Pinging/Pinking noise - help!

[Quagmire]

Some background to the (very long) post:

Car is a 1984 Landrover 90.

Engine is a Rover 3.5 (9.35:1)
10 bolt heads
Cast 4-2-1 manifolds
Flapper Efi top end (running resistors, so not PWM) controlled by Megasquirt.
EDIS ignition previously controlled by Megajolt, but has been driven by MS running ignition only for probably about a year before now with no issues.
NGK BPR6E plugs.
LPG (open loop) fed by a Bigas M84 vapouriser connected to a mixer ring on the plenum.
Air filter is a range rover filter, similar to the ones that were also used on the 50th anniversary defenders.
Innovate LC1 wideband to see what’s going on.

For ease of discussion (and as I don’t talk “lambda” all AFR’s quoted are petrol equivalent regardless of fuel).

So about 2 months ago I converted to EFi- I went from having twin SU’s to using a Flapper top end controlled by Megasquirt. Ignition is provided by EDIS using gen 1 coilpacks controlled via the MS.

LPG setup changed from being mixer plates on the carbs, to a single mixer ring on the plenum throat.

I was amazed at how much of a difference the EFI made to the car (on petrol) – it starts within the first crank, warms up quicker, uses less fuel and gives me better engine braking. Better economy too! Oh, and it goes like the clappers.

On LPG power also seemed to be up so I guess the EFI inlet is less restrictive than the old SU’s were.

I did however notice I was getting what sounded like pinging when accelerating on LPG, anything from 60kPa upward would induce a noise which was a kind of cross between marbles or keys being shaken about in a jam jar. If I lifted off the noise would go. The sound did not initially appear to be happening on petrol but is now.

When I did the swap I originally kept the older style rounded rocker covers – I piped the crankcase ventilation into the plenum via flame traps and a y-piece. My initial thoughts were that I was drawing too much oil vapour into the engine and this was giving me pinking. This has however not proved to be the case. Last week I swapped to proper EFI rockers with a factory breather setup (small foam filter on passenger side, with the tall breather on the drivers side feeding into the plenum). The issue with pinking has continued.


I have tried running rich at all times (i.e mid 13’s or richer) – no change

I have tried cutting spark angle right back, LPG is now running the same advance map as petrol – no change.

I have checked base timing running EDIS is standalone- it is running about 9 degrees, so only 1 degree out.

No sparks are leaking – running in the dark does not give any kind of light show.

No leads are touching – especially not 5 & 7.

I have checked commanded advance vs actual from MS and this seems to be correct. Even reloaded the MS firmware just incase.

Have tried reloading maps from before I went to EFi, no change.

Even went for a short run with EDIS running in standalone mode – so approx 10degrees of static advance, still happened.

I have removed the rocker cover on the drivers side and fitted the missing baffle that goes in the top, I hoped this would cause less oil to be thrown at the flame trap. – no change

Tried changing the oil as last oil change before this started happening I had to use Comma 20/50 “motorway” oil, as nobody locally had the classic green 20/50 I normally use. – no change

To eliminate oil vapour as a source I tried running with the rocker breather and associated plenum connection disconnected and blanked off. – no change.

Tried changing spark plugs – no change. The old ones although they look a little sooty don’t appear to show any signs of detonation. I will put some pics up later as I still have them.


Yesterday I was cruising on the M3 alongside my Dad in his 110- he said that when I accelerated you could hear what sounded like a machine gun under my bonnet!


So my next steps are going to be:

- Swapout coil packs one at a time. Maybe the EDIS module as well.
- Compression test
- Heads off.

Does anyone else have any ideas on what I can do before I get to the head removal stage? My possible list of things that may sound like pinging but not be are:

- Failed exhaust manifold gasket
- Leaking injector seals where they join the inlet manifold- although I would have thought this would manifest as a lean reading. Without a WB02 sensor on each port I’ll never know.

Any suggestions are greatly appreciated as I am running out of ideas!

Thanks all

[DaveEFI]

If pinking doesn't disappear (or at least change in sound) when you retard the ignition, it's not pinking that's making the noise. If the engine was once ok - and you haven't done something since like increase the CR.

Most likely thing to sound similar is an exhaust blow. The give away with this is pinking is usually at its worst noise wise with high engine demand at mid revs.
An exhaust blow will be much more constant, but may disappear or get much quieter when you lift off the throttle.

[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 had 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.