No power to fuel injectors

Tiny
DIRTY_95
  • MEMBER
  • 1995 CHEVROLET 1500
  • 5.7L
  • V8
  • 4WD
  • MANUAL
  • 315,000 MILES
I have a the truck listed above 5.7 tbi. I can't get the injectors to spray. I have replaced ECM distributor ICM and still nothing. I can unplug the wire from the back of the distributor and ground one of those wires out and they spray. Yesterday I unplugged the wires to injector to see if I get power and put a test light in each end of wire and it lit up. So I plugged it back in and it ran do about 10 seconds and stopped spraying now no flash from injectors. I'm stumped. Before yesterday no fuses were blown but I didn't check them after it stopped.
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Thursday, October 24th, 2019 AT 5:40 AM

26 Replies

Tiny
AL514
  • EXPERT
Hello thanks for using 2CarPros. Do you still have power to both injectors? Power comes from ECM 1 20 amp mini fuse. Each injector is driven by a separate driver directly from the ECM on the ground side of the injector. There is a splice on the power wire. If there is no power I would try to trace the power wire back looking for a bad connection. Also the ECM needs a signal from one of the pick ups in the distributor to pulse the injectors. But let us know first if you still have power at both injectors.
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Thursday, October 24th, 2019 AT 6:55 AM
Tiny
DIRTY_95
  • MEMBER
Yes, I have 12 volts to both injectors.
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Thursday, October 24th, 2019 AT 7:44 AM
Tiny
AL514
  • EXPERT
Okay, now both injectors are controlled each on a different circuit, so no pulse on either injector I assume. Are you getting spark while the injectors aren't firing? Also assuming you have fuel pressure? Make sure your ground wires to the engine block are good and clean as well, I believe there are 2. The ignition module and pick up coils control signal to ECM for injector pulse so you know.
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Thursday, October 24th, 2019 AT 9:22 AM
Tiny
DIRTY_95
  • MEMBER
No pulse on either injector. Yes fuel pressure is good and have spark. Can spray fuel in throttle body and it will fire up until fuel burns off.
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Thursday, October 24th, 2019 AT 9:36 AM
Tiny
AL514
  • EXPERT
Do you have a purple/white wire at the distributor? If you can back probe it and look for a pulse there while cranking, thats the reference high signal wire, then the red/black wire is signal low, both going to ECM. Try unplugging the throttle position sensor as well. Just to make sure it's not shorted sending ECM into clear flood mode.
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Thursday, October 24th, 2019 AT 9:51 AM
Tiny
DIRTY_95
  • MEMBER
I have checked all grounds and had ICM tested. Pickup coil ohms out also.
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Thursday, October 24th, 2019 AT 10:01 AM
Tiny
AL514
  • EXPERT
Okay, check the injectors ohms unplugged, make sure they're the not shorted out. Here's another test: Unhook the 4 pin harness from the back of the distributor.
Attach the clip of your test light to 12V positive.
Turn on the Ignition.
Tap the purple/white wire on the 4 pin dist harness (IC Reference High) with the test light probe; it should create a test signal and fire the injectors. I'm trying to find as many simple tests as possible for you.
Have you tried unplugging some sensors? TPS, MAP.
And does this truck have a security system?
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Thursday, October 24th, 2019 AT 10:12 AM
Tiny
DIRTY_95
  • MEMBER
No security system and yes I unplugged all my sensors and checked my codes. Yes, I unplugged the wire from the back of distributor and it did fire injectors. Both injectors ohmed out also. If they were bad they wouldn't ohm right?
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Thursday, October 24th, 2019 AT 1:03 PM
Tiny
AL514
  • EXPERT
Injectors usually have an ohm reading of around 15 ohms, low resistance can cause too much current flow to the ECM driver for the injectors causing it to burn out the driver. What was the reading on both of them? And did you get a pulse while back probing purple/white wire and the red/black wires at the distributor while cranking? These are the signal wires the ECM needs to fire the injectors. Since you have replaced so many components, I am suspecting a wiring issue. Possibly in the throttle body. Does the tachometer move while cranking as well? If you were able to pulse the injectors at the purple/white wire with your test light, that means the ECM has control and it's just missing the signal coming in to fire them. Also one more check just for good measures, check the grey wire at the map sensor for 5 volt reference signal. Just to make sure it's there.
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Thursday, October 24th, 2019 AT 1:25 PM
Tiny
DIRTY_95
  • MEMBER
Injectors ohm at 2 volts map sensor doesn't have 5 volt signal voltage. Yes tachometer moves. Will still start if fuel is in throttle body. No fuses blown.
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Thursday, October 24th, 2019 AT 4:34 PM
Tiny
DIRTY_95
  • MEMBER
While plugged in gray wire on map has 12 volts.
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Thursday, October 24th, 2019 AT 4:36 PM
Tiny
AL514
  • EXPERT
Check all 3 wires at the map sensor grounding from the battery, the map should not have 12 volts, also check the grey wire at the throttle position sensor, this is the 5 volt reference as well. There should not be 12 volts. Check all 3 wires at the map for a 5 volt ref and let me know if it is there and do the check at the TPS.
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Friday, October 25th, 2019 AT 7:10 AM
Tiny
DIRTY_95
  • MEMBER
Okay, will do. Also I tried my best but could not get an ohm reading on TPS. But plugged in I got the 12 volts and it read the petal moving up and down. So do you think my injectors are good?
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Friday, October 25th, 2019 AT 7:22 AM
Tiny
AL514
  • EXPERT
Now if you have 12v on the grey wire at the tps, and I'm going to have you do this anyway, I want you to watch the 12v on the grey wire at the map and start unplugging fuses until the 12 v disappears. This way we can isolate the circuit that's shorted the 5v ref to 12v. You have a wire or wires somewhere that's shorted out together. Check all 3 wires at the map for a 5 volt ref and let me know if it is there and do the check at the TPS. There is one other quick test I want you to try, with your test light to battery ground, does the test light up touching that grey wire at the map sensor?
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Friday, October 25th, 2019 AT 7:28 AM
Tiny
ASEMASTER6371
  • EXPERT
Good afternoon,

