V6 Ping/Detonate Under Load, Experienced Users Required

[down_n_dapper]

So, over the course of the last month my car has begun to ping (detonate) under load. (Car is a 1998 2.4L 30V (basically a 2.8 AHA))

Typically it occurs past 2000 rpm in gears 3-5 (Could be happening in lower gears but due to engine noise I can't tell).
So far I have changed fuels, used higher octanes, added octane booster (terrible idea, hate that crap), cleaned spark plugs multiple times (octane booster stained them red) and finally put in fresh NGK BKR6E's and gapped to 0.8mm. The car starts and idles fine, although the cct on both banks is quite noisy during idling as the chain sounds slack.

I am suspecting the CCT on both banks are failing as the noise of the chain is excessive. My car has also driven 180k miles, so I suspect bearing clearances to be excessive at this point in time. Oil pressure at hot idle when I last recorded was around 17 PSI, which is on the low side to me indicating clearances throughout the motor are increasing and cannot create enough oil pressure.

My question is, would failing CCT's cause the timing to change enough to ping?


Also on topic, I was finally able to connect to my ECU using vcds after trying for the last 3 years, funnily enough only while the motor is off, radio is off and aircon turned to fan speed 4 (i know this sounds retarded but trust me i've tried everything to get it to connect) The scan results are as follows:





The fuel trims are also alarming and I assume would also cause pinging.

Please help, I'm going insane trying to diagnose this with half a working VCDS

[redline380]

First off, are you sure it is pinging and not possibly something simple like an exhaust leak?

[down_n_dapper]

i had not considered at exhaust leak at all tbh, no idea what sound that makes! I just presumed as its load dependant, a timing component was more likely to be at fault

[down_n_dapper]

update: scanning the car after clearing the previous codes and driving for a week has yielded no further codes, though the detonation noise still remains. I can replicate it from idle if I stomp on the accelerator, and it does sound like its coming from cylinder 6.

After investigating and cleaning the MAF, i found by unplugging it, the detonation was less noticeable than when it was plugged in.

unplugging the cct's had no effect on their running, so I believe they're really not functioning well as they're ludicrously noisy.

I did find the vacuum line going to the FPR was not present (my mistake when replacing a coolant line) and fixed that, which didn't change anything. (possible source of too rich codes?)

I'm really perplexed, without scanning the car whilst running I'm literally guessing what could be wrong. Starting to suspect O2 sensors as well.

[Nollywood]

Dapper, I would start with the easy stuff.

Bad knock sensors could cause detonation. I would be looking at the knock sensor on the passenger's (left hand) side. Check the coaxial for split insulation, the sensors themselves are really sensitive to interferance, so damaged cabling will cause them to malfunction. The retaining bolt torque is also very specific. If the cabling is damaged, replace it. If you have a spare one, replace it even if it looks okay.

Excessive slack in the CCT chains could certainly alter the timing, but it'll have to be really sloppy, to over-advance timing beyond what the knock sensors could report to the ECU, and retard accordingly. It would also trigger a specific code.

Your fuel trims are off, but if it's running that rich, it wouldn't cause detonation. It would have to run lean to trigger detonation, from over-heated piston crowns. Saying that though, an excessive carbon build-up on the piston crowns would cause hot spots, and detonation will occur as a result.

If you have access to a boroscope, I would be looking at your piston crowns. Prolonged detonation will eventually lead to piston damage.

[down_n_dapper]

thanks for the reply nolly!

I should have considered a faulty knock sensor could actually cause detonation (talk about irony). I checked the RHS (looking at the engine) sensor from the connection end and it has a nice split along the sensor which probably hasn't been good for its capacity to perform. I looked up the P/N and it seems the knock sensor from my spare 1.8T AEB might work, 054 905 377G as its listed as the same one used in the V6. Would replacement require removal of the intake manifold?

would you hazard a guess as to why its running rich across all banks? or should I not be concerned as the code has not reappeared since clearing?

[walky_talky20]

A disconnected vacuum line to the fuel pressure regulator would cause a rich condition. Manifold vacuum backs off the fuel pressure. With the vacuum source disconnected, the fuel pressure would be at maximum pressure all the time.

Also, A+ for posting codes from VCDS. And in the first post, even!

If the detonation is one particular cylinder, you could have a fuel delivery issue to that cylinder. Like a dirty injector. When you unplug the MAF, the engine goes even richer, potentially helping to mask the problem. If you don't have easy access to spares, you might swap the questionable unit to the other bank and see what happens.

[down_n_dapper]

A disconnected vacuum line to the fuel pressure regulator would cause a rich condition. Manifold vacuum backs off the fuel pressure. With the vacuum source disconnected, the fuel pressure would be at maximum pressure all the time.

Also, A+ for posting codes from VCDS. And in the first post, even!

If the detonation is one particular cylinder, you could have a fuel delivery issue to that cylinder. Like a dirty injector. When you unplug the MAF, the engine goes even richer, potentially helping to mask the problem. If you don't have easy access to spares, you might swap the questionable unit to the other bank and see what happens.

thanks for coming to the table walky!

excellent to hear about the fuel trims, so if im correct, having cleared the codes and replaced the vacuum line to the FPR, the trims should normalise themselves as I drive again (sidenote, I've ordered new 3mm vacuum line to re-do the whole system)

as for the detonation, after unplugging the suspectedly faulty knock sensor on bank 2 (cylinders 4-6) and driving to uni (25k or 15mil) at temperature, I was unable to get the detonation to reappear (although i was babying it a little, I'll hammer it home). I do have access to another complete 30V motor, so swapping injectors could be done if you believe it will reveal something relevant.

I plan to replace the bank 2 knock sensor tonight with the 1.8T item as it looks to be in better condition and torquing to 20 Nm as per the bentley.