Injector Rates

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Slum Lord
Joined
Apr 3, 2006
Messages
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Slow starts when hot. Thoughts?




Cold: (checked with Peditor)
-----Idle-----In Gear
  1. -.15_____.51
  2. 1.3_____-.49
  3. -1.08____-.69
  4. -2.86____-3.92
  5. -1.19___ -1.05
  6. 2.77____ 2.77
  7. -2.74___ -3.83
  8. .80_____-.02

Hot: (checked with Peditor)
  1. -.63____-.65
  2. -.48____.12
  3. -.27____.21
  4. -2.24___-3.47
  5. -.63____-1.21
  6. .35_____2.50
  7. -2.52___-3.94
  8. -.63_____-.41
 
They are not really out of spec going by the books, but I just replaced a set in a truck with similar numbers after doing a return test. How much fuel do you get out of the return line to the tank while cranking?
 
Seems like the difference coupled with the hard start would sway them that way ?? Time to call a friend.
 
GM doesn't go by balance rate. They command 160 kpa fuel pressure and if fuel pressure is below 158 kpa the injectors are bad.
 
GM goes by whatever gets them out of buying you a set of injectors. My local dealer has tried telling plus or minus 7% is acceptable. Even though the truck smokes at an idle.
 
Used to be able to pump some diesel into the crankcase and have them replaced, but I don't think it's that easy anymore. :(
 
The only way GM will do it is with low fuel pressure if they command 160k rail pressure and it builds at least 158 you get no injectors. I've tried, almost got in a swinging match wit the tech.
 
Anyone know if I can do the 160kpa test with EFILive ?? If so Phil we'll check it with mine once I get some instruction on how to.
 
blackandstacked said:
The only way GM will do it is with low fuel pressure if they command 160k rail pressure and it builds at least 158 you get no injectors. I've tried, almost got in a swinging match wit the tech.
Click to expand...

This is not an accurate method for determining if the injectors are good or bad. What happens when the cp3 is weak or fuel filter is restricted?
 
They probably change the filter for the test and get that $100 from you too, j/k
 
yes, you can perform the test with EFI live. open the scan tool and go to teh DVT. then you can activate the master fuel control and ramp up the rail pressure at idle. THe only problem is like stated above, a weak or failing pump can cause a low pressure reading too. checking fuel return at each injector is the best way to test for bad injectors, but simply pulling off your main return line and measuring fuel flow to the will give you a good idea.
 
GRotman said:
This is not an accurate method for determining if the injectors are good or bad. What happens when the cp3 is weak or fuel filter is restricted?
Click to expand...

I agree fully, but thats the way they do it. If the rail pressure is really low then they know something else is wrong, and yes they have been known to screw you out of $100 for a fuel filter if they need to change it to perform the test.
 
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