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** MegaSquirting a V8 - "Basics of How to" ... The A-Z Saga


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Update on mine :)

Tuesday was "New Exhaust" day - a Thread will follow with pics n Info for those whio may find it useful, but, and its a BIG BUT, my MSQ map was as good as I could get it on the 90 up to Tuesday, .......then with a new exhaust things were suddenly very .....very different.

Many many people (and me included to a degree up to a while ago) think of an exhaust as just pipe under their truck,

actually a good exhaust can get you as much BHP as many of the more common "Must have" modifications, and,

with a proper company doing your exhaust you can even chosen where and HOW this extra unleashed BHP and Torque comes to you :)

In summary my new exhaust is 4-2-1, each side,

JED Big bore Manifolds, ported to match the enlargwed head ports,

exiting with 2 x 50mm Holes (std RR 3.9 are 2x 32mm), this has then twin downpipes conencted to it,

both pipes on each side are 2", the 2x 2" pipes collect into a 2.5" pipe,

this then mets the same on the other side and forms the Y piece this has 2x 2.5" entries and once these join exit in 3",

and this 3" then continues from the end of the Y to the massive silencer

and then out (3") and to the rear of the 90.

The Secondaries (pipes from manifold to Y pieces) are matched and are around 18" long to give bottom end grunt.

This exhaust has transformed the engine it leaps up the rev range faster crisper and revs freer,

as the maker pointed out the EXIT from the old Y piece is the same bore within a mm or 2 to just ONE of the 4 new downpipes :)

Even though the engine ran hugely better I did wonder re the MAP - so I have today, and part yesterday spend some 10 hours remapping it,

here are the results.

It also became a pig to start hot or cold, so the WUE table (still needs a bit more work) has had MASSIVE changes, as has the IAT Correction, and also to actually get it to fire I have to DOUBLE the cranking prime from 2.0 to 4.0 :huh:

This new MAP really sorts out the best from the new exhaust, bear in mind that although the cells may not look hugely different there is a major subtle remap of the majority of the performance parts of the MAP, say a cell was 70, if it is now 77 thats a 10% change and 30 to 34 is higher still FFS :)

It has richened the bottom end given a more 4 part map rather than 3 part map, increased fuelling in mid range and into high end, reduced in places the high end performance cells, WOT is minor changes, but you have to GET to WOT ....so the cells to it have to be right, .....and its these in the main that are changed.

Thought this may be useful, exhausts can have dynamic effects on both performance powerbands rev ability and fuel maps generally

post-22-1221670428_thumb.jpg post-22-1221670446_thumb.jpg

Here are the before and after MAPS form the exhaust build :)

1st Picture is the MAP pre the new exhaust, the 2nd after the day and 1/2s remapping :)

And Yes it does have "a bit of a Note" to it,

...Tonk opened the passenger window to hear the noise in full glory when I popped in to see him, ....see, he is a petrol head at heart :lol:

Nige

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I can pretty much guarantee that at some stage in everyday driving all of you will suffer from the ‘IAT heatsoak syndrome”

The MS algorithm correctly leans off the mixture as the IAT increases, however, if the IAT increase is due to heatsoak then the leaning of the mixture is detrimental as the actual IAT is a lot less than indicated.

The heatsoak issue usually arises when the engine is stopped and then restarted within a few minutes, or stationary in a traffic queue ……….. or in our case, moving slowly off road especially with the engine working hard.

The symptoms are easy to spot……………… the idle goes all to hell and the engine feels out of tune until the temperature drops. Once moving at a little speed the IAT falls rapidly to the correct numbers.

Heatsoak is caused by the latent heat from the engine venting to the inlet systems and these are normally the highest point ……… hot air rises.

Monitoring the IAT shows heatsoak values of 50C when the true temp is maybe 15 – 20C…………….Connecting a WB Lambda will show that the AFR has been leaned significantly. The problems start to occur as the IAT rises above 30C. I guess the truth of the matter is that we are very unlikely to see frequent true free air temperatures of over 30c – 60C in this country.

