In trying to determine why my 4.2 pings on light throttle, I've started chasing intake leaks.

I had my scan tool hooked up watching STFT while spraying carb cleaner around gaskets and vac fittings. Nothing made the meter jump, so a bit disappointing.

However, I noticed with the vanity cover off the engine, there's a definite hiss coming from the PCV line. I used a stethoscope and then just a piece of hose and it's localized to the half of the PCV line from the TB to the center. No vacuum leaks were picked up during testing and nothing I can see or feel with the line off the car.

Should this line make a hissing noise just because of its corrugated design? I'm half tempted to change it and the part load breather line know that they can cause issues, but hate to throw money at parts needlessly.

I did replace one o-ring on the PCV hose where it connects to the TB, but no change in the noise or the pinging.

 

I don't see why you can't remove the PCV lines and plug the holes with rubber bungs

temporarily just to see if they are leaking?

 

My XJR PVC hose hisses too. My LTFT are a little high but within spec. I can't seem to find and leak in the hose itself though. Just seems noisy cause of the plastic design of it I think.

 

These cars use corregated hoses, so they always hiss...even when everything is sealed. It makes looking for a vacuum leak a real pain! It is also very unlikely that you would have a vacuum leak large enough to cause rattling before you get a check engine light and mixture code.

What octane gas are you running?

 

Yeah, not a blip on the STFT when I sprayed around it. And nothing that I could isolate with the stethoscope.

I always run 93 from BP or Exxon.

This car has even had the dealer flash for the "pinging on light throttle" issue. I'm starting to get really annoyed because it seems to come and go, but always does it once up to full operating temperature. Today it was 35F outside and pinged more than it did the last 2 days when it was 70F.

I'm leaning toward a faulty MAF sensor, since the only common issue is pinging on very light loads (like steady speed going up a slight incline, even at interstate speeds). Techron did not stop it, and that's usually at least good as an octane boost. I just hate to start throwing parts at it. The only thing that makes me think MAF is because last summer I got a code for "MAF out of range." I cleaned it with MAF spray and it hasn't returned, but still makes me think it's not responding quickly to load changes.

I also noticed when I got the MAF code and the CEL was on, the PCM defaults to mass-air metering and the pinging was gone. Otherwise my LTFT are all in line with normal, < 10% both banks, and both banks about even. Just one time I got a "bank 1 too lean" code but it has never returned and the fuel trims are always fine. *banging my head against the wall*

 

Did you ever find a resolution for this? I've had some part throttle rattle sounds coming from the engine bay only under light part throttle and it seems to be to a T what you are describing here. All my hoses appear to be good and I recently had to clean my MAF because it had a light coating of K&N oil on it from the previous owner. I did put a fuel system treatment in the car yesterday because I know a few people have had this fix their problem. I'm just sick of my fine luxury car sounding like a hoopty under part throttle.

 

No, although I did have a PCV leak that caused a lean surging on the highway. I had to track down the correct size o-rings for the PCV and hoses. They're 2.65 mm CS, 16 mm ID for the PCV valve to cam cover, and 14 mm ID for the hoses. The breather on the other side didn't have any issue, and uses a smaller ID.

Also replaced my MAF. Still pings slightly under some conditions, so that hasn't been cured.

 

is it pinging or could it be a slight exhaust leak that your hearing. I had a sound I thought might be a ping under full throttle but now I think it might just be an exhaust leak at one of the joints

 

The crankcase vent valve is jaguars version of a Pcv. always makes a hissing sound. Its normal. I bought a brand new one thinking its bad. If there are no leaks detected start by changing All intake O rings. And then the MAP. Worked for me. I had lean codes on both banks. problem solved for almost a year now

goodluck buddy

 

I'm really starting to think it's a fuel issue of some sort for me or carbon buildup. It was almost a clattering sound. I put Rislone injector cleaner and upper cylinder lube and Shell fuel instead of Chevron for a change and so far it's dramatically reduced, but I can still cause it under part throttle up hills. It's now time to drive the hell out of it and see if I can clean it out or do an intake water mist cleaning if that doesn't clear it up completely. I'm sure this is what I get for letting 10% ethanol sit in the lines for 2 months in freezing conditions without starting it. I'm sure I'm due for a fuel filter too.

 

Torrid hows your MPG?

 

With the cooler weather I'm getting 19 mpg with mostly surface streets.

 

I get 22 in the neighborhood and 26 plus on highway. I drove to San Francisco from Vegas once on 3/4 of a tank. That tank got me almost 800 miles. Unbelievable!!

 

Yeah, I get about 26 highway. I think I may drive it too aggressively stop light to stoplight. A habit from many years of muscle and tuner cars.

 

When I pulled my intake to change the valley hose, you would not believe the amount of oil and "goo" that was built up around the ports and valves. I have no doubt that just physically cleaning the intake would help. Can't imagine what the combustion chambers look like.

 

I noticed the same thing when I pulled my supercharger out. Why is it that so much oil is going into the intake manifold? I really think these cars could benefit from an oil catch can.

 

I bet this is my problem then. My car was drinking a bit of oil when I first got it, but my oil consumption is pretty much gone now that it's driven daily. I think I'll get a catch can. Any recommendations on how to clean the manifold where fuel cleaners don't touch to clean it out?