Pinging/knocking sound

[paolotvl]

My truck, 1987 5.7 liter, unknown mileage (probably 200k plus). When I push it a little harder I hear a pinging sound from the engine. My guess is either pinging/knocking (although it does it also the same exact way with premium gasoline) or the timing chain. It does it, for instance, when I am at 65 mph and I floor it to over pass another vehicle while getting up to 75-80 mph. What's more common? Thanks.

 

[bucket]

What is your timing set at and what are your oil pressure readings?

 

[paolotvl]

Hi, I do not know my timing set. The oil pressare seme to be steady at 60 psi.

 

[bucket]

If it's always at 60, your gauge may not be working properly.

I'll use my '88 Burb as an example. When I got it, I advanced the timing several degrees, but not far enough to ever get pinging. Drove it for years like that and it was fine. Then it started burning oil pretty good at some point, and after a while of that, it started pinging/knocking exactly how you describe. I figured it was probably due to a lot of carbon buildup on the valves. So I started running premium in it and there was no longer any pinging/knocking.

So right now, my theories are: Your distributor hold-down is not tight enough and your timing advanced itself way too far. You have a lot of carbon buildup. Or you might just have rods knocking.

Timing will be the easiest to start with.

 

[350runner]

Unplug your vacuum advance for time being till you can narrow the issue down.

Sent from the dust in front of you!

 

[shortboxchevy77]

87 with TBI (if still all factory with TBI) has no Vacuum advance, all electronic. First thing to check is timing second to check is knock sensor. If it is pinging that hard and the knock sensor is functioning correctly it should have pulled all the time giving you a big loss of power while at the same time turning on the check engine light.

To time your specific vehicle you need to unplug one of two one wire connectors that are located directly over the steering column shaft in the engine compartment. The correct wire once unplugged will cause your check engine light to come on immediately. Once you have done this you can set your time to zero degrees and shut the truck off then plug the timing wire back in.

To check for knock sensor function get the engine to operating temp and while idling observe the harmonic balancer with a timing light. While watching the balancer with a timing light give the passenger side exhaust manifold a few good taps with a light hammer, you should see sudden movement of the balancer with the timing light as the ECM attempts to pull timing. If you do not you more than likely have a failed knock sensor.

Here is the odd part about your issue: The ECM will advance the timing under certain throttle loads until it senses a reading from the knock sensor and then will use that as a base line for a duration of time when everything is working correctly. If the ECM advances the timing and never see's a signal from the knock sensor at a certain point it will automatically pull all timing to protect itself and turn on the check engine light to let you know that it is not receiving input from the knock sensor. When this happens you will usually hear the engine ping momentarily followed by a check engine light.

 

[bucket]

The wire to unplug while setting timing is tan with a black stripe.

 

[paolotvl]

Man!! Thank you!! I think you are right on target since it does it when the throttle is completely open which is when a vacuum based System would switch to the anticipated curve. It is probably what the electronic system does but if it is not getting feedback from the knock sensor then it will be running with the wrong timing, it makes perfect sense. Furthermore, I didn't mention it in my post, because I was not sure it was related to this issue, but the service engine light comes on once in a while and often on the highway. I will perform the check you suggest next weekend and post here again. Thank you!

 

[paolotvl]

I just drove it and looked at the oil pressure gauge...it does stay between 30 and 60 all the time...it is probably not working too well...
http://www.youtube.com/watch?v=hmrmHvRyEr0


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