The V8 Owners Forum -

This may ring a bell with some of you in the collective as it's something I've been working with for a few years now, unfortunately due to other life pressures and being lazy it's still going on.

Some time back I converted my ignition to run via ECU control from the previous distributor based system. I initially played around with a Nodiz system, couldn't get running properly at all and in the end nailed on a Megasquirt 2 system which I'd had knocking about for many years, controlling sparks only, fuel still being controlled by standard 14CUX system.

Due to struggling with running issues I decided to go back to distributor ignition and have only recently gone back to the MS

I built up an ignition table based on some figures I had for the DLM v8 distributor as a starting point which put the advance at 20° at idle (not wanting to simulate ported vacuum). This ran OK but did give some issues with stalling. This was also evident with distributor but not quite as bad.

Tried to check the base idle RPM (stepper feed blocked) but this was not possible, could not get engine to run without stepper in >50% position so something definitely wrong.

Checked initial timing via the manifold vacuum/pressure method. Ended up at 35° and all was good but as this seemed like an extreme amount I decided to stop there, I may check higher values later.

I built up the MS ignition table around the 35° value at the idle kPa, around 50. Idle feels/sounds much smoother, checking back with Rovergauge shows that the idle stepper is now down at around 17% (and twiddling the bypass screw shows I can get this even lower so that system is now working) and out on the road the car feels good, I'm not getting any misfire or pinking under load.
Based on that I guess I should be happy and to a point I am but I'm just wondering why this value is so high and if this is 'normal'.


Questions
So after all that long preamble the question is "Has anyone else found it necessary or desirable to have the base ignition value so high?"
And in addition to that can anyone suggest why this figure should be at this level given that the engine appears to be running well and liking it?

Thought the 'issue' may be due to timing pointer/pulley scale relationship being wrong but I've checked with a plug stopper and worst case it may be 1° out but I don't really think it is even that.

If anyone can suggest an alternative to Photobucket to add images I'll post up the value I'm working with which may help this make some more sense.

Thanks in advance for any contributions.

That does sound very high. I'm running Speeduino (very similar to MS2) and I'm idling at about 9/10 degrees.

You can add photos directly into your post by using the 'Attachments' tab below the 'Save draft/Preview/Submit' buttons (or as it suggests just dragging the picture files into this edit box)

Where does the MS pick up its firing point? Presuming a toothed wheel with a tooth missing?

If so is the MS actually fire the spark? At the gap, at the next tooth or something like 15 degrees after the gap…….I seem to remember reading about 20 years ago it was the third option above.

So the MS could be firing exactly as it should but in effect the toothed wheel is out by the ??? 15 ish degrees?

Just my thoughts

Ian

scudderfish wrote: ↑Tue Jul 22, 2025 10:26 am That does sound very high. I'm running Speeduino (very similar to MS2) and I'm idling at about 9/10 degrees.

You can add photos directly into your post by using the 'Attachments' tab below the 'Save draft/Preview/Submit' buttons (or as it suggests just dragging the picture files into this edit box)

Thanks for the feedback Scudderfish.

The figure you are using is around the standard value used with a distributor when using ported vacuum, if you used manifold vacuum it would be higher BUT as it is the standard value the engine should be happy enough with it, should run fine and the idle systems (bypass and stepper) should work. In may case none of these work properly until I have the higher value. Even when I had 20° at idle it was not happy.
I'm wondering if the cam may make a difference to my setup as that's the main thing which is different on my engine, unfortunately it's a bit of an unknown quantity as I bought the engine with this in place.

Thanks for the tip on adding photo's, thought I'd been able to do it previously.

This is the information I used for the timing curve
And this is the table I'm currently using. The red highlight indicates the kPa row which is being accessed at idle.

Ian Anderson wrote: ↑Tue Jul 22, 2025 11:41 am Where does the MS pick up its firing point? Presuming a toothed wheel with a tooth missing?

If so is the MS actually fire the spark? At the gap, at the next tooth or something like 15 degrees after the gap…….I seem to remember reading about 20 years ago it was the third option above.

So the MS could be firing exactly as it should but in effect the toothed wheel is out by the ??? 15 ish degrees?

Just my thoughts

Ian

Thanks for the feedback Ian.

