Is there any truth to the rumor that with bigger primaries (IE 720s) and an SAFC controlling them, that the car will exhibit the hot start problem?

 

I dont think the SAFC has anything to do with starting the car as far as controlling the fuel goes.

 

I run 4 720's with an e-manage. I've never had a flooding problem; cold or hot start.

 

4x720 with afc and no startup problems here. I've even run 720s in the primaries with no afc (no correction) and still had no startup problems. This is on an s5 though, s4's flood so much more that it could be a problem.

 

From being older and probably having less compression?

Given a healthy s4 and a healthy s5 I don't understand why the s4 would be more likely to flood.

 

No, s5's have a programmed fuel cut feature, and it has even been rumored they have a slight injection delay compared to s4 cars which have neither. Havent you ever noticed that 90% of flooding posts are made by s4 owners, and rarely do s5 owners complain of flooding, even with old tired engines? Mazda made improvements to the s5 to prevent flooding.

 

Hmmm.. As I suspected.

This motor that someone sold me *Supposedly* had 120 PSI, and it was a 20,000 mile Mazda factory reman. Well, once I got it installed and warmed up, it only came up to about 90 PSI. **** a duck.. $1000 down the friggin drain. Been running this motor for a few months, but it has the hot start problem. And all the injectors installed were new, out of the box. 2x720s and 2x890s. God I should know better then to buy used motors by now.

 

Is that comparable to the SAFC?

 

Just a fancier way to manipulate the AFM voltage, does the same thing.

I noticed the trend, but chalked it up to fresher motors. Nice to know Mazda did a few good things to the s5 while bloating it up

 

Larger primaries can cause flooding as start-up, because all factory ECU's use rich mixtures during cranking. The S-AFC can't compensate for this, so the engine can flood.

 

s4's have lower compression by 1/2 point in the turbo and .3 for the na's

 

thats just what I was going to add. A S5 with lower compression than stock still might be at a S4 peak level.