cam retard 1999 blazer
#1
08-13-2007, 06:15 PM
cam retard 1999 blazer
1999 Blazer 4.3L 2door LSauto 4x4 196,000kms.
How is the cam retard reset after distributor install. Need a GM computer or anything.
Ignition advance is 20 degrees at idle 650 rpm.The scan tool I have does not have anything about cam retard reset What should retard be at.
Anyone know of a low cost scan tool that has cam retard reset if I need one?
thanks for any help.
How is the cam retard reset after distributor install. Need a GM computer or anything.
Ignition advance is 20 degrees at idle 650 rpm.The scan tool I have does not have anything about cam retard reset What should retard be at.
Anyone know of a low cost scan tool that has cam retard reset if I need one?
thanks for any help.
#4
08-14-2007, 07:38 AM
RE: cam retard 1999 blazer
How are you monitoring detonation? With your scan tool? KR (knock retard) is the value that you want to be viewing if you suspect knock (detonation). What octane fuel are you running when you are experiencing the detonation?
Spark knock can have several causes, or combinations of causes. Among the most common are improper ignition timing, carbon deposits in the cylinders creating hot spots, malfunctioning EGR system, ignition system crossfire posibly caused by carbon trails in the cap, a malfunctioning knock sensor or low fuel octane.
Have you attempted to *time the engine? Turning the distributor serves only to adjust what GM calls the cam retard offset. Actual ignition timing is controlled by the PCM, based on the information it receives from various input sensors. However, our distributors cannot be rotated by much (if at all) due to the square shoulder that the distributor clamp sits on at the base of the distributor. With that said, 20* of timing advance doesn't sound too bad for idle. I'd have to look at my scans from my old Bravada to tell you what it would run at idle...
So, moving down the list of possible causes:
If improper ignition timing is the cause, then mostlikely either the CKP (crank position) or CMP (cam position) sensor has either gone bad or is in some other way feeding poor information to the PCM. This may be possible if the CKP sensor has been changed recently and a crank true position variation learn (CASE learn) has not been performed.
Carbon deposits... A higher octane fuel will help to combat this problem as the octane rating is a measure of the fuel's ability to resist preignition. Now, this should be a fairly easy one, but if you have a lot of carbon buildup in the engine, it may take repeated cleanings to get your engine cleaned out. I recommend a Seafoam treatement (<--CLICK). I will add that inorder to pour Seafoam down the throttle body, you will need to disconnect the MAF sensor if you intend to use this method of introduction as the motor won't run long without air flowing through the MAF. While you're at it, now would be a good time to disassemble and clean the MAF sensor (there are many good threads on this) just make sure you use either electronics parts cleaner or a MAF specific cleaner.
A malfunctioning EGR system can lead to detonation under moderate to heavy throttle. By introducing spent exhaust gases into the process, the cylinder temperatures are reduced. Without those spent exhaust gases, the temperatures will increase, possibly causing detonation. It may be permissible to clean the EGR system while your in the cleaning mood... Use sensor safe carbon cleaner for this task.
Ignition system cross fire... Well, as I stated above, this is possibly caused by carbon trails in the cap allowing spark to jump between terminals instead of being directed to one cylinder at a time... This can be checked by removing the distributor cap and inspecting the inside for said carbon trails.
A malfunctioning knock sensor may not be detecting spark knock and compensating before it gets to the audible level. If this is the case, when monitoring the knock sensor by viewing either the KR (knock retard) or the knock sensor active count. If you see little to no activity but hear detonation, then you have a faulty knock sensor.
And last but not least, low octane fuel or bad gas... Have you tried a different gas station? How does it respond to higher octane fuel? As stated earlier higher octane fuel will help combat preignition due to hot spot creating carbon deposits, but bad gas or gas that does not meet the minimum 87 octane rating may cause detonation.
Hope this helps...
Spark knock can have several causes, or combinations of causes. Among the most common are improper ignition timing, carbon deposits in the cylinders creating hot spots, malfunctioning EGR system, ignition system crossfire posibly caused by carbon trails in the cap, a malfunctioning knock sensor or low fuel octane.
Have you attempted to *time the engine? Turning the distributor serves only to adjust what GM calls the cam retard offset. Actual ignition timing is controlled by the PCM, based on the information it receives from various input sensors. However, our distributors cannot be rotated by much (if at all) due to the square shoulder that the distributor clamp sits on at the base of the distributor. With that said, 20* of timing advance doesn't sound too bad for idle. I'd have to look at my scans from my old Bravada to tell you what it would run at idle...
So, moving down the list of possible causes:
If improper ignition timing is the cause, then mostlikely either the CKP (crank position) or CMP (cam position) sensor has either gone bad or is in some other way feeding poor information to the PCM. This may be possible if the CKP sensor has been changed recently and a crank true position variation learn (CASE learn) has not been performed.
Carbon deposits... A higher octane fuel will help to combat this problem as the octane rating is a measure of the fuel's ability to resist preignition. Now, this should be a fairly easy one, but if you have a lot of carbon buildup in the engine, it may take repeated cleanings to get your engine cleaned out. I recommend a Seafoam treatement (<--CLICK). I will add that inorder to pour Seafoam down the throttle body, you will need to disconnect the MAF sensor if you intend to use this method of introduction as the motor won't run long without air flowing through the MAF. While you're at it, now would be a good time to disassemble and clean the MAF sensor (there are many good threads on this) just make sure you use either electronics parts cleaner or a MAF specific cleaner.
A malfunctioning EGR system can lead to detonation under moderate to heavy throttle. By introducing spent exhaust gases into the process, the cylinder temperatures are reduced. Without those spent exhaust gases, the temperatures will increase, possibly causing detonation. It may be permissible to clean the EGR system while your in the cleaning mood... Use sensor safe carbon cleaner for this task.
Ignition system cross fire... Well, as I stated above, this is possibly caused by carbon trails in the cap allowing spark to jump between terminals instead of being directed to one cylinder at a time... This can be checked by removing the distributor cap and inspecting the inside for said carbon trails.
A malfunctioning knock sensor may not be detecting spark knock and compensating before it gets to the audible level. If this is the case, when monitoring the knock sensor by viewing either the KR (knock retard) or the knock sensor active count. If you see little to no activity but hear detonation, then you have a faulty knock sensor.
And last but not least, low octane fuel or bad gas... Have you tried a different gas station? How does it respond to higher octane fuel? As stated earlier higher octane fuel will help combat preignition due to hot spot creating carbon deposits, but bad gas or gas that does not meet the minimum 87 octane rating may cause detonation.
Hope this helps...
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