No power to injectors on 90' 7.4L...HELP PLEASE! - The 1947 - Present Chevrolet & GMC Truck Message Board Network

baclay9 · 07-09-2011, 09:40 AM

Just picked up a 1990 1 ton with a TBI 454. It wasn't running when I got it. I changed the filter and fuel pump.

The engine will run like a champ if I spray starting fluid down the throttle body.

I am getting no power to the injectors on the throttle body. There is no constant power on the hot side and no intermittent ground on the signal side. The injectors will spray if i jump them with a wire so I know they are good. I am just getting no power to the wires.

Can someone please give me a clue on where to look for a problem I have checked the wiring out and it all looks good but I am not sure which connector under the dash goes to the Throttle body.

onequickchevy · 07-09-2011, 02:37 PM

Module in distributor, it controls the pulse for the injectors. Very common problem.

baclay9 · 07-09-2011, 04:04 PM

Would that explain why there is no power on the "hot" side as well? I was under the impression the module just controlled the negative side. I am new to all of this so thank you for your help.

ChevyTech · 07-09-2011, 07:02 PM

Have you check for power at the injector fuse in the fuse box?

ChevyTech · 07-09-2011, 07:03 PM

Quote:

Originally Posted by baclay9

I was under the impression the module just controlled the negative side.

You are correct.

baclay9 · 07-09-2011, 07:19 PM

Yes, there is power at the injector fuse. I am just not sure where to go from there.
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ChevyTech · 07-09-2011, 07:23 PM

Is a 1990 1 ton still the old square body?

On the body style after the square body, the wires to the injectors go through a connector that is close to the ECM.

baclay9 · 07-09-2011, 07:50 PM

It is the newer body style. So do the wires from the injectors plug into the ECM at all or are they on a different connector?
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ChevyTech · 07-09-2011, 08:01 PM

The white & red injector wires splice together inside the harness to one red wire. One bad terminal in the connector will stop both injectors.

The red wire goes through a large connector (about 15 wires) in the area of the ECM and blower motor. This connector does not go to the ECM. It is close to the ECM. One side of the connector is one piece with two rows of terminals, and the other side is two seperate flat connectors that plug into it.

onequickchevy · 07-09-2011, 08:12 PM

It may be possible to run a temporary jumper wire to isolate the problem. Chevytech is your best bet for an answer on that .
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baclay9 · 07-09-2011, 08:34 PM

Ok, I see it. The red wire in it doesn't have power on either side of the connector.
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ChevyTech · 07-09-2011, 08:40 PM

Go to the fuse and test the terminals that connect to the fuse for power. Sometimes the terminal gets burnt that the fuse plugs into.

If you did not find the fuse terminal to be bad I would test the wire a couple inches away from the fuse.

baclay9 · 07-09-2011, 08:54 PM

Which fuse terminal should I be checking? Is it the one labeled (INJ A+B)?
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ChevyTech · 07-09-2011, 08:59 PM

Quote:

Originally Posted by baclay9

Which fuse terminal should I be checking? Is it the one labeled (INJ A+B)?
Posted via Mobile Device

Yes; Inj A&B

Check all the fuses around it because sometimes the label by the fuses are hard to tell if they go to the fuse above it, or below it.

The schematic I am looking at shows the red wire in cavity “E” of the connector by the blower motor. The letters on the connectors are small and sometime hard to find.

The red wire from cavity “E” (which is circuit 481) goes all the way to the injector fuse.

baclay9 · 07-09-2011, 09:09 PM

Ok I fiddled around with the fuse terminal and now I have power all the way out to the tbi plug. The battery is too low to crank the motor over right now so I put it on the charger. I will check back in after while and let you know what it does. Thank you so much for getting me this far.
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baclay9 · 07-09-2011, 09:29 PM

It just started right up. Thank you so much for your help! I never would have been able to figure that out on my own.
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scotts62 · 07-09-2011, 09:41 PM

Cool so it was a simpler fix than we thought huh? Glad you found it!

