Engine tapping noise only when accelerating

[Michael Kerich]

My car makes a tapping noise only while driving it. I tried to record the noise when driving, but the noise wasn’t audible in the video. I tried running it in idle for a while and pushing on the gas pedal hard, but no matter what I do, if the car is in park or neutral I can’t get it to make the noise. When she is in neutral she roars like a lion, but when I am driving I hear tap tap tap tap. When not pressing on the gas pedal, but moving I don’t hear it. This doesn’t sound like a noise I should be driving around with. Anyone have any idea what might be causing this noise? Or tips on finding out what is making the noise? If you need me to provide any other information I would be happy to do so. My car is listed right below this post (1999 suburban).

Topic

[Michael Kerich]

It will only take like 10 min. There are only 2 bolts that hold the egr valve in place just zip them off, start her up, look at the egr valve, turn the engine off, then bolt her back on and your done. I would really appreciate if someone could try this. I would test this on another vehicle on my own, but I don’t have another GM vehicle with an electronic EGR valve to test this on.

[Mike]

Thought I had replied already but obviously didn’t.

That guy’s video is silly.
Removing the EGR creates a huge vacuum leak which stalls the engine.

Engine timing, increased octane fuel and the EGR are frequent causes of engine noises upon acceleration.
There’s also the possibility that you have a minor exhaust leak at the manifold, which may only be apparent upon acceleration.

[Michael Kerich]

Well I did some more research on EGR valve testing and I found this site, http://easyautodiagnostics.com/gm/4.3L-5.0L-5.7L/egr-valve-tests-1 which seems like it has a pretty credible method of testing the egr valve. I intend on trying all of the tests. I did test 1, test 5, test 6, and test 7. What we were just discussing (unbolting the egr valve and running the engine with it off) may not have been a good way to test the egr valve, but as T. Thomas described in test 7 of his article referenced above, it did prove that the intake manifold was clear of any blockage. So, on the four tests I did my EGR valve passed with flying colors no issues at all. I did however attempt test 2 and I only got 5 volts. I think I may not have been getting good enough contact with the wire (I was backprobing), so I ordered some wire piercing probes to make sure my numbers are precise. I went to 3 different stores near where I live and none of them sold wire piercing probes. We will get to the bottom of this noise. I don’t care how long it takes. Legally I can’t even drive the car yet I don’t have tags on it, so not a huge rush. I should get some temp tags on it soon (haven’t taken it to inspection yet).

[Mike]

The site you linked typically has very reliable info….
Many believe that it is preferable to back probe connectors, instead of piercing the wires.
A T pin can be used for this .
If you do pierce the insulation, be sure to use a dab of sealant afterward to prevent water ingress.

As far as the 5 volts goes ; Are absolutely you sure you did not test the wrong wire?
There is a 5 volt reference wire to the ECM.

[Michael Kerich]

I used a T-pin for back probing just like you said. I know there is a 5 volt reference. I went back through an re-backprobed all wires with key-on engine off. Here is what I got…

1) EGR Valve Control = 0.03v – 0.04v
2) Sensor Ground = 0.04v
3) EGR Pintle Position Signal = 0.79v – 0.80v
4) 5 Volt Reference = 5.07v
5) 12 Volt Power Source = 0.04V

I tried like 5 times on the power source and one of the 4 times I accidentally went a little too far to the left so I got a 5v reading off it from the reference. I believe that is why I got the 5 volt reading before, because I just kept getting 0 and when I strayed too far I got the wrong number.

[Michael Kerich]

Out of curiosity I just went back out and rechecked the readings again, this time from the other side of the connector. I disconnected the connector from the egr valve and stuck the probe in the connector from the other side and I got the same 5.07v for the 5 volt reference, however, I got 11.79v – 11.80v for the 12v power source this time. I took it out for a short little drive and listening to the noise it sounds like it might have gotten better. Can’t really remember the old noise too well, but I know it sounds better now. The noise I hear now may supposed to be there, idk, but it sounds like a very exhaust related noise near the engine. Something I did definitely changed it some I believe.

[Mike]

If there’s a fault in the wiring, then repositioning the wires may have made for a better connection, at least temporarily.
An EGR that isn’t activating will definitely cause engine noise when accelerating, so it may not be your imagination at all.

[Author]

Replies