3.9 EFI Megasquirt idle and low speed running problems

[zim]

The air temp sensor in the plenum giving a false reading wasn't something I thought about at the time. I think it usually reads up to about 70deg but it isn't something I have really checked at this stage.

Wouldn't be too much trouble to move it though. Where did you site yours?

By the way what is idle quality like at 800rpm?

It's a bit late of a reply now, but my idle is more than happy at 800 - 830.

I set it to run at about this using the idle adjust screw on the plenum.

But i also run a 2 wire bosch idle control valve (instead of the stepper motor). With this it is set to idle faster at warmup - it hunts around a little bit when started till it knows what it's doing. It will hold my 830 when i have a load on the engine (i run a hydraulic pump directly off the front of the crank). *IF* i wanted, i could just type into megatune to change either idle speed and it's more than happy to do it. This is how i was shown to setup my MS, so i've not argued and followed their advice

My IAT sender is in a pipe before the plenum which doesn't really heat up.

Regards

Gordon

[BenL]

Cheers I checked some old datalogs last night and the heat soak to IAT is more than evident. You can see it steadily rise up to around 70-80deg and then drop as the car is driven off.

What a nugget! Going to make up a new boss today. Look like that NPT tap was a good investment!

Looking forward to seeing what difference it makes.

[BenL]

Interesting thread on the MSExtra forum with a discussion about MAT correction and placement of the IAT sensor.

Worth reading!

[v8rob]

just my two penth worth! you mentioned earlier that the car didnt idle very well on the 500 carb set up? contary to popular beliefs a carb will idle much smoother than an injected engine, purely fueling side not ignition being involved, if you had a problem with idle the chances are its in the motor not the efi system, i have set up quite a few m/s system and are very happy with them, the a/t sensor is irrevelent as you have correction factors, maybe these need setting? the piper 270 was ground on 2 lca's 107 and 110 and ocasionally 104! which ever one it was ground on is not going to give you a silky smooth idle at the rpm you want, all this is down to poor air flow, one thing you could try is opening up the butterfly to increase airflow and retard the ignition to bring the revs back down.

[BenL]

I've moved my sensor to the intake now but have the option to move back again. How do you go about setting the air temp correction factors? Maybe you have some example values, would be of much assistance. They definitely need setting as after a run I experimented with pulling the lead off the air temp sensor which immediately improved the idle!

Out of interest is there a cam you'd recommend that would give a good idle but still make reasonable torque.

BTW I'm not reallyl expecting it to idle at 600rpm but would be happy with a decent idle at say 800rpm. Surely that must be achievable?

Tried your suggestion re increasing airflow and retarding ignition but it didn't seem to make a lot of difference.

[BenL]

Just a quick post to say thanks so far for all the advice. I've moved the sensor from the plenum and the result has been a major improvement in both the idle and low speed/part throttle running.

I think the MAT correction still needs to be set up as I have noticed if pulling up at the lights after a fast run the idle is initially high but stable. After five/ten seconds it starts to falter a little. I am guessing that as the under bonnet temp rises with the car stationary the sensor is picking up the increase but over correcting the mixture.

Obviously need to get the laptop hooked up and observe what is happening but need a co-driver and some free time. Meanwhile it is more than useable- I took it on a 300 mile round trip at the weekend and it goes beautifully. Lovely big surge of torque and sits happily at motorway speeds with only 2500rpm due to very high top gear. Got over 25mpg too which suggest to me that things aren't too far out!

Will be back for more later I'm sure but meanwhile, happy motoring to all!

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[kiwicar]

Something that should help idle stability is if you put a heat shield below the air filter so it doesn't take in hot air from above the exhaust manifolds, if you can go further and direct cold air from outside into the car would be even better, it would probably help the fuel economy as well.
best regards
Mike

[Eliot]

I've got a MS1 V29 - I implemented the MAT correction by first ensuring and noting the engine AFR in a non heat soaked state. Then went for a blast in the car, pulled up in a layby and allowed the engine to sit there idling and getting really heatsoaked.
As it got hotter and hotter, it got leaner - so I adjusted the mat correction at a couple of points (say 25'c , 35'c , 45'c inlet temps) until it came back to my AFR before it was heatsoaked. Hot restarts are really good now.

