two stepper motors control problem

Hello

I'm trying to control two 28BYJ-48 stepper motor with Arduino Uno. Controll code is listing below .When I upload the code into Uno. Only one motor can rotate. And it rotates slowly. But When I remove the the code of previously moving motor. The other motor can rotate fastly. I guess there are something wrong in the code. Can anyone help me to fix it?

//first motor
int A = 8;
int B = 9;
int C = 10;
int D = 11;

//second motor
int E = 4;
int F = 5;
int G = 6;
int H = 7;

int del=2; //delay time

void setup() {
   
 pinMode(A,OUTPUT);
 pinMode(B,OUTPUT);  
 pinMode(C,OUTPUT);
 pinMode(D,OUTPUT);

 
 pinMode(E,OUTPUT);
 pinMode(F,OUTPUT);  
 pinMode(G,OUTPUT);
 pinMode(H,OUTPUT);
 
}

//steps of the first motor 
void step1()
{
 //S1
 digitalWrite(A,HIGH);
 digitalWrite(B,LOW);
 digitalWrite(C,LOW);
 digitalWrite(D,LOW); 
 delay(del); 
}

void step2()
{
 //S2
 digitalWrite(A,LOW);
 digitalWrite(B,HIGH);
 digitalWrite(C,LOW);
 digitalWrite(D,LOW);
 delay(del);
}

void step3()
{
  //S3
 digitalWrite(A,LOW);
 digitalWrite(B,LOW);
 digitalWrite(C,HIGH);
 digitalWrite(D,LOW);
 delay(del);  
}

void step4()
{
  //S4
 digitalWrite(A,LOW);
 digitalWrite(B,LOW);
 digitalWrite(C,LOW);
 digitalWrite(D,HIGH);
 delay(del);
}


//steps of the second motor
void step5()
{
  //S1
 digitalWrite(E,HIGH);
 digitalWrite(F,LOW);
 digitalWrite(G,LOW);
 digitalWrite(H,LOW); 
 delay(del);  
}

void step6()
{
 digitalWrite(E,LOW);
 digitalWrite(F,HIGH);
 digitalWrite(G,LOW);
 digitalWrite(H,LOW); 
 delay(del); 
}

void step7()
{
 digitalWrite(E,LOW);
 digitalWrite(F,LOW);
 digitalWrite(G,HIGH);
 digitalWrite(H,LOW); 
 delay(del); 
}

void step8()
{
 digitalWrite(E,LOW);
 digitalWrite(F,LOW);
 digitalWrite(G,LOW);
 digitalWrite(H,HIGH); 
 delay(del);  
}


void loop() {
 // put your main code here, to run repeatedly:
 
 //first motor rotate
 step4();
 step3();
 step2();
 step1();
 
 
 //second motor rotate
 step5();
 step6();
 step7();
 step8();  
 
}

Use the AccelStepper library? You can run several motors in pseudo-parallel very easily,
you just call run() method for each motor in loop () and don't ever delay().

The motor as such is pretty slow as it comes with a 1:64 gear (reduction).
Means: you send 64x64 steps = 4096 steps to get ONE rev.

As the max steps/sec of Accelstepper library are 4000 - you won't get lucky with this library. You have to look for another lib or write your own code - still I think, you won't get too much speed due to the internal gear.

If you need higher speed - there is no other way as to go with another stepper motor and no gear reduction!

Its 4096 half-steps, and its only approximately 4096, not exactly.