Hi guys, well it seems the MGM99 is in a slow downward spirl.

Big Problem right now is worsening engine ping. It used to occure in a narrow band around 103kph, now it's spreading to a spot near 60kph, and more at 80 to 110kph. It occurs when the engine is at -medium- load, very gentle or harder acceleration stops the ping.

So far I've replaced and checked these things, (nothing changed the pinging problem):

Fuel filter
Fuel pump - unrelated issue
Air filter
Coolant flushed and replaced, didn't change anything.
MAF - cleaned recently.
Sparkplugs - checked, nice OEM fresh and clean.
Carbon in combustion chamber - seems very minimal, Seafoamed and no accumulation found on piston tops.
ScanGuage shows coolant temp steady around 198-202. I think it may be pinging only once fully warmed up.
OBDII scan shows no error codes.

Seems that the pinging is spreading with the warmer weather?? Any tips?

Try a better cleaner like Gumout Regane, Techron Concentrate, or Redline SI-1.

I really dont care for Seafoam, I have never seen it make much of a difference.

psucrownvic, I've looked around for other cleaners, the only one I found was Seafoam. In any case, from what I can see, there is next to no carbon buildup in that engine. I Seafoamed it to help with the ping, didn't do anything. Then I peeked into the combustion chambers via the sparkplug hole and can see that the piston tops don't have carbon buildup.

Don't know what to check next!

Did you also seafoam through your vacuum lines? Crankcase? etc.
If not, you will be surprised how much it can help.
You may want to check for a vacuum leak, manifold vacuum leak, or EGR, etc. All can cause symptoms of pinging.
I use Gumout Regane in my tank every oil change, but for cleaning a motor, etc..........hands down, there is nothing on the shelf that can touch it. You shouldnt see much improvement through your fuel system if you properly keep it clean, change your fuel filter every 10K miles or so, and throw some cleaner through every oil change.

cop4, I fed the seafoam through the PCV line, and put the bit left over in the tank, that's it. Right now I've got some AutoRx in the oil, about ready to get flushed out.

Okay, so I'll have to start hunting through the vacuum system, and the EGR, sounds like a good possibility the problem is there. Anyone have any clues where I should start on a 99?

Any CEL? Considering the things you have already checked and cleaned it's most likely an EGR issue. The tube or the valve itself may be clogged, or it could be a malfunction with the DPFE sensor. Ping may also be cause by a lean condition, which, considering the mileage of the vehicle could be caused by dirty fuel injectors.

Honestly, don't put any of that crap in your tank, it's not going to do anything for dirty fuel injectors. The best way to clean them is with the WYNNS V.I.C. - Valve, Injector, and Combustion chamber cleaner. With the proper equipment you hook up to the fuel rail, then feed shop air to the canister. You kill the inertia switch to prevent the pump from running and you run the engine entirely on the injector cleaner. I just recently did this to mine and it really smoothed out the engine under all loads, but I didn't have any pinging problems.

I would find a shop that can do this for you after checking the EGR. You could also pull the vacuum line off the EGR and plug it up. Then go for a drive and try to reproduce the ping, if it stays the same the EGR system isn't functioning properly. If it gets worse then it still may indicate an EGR problem, probably a clog of some sort/lean condition.

try a tank of premium fuel?

You might check the fuel trims at idle, 1500 and 2500 rpm to find out if the computer is leaning the fuel mixture. If so, something is causing a sensor to tell the computer to lean, or a sensor may be defective. You didn't mention the o2 sensors; you might check the output to make sure they are operating properly.

DeadHead, I haven't gotten any CELs on that car, and nothing comes up with the OBDII scan. A few months ago I checked the EGR valve, passages, selenoid, and voltage. Everything seemed okay. Forgot to mention that in the list above!

Yeah, I'm not keen on stuff in the fuel tank. That was the only car I did it with. All the others I just fed it through the vacuum lines.

So maybe that points to the DPFE sensor or clogged injectors. I want to take the injectors out and have them ultrasonically cleaned and then tested. Given what I know about the shops in the area that might be better than getting them cleaned in the engine.

Modular, I tried that with the 96, and from what I can tell it just helped accumulate carbon in the combustion chambers!

jjacob, not sure how I would check the fuel trims at different RPMs. What is needed to do that?

Yes, using premium fuel in order to reduce ping is counter productive. Although it is harder to ignite, once it does it quickly raises combustion temps. This just causes more varnish and carbon deposits to build up in the cylinder walls, and especially on the injectors and intake valves when the vehicle is turned off. It does more harm than good.

Checking the fuel trims would require the use of a scan tool that can check more than just universal OBD codes. I think a scan gauge is able to access fuel trims, or you'd need an expensive scanner.

Yvan -
I had a pinging problem that I chased for a very long time and I tried all of the things you mentioned to no avail. I also checked for operation of the EGR Valve. It worked fine.
Then a couple weeks ago I did something that got rid of the ping and I am back to 87 octane.

I had to change the intake manifold due to the dreaded crack. So the whole intake was off the car. I cleaned the throttle body. It wasn't too bad, but, The plenum, my God, The Plenum! It was disgusting. It was very dirty and the inlet from the EGR had a ball of carbon and gunk about 9mm almost closing off the port. I completely cleaned the plenum to be shiny inside.

I also changed the thermostat to a 192°F from the 195°F that was in there and changed the hoses only because it was a convenient time to do them. My coolant was changed but it was only 4 months old.

So, I cannot say with certainty what exactly made the ping go away because too many things were changed but my strong suspicion is the EGR port in the plenum.
It is pretty easy to get to so check it out and Good Luck.

Auto RX is fine for the motor, and seafoam should have gotten the uppers. I still say something with the EGR, or a vacuum leak with the manifold.

Cop4, I think the list is narrowing down to EGR, DPFE, and vacuum leak. Maybe in that order!

jpa, now that sounds interesting! I think you might be onto something there! And it meshes with what the other guys are talking about....

BTW, starting to track down the DPFE sensor. Where is that thing?

Agree - clean upper plenum.

New EMP Stuart water pump. $149.00 Temps much better.
What is your water temp say via SGII?????

Mine is always on 190.

also you could go one range colder plugs.