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Randy92782
04-22-2011, 07:14 PM
Ok i've not messed with a whole lot of TBI motors before so i'm relatively new to it. :whistle:

Lets start with it's a '89 Burburban 3/4 ton powered by a TBI 454. I am getting fuel to the injectors and am also getting power but the thing when cranked will not shoot fuel out. I can hook a wire from the ground on the battery to a wire on the injector and it will shoot out like crazy when cranked.

I was told (by a member here)to hook a light up to one injector and when it was cranked it would blink dimly if the ECM was working. I did this and got nothing. I also checked ALL grounds and can't seem to get the damn thing to work at all. I pulled the motor and forgot where they went though so that could be wrong :doah:Anyone have any pics? I changed ECM's and still nothing.

I'm assuming the relays on the firewall have something to do with this. Is there a way to test them and see if they work? :confused:

I also see this thing and know it has to do something but what I have no idea.
http://i207.photobucket.com/albums/bb119/Randy92782/unknownwire.jpg
And since I have your attention WTH is this? I assumed a temp sender but it's on the other side :rolleyes:

http://i207.photobucket.com/albums/bb119/Randy92782/unknownwireplug.jpg

If I can't figure it out I have a quadrajet that will fit right on it :pimp:

89GMCK5
04-22-2011, 07:37 PM
My 89 350 TBI has the same type of connector, same place, also hanging loose. I thought the same thing, it has to do something and should be hooked up somewhere for something. I have purchased service manuals, wiring diagram manual, and emissions manual off e bay. Hopefully I will track it down when I get some guidance there. Still waiting for delivery though.

Interested in seeing what the folks come up with here. Someone will surely know right away.

Sorry I'm no help.

Interested

zombie1969
04-22-2011, 07:59 PM
Hope this helps.
Vehicle Application:1990 Chevrolet K3500 7.4L, GAS, Vin NCustomer Concern:No start. Has fuel pressure, has spark. No injector pulse. Was an intermittent problem. Has test light lit from ground when touching the ECM case. Has battery voltage at the Black/White wire at the fuel pump relay.
Tests/Procedures:1. Inspect the wires at the engine battery ground, thermostat ground, intake stud ground, engine to frame ground, chassis ground.
Potential Causes:Damaged Battery Ground
Damaged Engine Ground

Diagnostic Codes:None


Customer Concern:No start, no injector pulse, but has spark. Has a 12v supply to the fuel injectors. Service Engine Soon (SES) lamp is on.
Tests/Procedures:1. Run the engine on alternate fuel, look at engine RPM in scan data. Should indicate a normal RPM.

2. If no RPM, check for a 0-5v square wave signal on the Purple/White wire, pin B5 of the 24 pin Powertrain Control Module (PCM) connector.

3. If no signal, check the Purple/White wire for an open or poor connection. If OK, replace the Ignition Control Module (ICM)

4. If RPM is OK, check the PCM scan data, Key On Engine Off (KOEO): Manifold Absolute Pressure (MAP) voltage, Engine Coolant Temperature (ECT) value, Throttle Position Sensor (TPS) value.
Potential Causes:Ignition Control (IC) Module
Powertrain Control Module (PCM)



Vehicle Application:1988 GMC R3500 7.4L, GAS, Vin N, FI, Eng Cfg V8Customer Concern:No start. No injector pulse. No communication with scanner. No check engine light.
Tests/Procedures:1. At the Electronic Control Module (ECM) check for constant power at the Orange wires in pins C16 and B1. This comes from the ECM "B" fuse or on some models a fusible link at the positive junction block.

2. Check pin A6, a Pink/Black wire for key on power.

3. Pin A12 is the main ground. Backprobe and ground the Brown/White wire in B5 and the check engine light should come on. If so, and all the powers and grounds were good, the ECM is bad.
Potential Causes:Electronic Control Module (ECM)
Electronic Control Module (ECM) Ground
Electronic Control Module (ECM) Power Supply

zombie1969
04-22-2011, 08:06 PM
Some other tests.
Vehicle Application:1988 Chevrolet K3500 7.4L, GAS, Vin NCustomer Concern:No start, no injector pulse or fuel pump operation. Has power at the fuel pump relay, jumper relay socket, fuel pump runs.
Tests/Procedures:1. Test voltage backprobed at fuel pump relay Dark Green/White wire when key turned on and when cranking.

2. If B+ for approximately 2 seconds, then 0 volts cranking test for reference high signal from distributor ignition module 4 wire connector terminal C Purple/White wire.

3. Tap test light from B+ to reference high terminal Key On, Engine Off (KOEO). Injectors should pulse.

4. If injectors pulse test pickup coil output backprobed at pick up coil connector with AC voltmeter. Should be 0.7 volts AC minimum and stable at cranking RPM.

5. If the signal is weak replace distributor shaft and pick up coil.

6. If signal is OK replace ignition module.
Potential Causes:Distributor Shaft
Electronic Control Module (ECM)
Fuel Pump Relay Circuit Fuel pump relay drive.
Ignition Module
Pick-Up Coil
Reference Signal

Tech Tips:No injector pulse, replaced distributor, bad magnet. Vehicle would run for seconds then shut off. Low fuel pressure most likely due to rotten rubber hose between fuel pump and pipe leaking out. Replace pump and hose, solved all drivability problems.
Diagnostic Codes:None


Vehicle Application:1990 Chevrolet C3500 7.4L, GAS, Vin NCustomer Concern:No start. Has spark. No injector pulse. No fuel pump operation until the engine is cranked for a period of time.
Tests/Procedures:1. Check for the MIL operation at key on, engine off.

