Intake Manifold Off - Opinions Needed

[myles]

Hey Guys, I'm after your thoughts here.

My car has been pinging lightly for a while now and I have been thought the process of trying to find the elusive vacuum leak. The pinging happens under moderate to heavy load at any number of revs. I changed the spark plugs a while ago to a new set of Bosch W8LCR with no difference.

The only piece of history that may be relevant is that the when I bought the car, it was running full rich all of the time and needed a new oxygen sensor to fix it.

I recently adjusted the valve clearances and it has become a lot worse. So I have pulled the intake manifold off to replace the manifold gaskets and get a closer look at the inside of the engine.

I've never pulled the head on one of these before so I'm not sure what is normal.

What do you think?? These are pictures of number 2 and 5 intakes which are typical of all.

Options that I can think of here are
1. Put it back together with the new gaskets and hope it goes away
2. Do a compression test and reconsider
3. Pull the head, get it cleaned, reseat the valves and replace the valve stem seals

TIA

[Derek A.]

How did the car run otherwise ? What did the plugs look like after you replaced the o2 sensor ?

[632 Regal]

could be carbon buildup but I would check the cam timing first, if someone assembled it a tooth off would explain your problems.

[myles]

Before replacing the O2 sensor that car ran like utter crap. Misfiring all over the place. The spark plugs were so gunked up it was .
The O2 sensor and the plugs were replaced about 30000km ago. It has run very well since. The idle smoothed out a lot and gradually improved even more over the 5000 or so after the O2 change. The pinging started happening a little while after the O2 sensor was replaced, I can't remember exactly how long.
The plugs have stayed clean. The current plugs are only very new and I put them there because I thought the old ones(champions) could have been contributing to the pinging.

I've checked the cam timing too. It is spot on.

Thanks guys

[632 Regal]

Okay, I would guess carbon buildup. Theres ways of removing it with the head on but all the crap could fry your C02 sensor. Ryan has documented his experiences with probably every method known to man, might want to look that up.

[Jeff N.]

Some questions you might consider....

When you did the valves...where they loose or tight? If they were loose and you decreased the gap, you effectively raised the compression just a bit.

Have you checked your fuel pressure? Low fuel pressure would cause the car to run lean.

Do you run the same gas all the time? Have you tied high octane to see if that effects the ping?

Are you running a chip? If so, whose?

Has the head ever been off? Was it shaved?

If you disconnect the O2 sensor plug and run the car open loop, what happens to the pinging?

Have you run a compression test? If so, what numbers are you getting?

[myles]

Thanks Jeff

Valves were all pretty good. One or two were a fraction loose, but it was only by 1 or maybe 2 thou.

Fuel pressure was checked some time ago and was supposedly 3 bar. But I should probably check myself.

I have run it on a few different types of fuel, but always 95 or 98RON.

No chip at this stage, have tried one of Mark's chips a while ago, but it made things a little worse. (I cant wait to put it back in!)

The head hasnt been off while I've owned it (2.5 years now). I can't see any reason to think that it would have been off before I bought it.

I have never tried running with the O2 disconnected. Would that make the engine run richer?

Compression test has not been done, but is something that I think I should do before anything else.

[Jeff N.]

Hmm. Interesting. Running open loop (o2 disconnected) will generally richen the mixture.

The reason I asked if the head was ever rebuilt is because they can shave the head and that can slightly raise the compression leading to ping.

Checking the FP can't hurt if you can do it easily.

My guess is the same as Jeff's - carbon. Ever heard of an Italian Tune Up?

[Derek A.]

Go to a GM dealer. Get a can of Top Engine Cleaner. Run it through the tank when you r fuel is low. That stuff is great at removing carbon and will help to flush the injectors as well.

Do your current plugs have any color to them at all?

[GS535i]

GM sell a product called 'Cleens', a combustion chamber cleaner available as a liquid (992872) or an aerosol ( 993026). This is NOT a fuel additive.
Most fantastic stuff I've ever used, being wary of the 'doctor in a bottle' crap around. Feed into the intake of a running engine, using the last 1/4 container to flood and stall the engine. Allow to sit - up to overnight: start up and run to normal temp, but do so at night if neighbours are sensitive to monster clouds of white smoke. The product appears to be sensor safe.
One Chev 350 we did came so clean, that it would not start due to low compression - had to squirt a little oil into the plug holes to get it to fire: ended up with 180 +/- 2 psig all cylinders ..... not bad for < $10.