331 stroker problems

[87Mustang351]

hey fellas my buddy just got a 331 built and in the car...

car has

cobra intake
1.6RRs
b303 cam
afr 185s
75 MM throttle body
24 ILB injectors
flowtech headers

motor is totally rebuilt

the car willl not idle right it jumps from 500-1000 and half the time quits when u pull in somewheres coasting, and when u drive at about 2 thousand rpms the car bucks....he didnt upgrade his fuel pump hes using the stocker, which i told him to upgrade but wont listen, also told him to get a fuel regulator to and gauage to check and set his PSI....can you guys let me know what u think is wrong and what pump and PSI he should get and set PSI to...

thanks!

 

[1991vert]

check for vac. leaks

 

[FastDriver]

With regard to idle surge, find the "useful technical thread index" sticky in the 5.0tech forum and open it. In it click the link to the "surging idle checklist." The surging idle could be the TPS sensor, IAC, a faulty MAF, the idle set screw, the 10-pin connector or maybe the EEC just needs to be reset for the new combo. You'll just have to eliminate the possibilities 1 by 1 unless your computer is throwing codes.

Whoever was smart enough to put that combination together should've been smart enough to upgrade the fuel pump. I highly recommend not hot-rodding it until it is upgraded. Just get the Walbro 255 LPH in-tank pump. It's a stock replacement, and will provide more than enough power for that engine with room to grow.

I think that those injectors are too small for the combo and would personally use 30 lb injectors. The 24 lbs/hr ones should work, but they may need more fuel pressure than stock to keep their duty-cycle low enough. You can find conversion charts for fuel pressure and injector sizing.

My personal rule of thumb is to increase the flow of my injectors by 10 lbs/hr for every 100 rwhp. That's almost exactly the way ford seems to do it (19lbs/hr for the 5.0 ~190rwhp, 24 lbs/hr for the 93 Cobra ~230rwhp, 39 lbs/hr for the 03-04 cobra ~ 420 hp at the crank.

In any case, I don't think that a small pump or even small injectors would cause a surge as they should be fine for idle.

 

[87Mustang351]

ok thanks alot i will let him know and show him the check list on the sticky, anymore oppionons are welcome ..thanks

 

[5spd GT]

Did he upgrade mass air flow sensors (assuming it is a 89+ MAF car) to 'match' the blue 24 lb injectors?

Vacuum leaks is a good thing to check...

Yeah, stock fuel pumps are 88 or 95 lph...it needs to be upgraded...

 

[87Mustang351]

his car is a 88 he upgraded to mass air but im not sure about the sensors, ill let him know!

 

[5spd GT]

If he is using a stock replacement maf that was designed with 19 lb injectors in mind, that is a problem

Just ask him if they are calibrated for the 24 lb injectors and to make sure they are...