No Knock...Now Knock

[mearly65]

Hi everyone,
I bought my first 87 Grand National a few months back and absolutely love it. It needed a bunch of mechanical work done to it (mainly replacing a few parts and getting everything adjusted right), but finally got it running strong. I was driving it just about everyday and would get on it frequently to see what it could do. For about two weeks everytime I romped on it, it would pull strong and show 0 KR on the scanmaster. Then all of a sudden it started showing anywhere from 5.0-19.9 KR. The car still runs strong but I'm afraid to get on it again for fear of doing some major damage. I checked everything I thought to check: motor mounts and trans mount are good, downpipe isn't hitting, isn't losing antifreeze, antifreeze isn't bubbling, no "milk" in oil, not hearing any detonation while in the car. The only things I haven't checked that I've read about on here are things like worn out suspension parts or body bushings going bad. What's a good process of elimination to find out if what I'm experiencing is false knock or the real deal? Like I said the car still runs great, I'm just afraid to push it anywhere near its limit until I figure this out.
Thanks for any help in advance.

 

[QUIP'6']

put some good race gas in to verify false knock. is the knock during wheel spin or in first gear? what are your o2 readings showing when knock appears? also do you have a new fuel pump with a hotwire kit?

 

[mearly65]

The car is stock except for a K&N air filter and a new Walbro 340 with a hotwire. Turbo is stock but I rebuilt it a few weeks ago because it blew a bushing and was sending oil down the downpipe. My O2's are in the high 700's to low 800's when it's showing knock. And it will do it from a dead stop, slow roll, or at 55mph. As far as race gas goes do you recommend something like 103 octane? And if I put race gas in and the knock disappears, what's that telling me? Wrong plugs, time for bigger injectors?

 

[turb0buick57]

whats your boost set at?

 

[QUIP'6']

The car is stock except for a K&N air filter and a new Walbro 340 with a hotwire. Turbo is stock but I rebuilt it a few weeks ago because it blew a bushing and was sending oil down the downpipe. My O2's are in the high 700's to low 800's when it's showing knock. And it will do it from a dead stop, slow roll, or at 55mph. As far as race gas goes do you recommend something like 103 octane? And if I put race gas in and the knock disappears, what's that telling me? Wrong plugs, time for bigger injectors?

what ever you can get! if it dissapears then it is an octane problem due to fuel delivery or your boost has increased from the colder weather. at 19 degrees your motor would rattle like crazy. do you hear the knock or ping? just cause your pump is new doesnt mean its good. you need to verify 1:1 ratio with boost with a fuel gauge that is mounted out side on the windshield

 

[mearly65]

I can't recall boost going over 15psi. I'll admit my eyes were glued to the scanmaster to see what was going on. I'll check again to make sure. How do you adjust boost on a stock wastegate? And what is the factory setting for max boost on a stock car? I never heard ANY pinging or knocking even when it was showing 19.9. When I put the pump and hotwire in the first thing I did was make an extension for my fuel pressure gauge so I could verify that it went up with boost. Sure enough it did.

 

[~JM~]

Did you recently fill up your tank? Maybe you have a tank of bad gas.

~JM~

 

[mearly65]

I don't think it could be the gas. I drove it for two weeks and got gas many times and even took it on a 400 mile road trip stopping at different gas stations along the way.

 

[Fast4Ward]

lower boost to 5-10#. stock boost was 11# or so.
ease into in 3rd gear and get you wot readings, the available pump octane won't let most cars run more 14-15 lbs...on 94 octane i've been to 15# with minor KR.
if you get no knock and everything seems ok, then stop wasting time and get yourself an alky kit and crank it up

 

[mearly65]

How do you adjust the boost on a stock turbo? I'm thinking loosen the adjusting nut on the actuator and turn it which way?

 

[QUIP'6']

counter clockwise you want to make rod longer