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Basic Tuning help required


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So, after moving to New Zealand 2 years ago and my vehicles arriving just before Christmas last year I now have time to move along with my megasquirted v8.

I have him running, a push on the starter button, 10-ish turns of the engine and he fires up with no throttle application, OAT about 17 degrees.

The computer says the engine is idling at 10 to 11 degrees before TDC but when I put a strobe on the crank pulley it says the engine is idling at 70 degrees AFTER TDC.

The spark settings table shows the following:-

trigger angle 0

trigger angle addition 0

cranking advance angle -10

hold ignition 0

spark output inverted yes

experimental oddfire no

fixed angle -10

trim angle 8

I know it will be a simple fix but I cannot find how to get the crank timing marks to agree with the computer, a figure of 78 in the trim box would be rather excessive or would it?

As usual any advice would be greatly appreciated



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The computer doesn't say what the engine IS doing, it says what the ECU thinks it's doing. If your trigger wheel is not aligned how the ECU thinks it is, the numbers mean nothing.

Bit more info needed on your setup: Which variant of engine, what megasquirt version & setup, and in this case how is your trigger wheel & sensor set up and how are you determining TDC & measuring the timing? Could be as simple as timing light on wrong HT lead for all we know ;)

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Could be as simple as timing light on wrong HT lead for all we know ;)

I kind of expect this TBH, as it is *almost* 90 degrees out, take into account the advance amount and a potential error in the trigger wheel placement and you can get to 78 quite easily.

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so, I have rebuilt a rover v8 from a P6 which has the old rope type oil seal and fitted a 3.9 injection system to it, the computer has MS1 Extra 029v loaded on it. I was using a very basic timing gun to check the engine timing and the sensor for the pulse was attached to number 1 lead with the arrow pointing toward the spark plug.

I had thought that maybe the trigger wheel was on wrong but then how would it start?


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OK, EDIS it is, so it's back to the basics:

Are the trigger wheel + VR sensor aligned correctly, are the coil packs wired correctly (12v and HT side), what do you get if you set the fixed timing to 0deg to take the trim + ignition map values out of the equation?

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Hi Nige,

Thanks for the pointers, changing the settings made the engine run no better so I started to carry out a full wiring check, within 4 seconds I had found my problem. Whilst constructing the loom I had gotten 2 wires mixed, which was not a problem but I hadn't updated my wiring loom diagram.

The engine runs pretty smooth now and the misfires have miraculously disappeared. The crank pulley shows a little over 9 degrees of advance whilst the computer programme shows 10.

With the engine running I have found a weird thing, I squirted some fluid on each of the exhaust headers, numbers 5 and 8 although hot were no where near as hot as the other cylinders could this be signs of a failing coil pack?


Again, big thanks for the help

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  • 2 weeks later...

So, running a little rough but we're running on all 8 cylinders. The fuelling is very very rich, the fumes coming out of the exhaust pipe looks like I am running a badly serviced diesel.

The information on the computer screen tells me:-

Pulse Width 1 8.8 sec

Duty Cycle 7.3%

MAP 99 kPa

Air/Fuel ratio 28.00

Ign Adv 11 degrees

I connected the lambda sensor signal wire to a multimeter and on a 2v scale read 0.020v

As the engine was warming up I was tweaking the screw on the plenum chamber to raise the revs

At 75 degrees the revs jumped to 840 and the following was read:-

Pulse Width No change

Duty Cycle 11.6

MAP No change

Air/Fuel ratio 28.00

Ign Adv 9.4 degrees

Lambda sensor signal wire reading 0.025v

lambda sensor signal wire readings:-

82 deg 0.031v

84 deg 0.026v

86 deg 0.023v

87 deg 0.021v

A continuity check showed that the heater wire has a resistance of 5.6 ohms

Upon pulling spark plugs they are very sooty and wet though the exhaust manifolds dry immediately when squirted with water and very hot, I had the lambda sensor out and it was black with soot.

can I assume that the lambda sensor is causing the over fuelling?


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I'd guess your MAP sensor hose has fallen off or is in the wrong place, you should have <60kPa vacuum at idle. 99kPa is basically "wide open throttle". With no vacuum, it thinks you're going flat out and chucks in loads of fuel.

The Lambda sensor tells the ECU what it thinks the mixture is, it doesn't control the mixture - and if it gets coated or dunked in unburnt fuel, oil, soot, water or knocked, dented, cooled down too much it will read incorrectly. The lambda sensor should not have any influence at idle - EGO correction should only be active some RPM's away from idle unless you have a wideband one and are tuning to target AFR.

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Ok, couple of things- your MAP reading should be something less than 99kPa with the engine running. My 90 idles at 800 rpm and shows 30kPa, my Rover P6 idles at 650rpm and reads 40kPa.

