Chasing a timing gremlin
Thread Starter
Intermediate
Joined: Oct 2020
Posts: 47
Likes: 10
From: Walden NY
Chasing a timing gremlin
ok, '87 C4 auto - basically stock. Try to set the timing to 6 degrees. timing advance wire unplugged, engine warm, in drive and wheels blocked. Set it fine. go for a test drive and it pings all the time. set it to degrees - same thing. pulled #1 plug and brought up to TDC. marks point to 0 degrees. inertia ring didn't slip on damper. it pings under moderate acceleration. running 93 octane - from different stations. any ideas? I have used an advance light and a standard light - same diff.
oh, and it will set a 43, but that just tells me the knock sensor is working.
oh, and it will set a 43, but that just tells me the knock sensor is working.
Last edited by LokiFalkor; Sep 7, 2021 at 02:28 PM.
Le Mans Master
Joined: Sep 2013
Posts: 6,192
Likes: 750
From: near the thumb in the mitten
Carbon build up. EGR inop. Localized overheating. DTC43 knock sensor system isn't working. If you tap engine with a hammer while watching timing; does it retard? If not you need to find out why. If it does, excessive spark is probably causing it.
Team Owner
Joined: Aug 2004
Posts: 21,543
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From: Park City Utah
Also, what operating temp?
Drifting
Joined: Jan 2005
Posts: 1,354
Likes: 324
From: San Antonio Tx
If you can datalog, check to see if the reported advance matches the timing light advance throughout the rpm range. Is the Ignition Control module original? There is a long thread on thirdgen.org about using an aftermarket ICM or even a GM ICM with a different part number than original. They can affect the timing, sometimes + or - six degrees or more.
Melting Slicks
Joined: Aug 2003
Posts: 3,395
Likes: 393
From: Lakeville MI
Code 43 means that the knock sensor is not working.
The knock sensor diagnostic forced knock test will add ignition timing (as much as + 25 degrees over a span of 3.9 seconds, or until it knocks) which can lead to engine damage especially if it never knocks. This is a dangerous condition to be in. I will post a log showing the effect once I have a chance to dig it up.
The knock sensor diagnostic forced knock test will add ignition timing (as much as + 25 degrees over a span of 3.9 seconds, or until it knocks) which can lead to engine damage especially if it never knocks. This is a dangerous condition to be in. I will post a log showing the effect once I have a chance to dig it up.
Last edited by tequilaboy; Sep 11, 2021 at 11:17 AM.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
I was under the impression that this test was only run on start up, on GM's?
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Melting Slicks
Joined: Aug 2003
Posts: 3,395
Likes: 393
From: Lakeville MI
Knockout punch data as promised.
https://datazap.me/u/tequilaboy/forc...-6&mark=166-13
Note the difference in the spark advance behavior at the two yellow marker points. First WOT event shows the expected spark advance (Coolant temp interesting to note: 203 °F). This was a supercharged car with timing limited to 22 degrees at WOT. See the dramatic ramp up of spark advance during the 2nd WOT event (Coolant temp interesting to note: 204 °F). This is the forced knock test in action (for code 43 diagnostic purposes).
It also leaned out badly during the first event which didn't help matters.
Boost plus bad knock sensor plus forced knock test can literally knock you out (No knock count-knockout). I think this log actually captures the engine damage, or it failed soon afterwards.
https://datazap.me/u/tequilaboy/forc...-6&mark=166-13
Note the difference in the spark advance behavior at the two yellow marker points. First WOT event shows the expected spark advance (Coolant temp interesting to note: 203 °F). This was a supercharged car with timing limited to 22 degrees at WOT. See the dramatic ramp up of spark advance during the 2nd WOT event (Coolant temp interesting to note: 204 °F). This is the forced knock test in action (for code 43 diagnostic purposes).
It also leaned out badly during the first event which didn't help matters.
Boost plus bad knock sensor plus forced knock test can literally knock you out (No knock count-knockout). I think this log actually captures the engine damage, or it failed soon afterwards.
Thread Starter
Intermediate
Joined: Oct 2020
Posts: 47
Likes: 10
From: Walden NY
The timing is checked with the wheels on the ground, car warmed up in drive, e-brake on and wheels blocked with distributor wire disconnected. on the emissions sticker under the hood it states timing for an auto car is 6 degrees (DR) - in drive. 6 degrees (N) in neutral is listed for a manual car. the FSM states to follow the directions on the emissions decal.
This is for stock - you guys pulling wheelies are doing whatever you need to do.
This is for stock - you guys pulling wheelies are doing whatever you need to do.
Last edited by LokiFalkor; Sep 10, 2021 at 08:41 AM.
Melting Slicks
Joined: Aug 2003
Posts: 3,395
Likes: 393
From: Lakeville MI
The only reason for this is to get the engine to run at the (minimum) desired idle rpm setting (typically 550 rpm in gear for an auto trans car). Park/neutral adds a 50 rpm offset. In reality, makes little difference. Manual trans cars have no offset and have a desired idle rpm target of 700 rpm.
Back to the main topic. A car with a bad knock sensor is a ticking time bomb due to the potentially destructive nature of the code 43 diagnostic forced knock test. Fix it or disable it via tuning. You have been warned.
Back to the main topic. A car with a bad knock sensor is a ticking time bomb due to the potentially destructive nature of the code 43 diagnostic forced knock test. Fix it or disable it via tuning. You have been warned.
Last edited by tequilaboy; Sep 10, 2021 at 09:00 AM.
Team Owner
Joined: Jul 2004
Posts: 28,430
Likes: 3,279
From: Hartford WI
With the tan wire disconnected, does it matter how you want to do timing? It should still stay at base timing regardless of whether it is 500 or 1500 RPM, right? AS LONG AS YOU keep it running smoothly, I think.
Isn't the KS supposed to advance timing for the test till it feels like it should be knocking or how far will it go till it stops the test? On a stock system, that is.
Isn't the KS supposed to advance timing for the test till it feels like it should be knocking or how far will it go till it stops the test? On a stock system, that is.
Thread Starter
Intermediate
Joined: Oct 2020
Posts: 47
Likes: 10
From: Walden NY
So, after much fiddling - figured it out. It was a combination of a few items. 43 was being set by the bad knock sensor, but I still had detonation. I also had a bad egr valve - which was doubly bad as it was stuck and the diaphragm was ripped. so I was getting a vacuum leak and egr was not cooling the combustion chamber. so new knock sensor, new egr, about 6 feet of new vacuum line as every time I touched a hard line it broke, a new fuel pressure regulator since the plenum was off... and no more 43 or detonation. this also allowed me to correctly set the timing to 6 degrees. it's running really good now. thanks every one for your suggestions.
