Hello everyone!

I am having trouble diagnosing a sound that I recently discovered while driving with my windows down. Also I am having the codes P0420 and P0430. I first thought this was because I had trouble starting for a couple of weeks, but after I cleaned the MAF sensor, it starts like new but the codes are coming back after clearing them a couple of times.

The sound is close to 'pinging' as they describe it here on these forum pages. It can only be heard when the engine is up to temperature. You don't hear it when the engine is idling or when you are cruising. Only when accelerating from a standstill, or accelerating harder (especially just before shifting).

The noise is not coming from the catalytic converters or the gearbox. It's really toward the center/front of the engine.

The noise can also be heard without the v-belt on it. It is very difficult to hear which side of the engine it is coming from. The chain tensioners and guides have been replaced with the aluminum versions.

I am using E5 petrol and Castrol Magnatec 10W-40 (start/stop) engine oil. (I think the E5 is a European unit, I don't know which grade is equal to the USA variant, but this is the second most expensive fuel grade you can get here)

1 of the solutions that I encounter more often is to replace the catalytic converters. And since I have those 2 codes, I think I'm going to give this a try.

I have catalytic converters with part numbers NJA6701CJ and NJA6700CJ, but when I look for them I only see versions with 3 holes for O2 sensors? Maybe buy low km 2nd hand catalytic converters?

Does anyone have any advice or tips I could try?

PS.
I will check how the spark plugs look this afternoon or tomorrow and will update the thread based on what I find.

From experience I'm really looking forward to getting the catalytic converters out... (especially the left side with all the cooler lines and hoses) if this is indeed the best option.

Thanks to everyone on this forum. Many pages have already helped me countless times with my X308.

 

Check the fuel trims as they often reveal problems.

 

I have no experience with fuel trim data. I have recorded my fuel trim data on my way back home from work where I drove 20 minutes mainly on country roads and a little bit of city driving. I think 30-45 mph (40-60 km/h) on average.

Please see the attachment.

 

If you can take the same photo while the pinging is occurring, that would be ideal. Don’t try it at full throttle and try not to let it ping any more than you need to so you can get a good picture. As an example, hold the accelerator between 50-75%. If it’s less than that amount, then that’s fine too.

 

Could well be failing coils or a air leaks.

Look at the MANY threads for what to measure & when.

 

This morning I replaced some ignition coils and checked the spark plugs with the battery disconnected so that the computer was also reset before my long trip today (about 160 miles). I was very careful and didn't overtake quickly or accelerate hard. When I got home, I revved the engine a few times with the OBD2 scanner and live data while standing still in the parking lot (no higher than 2500rpm).

7 out of 10 times the rattle was noticable. It's guaranteed to happen when the engine is all the way back to normal idle speed and you're revving up.

With the help of red squares I indicated when the rattle was audible and also a kind of backfire shortly after giving the throttle. (a short series of dull thumps heard only with the windows open). The P0420 and P0430 codes are also back after this trip.

The oil looks good and the engine didn't get too hot. Are the characteristics something obvious or should I, as you mentioned as an example, see what the car does when you keep it at 50% throttle?

Revs with rattle/pinging/backfire

I took out the plugs and coils to inspect them. As I had 3 more spare coils laying around, I replaced 2 coils on the left bank and one on the right bank. It didn't make a difference. It's running fine on all 8 cylinders. The spark plugs are looking fine(ish?). They about one year old. Please see my attachments for how the spark plugs looked.
Spark plug
Spark plug

 

The plugs look whiteish but, that could be one of those things where I’d have to see them in person to be able to see if they’re more greyish brown vs whiteish grey. Having the same 420/430 codes come back could also mean your cats could be blocked from them breaking apart and laying sideways and blocking the flow of exhaust and can cause that detonation you have. If I were you, I’d take the cats off and inspect them. Another thing you could do instead is remove the oxygen sensors and use a bore scope. Either way you choose, make sure the exhaust is completely ambient temperature and spray the fasteners (or 02 sensors if you go this route) with a really good penetrating fluid. Here in the states I use PB Blaster. I know there’s others out there but WD-40 is not a penetrating fluid. After you soak them down, let it sit for at least an hour and use hand tools only.

 

The sound could well be due to pieces of cat conv.

 

I think you have bad or disconnected knock sensors. Assuming you are using a lower grade of gas instead highest test gas (93octane in the US). I don't see a catalytic converter issue, yet. Pull up all threads, including those in the XK8 forum on knock sensor issues.

 

Last summer, I already managed to remove the catalytic converters once when I replaced the gearbox. Luckily no problem at all so I assume it shouldn't be a problem now either. However, this is a big job for me so I don't know when I can get them off, but I'll let you know by then!
Yesterday I found a donor engine with catalytic converters on our national marketplace website. If the price is right (and the seller responds), I will pick it up this Saturday. This includes knock sensors and injectors. So if the catalytic converters aren't the problem in the end, I always have more parts to swap. I also found a chart on the internet with what the O2 sensors look like and in what circumstances (lean, rich and others) so when I start doing this job, I can also view the O2 sensors.