The MS picks up from a 36-1 toothed wheel as you suggest, the gap is placed circa 70° (actually 69) ahead of top dead centre. This is the value I have in the settings for Tooth #1 Angle BTDC as you can see in the graphic below.
The actual location of the missing tooth should not matter within reason as this value acts as an offset. I suppose it may need to be at least as far ahead of TDC as the maximum advance (plus a bit for processing time) which it is.
I think the other options you are describing are the "Ignition Input Capture" and possibly "Spark Output". I did believe this was related to whether it was triggering on the leading or trailing edge of the teeth but not absolutely sure. In any case I believe these settings are as per when the unit was delivered.

However this shouldn't really make any difference as I'm not simply measuring the physical location of the missing tooth with respect to TDC I have checked the point which the spark actually occurs with a strobe. This is initially done by setting "Fixed Advance" setting to "Fixed timing" which triggers at whatever setting is entered in "Timing For Fixed Advance". For setup I put this at 10° so that I could read it off against the timing mark I have on my crank pulley from using the distributor, this was reading spot on. When I re-enabled the table I could see that the timing was indeed triggering at 30°. I don't have a mark on the pulley for this but could see it was around 3x as far as the 10° mark and the teeth on the 36-1 also verified this (at least to a degree or two)


I'm thinking more along the lines of whether there is something specific about my engine configuration which actually requires, or "likes" this advanced timing.

Have you verified base timing ?

ie, flatline timing at 0deg, 10 deg, 20 deg and check/confirm with a timing light ?

If you're a wasted spark system bare in mind a dial back light will read double. Hence testing at various levels is essential to see any odd behavioural patterns.

35-50deg at idle, is not normal on any engine so is likely not correct or what the engine is actually seeing.

stevieturbo wrote: ↑Wed Jul 23, 2025 8:57 am Have you verified base timing ?

ie, flatline timing at 0deg, 10 deg, 20 deg and check/confirm with a timing light ?

Thanks for the feedback StevieT.

Yes. I'm not really sure what you mean by 'flatline' but I checked the timing at 10° using fixed advance (regardless or RPM or vacuum the advance will always run at this value), this was showing at the line I have marked on the pulley (used for the distributor).
I also checked the position at 30 (or possibly 35°, can't remember which), I don't have a mark on the pulley for this but it's distance from the TDC and 10° marks was consistent with that value - Around 3 times the distance. The number of teeth on the trigger wheel (which can also be seen adjacent to the timing pointer) also helped verify this. While I can't claim an exact figure I'm confident it was within a degree or two.

stevieturbo wrote: ↑Wed Jul 23, 2025 8:57 am If you're a wasted spark system bare in mind a dial back light will read double. Hence testing at various levels is essential to see any odd behavioural patterns.

It is a wasted spark system but I'm using an old fashioned, simple, timing light which simply triggers when it 'sees' a pulse to the plug hence what you see is what you get and obviously it reads against the mark on the pulley rather than dialling back to TDC mark.

stevieturbo wrote: ↑Wed Jul 23, 2025 8:57 am 35-50deg at idle, is not normal on any engine so is likely not correct or what the engine is actually seeing.

I agree with this hence the reason for my query, my first thought was that the pulley marks were out of position however I've checked these and confirmed that the TDC is correct at least to 1°

I would say that the value is not quite as bad as it sounds. If the distributor was using manifold instead of ported vacuum it would actually be reading around 24° at idle based on the table I've shown earlier (8° initial plus 16° vacuum) which would be the value the timing will jump to as soon as the throttle opens very slightly and the port is uncovered. Also I think that 8° initial is a little on the conservative side.

Admittedly I'm still circa 10° over and above that but also that the engine wouldn't run properly at lower figures.
Again this is really what I'm asking about, what property of the engine would make it "want" a higher than 'normal' value and what would make it not wan't to 'behave' with lower values?

Depends how you are determining "want" ?

At light loads, higher tiing figures would be fairly normal, aka vac advance, light cruise etc.

How was this table created ? on a dyno to see what the engine really wants ? Or just best guesses ?

At those load sites, what is manifold vacuum like ? Often intake vac is a better representation than TPS, at least in this regard of diagnosing, as 50% throttle opening really doesn't tell much

I have run engines in the 40-50 range, but literally only at light cruise, never under any real load.

stevieturbo wrote: ↑Thu Jul 24, 2025 8:50 am Depends how you are determining "want" ?

