Generation III Internal Engine - please help me figure out why I am pinging, going insane here

Allright I really need your help, lets put our heads together on this one.

I have '01 Z28 A4 with ~50k miles. Always used 92+ fuel in the car. :usa:

Couple of months ago I started hearing metallic rattle-type noise from the engine compartment. It would happen when I push on the throttle and RPMs get in the 1-2k range. In the cold weather it rarely happens and it is just a few clicks after I push the pedal, then it goes away. In the hot weather it is pretty consistent and rattles for 5-10 seconds as long as I am in 1000-2000 band. It never happens at WOT. It never happens in neutral.

Took it to the shop, the guy who worked on it knows f-bodys, he is on these boards. He said that the engine is definitely pinging. We replaced spark plugs and fuel filter. He also checked out the timing and said it looks good. He said that my rear o2 sensors are "a little slow".

The problem did not go away. :guns:

I am on the pretty tight budget at the moment and I really don't want to start replacing stuff without being sure that it is addressing my problem.
Please let me know if you had experience with this or if there is anything I can do to isolate the problem.

Thanks!

maybe try some top end cleaner the pcv system on our cars suck..
but don't forget to change the oil afterwards


good luck!

The engine getting too hot will cause ping, check your coolant, change to a lower thermostat and lower the fan temps.

It seems that I only near the rattle when temp gauge needle goes to within a hair of the middle mark(210) or higher. Are these kind of readings normal? What temp causes fans to come on with a stock setup?

The engine getting too hot will cause ping, check your coolant, change to a lower thermostat and lower the fan temps.

I think they come on around 210 - 220. Also make sure your coolant is full, low coolant will also cause the top half of the engine to get hotter. If you mostly get ping when the temp gets up there, I would focus on cooling it down.

the coolant actually looks like it is overfilled - ~ 2" above cold mark when cold and about 3.5" above the hot mark after daily commute (30-40mins in traffic).

Could the noise be the fan blades hitting something? (it sure sounds like it, but I never heard pinging/detonation before) - but then why wouldn't noise go away after few seconds...

I think they come on around 210 - 220. Also make sure your coolant is full, low coolant will also cause the top half of the engine to get hotter. If you mostly get ping when the temp gets up there, I would focus on cooling it down.

Many states recently switched from MTBE to alcohol for octane enhancement. It pings easier with alcohol.

160 deg thermostat, and turn the fans on earlier. That is the first thing I would do if it was my car. And it's the first thing I did with both my LS1/LS6 cars.

Or just run it off regular, and it will kick into the "low-octane spark table", you will lose 15rwhp, but the pinging should go away.

I Since I assume you don't have access to Edit to lower your fan temps, try this: Put in a 180 or 160 stat, and switch the A/C on when you get to about 2/3 operating temp. This will force the fans on, then try it.

there seems to be no diff running with AC on/off (tried turning it on before and after engine gets to operating temp)

the only thing that is consistent is the outside temperature - cold/rain - no ping or just a few "clicks" here and there, even when temp needle is near 210. hot/sunny - rattles almost every time I get on it once the temp gets to ~210. it even did it (for the first time) at WOT last saturday - and it sounded REALLY bad :bang:

taking a car to a different shop tomorrow to have them listen/look at it.

Let's pray they don't clean out my bank account (not too much $$ there as it is...) :(

I Since I assume you don't have access to Edit to lower your fan temps, try this: Put in a 180 or 160 stat, and switch the A/C on when you get to about 2/3 operating temp. This will force the fans on, then try it.

I heard of someone getting oil into the intake causing pinging from the PCV, is this true if there is a lot of it?

Any luck on this? I've had the exact same problem forever. California gas really sucks cause of the environment nazis here.

if you run an oil based air filter you may need to clean your MAF sensor wires.

Here's an update:

I replaced O2s, put 2 fuel filters inline with PCV (the first filter catches some oil - nothing major though, like a teaspoon every 1k miles - I drive it pretty hard), replaced PCV valve, put seafoam through intake several times, switched to synthetic oil. I still get ping on the hot days. I think it happens less often now, but I still hear it between 30-55MPH and 1500-2500 RPM.

intersting thing is that when I took a trip to western oregon and drove in the mountains it NEVER PINGED - EVEN ON HOT DAYS. as soon as I got back to seattle area, it started again!

another interesting observation is that if I reset my PCM, the problem gets worse for a day or two, then back to usual

I took the car to dyno shop they did not find anything wrong (was a cool day). The car dynos 286HP/310TQ with AF staying stable at ~12.4 all through 3rd gear run ('01 A4 with a lid and tb bypass) - so that's pretty normal, I guess.

What I am going to try:

find someone with known good MAF and try to swap for a day or two (I polished and cleaned mine - did not make a difference). I remember someone on fuel injection board having somewhat similar issue and fixing it by swapping MAF.

get a new injectors - cheaper then testing/cleaning existing ones

get 160 termostat. If detonation is due to chamber/intake contamination or decreased gas quality, it should help. If I am getting too lean due to MAF giving wrong readings when hot, this may or may not help.

I've spent almost $1000 trying to fix this so far :bang: , on the plus side, I have learned A LOT about my ride. :chug:

As always, any thoughts on the issue are welcome!