Ooo just noticed that i actually bothered to write it up all those years ago...
http://www.mez.co.uk/ms15.html

[BenL]

I was looking at possibility of enclosing the air filter in a box with a ducted supply from the front of the car. I expect on the move the air taken in is reasonably cool anyway but your suggestion of a heat shield is a good one.

@ Eliot: Thanks for the suggestion on setting up MAT correction, will take a look at your link now.

[daxtojeiro]

Hi
what air temp sensor are you using, is it the open style version or solid brass version?

I've fitted these in all sorts of positions in the RV8 intake and they didnt have any issues, even on my own car I've had it up to 80-90C in traffic over the past few days and idle wasn't effected at all.

Can you email me your msq file and a datalog of it doing it?

As Rob says, if you had this issue before going to EFI then I suspect its something else, you may be able to mask it with idle control using the MS though. What idle valve are you using, I have just done a major write up on stepper idle control and MS2/MS3 on my site if you want to have a read:

http://www.extraefi.co.uk/Drawings/PDF_ ... valves.pdf

I have mine running using the stepper and it is superb, but its really only suitable for MAP based tuning,
Phil

[unstable load]

I was looking at possibility of enclosing the air filter in a box with a ducted supply from the front of the car. I expect on the move the air taken in is reasonably cool anyway but your suggestion of a heat shield is a good one.

@ Eliot: Thanks for the suggestion on setting up MAT correction, will take a look at your link now.

Ben, if you look in the "go-faster" magazines you will see adverts for cool air intakes. Take a butchers at one and mod to suit your car. All it really entails is moving the inlet to the front of the car where it picks up cool(er) air and directs it to the engine. If you put your filter right up front then remember to use a foam element and not paper as it clogs when wet.

[DaveEFI]

I've got a MS1 V29 - I implemented the MAT correction by first ensuring and noting the engine AFR in a non heat soaked state. Then went for a blast in the car, pulled up in a layby and allowed the engine to sit there idling and getting really heatsoaked.
As it got hotter and hotter, it got leaner - so I adjusted the mat correction at a couple of points (say 25'c , 35'c , 45'c inlet temps) until it came back to my AFR before it was heatsoaked. Hot restarts are really good now.

Ooo just noticed that i actually bothered to write it up all those years ago...
http://www.mez.co.uk/ms15.html

Interesting. I have an SD1 EFI with the standard engine fitted with a MS2 V3, 2.89 software, and Tech Edge W/B sensor. it has the standard air intake which draws air from as far forward and low down within the engine bay as possible. I replaced the AFM with a plain tube, and sited the ATS in that - the same place as the original, which is built into the AFM.
The underbonnet temp does get quite high in a traffic jam on a hot day - I've seen over 60C. MS weakens the idle mixture from a nominal 14.1 to about 14.9, but the idle remains pretty steady at 600 rpm. I do, however, have to use some throttle for a hot start. The ignition timing is standard at idle - 8 BTDC. The inlet air temp compensation is the MS default.

Are you saying the A/F ratio shouldn't change with IAT at idle?

[BenL]

@Phil: I'm using the open style element that I purchased with the kit. I haven't got any datalogs at the moment as the laptop battery is KO'd. Will try and sort some logs out and send them to you sometime soon as I appreciate the offer to take a look.

What you say about the poor idle symptoms being attributable to the engine are correct. The idle is about 800rpm now but there is still a little fluffiness to it. I'm convinced that 270 is nothing in terms of duration of such a large cylinder capacity. The cam is supposed to be 110LCA but I suppose there is every chance it's got a tighter LCA than that and the increased overlap is causing a problem.

Anyway I'm very happy with the improvements I'm getting so far and suspect in the long run I will end up switching to 4.6l and being conservative in the cam selection. Once you get a feel for that surge of low down torque you just want more!

[bobtail84]

Try these settings..



I can dunk the engine in water or stop and start when hot with no problems.

Jeff