Engine No Injector pulse on 7 and 8 cylinder

[flraptor07]

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???

 

[HemiRick]

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]

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???

Do you have 12 volts on the injector red wires?
Have you checked the 10 pin engine mounted fuel injector harness connectors?

 

[flraptor07]

Do you have 12 volts on the injector red wires?
Have you checked the 10 pin engine mounted fuel injector harness connectors?

yes I have 12 volts and it doesn't have a seperate connector for the injector harness it's a painless stand alone harness.

 

[flraptor07]

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.

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]

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?

 

[flraptor07]

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?

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]

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?

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.

 

[flraptor07]

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.

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]

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

 

[flraptor07]

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

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!

 

[flraptor07]

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!

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]

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

 

[flraptor07]

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

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

 

[flraptor07]

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

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

 

[flraptor07]

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.....

 

[Mustang5L5]

Makes sense. Glad you figured it out

 

[dgollem]

Great troubleshooting what finally led you to the solution?

 

[flraptor07]

Great troubleshooting what finally led you to the solution?

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....

 

[Alley Oop]

Two thumbs up.