A good test is to stick a syringe on the map line and push/pull the plunger and see if changes are displayed on the screen (engine off, key on for this).

Secondly, my idle pulsewidths are around 2ms- yours are four times higher! Check your req_fuel value and if that is correct (around 15 I think?) Then bump the values down in the VE table to lean it out a bit.

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I've said it before and i'll say it again, you guys are great

Went into the req fuel table, the upper figure was 20 and the lower was 10, reset the upper to 15 and the lower changed itself to 7.5. Didn't change anything else.

Checked the MAP line and all seemed ok, gave the tube a good suck and the gauge on my laptop moved, a lot. Fitted a piece of tubing to the plenum chamber, gave it a good suck and blow (oo-er)...nothing. Did a bit of probing (fnarr, fnarr) with a 1mm drill bit and dislodged some paint (the plenum chamber is powder coated black, hot or wot!) Flashed up the engine and the clouds of black smoke had gone but the MAP still read 99kPa. Went back into the plenum chamber with a 1.5mm drill and dislodged some more carp.

The MAP then read 70 kPa but the revs had shot up to 1400, I screwed in the adjuster on the plenum chamber but cold only achieve 1100 revs so off came the PWM, adjusted the revs.

This is then what I read:-

revs 800

temp 81

pulse width 5.2 secs

duty cycle 6.7%

MAP 96

MAT 24 deg

ign adv 9/10 deg

I looked at the MAP figure and did a bot more probing into the plenum chamber and found the throttle butterfly was slightly stuck on a burr from my previous actions

this is what the computer then read:-

revs 820

temp 86

pulse width 6.4 secs

duty cycle 8%

MAP 93

MAT 24

ign adv 9 deg

the exhaust smoke is still a little sooty but nowhere near as bad as it was, with the engine running I disconnected the MAP hose from the plenum and gave it a good suck and the revs increased straight away.when I blip the throttle the MAP gauge moves on my computer, the tube is about 2 1/2 metres long, should I be looking for a stiffer walled length of tubing? I have built a series 2 lwb truck cab and the megasquirt computer is in the cubby box between the seats which is why the MAP tube is so long

I have been looking for the simple instruction guide but can't find it, could you point me in the right direction please.

As usual, any advice will be greatly received


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Where is your map hose connected? What you have posted above makes me think maybe its on the nipple that used to go to the dissy? If so its in the wrong place and will read atmospheric pressure when the throttle is closed.

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Length doesn't seem to effect things (oooerr), on my P6 the ECU is in the boot and has about a 4 metre run!

On the 90 the ECU is behind the passenger seat on the bulkhead so probably a similar length run to what you have... The 90 is using washer pipe, the p6 has some small diameter nylon stuff.

When you say the "req_fuel table" do you mean the calculator thing in Tunerstudio?

Just you have stated two values when req_fuel is just one, which makes me think you may be in the wrong place.

Making progress though, Keep going!

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hi Quagmire,

thanks for the reply, went into Basic Settings, Engine Constants and the table that came up is the same as the link you gave me. Other than the Fast Idle Threshold which I have set to 20 and the link shows 68.8 all of my settings are the same.

I shortened the MAP pipe and it made no difference at all.

I also unshipped the air filter, that made no difference either.


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Hi ,

Yep, the MAP hasn't changed at idle which is why I unshipped the air filter to see if it was blocked even though it's brand new and asked about the length of tube, I rerouted the tube this morning and took over a metre from it's length but still no change. if I blip the throttle or take the wagon for a run down the drive then the MAP changes.

one question I have just thought of, am I taking the MAP feed from a suitable place. I have a 3.9 v8 plenum chamber fitted and am running my MAP tubing from the fitting above and in front of the throttle butterfly where the advance tubing for the distributor would be ran from.


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So, just did some research and it is obvious I am taking the feed for my MAP from totally the wrong place.

1 chap mentions that he tapped a fitting into the plenum chamber itself and another said he put a t-piece into the fuel pressure regulator line.

What is the general opinion for the best place to take a tapping?

As always, a very big thank you to everyone who has read this and any comments are most welcome but please keep them clean, unless you are female, know how to tune megasquirt and fancy a holiday in New Zealand


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Hi Andy,

I have a non MS related comment, assuming this is a LR vehicle? If you expect to go any way near water I Would try and get a non rope sealed timing chest! My first engine was a P5 engine and was great until I stuck it some sandy water. Later in the day the oil preasure dropped and the main bearings made a bit of noise.

After pulling it open there was a clear trail of sandy water through the rope seal and down into the sump!

Enjoy your engine,


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