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Engine No Injector pulse on 7 and 8 cylinder

  • Thread starter Thread starter flraptor07
  • Start date Start date Oct 22, 2020
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flraptor07

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Oct 22, 2020
#1
  • Oct 22, 2020
  • #1
1992 5.0 GT I have no injector pulse on # 7 and 8 cylinders, the car runs no noid light at the injector and checking by back probing at the EEC no pulse there either. have had three different EECs and all do the same thing this is a 1986 car with a transplanted 1994 engine and EEC with a painless stand alone harness. Any Ideas???
 
Last edited: Oct 23, 2020

HemiRick

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#2
  • Oct 22, 2020
  • #2
Only thing I can imagine is to check the resistance of the injector wiring and see if its the 12 ohms its supposed to be, if shorted to ground, you might have killed the injector drivers in multiple EEC's.
 

jrichker

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  • Oct 23, 2020
  • #3
flraptor07 said:
1992 5.0 GT I have no injector pulse on # 7 and 8 cylinders, the car runs no noid light at the injector and checking by back probing at the EEC no pulse there either. have had three different EECs and all do the same thing this is a 1986 car with a transplanted 1992 engine and EEC with a painless stand alone harness. Any Ideas???
Click to expand...
Do you have 12 volts on the injector red wires?
Have you checked the 10 pin engine mounted fuel injector harness connectors?
 
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flraptor07

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#4
  • Oct 23, 2020
  • #4
jrichker said:
Do you have 12 volts on the injector red wires?
Have you checked the 10 pin engine mounted fuel injector harness connectors?
Click to expand...
yes I have 12 volts and it doesn't have a seperate connector for the injector harness it's a painless stand alone harness.
 
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flraptor07

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  • Oct 23, 2020
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HemiRick said:
Only thing I can imagine is to check the resistance of the injector wiring and see if its the 12 ohms its supposed to be, if shorted to ground, you might have killed the injector drivers in multiple EEC's.
Click to expand...
ok I just checked the wires seperate and not shorted to ground but I have almost no resistance, .001 on all eight. why would there be 12 ohms on each?
 

Mustang5L5

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#6
  • Oct 23, 2020
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The EEC closes the pin to 12V- to trigger the injector. The injectors have 12V+ fed to them.

If you tried 3 EECs and then all do this, my assumption is you've lost continuity somewhere in the harness between the injectors and the EEC. Can you test for continuity at the injector back to the EEC pin for each injector and see if you've lost it?
 
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flraptor07

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#7
  • Oct 23, 2020
  • #7
Mustang5L5 said:
The EEC closes the pin to ground to trigger the injector. They have 12V fed to them.

If you tried 3 EECs and then all do this, my assumption is you've lost continuity somewhere in the harness between the injectors and the EEC. Can you test for continuity at the injector back to the EEC pin for each injector and see if you've lost it?
Click to expand...
Already done, I have continuity on all eight. I checked each seperate and also checked for shorted to ground. if I had wire shorted to ground injector would be wide open and flooding cylinder. Right?
 

Mustang5L5

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  • Oct 23, 2020
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flraptor07 said:
Already done, I have continuity on all eight. I checked each seperate and also checked for shorted to ground. if I had wire shorted to ground injector would be wide open and flooding cylinder. Right?
Click to expand...

Correct.

Unplug the injector harness and check the resistance across each injector. Should be 12-16 ohms of resistance. If it's open, the injector coil is fried.
 
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flraptor07

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#9
  • Oct 23, 2020
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Mustang5L5 said:
Correct.

Unplug the injector harness and check the resistance across each injector. Should be 12-16 ohms of resistance. If it's open, the injector coil is fried.
Click to expand...
the whole set are new, but I did check each one with a injector tester and a meter. all within spec and all fire on the tester under preasure and static. this thing beats all I've ever seen.. lol
 

Mustang5L5

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#10
  • Oct 23, 2020
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Disconnect the ECU.

