So Ive been fighting with these 315cc brown top supra injectors for the last couple of weeks. When the truck is running they run great, very consistent, quiet, and lots of power. Problem was that after driving it and leaving it for 20 minutes or more the motor was incredibly difficult to start taking 30 seconds or more of cranking to get it to stumble and start. I tried pulling fuel during cranking with my piggyback, adding fuel, and leaving it alone to let the stock computer learn what it needed to do but none of the changes seemed to make a difference. Last week we got hit with a snow storm that dropped the temps into the 30s which did seem to improve the starting some but not a whole lot.
I went and picked up a 99+ air box and maf at the junkyard for 10$ and swapped it in just out curiosity with no change. I finally said screw it and bought 6 brand new stock injectors to swap in and see if it improved starting at all. Swapped those in this morning and the truck fires right up every time but runs like total shit since the injectors are maxed out and my fuel trims are pegged at 19% all the time. So back to the drawing board I went.
So what are the differences between the supra injectors and the stock injectors?
Visually they are quite a bit different but they interface with the fuel rails the same.
Supra injectors
Flow rate @46psi: 315cc/min
Tip style: non air assist
# of spray holes: 2
Designed seal type: one large oring at the very end of the injector right at the spray tip
Stock injectors
Flow Rate @46psi: 240cc/min
Tip style: air assist
# of spray holes: 2
Designed seal style: 1 smaller oring at the spray tip and a "dust seal" where the injector sits in the intake plenum.
So obviously the flow rates are different, the whole reason we want them, but the sealing and air assist tips are entirely different. What iv'e seen most people do is swap the dust seal from the 4runner injectors onto the supras and run just that but Im not confident this is giving a really good seal. The other issue I see is the air assist tip, toyota used this in the 90s both to better control idle by having a more controlled air inlet through the iac valve and to better atomize the fuel during cruise. After talking to a few others that have had this same starting issue with the supra injectors my theory here is with the iac system essentially bypassed with the supra injectors the stock computer essentially cant control the air fuel mix properly when cranking causing it to flood the engine out or run it too lean.
So whats the solution? well I went searhing to find info ad see if I could find a 300ish cc/min injector with an air assist tip. After searching the old MR2 forums for a few hours I stumbled across this.
Injector flow rates for 3VZ, 1MZ (w/ some 2JZ, 1UZ, 3MZ) | Toyota Nation Forum
Within the first post they list out all the injectors toyota used through the 90s and the one that caught my eye was the blue top 2jz injectors. Denso p/n 23250-46050
Available on amazon here:
https://www.amazon.com/Re-Manufactured-Denso-23250-46050-Injectors-Toyota/dp/B074P7CRGX
This is a 310cc injector with an air assist tip that looks like the dimensions on it that match the 5vz injectors. Ive ordered a set of these and sent the brown top supra injectors back. Im hoping to install these this week and will report back with my findings.