Running lean on hot restart

[DaveEFI]

I have a Rover SD1 EFI - one of the earliest electronic injection factory setups, dating from about 1980. The factory offered a mod for those suffering hot re-start problems - but it was never fitted from new. A thermostat mounted on the rad controlled a solenoid valve on the fuel return line, and closed it during cranking if rad temp was above a certain figure, raising the fuel pressure to the maximum the pump could manage. Up from 36psi to about 46 psi.

I dunno how well this worked - and would obviously only help starting, not running after starting. But just offered it as perhaps confirming it is a fuel supply thingie rather than inlet air temp.

My SD1 now has a MegaSquirt - but the original injectors and fuel rail. And it does suffer from hot restart problems and weak mixture immediately afterwards which I've never been able to sort fully. I have to open the throttle slightly for a hot start, and it takes about 30 seconds for it to idle normally. Once started and stabilised it will then idle happily all day regardless of temperature. it doesn't have an electric fan - just the engine driven one.

[142 guy]

That is an interesting / unusual mechanical patch. That must have been one of those ad hoc HICOMP strategies that the Ford patent application referred to.

I have effectively implemented something similar in software on MS2 Extra by increasing the ASE % and taper above 70 C coolant temperature. The change in % was not huge; but, I made a significant increase in taper to manage the lean condition in the 10 - 15 seconds it takes before the O2 sensor has come up to temperature and starts operating.

I run fairly low hot cranking % values (70% at 70C) and have never had a problem getting the engine started, which in retrospect is surprising. My problem seems to be just managing the lean condition and attendant rough running in the initial period after a hot restart.

[Yves]

Thanks for this.

I have been experiencing the same thing.

May I just ask a question : what type of FPR are you using ?