuel? What else can I do?

 

[strikeeagle]

Matt,

Drain your tank and put in 7 or so gallons of 100 octane or better. If the knock persists at these boost levels at least you'll know it's not octane related.

 

[Steve Hill]

well you should definately check your FP to know where this is at. Another thing to consider is it might not be your *total a/f at fault, rather just one faulty or clogged injector.

 

[Matt Weiser]

Thanks for the feedback guys. I don't have a source for 100 octane or anything like it nearby. Will octane booster do the trick? Or what about xylene? Any side-effects to that?

Is there a way to test each injector without pulling them?

 

[Steve Hill]

The problem with filling up with high octane is that it could mask a real, and, assumably, solvable problem.
Here’s some things to think about and keep you busy <grin>:

First and foremost, you need to be confident that your regulated fuel pressure is tracking your boost pressure. I do not trust any FP regulator, regardless of cost or manufacture, until I do the following test to verify.
You will need a known accurate fp gauge with a hose long enough to reach at least the windshield. Have a friend watch the fuel pressure as you go into boost. The regulated fuel pressure should *always and precisely* track the ‘base’ fuel pressure by the exact amount of boost. No more, no less.

How about your boost gauge.... is it accurate?
The chip you use.....is it matched to the fuel injectors? Take a look at the WOT timing. You can’t be too aggressive with only 91 octane.

And then there is the possibility of a clogged or faulty injector. This would be tough to find without pulling them out and testing on a bench.

Your problem could also be from a faulty coil, spark module or even spark plug wires!. Either of these can cause some really strange symptoms.

This is just the stuff that immediately comes to my (slowly dementing) mind. Good luck.

 

[ghall]

To answer your original question--if too much fuel can cause knock--YES----my o2's were right in your range or a bit higher and i could not get the car to run.Every time i took some fuel pressure out out--you could see(and feel) the car waking up on the scanmaster and direct scan until it was dialed in right.

Geoff

 

[Matt Weiser]

Thanks for all the feedback. Sounds like I need to check my fpr, and maybe end up going with an adjustable.

I'm using a stock chip, but it's possible even the timing in a stock chip is too much for this gas (not only is it 91 octane, it's also "oxygenated", which probably is not helping). I was considering going with the new Ramchargers spark translator to deal with this, or getting a custom-burned chip, but I want to find out if I have a real problem first instead of just band-aiding it.

The boost gauge is a new VDO unit. I've heard they can be off a little. Likewise, the coil, spark modure, plugs and plug wires are new. I replaced all the usual "wear" items when I built the car, including valve springs, wastegate solenoid, PCV valve, all the vacuum lines, a Casper's ground stretcher kit, and replacement stock headers that are leak-free. I bought the injectors used off this list and they are low-mileage, but you never know. The O2 sensor came with the headers and is also supposed to be low-mileage, but I it could be suspect.

Thanks again. Looks like my weekends will be busy for a while!

 

[tlp]

From everything I've seen while reading this board and the other one, it is standard practice to upgrade the regulator as one of the first mods. this is right up there with changing FP and hot wire. Also you stated " stock chip" if you are using the chip that came with the car from the factory I thing that is a no no also. Someone chim in here if I'm wrong but I think that you should upgrade your chip to match your injectors and octane and install an adjustable regulator to be able to adjust the fuel pressure to what the chip company or burner specifies.

 

[Matt Weiser]

Good points, tlp. On that note, can anyone recommend a chip burner familiar with the "unique" challenges of Calif. gas?

 

[Buick Beginner]

Just my 02

I'd steer clear of over the counter octane boosters, like "wild stallion rocket blend", you know, a 12 oz bottle is $9.99 at the local auto parts store? Do a search on Xylene or Toluene and then, copy the formula and make the mixture at home. I've run Xylene off and on for a year with no trouble and BIG returns. Just make sure to mix in some oil for lubrication. - BB