No fuel from injectors

Asked by May 07, 2017 at 03:54 PM about the 1991 GMC Sierra 1500 C1500 Standard Cab Stepside SB

Question type: Maintenance & Repair

I have replace the injectors and rebuilt the fuel
pressure regulator and replaced throttle
positioning sensor replaced computer and got a
noid tester it says possible problem with signal
voltage where do I look or how do I fix it

54 Answers

74,595

You check the wiring from the injectors back to the ECU to find the problem. 1991 those wire connectors and wires at the fuel injectors are probably pretty baked by now, I would start looking there at the wiring. Check continuity from the connector back in the wire a ways away from the TBI.

1 of 1 people found this helpful.

Ok but I do have power at the plugs for injectors

74,595

I don't know why it says possible problem with signal voltage unless the voltage is intermittent. Was the noid light steady while turning the engine over? Keep a steady beat so to speak? May be just a bad connection in the circuit at the ECU.

1 of 1 people found this helpful.

No light at all but when checked with tester there is power to pos side of plug in for injectors

74,595

And your check this while turning the engine over? Otherwise there would be a break in the wire on the other side, not getting ground.

1 of 1 people found this helpful.

That would be when I checked it with the test light no I didn't roll engine over then

I rolled engine when I had noid tester connected though no flashing or nothing with it

74,595

Ok, you have no injector pulse. That comes from the ECU.

That would be the chip in the computer? When I replaced computer they told me I had to switch out the chip from mine to the new one

74,595

That could do it.

So I wasn't suppose to change out chip then l8ke they told me

74,595

Not if the new computer was flashed to your vehicles vin number.

1 of 1 people found this helpful.

No it wasn't how do I get it flashed to my vehicle if I buy a new chip

74,595

Ok, when you get a new computer, everything is new and either it comes set-up for your vehicle, pre-programmed, and if it is not then it needs to be flashed, meaning programmed to you vehicles specifications to run that motor and transmission. Getting one from a junk yard you look to see if the numbers match on the sticker on it and if it don't match and it came out of a similar vehicle, they can flash it to match what was set-up for your vehicle.

1 of 1 people found this helpful.

I got it from a junk yard the numbers matched but the guy told me I had to switch the chip from mine to the other one I just got does that mean I need a new chip to put in it and how or where would I get it configured at

74,595

So what was the reason for changing the computer? And yes, you can change that chip out to the one that was in your old one. This video shows basically how to change your chip out. This video shows how to put in a performance chip that uses-es an adapter board that you will not be doing, but this should give you enough to explain how to change that chip out... https://youtu.be/KcWrlIiH-wQ

1 of 1 people found this helpful.
74,595

You said there is power at the injector plug but the noid light did not flash, so that means there is a problem with the other side of the wire at the injector.

1 of 1 people found this helpful.

No injector pulse was why I changed computer and as I stated earlier they had me switch chips while I was there so I had original chip that came with truck in replacement computer that's why I'm thinking chip is bad

I followed the injector wires all the way back to firewall and found no bad spots or places that looked like it got hot and as far as I can tell wires are good going to computer

74,595

But you have voltage on one side of the wire. Makes me believe there is a break in the other wire. You would want to verify by doing a continuity check on that wire. If it is good, then putting in your old chip into the other computer is just transferring the problem. If you have the original chip for the computer you got, try it with that chip. What vehicle did this computer come out of, and was it for the same size engine?

1 of 1 people found this helpful.
74,595

I got a head of your last post, I see you checked wires.

1 of 1 people found this helpful.

It was the same type computer the #'s on it matched exactly with mine and yes same size engine and year of truck

74,595

Put the chip that came with it back in and try it. Thinking about this, there is nothing wrong with the wiring.

1 of 1 people found this helpful.

That's what I was afraid of they wouldn't let me have my original computer and other chip they kept it

74,595

But you have the same problem with this computer.

1 of 1 people found this helpful.
74,595

When you checked for voltage at the injector plug, did you check it across the two wires that run to the plugin?

1 of 1 people found this helpful.

Yes I do but it's the original chip in the newer computer from my old computer

I plugged a noid tester into plug in and checked both of them that way and got no flashing or light at all when I rolled motor over

74,595

Thats the problem. So, also did you check for injector voltage across the two wires at the plugin?

1 of 1 people found this helpful.
74,595

Yea, I know on that one.

74,595

So, if you are sure the wires are good, the problem is with your old chip.

1 of 1 people found this helpful.

That's what I was afraid of What should the voltage be if any when I check it with voltmeter and do I roll motor over when checking voltage

74,595

Checking it across the two wires, the voltage is around 5-7 volts. How did you check for power before?

Home made test light

They shipped chip out with all the other cores, is there a way that the chip can be tested

74,595

No idea on the testing of the chip... say, I have to go to work, I'll be back later on. A test light is fine for testing. Make sure those wires are good. You can use that test light across the two wires, but if on is broken, there will not be a circuit, if there is a live wire and you have the test light to another ground, it will light up as you know.

1 of 1 people found this helpful.

Ok thank you only one of the 2 should be hot right

74,595

Hello, I am back for a bit. So what did you find? Yes one of the injector wires are hot.

When I use my tester on the 2 wires it lights up

74,595

Did you happen to test while turning the engine over? Just wondering if you notice the test light flicker.

It dims very little I think that's just the draw on power to roll it over. No flicker at all with noid tester on

74,595

Have you checked to see if there is spark to the spark plugs? Everything seems to be good to the injectors. I may have ben focusing too much on your original question. If there is no spark, check the Ignition Control Module, and the coil. They can test these at an auto parts store. Make sure the rotor does not have a burn mark threw the center of it also. I work again today at 11:00AM, worked yesterday also, thats why I couldn't get back sooner.

1 of 1 people found this helpful.

It will run all day long as long as I pour fuel into throttle body

74,595

Have you checked fuel pressure? Was the fuel filter changed out? Has the fuel regulator ben rebuilt?

New filter regulator rebuilt I have no way to check fuel pressure when I turn key on I get a stream of gas shooting 4-6" out

74,595

I'm researching, be back in a bit.

1 of 1 people found this helpful.

Ok, I was just told it could be dist module and or pickup coil These newer ones are a pain in the butt at time's

74,595

This is one thing I have found, "your PCM does not get a reference signal from ignition control module ( you should check it with a scan tool- if it sees RPM, or, wiring continuity between ign.module and PCM)." Have you checked the wiring between the ICM and PCM?

74,595

Yes, everything else seems to be in order.

Ok I'll check that stuff and let you know what I find out

74,595

Check at the connectors, wires like to break at connectors. Make sure the ICM is good, have it tested if need be at an auto parts store. Check the wires from the distributor on down. Look for corrosion in the plugin at the ECU, or in-other words the PCM. I'll be back around 7:30 PM. It is 10:35 AM my time now.

Okwill do, it's same time here also

74,595

Back from work, just touching base...did you work on this at all today?

Checked wires at connectors they all seem good tested coil it checks ok wasn't able to test the module on distributor yet

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