Hi guys, first post here. I have a 96 automatic coupe and recently it's started pinging at low rpms. At least I think that's what's going on.

There is a rattly, metallic vibration noise from under the hood that's linked to the throttle position/rpms. It happens in a narrow range around 2k rpms and at lower speeds (yes at 30, not at 50), and more so when accelerating. I tried revving the car to this level when in park and the noise didn't happen then. I don't have a check engine light and scanning the car with a bluetooth OBDII reader did not return any codes.

I am really new to working on cars but I want to learn so I'd like to fix this myself if I can. I think the cause might be a faulty EGR valve, since I've read that is a common cause of pinging, and my car has a couple other possibly related symptoms:

• Slightly rough idle (rpms are fairly constant, but it shakes the car a little in an uneven pattern). Didn't bother me previously, but it might be related.
• NOx emissions were relatively high when I got it smogged (in CA). It passes, but everything else was way under the limit and this was somewhat close to it.

Does anyone have advice on what to try to diagnose this? Either related to the EGR valve or to other possible causes of the pinging?

Thanks in advance!

 

Welcome to the forum! What grade (octane) fuel are you burning?

 

Hi Jud, thanks. The best that's widely available in CA is 91 octane so that's what I always use. That's what I've used since I've had the car (for about 5 months, 4k miles) and this problem started about a week and a half ago.

 

Have you pulled the trouble codes, if any. If you don't have a scanner to do this, I believe AutoZone does it for free. This is what I'd do first.

 

Yes, I have a bluetooth obdii reader and an android app called torque that connects to it, and it said I have no codes.

 

Sorry, I see you have already pulled the codes. I would suggest a search on this forum to see if if you can find some related info. At this point, if I understand you, you are not sure it's pinging.

 

Welcome to the madness!

How many miles on the clock?

Have you heard (Before) this vehicle, an engine "Ping" and do you really understand what they sound like?

There should not be any vibration associated with a real engine ping, (audible) only, and with your car 96, and mine 95.. Grade of fuel will not be an issue, the PCM will compensate for a few [points] difference in fuel grade.

You need to find your self a Factory Service Manual set, it will give you the correct troubleshooting steps for the EGR system, I would reframe from buying an EGR valve until you've done some comprehensive trouble shooting.

 

Check the heat shields on the exhaust manifolds.

 

EGR is a good starting point. However, many have removed theirs without having pinging. Slightly rough idle is a clue.

EGR will only report a code if there is a system fault with it. It and the manifold could be carboned up and since the valve is still "functional" it won't report a code. The pintle in the valve could be slightly open due to carbon causing the rough idle.

Being that it's a 96 then you OBD II which would report a lean code bank one or bank two if there was a vacuum leak or actual lean condition which also would also cause pinging.

I'd check out the EGR system first and make sure the manifold passages and the valve are free of carbon.

It's the best course with no codes.

 

Thanks for all the replies!

No, I hadn't heard pinging before, which leads to my uncertainty here. I want to be clear that there is no felt vibration, I just meant that it is a vibration sound, like metal rapidly rattling against metal. I really think it's pinging though since it's always related to throttle position/speed. I've found (on the few times I had to drive the car, I haven't been doing so much out of caution) that it happens less when I use "2" on the transmission when at low speed. This way, I guess, it doesn't sit in that just-under-2k rev range where the pinging happens as much.

I now have a factory service manual though there is not much in there about egr diagnosis. I found more info at these sites: http://tech.corvettecentral.com/2012...egr-diagnosis/
http://shbox.com/1/4th_gen_EGR.html My car has 109k miles, btw.

I tried manually pushing on the valve with the engine running and the revs dropped a bunch (as recommended on that second link), so it's not completely clogged, but there are other things I haven't tried yet. I don't have all the tools yet for the next steps though.

One silly question though: How do you remove the vacuum lines to check them or to remove the egr? The manual just says "remove", but they don't pull off easily and I didn't want to pull hard and risk breaking anything. Do they just pull straight off or is there a trick to it?

Thanks again for the help!
Curtis

 

manwithnoname: if you are able to lift the car so able to get under it; use you hand / fist and bang on the cats and listen for any kind of rattle. Just use your hand, no hammer.
If you hear a rattle, then the internals have broken loose and you get to replace the cat(s). AND good luck finding cats for CA.

Vacuum line removal usually requires a small screwdriver or similar to get under the hose to break the seal. Have also lifted an edge of the hose and squirted a small shot of silicon spray to get the hose loose. Then it will twist right off and will go back on.

Good luck.

 

Curtis,
I have had more pinging this "winter" gas season and still into spring more than any year in memory here in SDCo. I think the gasoline is off, especially with the Torrance refinery down. Where do you live? I would like to put my finger on the gasoline situation before I would say to service the car.

That said, a malfunctioning EGR, high ignition timing, high ambient temps, high coolant temp could all affect pinging. As would a bit of carbon build up on the pistons (not as likely). In my case I'm running custom ignition timing on my LT5, and have taken timing away in the past. It seems like I will have to do it again. Before I do that I was going to drive down to a certain station that sells 100 octane unleaded and get a couple of gallons.

 

You can test the EGR vacuum line by putting a vacuum gauge on it while you drive under a load. Tape it to the windshield. You should get a little oscillation of vacuum there right as you transition into the gas pedal. It will only be at those moments when you crack the throttle. that's what it does- introduces a puff of dirty air into the intake to lower combustion temps reducing the NOx (oxides of nitrogen). On the GM cars, usually the rubber diaphragm leaks and won't open very far.
That said, constant pinging is fuel/ engine temp/ ign timing related.

 

Happens in a narrow RPM range? Optispark. Sorry to even have to bring that up but it's possible. If I'm not mistaken this would be the "spark" part of it and not the "opti" part (which for me is what always fails instead). There's a multi-page table in your new FSM about Optispark diagnosis (you did buy the correct red-cover ones instead of the white highly-abridged version, right?).

I've also had plugged cats before which caused a hell of a lot of pinging and eventually the car wouldn't run at all. They were in this condition when I purchased the car. Solved that with a pair of straight pipes because I was in Kentucky and eager to get back on the road.

 

If you purchased the Two Volume FSM set, then there will definitely be a section covering the EGR system, in detail! you may try looking under (DTC 32) Exhaust gas recirculation system trouble code. To help you along.

The FSM's take a little getting used to in order to find things.

You can test the exhaust system for a restriction by simply hooking up a Vacuum gauge to the intake manifold and Observing your readings in hg/in on the gauge.. check out this ETCG video for clarification!

 

Just thought I would come back and close the loop on this to help other people in the future...

It turned out my problem was not pinging, but it was just a broken-loose exhaust heat shield that rattled when the engine was under load. I'm pretty glad it wasn't anything more serious! The car is feeling great now!

Thanks for all the input!