The V8 Owners Forum -

Hi Guys, this will test you,

have had a problem from day one of a type of miss fire and very lean surges under light throttle, have tweeked the fuel table no end to no change,
BUT then last night by sheer fluke we have now sorted this, it was a high spot in the ignition map which when under light throttle the car was on the edge of the high and low spot and was jumping back and forth on the ignition map

BUT this other one i can't seem to cure,
I'm still having this hot start problem, where you go for a drive park up for say 15-20mins come back fire the car up and it then gives an afr of 17-23 and hunts up and down like a bitch, switch engine off and start again straight away and it gives 13.7-13.9 and runs as normal??????

Im beat on this one,
Any clues????? IAT sensor????

It's unlikely the ATS output would go intermittent or whatever under exactly the same circumstances each time?

My SD1 EFI has always been temperamental if you stop the engine when very hot and leave it a few minutes, so it's still cooking when you try and restart. It's better with the MS, but still not perfect. What does help is to run the pump for 30 seconds or so before attempting a start to cool down the fuel and get rid of any vapour locks.

I had something similar where it would do this randomly when hot and run really lean initially high AFR, i changed skip pulses in ign settings from 5 to 10 and cured my problem it was like the MS was syncing up badly with the EDIS module not quite ready or not giving a clean/steady signal

if you run the car while lean and drive down the road for a say 1/8 mile and pull over idle will still be lean and hunting up and down, as per first post.

Im running coil packs and crank trigger Simon,

Coops wrote:if you run the car while lean and drive down the road for a say 1/8 mile and pull over idle will still be lean and hunting up and down, as per first post.

Im running coil packs and crank trigger Simon,

Strange this one Coops, mine did similar until you blipped the throttle certainly did not last as long as driving off (like yours) annoying all the same as it did not run cleanly until the blip 17.1 AFR as i remember the motor was not happy this what IAT are you registering from hot start then? have you tried Data-logging to see what changes when the car rights itself ?

so far every time we do the datalogging the fekkin thing wont do it,

will see what it does at the pod tomorrow and if we can get a log if it does it,
could we be resetting something when we turn the car off then start again when it plays up?


otherwise car runs sweet as a nut,

would be interested in seeing how everyones ignition maps look in relation to mine, i know they wont be the same etc,

Have you try to adjust Inlet Air Temparature table? I notice my old Haltech and new MS3X that when car is park approx 30-45min then idle AFR is over 18 and engine will stop etc.. I slightly adjust IAT curve richer when engine is cold and warm.. Zero range -0C to +35C and slightly richer over +35C and under -0C
Normal driving IAT is approx +20-25c in summer +20c outside temparature. When engine is park say 30-45min IAT is approx +45c then.. And cool quite quickly to +20C when i go to road..
I say it will need more fuel to burn correctly..

yup have tweaked the IAT table too

I'm still having this hot start problem, where you go for a drive park up for say 15-20mins come back fire the car up and it then gives an afr of 17-23 and hunts up and down like a bitch, switch engine off and start again straight away and it gives 13.7-13.9 and runs as normal??????

OK, first let me start off saying I know nothing about fuel injection per-se, but this sounds like a sensor that is getting confused by changing conditions.

You have an engine starting from ambient and going for a drive - all is normal.
Then it parks and the sensor heat soaks for 15-20 mins until you start it again and flood it with cold air that somehow pushes it's cheese of the cracker.
You switch off and re-start it which allows the computer to reboot to what is effectively a cooled sensor due to the ambient air that has passed over it in the first start, and the reset computer then functions as normal.

Could it be a wiring fault or a duff connection giving you a false reading due to the heat soaking?
Either way, it all points to whichever sensor controls that function and it's associated wiring/circuitry.

Of course, not having any idea how that particular system functions, I could be talking through a hole in my head.

The ATS is just type of resistor that varies with temperature. They tend either work or not, as it were.
Logging is the way to go, as this records the actual air temperature it's seeing. If it changes dramatically between stopping then restarting, something isn't right.

I dunno how much hysteresis there is in that sensor input. Obviously under running conditions, the air temp isn't going to change suddenly by a large amount. With the engine stopped and high under bonnet temperatures, it will read the temperature of whatever it's mounted in, which can be well above the true air temp. Especially if it's mounted in the actual inlet. I positioned mine where the original was - in the inlet trunking. But I'd expect MS to correct things quickly when it sees the true air temp. Which obviously isn't happening.

You could set IAT correction to zero above a figure the actual air temperature would be when running, a see if that helps.

But probably best to ask on the appropriate MS forum. Lots of expertise there - often from the horse's mouth.

car ran faultless all the way to the pod today, then ran like a bitch on the way home 7hrs later, drove for 70 miles stopped had a cuppa tea, got in car to drive 10 miles home and it ran like a dream again WTF?????

Best to log every journey. Sooner or later you'll get a log of it running badly.

Phil (what a star) has advised it could be a heat soak error still and the IAT sensor is getting hot, where have you guys mounted your IAT sensors?

Coops wrote:Phil (what a star) has advised it could be a heat soak error still and the IAT sensor is getting hot, where have you guys mounted your IAT sensors?

I was concerned about this as my SD1 EFI with A/C suffered badly from heat soak and vapour lock as standard. Indeed, had a factory retrofit mod to try and cure hot re-starting.

I mounted mine in an ally tube which replaces the flapper - so effectively in the same place as the original - but insulated the ally tube. It's not perfect, but generally ok. I did wonder about mounting it in the air filter housing. Although the vapour lock is a separate issue - although both caused by excessive under bonnet heat.

mines also in an ally tube between the plenum and filter, and wondered if mines getting to hot in the tube,