I had always considered that the answer was to use IAT correct (from the advanced menu options) but it is not quite that straight forward. However, whilst I was looking into the issue Elliot Mansfield had exactly the same issues and answers for his 5.7L chevy engined Dakar. Indeed we were both thinking in parallel, even to the point of the testing procedure.

Firstly you need to go into the MSNS ini file and make the following changes (highlighted in bold). This gives you the correct graph and puts up the AFR guage.

[CurveEditor]

curve = clt_IATCorrC, "Coolant corrected Air Density, see Settings", 9

topicHelp = airdenHelp

columnLabel = "Temp", "Offset"

xBins = IATCTemp, mat

yBins = IATCorS

gauge = afrGauge

Then go into the advanced options and select coolant related air density and then settings ….. set it to IAT correction.

gallery_269_524_2014.jpg

My correction curve looks like this. The curve was determined by fitting the WB sensor and correcting the AFR as the temperature increased. As you can see, the correction required is significant.

gallery_269_524_22179.jpg

The results are good…. The AFR stays constant (as per the programmed afr table) regardless of the IAT heatsoak temperature.

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^^^

100% wot he says

I had the benefit of the IGMK1 version (Ian Guildersleeve Mk 1 version :P) and yes it makes a huge difference.

Tweaking it to get it right is fun, its def part of the 3 legged table syndrome

Made a huge difference when Ian discovered it I think by accident buried deep in the advanced settings :lol:

Similarly with me today as I now with the new exhaust am having "Fun" get the engine to kick n start in a few turns of the key

I have cracked the hot starting with a twice pulse of 6.0 - yes 6.0 FFS :blink::huh: and then saw there is a table for temp vs prime pulse :)

(Hot with 6 is OK, cold even with 6 is 12 cranks :(, with 2 and twice was 18 :blink: )

May the fun now commence, whern I have sussed this I'll report back

In the meantime I'll 2nd IGs comment - Ians post above is a "Must have" tweak for all who have MS :)

Nige

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Given that IAT heat-soak is caused by under-bonnet teperatures, and that one could reasonably assume that the air the engine breathes is the same air as around the vehicle, is there any reason why one couldn't mount the IAT sensor somewhere else on the vehicle?

I know that begs the question 'where', but is it a viable solution? Seems better to me to remove the problem, rather than compensate for it.

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The IAT is only giving an idea of the latent heat build up in the engine, so it needs to be on it / in it, as otherwise the IAT will say all is well when in fact the engine is cooking ! The IAT will read differently to the CTS, its another measure via another route, but we have all been near engines where the heat coming off it makes you step back, yet the coolant is still OK. This the IAT is there as a measure stick, the table allows you to say "If its this hot add x" and "This hot add Y" and in betwwen etc etc

Nige

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Er yes and no (thats a balanced answer BTW :lol::P )

It does measure the temp of the air going in,

if IAT correction is switched off then thats that,

if its switched on then the temps it is reading can then be used to extrapolate a series if enhancements / ie enrichments to the fuel table

so that when it is hot is has additional percentages applied, there are a number of the buckets that can be programmed,

via TS this can be seen grapically and tweaked accrodingly but there needs to be human input as to what the additional fuelling percentages need to be.

Without the IAT you can easily run lean when the engine is seruiously hot,

and this can give sympotoms of hunting lurching misfiring even abd a general unsmoothness,

with IAT correction - and some work these can all be removed,

many engines due to the build and 4x4 placed in means this is a 'seat of the pants' modification / tune as most will vary :)

Nige

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I think we're at risk of confusing the issue here:

MS as normal corrects for coolant temperature (CLT) and inlet air temp (IAT).

The lower the coolant temp, the richer it gets (the warmup enrichment table, bit like putting the choke on)

The higher the IAT, the leaner it gets (IAT correction)

You can't turn coolant or air temp correction off as such, you can set the corrections to 100% (flat) which will mean no correction will be applied.

