2002 Savana Pinging

badsavana · February 19, 2014

I am new to the forum and want to say thanks for all of the helpfull advice you all give.

Now down to it. 2002 GMC Savana 5.7 4l80 125K. It started pinging at low rpm. Once it gets higher in the rpms it stops. Not knowing anything about computer controled I reverted to what I do know. Seems like timing is advanced. So I looked up how to time this vehicle and from what I can tell, without a tecktool, it is right on. I have a digital service manual but it seems to be missing any troubleshooting procedures.

Can someone please direct me as to where to start and what to test?

Thank you

txab · February 19, 2014

Check for codes being set in the ECM for starters with an OBDII reader. Most auto parts stores can do it for you, if you don't own one. It could be knock sensors

Doug_Scott · February 19, 2014

If you are hearing it ping under load at low rpms, then something is not working correctly. The engine has knock sensors (as txab has posted) that are there to prevent pre-ignition. If you have a scan tool you should be able to see that timing is not being retarded by the ECM. I do not recall if the knock sensors will turn the CEL on or not. What fuel are you using? Did this just start one day, or has it been doing this for a long time? If the engine has only been driven easily it may have a build up of carbon in the combustion chamber. Putting the gas pedal to the floor from a dead stop and running the engine up to max rpm in low gear until is shifts into second gear will loosen the carbon up and clean it out of the combustion chamber without violating the speed limit too much. Let off after the shift to second gear. If you are seeing a lot of smoke during this, you may have to do it a couple of times. This can be done on the on-ramps to the highway as well. No need to do a high speed run on the highway.

This will not fix the reason why you can hear the pinging though, You need to get the timing retard checked to see if the knock sensors are working;

badsavana · February 19, 2014

The CEL is not lit. Every once in a while I will see it flash breefly but it does not stay on. This is a new problem but there are other ongoing issues as well. I will hook it up to my scanner and see if there any codes stored and teport my findings. This is my daily driver work truck it is not druven like an old ladies buick, so I doubt that there is any carbon buildup. Sorry about the spelling errors. Very hard to edit on my "smart" phone.

Chris · February 19, 2014

If it flashes, its misfiring

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badsavana · February 20, 2014

I just looked at it with my scanner and there are no codes. I used scan xl pro and I can log to a file if any of that info will help. I have no idea what the values should be so I don't know what I am looking at. If you want I will set up a log for whatever pids you want to look at.

badsavana · February 20, 2014

"If you have a scan tool you should be able to see that timing is not being retarded by the ECM. "

I do have a scan tool. What values should I be looking for?

"Did this just start one day, or has it been doing this for a long time? "

This just started about 2 days ago. I have been having other lack of power and fuel milage issues for a while now.

"You need to get the timing retard checked to see if the knock sensors are working;"

Retard should be warm at 1000rpm? What is an acceptable value for this?

Doug_Scott · February 21, 2014

Try to find Knock Control. That should tell you if the knock sensors are working. They will retard timing to stop the ping. I do not know the limits for this. Are you not getting error codes at all? If the knock sensors are working, they should be setting a code for being at max retard and still not being able to stop the ping.

I don't have enough practical experience to suggest what would be acceptable limits for knock control.

badsavana · February 21, 2014

No codes. Seems kinda silly to me but the way it was explained to me is that the CEL will only illuminate for emissions issues not necessarly driveability issues. This has been the root of all my issues. I downloaded the service manual hoping that there would be some troubleshooting procedures and values but I got nothing.

The scan software I have will look at almost anything. It's on my laptop and I can do realtime data logging but like I said I haven't been able to find what values should be for all of these sensors. If I had that info I could go through and watch to see what one is out of wack and reaking havoc.

badsavana · February 22, 2014

I there a digital gm troubleshooting guide that has acceptable values for these control sensors? I need my truck, without it I am out of business.

badsavana · February 23, 2014

There has to be a chart of sensor values. What do you guys use? Where can I get this info?

Doug_Scott · February 24, 2014

I doubt a knock sensor has a range of values. It is either sensing a knock(ping) or it isn't. When it senses a ping, the ecm makes adjustments to reduce/stop it, Not sure if you have searched for the term "knock retard" in google or not, but, I just did, and found this right at the top of the list... Not sure if posting links is allowed or not, guess I will find out now.

Nope, you can't post links. Use google for knock retard and read the link to Knock Retard and you...

badsavana · February 24, 2014

This came from the first result

"KR is an electronically determined value based upon signal input from the knock sensors. As such, the best way to determine whether or not you have KR, and if so how much, is to use a scan tool to actually read that parameter ID (PID) from the PCM."

I see KR but without knowing what if any is acceptable I am unable to determine if this is a factor in what is going on.

I have spent many hours looking for info. I have downloaded two "GM factory service manuals" neither have any troubleshooting info or procedures that the hard copies have.

I'm not asking for a diagnosis. I'm just looking to find the tools to help myself.

I am not looking to change parts I am looking to gain some knoledge, and hopefully pass some on to others in the same or similar position, and make an educated diagnosis based on known good parameters, Unfortunatly to this point I have been unable to find these parameters.

oldscsc · February 24, 2014

Easy way to test the knock sensors is to tap the engine block with a hammer and watch the PID. If it spikes, the sensors are working.

Doug_Scott · February 24, 2014

What numbers are you seeing in KR? I would expect the best place to find out if that number is good/bad/indifferent is one of those companies that sell pcm tunes. You may be able to get an answer from Justin at BlackBear. BlackBear has its own forum here as well.