With the key in the on position (to power the injectors), ground the injector pin at the ECU connector. Does the injector click? If yes, it's an ECU issue. If not, it's a wiring issue
 
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flraptor07

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#11
  • Oct 23, 2020
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Mustang5L5 said:
Disconnect the ECU.

With the key in the on position (to power the injectors), ground the injector pin at the ECU connector. Does the injector click? If yes, it's an ECU issue. If not, it's a wiring issue
Click to expand...
that is one thing I haven't done, let me check that out. be back in a few, just a little background I've been a ASE master tech for about 30 years and been a mechanic for about 40 years... but sometimes you need extra heads to find stuff lol thanks much!
 
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flraptor07

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#12
  • Oct 23, 2020
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flraptor07 said:
that is one thing I haven't done, let me check that out. be back in a few, just a little background I've been a ASE master tech for about 30 years and been a mechanic for about 40 years... but sometimes you need extra heads to find stuff lol thanks much!
Click to expand...
OK Yes both #7 and #8 fire by grounding injector wire with key on and EEC unplugged... But like I said I've had three different EECs and all do the same thing, what are the chances of three bad EECs ?? I mean it's possible but....
 

Mustang5L5

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#13
  • Oct 23, 2020
  • #13
Now, since you say 3 ECU's don't work, my next question is does the pin for the #7 and #8 injector on the painless harness actually match the pin location for those injectors on the ECU? WHat ECU are you running?

If it does, then the question is whether something in the wiring is causing the injector drivers for 7 and 8 to fail. I've never actually seen this happen
 
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flraptor07

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#14
  • Oct 23, 2020
  • #14
Mustang5L5 said:
Now, since you say 3 ECU's don't work, my next question is does the pin for the #7 and #8 injector on the painless harness actually match the pin location for those injectors on the ECU? WHat ECU are you running?

If it does, then the question is whether something in the wiring is causing the injector drivers for 7 and 8 to fail. I've never actually seen this happen
Click to expand...
Yes, pin location is the same and even wire colors are the same. (surprise surprise lol) one thing I just thought about is it also has a Piggyback chip on it that was programed by a outside company. I'm gonna pull the chip and see if that changes anything. I'll let you know the result....I'm running a stock EEC
 
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flraptor07

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#15
  • Oct 23, 2020
  • #15
Mustang5L5 said:
Now, since you say 3 ECU's don't work, my next question is does the pin for the #7 and #8 injector on the painless harness actually match the pin location for those injectors on the ECU? WHat ECU are you running?

If it does, then the question is whether something in the wiring is causing the injector drivers for 7 and 8 to fail. I've never actually seen this happen
Click to expand...
Well pulling the chip didn't change anything still #7 and #8 injector no pulse. I've never seen anything like this either.....BTW Injector 7 and 8 are pin 42 and 52
 
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flraptor07

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#16
  • Oct 23, 2020
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OK I figured it out, the harness is Ron Francis for supposedly 91 to 95 but 92 and 94 have two injectors that are in different pins 92 uses pins 12,13,14,15,42,52,58,59. 1994 uses pins12,13,14,15,35,39,58,59 now you know the rest of the story.....
 
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Mustang5L5

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#17
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Makes sense. Glad you figured it out
 

dgollem

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#18
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Great troubleshooting what finally led you to the solution?
 
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flraptor07

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Oct 24, 2020
#19
  • Oct 24, 2020
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dgollem said:
Great troubleshooting what finally led you to the solution?
Click to expand...
I had been looking at the diagram for the 92 thinking that 91-95 were the same then I just happened to look at a 94 injector diagram and noticed the difference so I tested pin 35 and 39 that were empty and they both pulsed so I took the wires out of pins 42 and 52 which were cylinder 7 and 8 moved them to pins 35 and 39 and I had all 8 pulsing. I just need to move them all to the correct sequence and I'll be done....
 
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Alley Oop

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Two thumbs up.
 
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