Pinging and vacuum leak question
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Pinging and vacuum leak question
My 97 4.2L 65k miles has a pinging problem on a slight load. I also know I have a slight vacuum leak based on LTFT. They stay between 5 and 10% at idle and drop below 5% at cruising. No code, no pending code.
I know vacuum leak can cause pinging. But always? Does every engine with vacuum leak ping? Rephrased, do all lean code engines because of vacuum leak ping? Reason why I ask. I did a thorough vacuum leak check using a home made fog machine. Replaced all vacuum hoses within reach. I haven't done plenum gasket yet. I also measured vacuum at several locations. All within range. I wonder if I have done enough homework to start throwing parts like knock sensor, maf sensor, oxygen sensor, etc. Individually maf sensor and oxygen sensors are okay. For instance oxygen sensors output 0.7V downstream and 0.2 to 0.7V swing upstream. I don't remember maf sensor voltage output, but remember within range. Thank you.
I know vacuum leak can cause pinging. But always? Does every engine with vacuum leak ping? Rephrased, do all lean code engines because of vacuum leak ping? Reason why I ask. I did a thorough vacuum leak check using a home made fog machine. Replaced all vacuum hoses within reach. I haven't done plenum gasket yet. I also measured vacuum at several locations. All within range. I wonder if I have done enough homework to start throwing parts like knock sensor, maf sensor, oxygen sensor, etc. Individually maf sensor and oxygen sensors are okay. For instance oxygen sensors output 0.7V downstream and 0.2 to 0.7V swing upstream. I don't remember maf sensor voltage output, but remember within range. Thank you.
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Ping Causes: Ignition timing to far advanced. EGR leakage, fuel pressure to low, fuel quality poor, deposits in combustion chambers from burning oil or other causes.
Vacuum leak seldom causes a Pinging condition but can be a secondary cause.
The Knock sensor normally causes the PCM to retard the ignition timing to stop the Ping until it clears.
Ox sensors are not a cause.
Maf could if it commands too Lean fuel a condition.
.
I would check the ignition timing (with a Scanner) when it is heard to see if ignition timing goes advanced from normal as the cause of the Ping, then look for the cause depending on what you see.
The EGR ports in a V6 are separate in the intake runner for each cylinder. On V8 it is common to all the cylinders from one source point. An important difference between the two motors.
Good luck.
Vacuum leak seldom causes a Pinging condition but can be a secondary cause.
The Knock sensor normally causes the PCM to retard the ignition timing to stop the Ping until it clears.
Ox sensors are not a cause.
Maf could if it commands too Lean fuel a condition.
.
I would check the ignition timing (with a Scanner) when it is heard to see if ignition timing goes advanced from normal as the cause of the Ping, then look for the cause depending on what you see.
The EGR ports in a V6 are separate in the intake runner for each cylinder. On V8 it is common to all the cylinders from one source point. An important difference between the two motors.
Good luck.
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Thank you, Bluegrass7, for the pointers. I will check one by one. I have 2 followup questions.
1. EGR leak: Do you mean exhaust gas leaking to atmosphere from somewhere in the EGR system?
2. Ignition timing advance: Is this what I am supposed to do? With the scanner attached to OBD2 port, go up on a hill to increase engine load. Timing will advance. When I hear pining, see if timing gets retarded immediately? My wife is the only helper I have and I am not sure if she would like this assignment, to watch a graph on a laptop screen in a moving vehicle.
EDIT Question 2: I can record ignition timing advance and engine load. Uphill will be marked by a sharp rise of engine load. I will not need to hire my wife as a helper.
1. EGR leak: Do you mean exhaust gas leaking to atmosphere from somewhere in the EGR system?
2. Ignition timing advance: Is this what I am supposed to do? With the scanner attached to OBD2 port, go up on a hill to increase engine load. Timing will advance. When I hear pining, see if timing gets retarded immediately? My wife is the only helper I have and I am not sure if she would like this assignment, to watch a graph on a laptop screen in a moving vehicle.
EDIT Question 2: I can record ignition timing advance and engine load. Uphill will be marked by a sharp rise of engine load. I will not need to hire my wife as a helper.
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Exhaust leaking back into the intake tract usually causes the ignition timing to advance and/or leans out the mixture.
Either or both can cause pinging.
In "normal" EGR operation, the timing goes advanced by design, fuel is cut back.
Under "normal" EGR operation this is transparent to the driver because the Ox sensor get into the action..
When it occurs any other time, Ping and spark knock can occur.
This is why you need to observe when it occurs and under what circumstance.
Ordinarily you should almost never hear Pinging unless your hearing is quite good and then only hear it a very short times until the program takes action upon hearing from the Knock sensor, especially towing a heavy load for instance..
What normally happens with towing, the programs self adjusts the fuel and timing for the expected higher loading on the motor..
Once you run without a load after towing for awhile the motor may seem to be a bit more torquey until the PCM reverts back to more or less normal unloaded conditions.
Either or both can cause pinging.
In "normal" EGR operation, the timing goes advanced by design, fuel is cut back.
Under "normal" EGR operation this is transparent to the driver because the Ox sensor get into the action..
When it occurs any other time, Ping and spark knock can occur.
This is why you need to observe when it occurs and under what circumstance.
Ordinarily you should almost never hear Pinging unless your hearing is quite good and then only hear it a very short times until the program takes action upon hearing from the Knock sensor, especially towing a heavy load for instance..
What normally happens with towing, the programs self adjusts the fuel and timing for the expected higher loading on the motor..
Once you run without a load after towing for awhile the motor may seem to be a bit more torquey until the PCM reverts back to more or less normal unloaded conditions.
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