2. If the MIL is not on, check for battery voltage to the Powertrain Control Module (PCM). Verify battery voltage at pin B1 on the Orange wire, this should have voltage all the time. This is powered by the ECMB fuse.

3. Verify battery voltage at pin A6 on the Pink/Black wire. This should have voltage at key on, engine off. This is powered by the ECM IGN fuse.
Potential Causes:Open Fuse

Diagnostic Codes:None

bronc3buster842001
04-22-2011, 10:55 PM
If you dont have this figured out in the next day or so, let me know and Ill come take a look at it. But check the fuses. The injectors wont spray if a fuse is blown. :flipoff5::D

Randy92782
04-23-2011, 10:14 AM
Thanks zombie that's awesome! Where'd you get the info?? If you dont have this figured out in the next day or so, let me know and Ill come take a look at it. But check the fuses. The injectors wont spray if a fuse is blown. :flipoff5::D
I checked fuses. The ECM fuse WAS blown but I changed it a while back. Still good now too. I'll be sure to hit you up soon :waytogo:

zombie1969
04-23-2011, 01:34 PM
[quote=Randy92782;2907235]Thanks zombie that's awesome! Where'd you get the info??

http://www.identifix.com/create_vehicle.aspx?LogSL=17&LogDL=19&LogWL=2&LogWA=8&LogDI=

Its one of the paid websites we use for work.Its the only one that allows me to copy and past from it though.

4X4HIGH
04-23-2011, 03:10 PM
Ok, the red wiring hanging from the fuel pump relay is so you can test the fuel pump by adding 12 volts to that wire and "force" the fuel pump to run (assuming it works).

The sender in that cylinder head is a water temp sender and since the heads are identical and can be swapped left/right it is just that someone sometime in the past installed a left head on the right side without removing and plugging the sender hole OR they installed a sender in the right head (probably the first scenerio).

If the fuel pump works, you have spark, but no fuel coming from the injectors then you probably have a bad ignition module (the ignition module sends a reference signal to the ECM to pulse the injectors). The ignition module can be good to give spark but be bad to send the reference signal. This is a very common failure on ALL GM vehicles. I would strat with replacing it first.

bronc3buster842001
04-23-2011, 03:51 PM
i have a couple ignition modules if ya need one.

4xcrazy
04-23-2011, 04:36 PM
If the fuel pump works, you have spark, but no fuel coming from the injectors then you probably have a bad ignition module (the ignition module sends a reference signal to the ECM to pulse the injectors). The ignition module can be good to give spark but be bad to send the reference signal. This is a very common failure on ALL GM vehicles. I would strat with replacing it first.
wow, this all sounds very familiar... :whistle: :D

Randy92782
04-24-2011, 07:01 PM
http://www.identifix.com/create_vehicle.aspx?LogSL=17&LogDL=19&LogWL=2&LogWA=8&LogDI=

Its one of the paid websites we use for work.Its the only one that allows me to copy and past from it though.
Thanks again man! Gonna work on it tomorrow in between showers I guess
If the fuel pump works, you have spark, but no fuel coming from the injectors then you probably have a bad ignition module (the ignition module sends a reference signal to the ECM to pulse the injectors). The ignition module can be good to give spark but be bad to send the reference signal. This is a very common failure on ALL GM vehicles. I would strat with replacing it first.
It wasn't the ECM I changed. It was the ignition module. Idk what I was thinking there.
i have a couple ignition modules if ya need one.Thanks but I just bought a new one :pimp:

wow, this all sounds very familiar... :whistle: :D
You have the same problem?

4X4HIGH
04-24-2011, 07:55 PM
Are you getting spark to the spark plugs? If not it could be a bad pick-up coil inside the distributor which would also not allow the injectors to pulse. These rarely go bad but I like to replace the pick-up coil and ignition module at the same time.

bronc3buster842001
04-24-2011, 08:26 PM
Randy clean your inbox out. Wont let me reply to your last PM

Randy92782
04-24-2011, 08:27 PM
Are you getting spark to the spark plugs? If not it could be a bad pick-up coil inside the distributor which would also not allow the injectors to pulse. These rarely go bad but I like to replace the pick-up coil and ignition module at the same time.
Yup getting fire at the plugs.

It can't be that hard to figure out. I just know nothing about this crap :doah:

4xcrazy
04-25-2011, 07:40 AM
You have the same problem?

Yes, which is why my truck is still back in Indiana at the moment. It was too cold to work on it, and it doesn't fit in the garage. So I flew back out to Phoenix.

Same issue, no signal at the injectors, I didn't have money for new ignition module, so I had a friend here send me a few out, I replaced it, it ran for a few days then started acting up again and now won't even start.

If it ever did start, it would run for a few seconds and then just quit instantly like the key was turned off, no sputter or anything, injectors just stop spraying. I can refire it with ether or something, but only fires off of that stuff until the injectors pulsing issue starts to work again.

I need to get back there and check out all the wiring and possibly the computer as I am also having issues with getting the codes from the dash light, tends to fade out during the flashing sequence down to where it doesn't flash any more, weird issue, but has done that for the past few years.