l98 spark knock
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
Have you scanned it to see what the knock counts are? Have you checked the knock sensor by tapping on the engine block while at idle to see if the RPM drops? Are you getting a code? Checked timing?
Safety Car
Joined: Sep 2003
Posts: 3,599
Likes: 24
From: Orange County NY
St. Jude Donor '10-'11-'12-'13
Generally, knock is caused by too much timing, very high combustion temps, bad gas, or a lean condition. There are other causes, but these are the most common.
Since your engine seems to knock only when cold, I would start by troubleshooting a lean condition, then go from there. What do the plugs look like?
Since your engine seems to knock only when cold, I would start by troubleshooting a lean condition, then go from there. What do the plugs look like?
Safety Car
Joined: Sep 2003
Posts: 3,599
Likes: 24
From: Orange County NY
St. Jude Donor '10-'11-'12-'13
If you are getting / hearing "real" knock and don't have any codes, the sensor is probably functioning correctly (by signaling the ECM, which will in turn, retard the timing).
Tech Contributor
Joined: Jun 2004
Posts: 20,905
Likes: 962
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Before you lose too much sleep on the deal, check your ESC software calibration. Some vehicles of that vintage had a low coolant temp disable of the retard function. While the engine is warming up, the piston slap noise is very similar to detonation noise (they both excite the cylinder walls, causing ringing), and the ESC system can't tell the difference. Rather than pulling out spark, and losing torque and driveability, the software just assumes that the most likely cause of the noise is piston slap, and ignores the ESC system's request for retard. Once the coolant reaches 150-160 degrees, the software assumes that the pistons have expanded sufficiently, and any further noise is actually detonation. The retard function is then enabled.
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Tech Contributor
Joined: Jun 2004
Posts: 20,905
Likes: 962
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
A cold engine can knock in many circumstances, particularly when the absolute humidity is low. You've obviously experienced the right situation for knock. But an engineering decision had to be made what to do while the engine was warming up and the internal clearances weren't ideal. Either act on false knock, or ignore real knock. Driveability requirements led to the decision to ignore knock requests while the engine is warming up. (This assumes that you have a low temp ESC lockout in the software.)
Burning Brakes
Joined: Apr 2004
Posts: 762
Likes: 2
From: Huntington ma
The constants table in the "OEM" .bin file I have for an '85 has a "Minimum coolant temp to enable knock control" setting of 66.5 deg C (151.7 deg F). Cooler than that and there isn't going to be any timing retard because of knocking. Of course, it Shouldn't Have a knock problem that cold - less timing, better gas - Something isn't what it should be.
You can always edit the .bin file and burn a new chip...
You can always edit the .bin file and burn a new chip...