Chevytech is the hero again

onequickchevy · 07-09-2011, 10:05 PM

Excellent news!
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ChevyTech · 07-09-2011, 10:20 PM

You’re welcome!

Glad to hear you got it running.

Clean the fuse terminal real well so it does not give you more trouble.

You may need to bend the terminal to pinch the fuse tighter.

ChevyTech · 07-09-2011, 10:25 PM

Quote:

Originally Posted by scotts62

Chevytech is the hero again

Thanks!

ah

um

Does that mean I can take a break from the board again?

scotts62 · 07-10-2011, 03:07 PM

Quote:

Originally Posted by ChevyTech

Thanks!

ah

um

Does that mean I can take a break from the board again?

yeah you can have a couple days off

07-09-2011, 09:40 AM	#1
baclay9 Registered User Join Date: Apr 2010 Location: Newcastle, OK Posts: 1,344	No power to injectors on 90' 7.4L...HELP PLEASE! Just picked up a 1990 1 ton with a TBI 454. It wasn't running when I got it. I changed the filter and fuel pump. The engine will run like a champ if I spray starting fluid down the throttle body. I am getting no power to the injectors on the throttle body. There is no constant power on the hot side and no intermittent ground on the signal side. The injectors will spray if i jump them with a wire so I know they are good. I am just getting no power to the wires. Can someone please give me a clue on where to look for a problem I have checked the wiring out and it all looks good but I am not sure which connector under the dash goes to the Throttle body.

07-09-2011, 02:37 PM	#2
onequickchevy Registered User Join Date: Sep 2009 Location: Marianna, Florida Posts: 339	Re: No power to injectors on 90' 7.4L...HELP PLEASE! Module in distributor, it controls the pulse for the injectors. Very common problem. __________________ Slowly but surely getting it done.

07-09-2011, 04:04 PM	#3
baclay9 Registered User Join Date: Apr 2010 Location: Newcastle, OK Posts: 1,344	Re: No power to injectors on 90' 7.4L...HELP PLEASE! Would that explain why there is no power on the "hot" side as well? I was under the impression the module just controlled the negative side. I am new to all of this so thank you for your help.

07-09-2011, 07:02 PM	#4
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,621	Re: No power to injectors on 90' 7.4L...HELP PLEASE! Have you check for power at the injector fuse in the fuse box? __________________ For those of you that are wondering why you are not getting replies to your thread: Did you give the model, year, engine, fuel system type, and transmission information? If it is modified from what came stock from the factory, let us know that too.

07-09-2011, 07:19 PM	#6
baclay9 Registered User Join Date: Apr 2010 Location: Newcastle, OK Posts: 1,344	Re: No power to injectors on 90' 7.4L...HELP PLEASE! Yes, there is power at the injector fuse. I am just not sure where to go from there. Posted via Mobile Device

07-09-2011, 07:23 PM	#7
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,621	Re: No power to injectors on 90' 7.4L...HELP PLEASE! Is a 1990 1 ton still the old square body? On the body style after the square body, the wires to the injectors go through a connector that is close to the ECM. __________________ For those of you that are wondering why you are not getting replies to your thread: Did you give the model, year, engine, fuel system type, and transmission information? If it is modified from what came stock from the factory, let us know that too. Last edited by ChevyTech; 07-09-2011 at 07:38 PM. Reason: Add more

07-09-2011, 07:50 PM	#8
baclay9 Registered User Join Date: Apr 2010 Location: Newcastle, OK Posts: 1,344	Re: No power to injectors on 90' 7.4L...HELP PLEASE! It is the newer body style. So do the wires from the injectors plug into the ECM at all or are they on a different connector? Posted via Mobile Device

