EDIS Tuning Issue

I converted last year from my 123 to EDIS. The car runs wonderfully, but I’ve found a bug that I’m not sure what the solution is. On the 123, the car had a pretty aggressive ramp up from 1000-2000 and it accelerated really well, then I had vacuum advance to get some extra advance on the highway (all in it was around 28 on the highway).

With the EDIS and Ray L’s standard 4.2 map, the engine pinged a lot in the 1500-2000 range on normal acceleration (but not on heavy acceleration). So I had to back off that mid range 3-5 degrees. It no longer pings, but when I’m cruising at 60-70 mph I’m in that same range, meaning I’m cruising on the highway at only 16 / 18* timing. There is no vacuum advance on EDIS, so I end up cruising with too little timing on the highway.

Any ideas to solve this? I run 91 octane, and I switched to cooler plugs to solve the pinging no luck…

The E-type UK forum has an entire EDIS section in ‘Upgrades’ devoted to maps and customisation of Ray’s maps and other aspects.

Ya I’ve read the whole thread, and posted there. No helpful responses.

Theo – what EDIS controller are you using? I have EDIS on my 3.8 Mk2 engine with the MegaJolt controller from Autosport Labs. It has a built in MAP sensor. This serves as the vacuum advance. At low vacuum/low load you should be able to program greater advance in that same RPM range. This should be quite a bit more programmable than a traditional distributor with vacuum advance.

Maybe you need to play around with more granular RPM and load bins? (see config screen in second snip). That could help smooth transitions from one RPM/load bin to another.

Assuming you have the MegaJolt controller my recommendation would be to utilize the switch to enable a switchable second map. That way you could leave your existing map as the baseline and play with configurations on the second map. Should the second map not work correctly you can always switch back to your known baseline first map.

Caveat that my engine remains on my test stand…so my commentary is purely based on what I’ve done and what I’ve read to date. I don’t believe there’s a more tunable ignition system though…so seems like something you can program out.

Yes it’s all setup properly etc. it’s a specific tuning question I have. I spoke with someone in DM’s and they gave some ideas and advice, so no worries. Thanks

Why are you running without vacuum advance?

I’m not running without vacuum advance.

EDIS runs on a 3D ignition map that responds to load (total manifold vacuum) x rpm. Distributors have a single linear curve based on rpm, augmented by a vacuum advance that comes on at certain conditions driven by ported vacuum.

My issue is that the same values in the EDIS map is used for both regular acceleration and highway cruising, and I was wondering if there was a way to “add advance” when on the highway. The answer is, there’s not.

I’ve been running EDIS/Megajolt for about 17 years now on my 4.2 and this has never been a problem I’ve noticed…

I ran the MJ/EDIS system on my Jag, for 7 years, and never saw any issue either.

This included drives at 3700’ altitude, to over 14,000’.

Do you know what your real compression ratio is? Aka head volume & calculation? If not, do you know what your warm WOT compression ratio is?

Ray L. had a similar detonation issue, went to a custom (thicker) head gasket to bring cylinder pressure down.
Usually caused by excessive head skimming.
I run 30+ degs over 2500rpm and run 91 octane and the engine likes it.

I bought the already engine rebuilt from a shop, it’s a S1 E type 4.2, rebuilt to be 9:1, but not sure of the actual / final compression. That said, I replaced an 8:1 engine with this one and it “feels” higher compression by a lot. Starts very quickly, pulls hard, required bigger carb needles, and the exhaust coming out of the pipes feels a lot stronger than my old engine.

Hi Theo - Is it the case that you know for certain that you’re at the same “load” for normal acceleration and cruise? To know this you would need to register the same manifold vacuum, or the same load cell on a display like the one shown by tapped.

Yes of course, I have a laptop in the car so I can monitor the EDIS while driving.

If you’re at the same RPM and load in the two driving scenarios (normal acceleration and highway driving) I don’t understand why the timing would need to be different. Isn’t timing a function of RPM and load? The only thing I can think of is that these two scenarios are not quite identical in RPM and load…but the bin settings in your ignition map are not granular enough to differentiate the two scenarios so your ignition map gives them both the same advance.

Can you share the map you’re using?

If the RPM and load were the same for anything longer than a second or whatever, then the outcomes would be identical for both conditions. I.e. both would accelerate or both would cruise at steady speed. You can’t have identical scenarios with different outcomes.

The whole reason for vac advance is to give more time for the lean, poorly-stirred and hard to burn cruise mixture longer to burn. Acceleration is not typically a lean/low turbulence condition.

Here’s the map. On lazy around town driving, the engine pings in the 1500-2000 range in the mid load. So I had to reduce the timing, you’ll see in that middle area the timing is less than the expected amount. When I drive hard, it doesn’t ping, only slow acceleration. The point I’m making above is, those same cells are active when I’m cruising down the highway. Which leads me to wonder if I should have more advance, like the old distributor did at that point.


One must be careful: detonation can happen at high speed/high loads, and not be audible.

Theo – assuming the screenshots are actuals while your engine is running (mine were not…they were grabbed from the Autosport Labs site)…your load gauge is showing 102 KPa…yet if you look at where the timing is set currently (the green cell) you’re showing in the 60-70 KPa range. Do you have a correction factor assigned here?

Also, in general as load increases the advance should decrease. In your 500 and 1000 RPM bins you’ve programed out any advance based on load. Similarly, in your 1500 RPM bin your low load and high load settings are the same. That doesn’t look quite right. In theory I would think the ignition settings in these columns should go high to low from top of the column (low load) to bottom of column (high load).

The engine is not running so disregard the vacuum. The 1500 and 2000 columns have a low spot in the middle because the engine was pinging in that range. The map is otherwise the stock 4.2 map from Ray L’s post on the UK forum.

Theo - what load are you at (in kPa) for lazy around town driving (and slow acceleration)?

Also what load (in kPa) do you see at wide open throttle (WOT) at 1500 and 2000 rpm?