What Nige and Ian are talking about is correcting the correction - basically telling the ECU that once the engine gets warmed up past a certain point, the IAT sensor reading will be off, or at least untrustworthy, by a certain amount. You are using the value of CLT to correct the effect of the IAT.

The reason for this is that, although the IAT is there to measure the air temperature, it's attached physically to the engine and is stuck in a potentially quite warm engine bay, so some heat will be conducted into the body of the sensor to give an artificial reading. The air being drawn into the engine could be from a snorkel that's breathing fairly cool air, but under the bonnet the IAT sensor could be experiencing much higher temperatures.

On a slight tangent, has anyone played with the IAT/CLT ignition advance settings? :ph34r:

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I can see where this would/could be an issue, especially at low engine speeds, but I'd have thought that this would have been taken into consideration in the design of the sensor and it's positioning. I'd have expected the IAT to be used purely as a baseline input rather than one that has a huge influence on the fuelling. Obviously it's used in conjunction with the startup barometric pressure to determine air density but the majority of tuning and therefore fuelling is based on the exhaust gas "outputs" rather than the "inputs". It's one of the compromises we face as an alternative to a MAF meter I guess.

I can see that this would be more of an issue if you were running without a lambda sensor, maybe I've never found an issue with this because I tend to run closed loop lambda low down in the rev range or it may be that it's because my IAT has always been thermally protected from the engine in my installations. Even on the LS1, where the IAT is built into the throttle body, the throttle body itself is thermally insulated from the engine as the inlet manifold is plastic.

Not sure how much spare memory there is left in MS but I can see an argument for having some sort of CLT comparative IAT adjustment for those that need it. Still think they'd be better off repositioning the sensor though :)

Next time I have my snorkel uncovered I'll look at fitting an extra IAT somewhere nearer the intake(at the back of the cab) so i can see the difference in reading between that and the engine mounted one as the engine temp goes up. It'll be an interesting exercise anyway as I've often wondered how much the air is heated as it passes along my snorkel which runs from the back of the cab, alongside the gearbox and then up and over the engine !

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Thanks for the explanation.

So, like i said a few posts ago, why not move the IAT sensor, and remove the problem, rather than compensate/correct it?

Luke,

Yes, you could move the IAT but it would still suffer from heatsoak in other ways………

The outside air temp displays that are used in modern vehicles (and aftermarket displays) only read the actual air temp accurately whilst the car is in motion. Once the vehicle is stopped then the sun together with heat from various areas of the vehicle give false readings. However, these displays LOOK like they are accurate as they have a certain amount of built in intelligence. They respond to a falling temp faster then a rising temp (about 5 times faster) as a lower temp will be more accurate. Also they do not respond to fast rising temps………….. the software takes several readings to average out any sudden rise and it will only display that rise in gradual steps, however, a fall if displayed almost immediately. This type of intelligence could not be easily employed in engine management.

With MS, the processor just reads the IAT resistance and then calculates the temp and it does this many times a second. The fuel algorithm to derive the fuel required essentially takes into account the engine speed, manifold absolute pressure (MAP), inlet air temp (IAT), and VE table……….and is corrected if the coolant temp is low by yet another table(CLT),

The VE (Volumetric efficiency) numbers in the table represent the following formula

VE = (actual air mass)/(theoretical air mass)*AFRstoich/AFRactual

The Mass of air is computed using the ideal gas law of PV=NRT ………….. the important bit here is that T is the air temp……………as we are calculating N (the mass of inducted air) it can easily be seen that a rising T is significant in leaning the mixture.

The actual fuel sent to the engine is then further calculated as an injector pulse width,

PW = REQ_FUEL * VE(kpa,rpm) * MAP * E + accel + Injector_open_time

Here the REQ_Fuel is the injector flow rate and the rest is fairly self explanatory.

