Intermediate Fuel Injector Issue


#1

Once again back to the ol’ 92 GMC C1500 V6 that I’ve post on in the past. Had my Ford Escort air assembly disassembled to clean something and recieved an emergency phone call, the truck seems to start just fine so I took it to get were I needed to go. Ran fine no issues even took it on the highway, ran just like she used to. On the way back I stopped at a gas station, when I went to start it she wouldn’t start (towed it home again).

Checked ignition system and it was fine, removed the top of air filter housing and filter and looked down into the fuel injection system and had a person crank the engine and once again no fuel was squirting out. Ohm’d out the injectors and they both tested good and the same, 1.7 ohms each, going out to rent noid light again but doubting it will do any good to test again but who knows at this point. In theory if it they were dirty (when we cleaned them lots of stuff came out) I’m thinking its maybe possible the got old gunk that was in the line pushed in them?


#2

Update:

Rented noid light kit, no go at injectors (not even solid light).


#3

Fuel should squirt out the injectors if

  • the injectors work
  • the rail fuel pressure is within spec
  • and the injectors are getting the “inject” electrical pulse

In my experience injectors on a properly maintained vehicle rarely fail, and this is especially true for two of them to fail at once. I’d discount that for now. Probably start with a fuel pressure test, then the noid light test. (I’ve used a timing light to do this test before. If there is electrical current flowing in the injector electrical line, it will usually be enough to trigger the timing light to light up.)


#4

Nothing showed on noid light test (not even a solid light). Checked the wiring in my book and the injectors are wired to EGR…if thats clogged might it cause no signal?


#5

I’m looking at a too-blurry-to-read schematic for the 92 V6 without the HD Automatic xmission.( 1992 GMC Truck C 1500 Truck 2WD V6-262 4.3L VIN Z). It appears there should be a 12 position and 16 position connector for the ECM, then from that the injector lines go through something labeled GT101, a connector of some kind I presume, then directly to the injectors. Are you certain the EGR is part of the electrical path from the ECM to the injectors?

First thing to do is to check the fuses, esp the one that powers the ECM.


#6

I’ll see if I can upload the ones out of my book or if Ebsco has one on their website. What it shows on the diagram I its tapped into EGR solenoid though. Checked fuses for looseness etc, they are all good.


#7

Also shows EVRV.


#8

There appears to be a TSB that the injector wires can get pinched under the air cleaner, or between the air cleaner and throttle body, if those parts are not installed correctly. Worth a go to do a visual on those, make sure they aren’t pinched. The left injector may have a blue and red wire, and the right injector has a green and white wire. The green/white pair is supposed to be routed under then over the other pair apparently. Maybe remove them, make sure they are twisted correctly, then re-connect.


#9

BTW, when advised to “check the fuse”, that means to check that it has proper electrical conductivity, not just how tight it is in the connector.

I can’t think of a reason why the injectors would be connected to the EGR. There may be one, but if so, I haven’t a clue. It may be what you are seeing is the routing of the ground wires, not the wires that do the pulsing. The injectors and EGR may share the same ground wires in other words.


#10

Check your throttle position sensor voltages. If reads incorrectly the Ecm may think you are flooring it and it doesn’t fire the injectors. Its the “clear flood mode”


#11

As above, just b/c the injectors aren’t getting pulses, that doesn’t mean there is something wrong with the wiring to the injectors necessarily. Or that the ECM isn’t working. More likely it means the ECM doesn’t think the engine is running. Could be a faulty Crank sensor, etc.


#12

I have had some thoughts about crankshift sensor going bad, located it on truck and think I’ll remove it for further analysis. Does any one know how much resistance they should have?


#13

Most injector systems are connected to a power source and rely on the ECU to make the ground return connection in order to turn the injectors on. The fact that you saw no signs of power getting to the injectors makes me think you have a bad connection on the power side of the wiring. The bad connection may have heated up while running and suppling power and then when you shut off the engine there wasn’t enough voltage to run the injectors due to the high voltage drop at the bad connection. You could try running a temporary jumper wire to the injectors to see if that gets it going and prove that case.


#14

Back up a little bit. I don’t think you stated whether you have power to the injectors or not. Grab a test light or a voltmeter. Disconnect the wires to one of the injectors. When cranking the engine you should have a steady 12 volts or more at one of the wires. Whether or not you do would determine the next step in your diagnosis.


#15

@asemaster when I plugged in the noid light and crankec they did not light up. Also I thought the injectors pulsed so wouldent be a up and down of 12v DC?

@Cougar could be. Could try were would i run the jumper from kinda lost lol.


#16

Noid light won’t tell you much other than system not working. Injectors have 12v all the time and the ground is switched on and off rapidly (pulsed) by the ecm. This is a pretty simple system, but we need to determine if the fault lies with no power or no ground. Noid light won’t help with that. Need a test light or voltmeter.


#17

You really need to check for battery voltage at the ECM fuse; according to the schematic. That fuse powers the ECM, injectors, and EGR solenoid in both the RUN and START positions.
A test light or voltmeter

If there is no power present at both sides of that fuse, the ignition switch may have been intermittent and finally decided to cash it in.


#18

@asemaster never thought of it like that. Looks like I’ll have to rig up or buy some gator clips today:)

@ok4450 so pretty much just remove fuse and use volt meter?


#19

Gator clips? Do you have a simple test light? Frankly that’s what I’d start with. If not, get a voltmeter and it will have all the ends you need. See if you can grab a wiring diagram too.

ok4450 wants you to check the fuses, I’d check for power at the injector first and go from there. Just 2 different roads to get to the same place.


#20

It is good to have some jumper leads to make tests with but if you don’t already have a test light probe to do testing, that is even more important to have on hand for checking trouble like this.