I read myself a little deeper into the knock sensors. Although I don't have any codes for them, the symptoms are very similar. I still have 2 knock sensors from an older engine from which I used my current gearbox. The engine had about 130,000 km (80,000 miles) so I'm assuming the knock sensors are still good. So using the instruction on the thread "Thread for replacing How to change Knock Sensors Post 1 & 2" this shouldn't be such a difficult job.

Thank you for your responses. I'll do some tinkering and let you know.

 

You know -- I see red flags whenever someone has a problem and I read "Last summer, I already managed to remove the catalytic converters once . . ."

Besides buying better gas, maybe review your work, particularly the wiring to those four sensors . . . frays, bad connectors (a British heritage!), sloppy install, leaking exhaust . . .

 

I know, I know . It should all be good.
I was very careful with removing the catalytic converters including the middle muffler. No hammering or drilling.
The exhaust clamps came off very well. After removing and before installing, I checked for debris in the catalytic converter and used new gaskets.
I disconnected the O2 sensors from the connector on top of the gearbox and marked them with colors to get them back 100% correct.

While lowering the exhaust, I first removed the cooler lines from the gearbox so that there was more than enough space for the wires not to bang against something.
But I will check the wires/connectors indeed!

Thanks

 

Hello everyone,

I did some testing and I think I'm onto something. The knock sensors are good, they measure 198k (right) and 197k (left) ohms. These should be about 200k ohms if I'm correct.
The top O2 sensor on the passenger side (EU) looks perfect. No weird deposits on the sensor and it was very clean actually. Unfortunately I forgot to borrow a boroscope so I couldn't see inside the catalytic converter, sorry.
Last Sunday I bought a complete engine with catalytic converters and gearbox. Today the plan was to change 1 of the catalytic converters to see if any of the catalytic converter codes would disappear, but unfortunately the bolt of the exhaust clamp is welded. Unfortunately I currently do not have the possibility to use a carlift or grease pit so that's why I built everything back.

On the positive side, all the bolts connecting the catalytic converter to the exhaust manifold came loose with the stud.

I went for a drive to see if the noise had decreased in the time that the car has been standing still, but unfortunately this was not the case. I decided to disconnect the MAF sensor while the engine was running and guess what? When I got the engine revving from idle using the throttle body, the sound was not present.
So this sound is only audible with the MAF sensor connected. Isn't it also a coincidence that after cleaning the MAF sensor, this problem kind of started?
Should I risk buying a €100-130 Bremi or Denso MAF sensor or do you have any other ideas?

 

Not sure of pricing in the Netherlands, but a new Denso MAF sensor seems cheaper that another engine or extra Cat converters filling up garage space.

 

Installed the new Denso MAF sensor 2 or 3 weeks ago together with a new air filter (+ reset). I thought the issue was fixed after a long drive with a couple of hard accelarations without noise or issues. Today I went for a drive with the windows down and the sound is back again... The P0420 and P0430 are still there and I don't believe the new sensor is already bad.

I guess I will change out one of the CATS if I have access to a lift or grease pit because the clamps are welded. Also I will be checking the ground cables in and around the engine bay.
Are there any other things I could try?

 

Crankcase breathers going back into the intake causes excessive carbon build up and lowers octane. This is a recipe for detonation(pinging). So is excessive heat which it as well as cats cause. Now throw in overly lean AFRs also brought to you by your ignorant EPA and EU5 mandates and the problem is compunded.

 

Received confirmation from a mechanic that it is indeed pinging.

Last night I delved deeper into this problem since the weather is going to
be nice again and I want to get rid of this problem.

I replaced the right-side catalytic converter to see if the code goes away on 1 side.
So far (100+ km's later) both codes have not come back. Pinging still present, sadly.

I did start the engine without the exhaust... I couldn't resist

I had borrowed a SnapOn scanner from a friend that is a bit more advanced
than my cheap bluetooth scanner and just kept an eye on the live data.

What I found remarkable is that the Intake manifold pressure values ​​actually
didn't change under any circumstances (light or hard throttle, engine off, etc.).
They stayed around 3.98 and 3.99 volts all the time.

Also, the live data updates LITERALLY 5 seconds later (based on eg values
​​of RPM or throttle position).

If I understand correctly, does the 3.2 NA has no MAP sensor at all?
How does he measure this intake pressure value then? Is this calculated by the computer
from other sensor values?

Can a bad fuel pressure regulator or purge valve cause pinging?

 

Are many parameters being read? If so, drop most of them.

 

According to the internet: Possibly.
In my case: No.

Replaced both without any improvement. I think I'll have a good look for vacuum leaks with a can of brake cleaner. I don't know what else it could be.

I haven't replaced the knock sensors with the ones I have laying around yet because I don't have any codes for them. They both measure the same resistance. I don't know if that also confirms whether it works correctly. I think I'll have a look through the knock sensor related threads this weekend.

 

Small progress!
No vacuum leaks around the throttle body.

The code for the driver side has returned (P0430) has returned, but the other side (which I had replaced) has not come back!
I also now suddenly have P1647 (which comes right back after every reset).
Looks like I'm going to replace the driver's side catalytic converter (under the coolant reservoir) as well. I'll check the top O2 sensor and see if it's really faulty, or just a loose connection/damaged wire.