The lower the better (within reason).

It all depends on how much power you are planning on running and how big your fuel system is.

I'm only shooting for 500whp and have a decent fuel system. There is no point in leaving capacity on the table up top to sacrifice start up on the bottom. Under WOT what kind of duty cycle are you seeing? That would be the best way to determine how far down you can go.

 

Be careful with this though.. at 20psi the injector pulse is going to be so dodgey the car will likely start worse than at 35psi.

 

Well I do not get tuned until the 20th of this month so then a retune doenst matter. Ill try to put the pressure around 40 psi and see what happens. If its still not fixing I might inquire for altered to reflash the ecu.

 

Sometimes, my car will shut off! Always when I'm at a light, I had issues with hot starts, had to give it a little throttle. I have UTEC/650's.

 

I wouldn't think (I guess I shouldn't assume though) that you would be able to get away with dropping it that low. I guess if someone has a huge fuel system with smaller goals its possible.

If everything is sized within reason I wouldn't imagine you would be able to deliver enough fuel at WOT at 20psi.

Thank you for pointing this out though, you definately don't want the pressure too low!

 

I have HKS low impedance 1000cc, f con v pro, GTM ECU reflash and no problem with hot starts.

 

The spray pattern gets pretty rough if you drop the fp too low. Never hurts to test this out though, just keep lowering and testing. Also, I would only drop the fuel pressure low if you are using a boost-referenced fpr. Without a boost reference fpr: 20psi fp with 10 pounds of boost leaves you with 10psi of fuel pressure to use. The more boost, the less fuel... not good.

 

Mine does that bad and often! I have the UTEC and 650cc injectors. The last scenario had it die on a railroad track and then would not start back 85 outside!!!

The car pulls like a monster when its moving though, lol. My Fuel pressure is set higher, can't remember exactly how high.

 

Turbo xs blows then......

 

Thats another great point. I sometimes assume that everyone is running a boost referenced regulator.

If you arn't running one, it might help, as it will lower fuel pressure while cranking as the motor draws a vacuum.

I know some people hate them, and I'm not really a big fan of them, but they do have their benefits.

 

If you guys are having your cars shut off at stop lights, your issue is tuning. Especially if you have 650 injectors, because I have the same setup and definitely no symptoms like that. That wouldn't be acceptable to me, its a safety issue...

I think with good tuning and a fairly low base FP you will really avoid 90% of this hot start problem all together. I should clarify on my earlier post and say that my car will START every single time, hot or not. If the car is hot and I dont blip the throttle right as I turn the key it might fire up and then immediately die or it might not.

 

I have the injectors supplied in the APS TT kit & the Utec.
I have to prime it 3 times every time or else I get a SES light.
Once it's cranked I have to blip/touch the throttle or else I get a rough start up.

 

Who tuned your car?

 

wow, 42 psi fuel pressure, 600cc injectors, utec and no hot start problems.

get a better tuner!

 

I only had my shut off twice, not common, but enough times for me worry about potential problems. Car was tuned at Forged and I know they dont let faulty products out. May be defective equipment.

 

Past fuel pressure, hot start issues can't be "tuned"

Since the car isn't running the car starts up in open loop. There is no way, besides reflashing the ECU, to change this. I wonder what would happen if we modified the MAF voltage going to the ECU during start up. I would guess that the starting is temperature compensated. If we adjust the temp so that the car injects less fuel during start up it would help the issue. Now if I only knew someone who could come up with something like that....

 

I have the hot start issues every day. If I could afford a stand alone I'ld be all over it. TurboXs really dropped the ball on this one.

 

Your time may be better spent modifying the coolant temp signal to the stock ecu for starting. A stock Z will still start with the MAF/air temp unplugged.

 

Really? Thats interesting. In reality, MAF wouldn't be what I wanted anyway - I should have said intake air temp. I would guess that different fuel amounts are deleivered for different temps. I guess the same would be for coolent.

That would be a fun project, but I feel it is one I'll never move forward on

 

That is very strange. I've had my utec for a year now with my aps tt and never had a problem starting. Are you still using the aps fuel set up?