07-09-2011, 08:01 PM	#9
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,621	Re: No power to injectors on 90' 7.4L...HELP PLEASE! The white & red injector wires splice together inside the harness to one red wire. One bad terminal in the connector will stop both injectors. The red wire goes through a large connector (about 15 wires) in the area of the ECM and blower motor. This connector does not go to the ECM. It is close to the ECM. One side of the connector is one piece with two rows of terminals, and the other side is two seperate flat connectors that plug into it. __________________ For those of you that are wondering why you are not getting replies to your thread: Did you give the model, year, engine, fuel system type, and transmission information? If it is modified from what came stock from the factory, let us know that too. Last edited by ChevyTech; 07-09-2011 at 08:04 PM. Reason: Add more

07-09-2011, 08:12 PM	#10
onequickchevy Registered User Join Date: Sep 2009 Location: Marianna, Florida Posts: 339	Re: No power to injectors on 90' 7.4L...HELP PLEASE! It may be possible to run a temporary jumper wire to isolate the problem. Chevytech is your best bet for an answer on that . Posted via Mobile Device __________________ Slowly but surely getting it done.

07-09-2011, 08:34 PM	#11
baclay9 Registered User Join Date: Apr 2010 Location: Newcastle, OK Posts: 1,344	Re: No power to injectors on 90' 7.4L...HELP PLEASE! Ok, I see it. The red wire in it doesn't have power on either side of the connector. Posted via Mobile Device

07-09-2011, 08:40 PM	#12
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,621	Re: No power to injectors on 90' 7.4L...HELP PLEASE! Go to the fuse and test the terminals that connect to the fuse for power. Sometimes the terminal gets burnt that the fuse plugs into. If you did not find the fuse terminal to be bad I would test the wire a couple inches away from the fuse. __________________ For those of you that are wondering why you are not getting replies to your thread: Did you give the model, year, engine, fuel system type, and transmission information? If it is modified from what came stock from the factory, let us know that too.

07-09-2011, 08:54 PM	#13
baclay9 Registered User Join Date: Apr 2010 Location: Newcastle, OK Posts: 1,344	Re: No power to injectors on 90' 7.4L...HELP PLEASE! Which fuse terminal should I be checking? Is it the one labeled (INJ A+B)? Posted via Mobile Device

07-09-2011, 09:09 PM	#15
baclay9 Registered User Join Date: Apr 2010 Location: Newcastle, OK Posts: 1,344	Re: No power to injectors on 90' 7.4L...HELP PLEASE! Ok I fiddled around with the fuse terminal and now I have power all the way out to the tbi plug. The battery is too low to crank the motor over right now so I put it on the charger. I will check back in after while and let you know what it does. Thank you so much for getting me this far. Posted via Mobile Device

07-09-2011, 09:29 PM	#16
baclay9 Registered User Join Date: Apr 2010 Location: Newcastle, OK Posts: 1,344	Re: No power to injectors on 90' 7.4L...HELP PLEASE! It just started right up. Thank you so much for your help! I never would have been able to figure that out on my own. Posted via Mobile Device

07-09-2011, 09:41 PM	#17
scotts62 One day... Join Date: Apr 2008 Location: Tuttle, Ok Posts: 9,243	Re: No power to injectors on 90' 7.4L...HELP PLEASE! Cool so it was a simpler fix than we thought huh? Glad you found it! Chevytech is the hero again __________________ Scott 93 crew cab build Project 62



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07-09-2011, 10:05 PM	#18
onequickchevy Registered User Join Date: Sep 2009 Location: Marianna, Florida Posts: 339	Re: No power to injectors on 90' 7.4L...HELP PLEASE! Excellent news! Posted via Mobile Device __________________ Slowly but surely getting it done.

07-09-2011, 10:20 PM	#19
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,621	Re: No power to injectors on 90' 7.4L...HELP PLEASE! You’re welcome! Glad to hear you got it running. Clean the fuse terminal real well so it does not give you more trouble. You may need to bend the terminal to pinch the fuse tighter. __________________ For those of you that are wondering why you are not getting replies to your thread: Did you give the model, year, engine, fuel system type, and transmission information? If it is modified from what came stock from the factory, let us know that too.

Register or Log In To remove these advertisements.