Hot start problems - megasquirt

seight · Post by **seight** » Sat Jul 04, 2015 6:30 pm

Ok, following on from my battery question ...... It seems that was not the issue. I have a nice new RedTop 30 and I still get hot start problems.

I am beginning to think it may just be heat soak in my inlet air temp sensor. I may have put it in the wrong place. To be honest I copied another Wetfield owner with a carbon plenum assuming his was fine. It is mounted in the plenum itself when perhaps it should be on the other side of the throttle

Have I been a dumbass all along?

After idling for a while and engine fully up to temperature I see IAT up to 48-50 C today. All runs fine then stop the engine and it won't start or eventually starts after about 10 attempts but runs badly.

Does this sound like typical heat soak problems?

I guess I could get another sensor and connect that in 'free' air when it happens. If that works then I guess that's it.

Any ideas?
Thanks
Mike

ChrisJC · Post by **ChrisJC** » Sat Jul 04, 2015 7:48 pm

Is there a diagnostic facility where you can find out what the IAT is reading? That might tell you that the IAT is reading 90degC when you try a hot-start, clearly bobbins.

Chris.

Post by **Coops** » Sun Jul 05, 2015 12:44 am

get this with mine mate badly,
https://www.youtube.com/watch?v=5Ie47Bfgbb8
when it plays up try turning it off and restarting to see if it cures it

DEVONMAN · Post by **DEVONMAN** » Sun Jul 05, 2015 7:52 am

Just a suggestion.

I had a similar case and it was too much fuel at hot cranking.

I discovered that by stopping the engine by unplugging the fuel pump's 12v supply and not using the ignition key it started at the first try when I had stopped the engine buy starving it of fuel. Worth a try.

If it was heat soak at the air temp sensor it would not happen straight away but only after a few minutes.

I have a permanent fuel pump switch installed now which is handy at other times also.

Regards Denis

DaveEFI · Post by **DaveEFI** » Sun Jul 05, 2015 9:38 am

Does it start more readily with some throttle? If so, that means it is likely too rich. If not, too weak.
There is an ATS compensation curve in TunerStudio. If you log a hot start, your wideband should show what the mixture is doing. Since you're only likely to get very high under bonnet temps with the engine stopped, the ATS compensation can be used to correct the mixture at at those temperatures - so a sort of hot after start correction.

Not sure about the very best position for the ATS. Mine is in the trunking about half way between the throttle and air filter.

SimpleSimon · Post by **SimpleSimon** » Sun Jul 05, 2015 10:17 am

I wouldnt mount the ATS anywhere near the plenum on the RV8 too much heat soak which on hot start wil pull poop loads of fuel from the MAP so you basically get poor hot starting coupled with a really lean run post hot start condition whilst you wait for the ATS to bring the fuel back into the MAP as it cools

mine is in the air filter trunking close to the air cleaner & miles away from the engine I want it measuring outside ambient air temps not under bonnet temps

on the TVR the air cleaner is mounted in the nose section about 3 feet away from the TB

stevieturbo · Post by **stevieturbo** » Sun Jul 05, 2015 11:29 am

A hit IAT sensor will only be a problem if you have silly values for air temp correction.

Just because gas laws or whatever say they should be certain values, doesnt mean that's what the engine will want as it is installed.
Although on that theory, hot air would generally lessen any fuel quantity being supplied...again the tuner will have set all these parameters.

But pulling the sensor away from the hot engine is easy to do as well so less chance of false hot readings when the actual air temps arent really hot.

@Coops, your problem is a dodgy wideband reading, not anything relating to IAT.

And as has been said, the biggest mistake many make is throwing too much fuel on for starting when the engine is already warm. Most engines need very little enrichment for starting when hot.

And equally important, they need air too.

seight · Post by **seight** » Sun Jul 05, 2015 8:17 pm

Update ... did some logging yesterday.

1.
Warm start, started ok with:
CLT 67 c
MAT 39 c
Gair 94 % - whatever that is

2
Hot start - wouldn't start with:
CLT 97 c ( idling on drive on a hot day

)
MAT 49 c
Gair 91%

In fact most, if not all, the logs for failed hot starts have Gair down at around 91%. I gather Gair is from an internal calculation based on MAT among other things.

I am running 100% 'MAT Correction PV=nRT' and all zeros 'non linear MAT correction' table.

Does this mean the Gair is only giving me 91% fuel? Could this be why it won't start?

I've also read about possible changing the MAT correction to compensate for the low Gair up. But moving the temp sensor may be more sensible.

This is all new to me

Mike

stevieturbo · Post by **stevieturbo** » Sun Jul 05, 2015 10:46 pm

MS really do some weird poop, and call things strange names..

Who knows what's going on in there lol

DaveEFI · Post by **DaveEFI** » Sun Jul 05, 2015 11:06 pm

Which version firmware?

IIRC, older versions used an embedded correction which you could then alter (so would start out 'flat') - later shows the actual correction.

SuperV8 · Post by **SuperV8** » Mon Jul 06, 2015 12:47 pm

Has it ever started well from a hot start?

Does it start easier if you open the throttle?

If it does not fire at all the only fuel calculations are taken from the cranking pulse% - try adjusting this at the temps where it won't start.
If it starts then dies try adjusting the After Start Enrichment %

Is MAT timing advance correct? You can adjust the timing for high air temps, maybe this is coming in too early?

Cranking Fuel Pulse Rate?
Engines with many cylinders such as V12s may find that the injecting fuel on every tach event gives difficult hot
starting due to small pulse widths.
This option allows the fuel to be injected on alternate events (with twice the pulse width.)

Tom.

Quagmire · Post by **Quagmire** » Mon Jul 06, 2015 3:14 pm

On my MS1 powered Landrover I used the guide that Elliot posted on his website to minimise heatsoak issues:

http://www.mez.co.uk/ms15-new.html

sorted it right out.

seight · Post by **seight** » Mon Jul 06, 2015 6:12 pm

I think it's 2.1.0p but I've not got it to hand at the moment. It's probably WELL out of date. I tried looking at the release notes for later releases but it's hard to see what's what.

It's never really started well from hot even before the rolling road.

I think the cranking pulse adjustment drops off by 70c (coolant) but I'll check that. Not sure about timing but when I get my laptop back I'll find out.

I guess it's one thing at a time to see if it improves.

I'm off to read Elliot's site now

and have a spare temp sensor on the way - it will be a real pain to move the current one.

Thanks everyone, I'll update this when I have some news.
Mike

Cobratone · Post by **Cobratone** » Tue Jul 07, 2015 3:17 pm

Is it possible to apply some heat from a hairdryer to the air temp sender whilst the engine is cold and then try and start it, if it starts ok then the hot air isn't an issue? hope that makes sense, it does in my own head

DaveEFI · Post by **DaveEFI** » Tue Jul 07, 2015 3:44 pm

I'd do a log of a hot start. Start the log before starting the engine, and make sure the wideband has heated up too. That will show the AFR immediately after starting. I'll bet it is weak. The ATS is likely showing something like 60 plus C - something it won't see with the engine running. And as soon as the engine starts, the actual air will be much cooler. So you set the ATS correcting to give a decent AFR just after a hot re-start at that temperature. Which won't be in play under normal running.