It can now be seen that the coolant temp plays a very minor role………. All that happens if the engine is cold then we add a correction factor to the main table based upon the coolant temp, however, the IAT (or air temp) is very much a part of the ideal gas law calculation and integral to the algorithm.

Once the fuel has been burnt then the exhaust gases are passed across the oxygen sensor and a voltage is fed back to the ECU that indicates how complete the combustion is (closed loop). The O2 feedback (EGO) is then used to correct the fuelling to give a complete burn, however, it should be noted that the corrections should be kept to an absolute minimum (usually +/- 5% or less)

I guess you are now thinking that if the O2 sensor is doing the correcting, then why correct for an erroneous IAT …………….. well the answer to that is two fold. The gas sensor reaction is not instantaneous and there is a significant delay in its response that is more noticeable at low rpm than medium to high rpm, also we only read the sensor at 32 or 64 ignition event intervals. Increasing the readings serves no useful purpose. Therefore it is normal to disable the O2 sensor below 1200 – 1500 rpm to avoid idle issues such as lumpiness and wild hunting.

Hope this all makes sense and explain why the IAT is so important to the ‘tune’ of the engine. ;)

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I can see an argument for having some sort of CLT comparative IAT adjustment

That's exactly the function documented in Ian's post :P

There's not really an issue here, it's just fine-tuning as people explore the software. More often than not, you find someone has already built a solution into MS, you just need to find it!

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So ive planned to fit my IAT sensor somewhere in this intake pipe in the hope it will not suffer as badly from the heat soak.

post-1274-1221828656_thumb.jpg

How much of an effect will the heat soak have? How do you think it will perform? Do I need to re think?

Imagine the inlet pipe to be a chimney on top of a fire ............... or a heat vent on top of a piece of machinery. Yes, you will have unavoidable heatsoak, but this can easily be effectively corrected as per my previous post.

Heatsoak to the sensor occurs my two routes………… heat placed into the body of the sensor by its surroundings, and the other is general heat that vents from the engine intake whilst stationary. The combination results in higher than ambient readings.

I have mine mounted on the rear if the air filter housing so that it act as a bit of a shield from direct heat ………….. when it was mounted above the engine in the inlet tract it was not usual to see temps of 60C + after being stationary or a few minutes.

I guess that position will be fine …………. But you will need some correction regardless of position. ;)

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In the case shown in the photo, would cab temperature not have a significant effect, especially say on a cold day, when the differential between cab and ambient teperature is more significant?

That would of course assume that the LR heater was working! :P

Good point but not really going to be an issue I dont think, There's no door tops on the truck, The heater only works for de mist and I should think the air flow through the pipe would keep the temp lower than the cab, It always feels iccy cold at the moment.

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Just to add a little more to this HFH has played with my IAT settings. I was in an event yesterday and it was a warm day with lots of winching then waiting so the under bonnet temp was quite high but when i stalled the car or turned it off to mock my team mate, it started on the button every time. The temp sensor is in a silicon reducer on the end of the standard flexie that comes off the plenum not quite over the inner wing so i still get heat rising from the headers. By the way we came 3rd and the MegaSquirt was outstanding, best thing since sliced bread. Did i mention we came 3rd... got a bronze medal as well.. :lol:

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Anybody reading this thread and thinking about fitting megasquirt may have a question about the MOT emissions test and how megasquirt might effect it....

As mines just gone through its MOT today i thought i would input into this thread.

info about the age of the vehicle and what test they perform can be found here http://www.bobmckay.co.uk/p_emissions.html

basically

First used before 1/8/1975 - Visual test only. Failure for excess idle speed, dense blue or black smoke for 5 seconds at idle or during acceleration up to 2500rpm or half engine max speed whichever lowest.

First used between 1/8/75 and 31/7/86 - meter test CO <=4.5%, HC<=1200ppm.