I thought I would help out as well.

The ECM should only provide 5 volts to the MAP sensor, TPS, and the EGR valve grey wire. If you have 12 volts, it is either a short in the harness to the 5-volt circuit or a bad ECM.

I attached a wire diagram for you to view the system.

Roy
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Friday, October 25th, 2019 AT 8:36 AM
Tiny
DIRTY_95
  • MEMBER
My apologies I was on wrong sensor. Grey and green wire both have 5 volts and ground lights up with test light on positive side of battery. TPS has 5 volts on grey wire. It was EGR that has 12 volts to grey and red wire.
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Sunday, October 27th, 2019 AT 10:22 AM
Tiny
DIRTY_95
  • MEMBER
Now I put my test light in the EGR grey wire that is supposed to be 5v and pulls fuses until it went out and both ignition a fuses made the test light go out.
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Sunday, October 27th, 2019 AT 10:34 AM
Tiny
AL514
  • EXPERT
Okay, are you getting 12v to the fuel pump while cranking? Here's some diagrams to check it correctly: https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator
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Sunday, October 27th, 2019 AT 11:49 AM
Tiny
ASEMASTER6371
  • EXPERT
Also, check the end wire on the EGR. I sent you a diagram that included the EGR. It should be 5 volts as well.

Roy
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Sunday, October 27th, 2019 AT 12:04 PM
Tiny
ASEMASTER6371
  • EXPERT
I sent you the complete diagram for the power train management system. There are 3 parts.

Let me know if you have an issue reading them.

Roy
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Monday, October 28th, 2019 AT 8:22 PM

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