fl_799

Doing some additional data logging yesterday (Datamaster 32) to troubleshoot double digit knock counts jumps at WOT.

When the CCP DC value jumps to 100 at WOT, I'm seeing double digit knock counts register. Is is normal for the vapor canister to purge at WOT? No question, when the vapor purge duty cycle approaches 100 under these conditions, rapid knock counts occur.

I have not found too much information on this, just a brief mention of this issue at the 3rd gen boards.

Any ideas? I'm going to dig into this further over the weekend.

JackDidley

I dont know about the CC purge but I can tell you about my particular situation with knock counts. When I first started logging I got Knocks sometimes but not always. I finally figured out that, if the tires were spinning, I got knocks. If it hooked, no knocks. Never found a real solution or even confirmed that the knock counts were not from the driveline or something other than the motor.

fl_799

Sometimes ignorance is bliss. What is strange is that the BLM's and all of the other data looks great. My '89 has 16,400 miles and was 100 percent original down to the original gatorbacks. It has no vacuum leaks and runs, drives like new. That is what is perplexing.

For piece of mind, I replaced all of the O-rings in the fuel rail, installed 8 new OEM style Delphi injectors (I had one lazy multitech), a new Delco fuel pump, changed the plugs to new Delco's, checked the base timing, set TPS voltage, reset IAC, cleaned the throttle body, new delco cap and rotor...you get the idea. I have a new knock sensor in hand to install tomorrow and put in an updated ESC part number 16038331 yesterday (did not lower knock count at WOT).

I'm going to test that vapor purge system from top to bottom. I read that a vacuum leak in the vapor purge solenoid can cause a lean condition-knocks at WOT? No question that if the vapor purges at WOT, I see knocks, when it does not, there are no knocks. There is a correlation but I have not figured it out yet!

James

Cliff Harris

The vapor canister purge solenoid works backwards from what you would expect.

When it is OFF the canister is in purge mode. That means that you can't just unplug it to disable it.

You need to plug the vacuum line that goes to either the throttle body or the intake manifold (depending on the year -- you didn't mention one). After doing that you'll know if the canister is indeed the cause of your problem.

According to my info, these are the conditions for canister purge:

Engine run time > 60 seconds
Coolant temperature > 158.5°F
Vehicle speed > 5 MPH
TPS > 3.9%
MAF air flow > 0

Unfortunately these are all "greater than" parameters and WOT would still fit within them. I don't know offhand how the ECM decides it's time to turn on canister purge. Since it's sucking in outside air through the canister, you would think WOT (when you want to be rich) wouldn't be a good time for that. It would take a close examination of the code to determine what's happening.

fl_799

Thanks Cliff.

Just thinking this through, the car runs great and is in a perfect state of tune. Might just be some bad gas at the end of the day. Sure, I'll perform some due diligence on the purge circuit and play around there but I'm not going to let it drive me crazy

JackDidley

Are you using premium gas? My car pinged real bad when I used the cheap stuff one time.