First used between 1/8/86 and 31/7/92 - meter test CO<=3.5%, HC<=1200ppm. *** This is the category mine fitted into***

First used between 1/8/92 and 31/7/94 - advanced emission test (CAT) if its running on petrol when presented, to the vehicle specific limits usually around CO<=0.3%, HC<=200ppm and Lambda 0.97 - 1.03. Remember from 1st August 2001 a basic emission test will be carried out initially.

View the web site for more info on specific tests.

Any way a handy diagram of how this all relates is shown in the back of the megasquirt tuning manual.... This is shown below

post-5991-1222183187_thumb.jpg

All I did was try and get my Wideband Lambda sensor to show between 14 and 15 at idle. it sits about 14.3:1 ish

Results of the emissions test.... 1.14% CO and 97ppm

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Anybody reading this thread and thinking about fitting megasquirt may have a question about the MOT emissions test and how megasquirt might effect it....

As mines just gone through its MOT today i thought i would input into this thread.

info about the age of the vehicle and what test they perform can be found here http://www.bobmckay.co.uk/p_emissions.html

basically

First used before 1/8/1975 - Visual test only. Failure for excess idle speed, dense blue or black smoke for 5 seconds at idle or during acceleration up to 2500rpm or half engine max speed whichever lowest.

First used between 1/8/75 and 31/7/86 - meter test CO <=4.5%, HC<=1200ppm.

First used between 1/8/86 and 31/7/92 - meter test CO<=3.5%, HC<=1200ppm. *** This is the category mine fitted into***

First used between 1/8/92 and 31/7/94 - advanced emission test (CAT) if its running on petrol when presented, to the vehicle specific limits usually around CO<=0.3%, HC<=200ppm and Lambda 0.97 - 1.03. Remember from 1st August 2001 a basic emission test will be carried out initially.

View the web site for more info on specific tests.

Any way a handy diagram of how this all relates is shown in the back of the megasquirt tuning manual.... This is shown below

post-5991-1222183187_thumb.jpg

All I did was try and get my Wideband Lambda sensor to show between 14 and 15 at idle. it sits about 14.3:1 ish

Results of the emissions test.... 1.14% CO and 97ppm

Sooo what your saying is that with MegaSquirt fitted your car is better than it was when new... and better than alot of new cars with cats aswell.. B)

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Sooo what your saying is that with MegaSquirt fitted your car is better than it was when new... and better than alot of new cars with cats aswell.. B)

When I first MegaSquirted the 109, I took it for it's MOT and the tester said "Ahhh, so you've fitted the catalytic converter to go with the engine then?" :lol:

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A point worth noting ................ when setting and testing the valve, you should disable the 'over run cutoff' as its final activation value will need to be empirically set in order that it does not effect the operation of the valve .............. this caused me a load of problems until I understood what was going on.................

Once the valve is happy and is working well, then implement the 'over run cutoff' in such a way as not to interact with the idle valve settings.

The symptoms are that the valve cannot find its 'idle value' as the revs are dropping and the overrun cutoff has shut down the fuel until the TPS idle threshold is passed and the fuel is reapplied ........... ;)

:)

Ian

HFH and myself have been trying to work out why when i coast to a stop and dip the clutch the revs drop to 400ish then recover, at least most of the time they do some times it just stalls.. It starts on the button so im wondering if BBC's post above has any thing to do with my problem.

Over run fuel cut settings are:-

RPM 1600

KPa 25

Raw ADC 30

Deg C 72

Sec 1

A step by step to set the PWM and fuelcut off would be a help please just so i can see what im doing and why.

Jeff.

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Ok a little update to the post above.. I was removing the PWM valve to check and clean the aforementioned and found the pipe between the plenum and valve was more or less totally collapsed... I have replaced the pipe and it has improved no end the overrun problem. Cant tell if the draw from the fans has been improved as its too cold so its not getting hot enough so i will "pop" round the block later. :rolleyes: It was the inside of the pipe that had collapsed so from the outside it looked ok.

Jeff.

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