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Forum » General Tuning Discussion » Hot restart

Hot restart

General Tuning Discussion

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Hi guys I'm struggling with my car it does not want to start after it has been driven for a while. When its cold the car will start in an acceptable manner (still not happy with the way it starts) the throttle needs to be 100% open for it to start but when the car is hot it will take several cranks to get it to start and it really struggles to come alive I see my afr on cold idle is pretty high around 10.2 and hot it sits at 12.2 not to sure if its running too rich. car seems to hunt alilllte on idle aswell.

Running too much fuel can cause as many problems as not enough. This can cause the hunting and difficulty starting.

If the motor is mechanically solid I'd get the map looked at and some fuel pulled out

Running too much fuel can cause as many problems as not enough. This can cause the hunting and difficulty starting.

If the motor is mechanically solid I'd get the map looked at and some fuel pulled out

Cold start (and hot restart) are actually some of the more time consuming parameters to optimise if you want to replicate a factory-like tune.

Before you worry about any of the start up tuning, you must make sure that your actual fuel and ignition tables under normal hot operating temperatures are correct. All of the compensation maps are applied to these base tables so this is the first step. Next I suggest tuning your cold start and getting that right. I've included links to a couple of previous webinars that explain the procedure. You definitely shouldn't need to be using full throttle to get the engine started cleanly. 10.2:1 is very rich for a cold start AFR and ultimately you will end up fouling the spark plugs and the engine simply won't start. I suggest trying to keep the AFR no richer than about 12.8-13.2:1 under cold start. This should give good startup response but won't foul the plugs.

Once you have the engine cold starting properly then you can address hot restarting. Often you may need to trim 10-20% more fuel in during the first 30 seconds of running after a hot restart. You will find this is a compromise as most aftermarket ECUs don't really offer complete control over hot restarting.

https://www.hpacademy.com/previous-webinars/tuning-cold-start/
https://www.hpacademy.com/previous-webinars/cold-start-tuning-motec-m1/

What ECU are you using .

thanks for the reply! I am using one of our locally made ecus called spitronics

Your ability to get great results will to a degree obviously depend on the capability of the ECU. Some ECUs offer more tables to deal with startup parameters than others.