First of all lets just forget about the timing table for a moment, this is early days with this and I'm focussing first on getting the idle condition something like right as I was having issues in this area.
As a test I decided to see how the timing worked out using the manifold pressure (vacuum) readings. I've read about this method some time back but never used it in anger. Basically the method is to increase the advance, while keeping the RPM at idle speed, until the lowest MAP reading is achieved (most vacuum) at this point the engine is working most efficient for this condition hence it is what the engine 'wants'

As the standard 14CUX system is equipped with automatic idle speed control via the stepper motor you can forget abou the "keeping the RPM at idle speed" bit as this is done automatically so I simply increased the advance by increasing the fixed advance figure and watched the kPa reading from the Megasquirt which was still decreasing even at the 35° but I decided to stop there as I thought it was getting 'extreame'.
Although I wasn't monitoring it during the test I also checked the stepper motor position before the test and again after. This dropped from somewhere in the 50% area to less than 20% - Obviously this goes hand in hand with the decrease in manifold pressure, less air (and hence fuel) getting in will increase the vacuum. Given that the engine is still producing the same power (it's turning at the same speed as before and load hasn't altered) with less charge getting in it must be working more efficiently.

stevieturbo wrote: ↑Thu Jul 24, 2025 8:50 am
Depends how you are determining "want" ?

At light loads, higher tiing figures would be fairly normal, aka vac advance, light cruise etc.

How was this table created ? on a dyno to see what the engine really wants ? Or just best guesses ?

OK, moving on to the table now.
The area I've highlighted in the graphic above at 50kPa is where I am at idle, this effectively light load, the only way I can see of getting a lower kPa is on overrun when I'm not really concerned about the timing as it won't even be firing at higher RPM due to fuel cut-off and at lower RPM it is unlikely to get thre, this is why I've left the advance the same as it is at 50kPa.

The advance 'curve' at the 50kPa uses the same increments as the data I have for the distributor advance curve (I don't know how reliable this is and I don't even know where it came from!), again in the graphic above, but starting at the 35° value as established. In fact I've dialled it down a bit with higher RPM, the range for the distributor works out at 27° I've dialled it down to 21.

At atmospheric pressure, which would be encountered at WoT, the timing values are obviously lower. Again this curve follows the same increments but dialled down by 16°. the data between has a pro-rata decrease in timing to give a smooth transition between closed and wide open throttle.

So not on a dyno but hopefully a little better than 'best guess', let's say "best educated guess"!
The table should give very close to what the distributor would give (albeit I don't know the provenance of the data I've used) although dialled up by around 10° in general but tapering off at higher RPM by 5° - I hope that makes sense, I'll try and qualify it.

The distributor data shows 35° maximum as RPM increases, at WoT this would be the only advance in place, there would be little or no vacuum. In this condition the table I've created would be giving 40° - Not massively different.
At idle the distributor would be running at 24° - 8°initial plus 16° Vacuum - if we remove the ported "bodge", I'm running at 35°. Given that the 8° value seems a little conservative (I was using around 12° with the distributor) I don't think I'm massively different here either.

So really my "issue" and reason for the question is related to why my setup doesn't run well below this figure at idle and why it may need more advance. The only thing I can think of is cam profile as this is the only area where my engine differens from standard.

stevieturbo wrote: ↑Thu Jul 24, 2025 8:50 am At those load sites, what is manifold vacuum like ? Often intake vac is a better representation than TPS, at least in this regard of diagnosing, as 50% throttle opening really doesn't tell much

Unfortunately I don't know what the MAP is like at any other RPM value as I'm currenlty not setup to measure/log this.
Bear in mind the row values on the table are kPa not %age TPS, that is not 50%

stevieturbo wrote: ↑Thu Jul 24, 2025 8:50 am I have run engines in the 40-50 range, but literally only at light cruise, never under any real load.

That 50kPa value is what I'm getting at idle (possibly a little lower) which would represent light load, during normal driving I don't see how the engine can get to any lower rows on the table so this is the 'worst case scenario' for advance numbers, I also don't see how I'd get to the higher RPM columns on this row.
As the load increases the timing will also dial down due to running higher kPa so I think we're working along the same lines there.