Causes of pinging if not fuel or spark?

[Quagmire]

Guys,

After swappng my SU's for an EFI (flapper) top end controlled by MS tihngs have been good. Petrol was running well but LPG was pinging slightly initially. MS (MJ before) has been running ignition for some time now and i have not changed my spark maps for a year or more.

I originally put this pinging down to the fact that I still had the old round style rockers and had simply piped the crankcase vent connections from the rockers, via flame traps and a y-piece into the plenum. My thoughts were that the larger diameter port on the plenum (compared to the SU's) was drawing in more oil vapour and causing the pinging. I thought perhaps the cooling effect of petrol was inhibiting the symptoms when not running on LPG. This was not initially a problem as I was busy hooning around tuning for petrol.

Anyhow at the start of the week I fitted "proper" Efi style rockers with the foam filter on one side and the brillo pad filled outlet on the other that goes to the plenum.

Still the same. Pinging on gas. This happens on medium to hard acceleration.

I have tried running uber rich at all times (like 13:1 or better)- no effect..

I have cut timing so that LPG is now the same spakr map as petrol - still pinging.

Worst of all it now seems to be pinging on petrol too.

So what else could it be?

My thoughts are:

1- Soot from tuning petrol causing detonation - things were a little rich when I started out tuning the MS

2- My wideband is lying to me and I am not running as rich as I think I am

3- My air intake is now above the drivers exhaust manifold and hot air in may be contributing. (MS reports 30-35degree air tems when cruising on a hot day - i would not have thought that was too high)

4- I had initially thought a weeping petrol injector, but now it is pinging on petrol too I think this is pretty much ruled out.

5- My trigger wheel has moved.

My plan of action is to check base timing, then recalibrate the wideband, check the plugs and then the injectors.

So does anyone have any further suggestions on causes or things to check?

The noise sounds like a cross between a bunch of keys or a couple of marbles rattling around in a jam jar. It is definitely load related and backing out of throttle ior shifting down a gear instantly stops it

[zoltan]

Two or five sound plausible. have you access to a timing light?

[TSD]

Is it pinking on only a couple of cylinders, or all/most of them? The sound is quite different.

If it's only on one or two, you might be mistaking a blowing exhaust manifold to head joint (BTDT)

Detonation can be hard on plugs - don't just check them, stick a spare set in anyway.

Soot from tuning will burn off with a few miles of dual carraigeway - not like coked up heads from 50k of badly tuned carbs.

In my experience, overfuelling (to the point where the plugs get wet when starting) can pollute the plugs so they're never 'quite right' again.

It was misbehaving only on lpg, now on petrol also... starts to sound like a creeping ignition failure. You don't mention what you have for ignition, but check all the usual suspects leads/cap/rotor etc.

[Quagmire]

Ordered a spare set of plugs lat night - also ordered some cheap ear defenders so I can make some "det cans" and listen properly. Have unfortunately left my timing light at my parents but am over there tomorrow so will check timing then.

Ignition is EDIS, so usually reliable.

I might try and capture a sound recording to put up on here... Sounds like all cylinders to me but I could be wrong, and don't want to risk being wrong with an issue like this!

[Quagmire]

Right so no further in getting to the bottom of this. Over the weekend I have done the following:

Checked base timing when running on EDIS only (Megasquirt left unpowered, running on LPG) - this was about -2 degrees off, same as it has been from day one with megajolt. Trigger wheel moved is therefore off the list.

Checked timing with Megasquirt in charge. Actual vs commanded was totally spot on with 1 degree of trim added in spark settings. This was the same as before. I set the spark map to all the same values in the bottom left quadrant of the map, but due to not having any timing tape I only checked timing values at idle of 6 and 9 degrees. Both were fine.

Then took the drivers side rocker cover off to check if oil contamination was still a potential cause. The flame trap was free from oil, but I noticed that I hadnt fitted the baffle into the lid of the rocker cover itself, potentially allowing oil to get splashed up into it. Fitted the baffle and refitted rocker cover.

No change.

Then took the hose off that feeds into plenum from the flame trap and noticed I was getting a steady stream of oil vapour coming out of it. I then realised the pinging sound had started soon after I changed oil - I normally use Comma classic green 20/50, but couldnt get any locally so had used Comma "Motorway" 20/50. Decided to change the oil back to my normal stuff.

No change.

Then decided to remove the hose from flame trap to plenum and block each end off to see if that made a difference.

No change.

Then changed the spark plugs. The old ones had been in about a year (NGK BPR6E) and when they came out they looked fine, although a couple were a little sooty.

No change!

Finally, i recalibrated my wideband this morning- readings are the same as before so it must have been ok previously...

I have tried recording the sound but using my phone doesnt work - it picks up the wrong frequencies.

So now I have no idea on what to do other than take the heads off (which I don't really have the time, money or inclination to do).

So does anyone have any further suggestions on things I can check/ test/ do?

Thanks!

[rusty_wingnut]

Swap a coil pack? Your old man has got two good ones from my old engine. Shame this as it sounded quite tasty when I saw it

[Quagmire]

I'm thinking that is going to be my next step. I guess that just because #1 is showing as correclty timed on the strobe, doesnt mean that any of the other coils arent doing something weird/ out of time.

and thanks for the compliment on the sound- its understated but still a v8

[FridgeFreezer]

If you've got the mounts on the block I can send you a pair of P38 V8 knock sensors that came off my new heads. No idea what the deal would be setting them up, but could be of interest.

[Quagmire]

Thanks for the offer Fridge, top man - I do actually have a set kicking about somewhere just never got round to fitting them - dont think my heads are tapped to accept them, which is a ballache.

Plan at the mo is to make myself a pair of det cans and use those. I guess the idea with knock sensors would be to drive about and somehow tweak the sensitivity of the knock sensors using the det cans to decide what is real knock and what is just basic engine noise.

Have swapped out a coil pack this evening (I only have one good spare) will drive to work and if no improvement will swap it for the other one.

Failing that I have taken Thursday and Friday off to do a few more tests before I open it up and see whats going on.

[zoltan]

Have you tried doing a plug cut when it is pinking?

[Quagmire]

Update on this one- stripped it all down and found that the head gasket on drivers side had failed and passenger side was on its way out. When compression testing before the strip down you could hear a strange "crack" sound every so often, which must have been a manifestation of the same problem. Compression was slightly lower on these pots, but not drastically so.

Gaskets had failed on the lower edge on pots 5 and 4. Also 4 of the eight pots were quite coked up - two outer on drivers side, two inner on passenger side - this would match with a carb over fuelling prior to the swap to efi- it used to over fuel sometimes if you were forced to run petrol after having run LPG only for a few weeks and the carbs ahd dried out.

I put the gasket failure down to me not having retorqued the heads after 500miles when I rebuilt the engine (4 years ago) coupled with the extra power being developed by the efi and the ability to run at leaner mixtures giving a tougher working environment for everything.

Put engine back together last night and have a water leak on drvers side bewteen head and block - head was corroded around the waterway slightly, but no more than it was when I assembled last time (or so I thought!).

I made a tactical retreat late last night and have left it at my parents where my Dad is (being the legend that he is ) stripping everything back off again to get the offending head off.