Running lean at the end of a run?

[angus337]

I’ve had a frustrating problem for a while now, and still haven’t been able to figure it out.

The car starts and idles fine and drives well without any issues, until I need to stop and park-up, at which point the car will run very lean on low throttle. I have to really keep the revs up to prevent it stalling, which is a bit embarrassing when reversing parking in a busy car park.

I’ve checked numerous megasquirt logs and adjusted the fuel map, but this doesn’t seem to help, so I’m pretty sure it’s not the fuel map. Also looked at the MAT but this doesn’t seem to be too high so don’t think it is a heat soak issue either.

There seems to be a number of potential causes, including:

Stepper motor – Already checked and Cleaned, but may be sticking when hot?
Low Fuel pressure or vaporising fuel when hot – Possible fuel pump or pressure regulator problem?
Vacuum leak?
Faulty Throttle position sensor?


Any thoughts on how to narrow this down, or could it be something else?

[cinquecento]

My MS griff loves to idle rich..abt 12.8 afr at 12 deg adv. At anything over 13.5 it hunts and the idle just isn't as smooth.
Cam, mods, advance and MAT all have an effect.

Post your logs?.

[Boosted LS1]

I'm thinking fuel vapourisation or heat soak in the fuel rail. Have you tried insulating the rail to see if you get an improvement? If you increase rail pressure what happens?

[angus337]

Thanks for input guys.

Fuel pressure or vaporisation was my first thought. Not sure how old the fuel pump is so ordered a new pump and filter. Also hoping to get a test kit to measure fuel rail pressure at the weekend.

[cinquecento]

Just looked at my MS config. I have large amounts of ASE taper at over 80 deg C coolant to compensate for heat soak. So after the car starts, I have 16% ASE for 800 cycles. HTH.

[carsy]

Initial thoughts are some sort of heat soak and most likely is air temp sensor. Where is it located.

Although you say air temp sensor is not reading really high have you checked your fuel and ignition correction tables in relation to ats just in case.

[angus337]

My MAT sensor is located where the AFM used to be located, so it does suffer from heat soak, especially when I park up for a few minutes at a shop or petrol station. To compensate I've added quite a bit of non-liner MAT correction at high temperatures, which does prevent the engine leaning out on restart, and prevent any embarising kangeroo hops out of the petrol station!

I don't think I'm seeing the same issue when parking up after a run, as there is still air flowing through the inlet, so the sensor should still be fairly accurate. I'll try a it more experimentation with this though.

Also considering updating the firmware as the newer version seems to handle this a little better, but worried about messing up the current map.

[angus337]

cinquecento said:

My MS griff loves to idle rich..abt 12.8 afr at 12 deg adv. At anything over 13.5 it hunts and the idle just isn't as smooth.
Cam, mods, advance and MAT all have an effect.

Post your logs?.

Mine seems to be fairly similar.

Idles at about 12.9 AFR & 12 deg advance when cold, increasing to about 13.5 AFR when warmed up.

I'll have a look at the ASE later, but I don't really have any issues stating the car from either Hot or cold