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My 93 gmc sonoma turns over but won't start. I replaced fuel…

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my 93 gmc sonoma turns...
my 93 gmc sonoma turns over but won't start. I replaced fuel pump, fuel filter and a part that goes on the throttle body.
Submitted: 7 years ago.Category: GM
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Answered in 7 minutes by:
12/6/2010
GM Mechanic: Dave Nova, GMC Technician replied 7 years ago
Dave Nova
Dave Nova, GMC Technician
Category: GM
Satisfied Customers: 19,452
Experience: ASE Master Certification. GM World Class Certification
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Hello and thank you for using justanswer.

On the firewall behind the engine, locate the battery junction terminal and the fuel pump test connector as shown below. Connect a jumper wire from the battery junction terminal to the fuel pump test connector and attempt to start the engine. Does the engine start?

David

.

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Customer reply replied 7 years ago
I didn't get a picture. Can you resend.
GM Mechanic: Dave Nova, GMC Technician replied 7 years ago

Sure. Hopefully it goes through this time. Let me know.

graphic

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Customer reply replied 7 years ago
Okay the battery junction box (red and two bolts) on my sonoma is vertical and the wire leading the fuel pump test connector (black I guess and on the fire wall also) it arced a little but I connected it and it didn't start. The truck cranks but nothing. Should I have used both bolts on the battery junction box and is the fuel pump test connector supposed to be black.
GM Mechanic: Dave Nova, GMC Technician replied 7 years ago

The fuel pump prime connector may be black, the wire should be gray. You can connect the prime connector to either terminal on the junction. If the engine will not start like this, then we need to do some other testing.

Disconnect one of the connectors at the injector on top of the throttle body. Connect a test light across the terminals at the connector and crank the engine. The light should flash. Does it?

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Customer reply replied 7 years ago

I'll do this, but I have a question. Why does the engine run when I put gas into the trottle body and keep running. If I turn it off then I can't restart it without putting gas?

GM Mechanic: Dave Nova, GMC Technician replied 7 years ago

By connecting the wire as we did earlier, this bypasses the fuel pump relay to make sure the fuel pump is powered up when starting.

Testing the wiring at the injector will determine if you are getting injector pulse while cranking. You are not getting fuel while cranking the engine for some reason, that is what we are trying to figure out.

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Customer reply replied 7 years ago
I'm going to have to wait til tomorrow because it's late and I need for my brother-in-law to come and help and bring his tools. I'll login tomorrow and let you know if it worked or not. Thank you for tonight.
GM Mechanic: Dave Nova, GMC Technician replied 7 years ago
You are welcome. Let me know tomorrow what you find and we will take it from there.
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Customer reply replied 7 years ago
I'm up and ready to get this truck fixed. I'm having my brother in law come and bring his electrical equipment.
GM Mechanic: Dave Nova, GMC Technician replied 7 years ago
Sounds good. Let me know what you find after testing the wiring at the injector.
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Customer reply replied 7 years ago
I checked the the injector wiring and one seems to get voltage the other doesn't now what? Are these attached to relays and where?
GM Mechanic: Dave Nova, GMC Technician replied 7 years ago

There should be power on one side of the injector. The other wire gets a ground pulse from the ECM. Connect your test light across the terminals of the injector. Connect one side of the test light to one terminal and the other side of the test light to the other terminal and crank the engine. The light should flash. Let me know what you find.

You can insert a small piece of wire into the clip on the test light and use it to connect to the injector terminal.

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Customer reply replied 7 years ago
Only one of the connections showed this.
GM Mechanic: Dave Nova, GMC Technician replied 7 years ago
One connection flashed, but the other would not? Is this correct?
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Customer reply replied 7 years ago
that's correct
GM Mechanic: Dave Nova, GMC Technician replied 7 years ago
On the connection that will not flash, is there power at either of the wires?
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Customer reply replied 7 years ago
Power would be what color wire because there are different colors.
GM Mechanic: Dave Nova, GMC Technician replied 7 years ago
The red and white wires are the power wires to the injectors.
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Customer reply replied 7 years ago
Okay, we put positive and negative to each injector (one at a time) and it powered up alone. I bought one relay but it won't turn on with the new relay a set of 2 on the firewall on the driver side (2195 is the number on the realy with a GM number that is long) so we are not getting power to the injectors. What now?
GM Mechanic: Dave Nova, GMC Technician replied 7 years ago
Make sure you are testing for power at the injectors (red wire or white wire) with the key on. This power comes from the ECMI fuse. Test for power at this fuse with the key on.
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Customer reply replied 7 years ago
We got part at the fuse with the key on. We checked each individual connector but we're not getting negative. Only with the power (white and red)
GM Mechanic: Dave Nova, GMC Technician replied 7 years ago

You do have power at the injector but not the ground pulse. Make sure you still have power at these wires with the key in the start position.

If you do, then the problem is in the ground control side of the circuit. This comes from the ECM. The wiring is obviously okay because it will run once started with fuel. The problem is going to be in the ECM.

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Customer reply replied 7 years ago
Where is the ecm on this truck because I looked under the cash on the drivers side and can't find anything.
Customer reply replied 7 years ago
We don't have any reading on the ground side (blue and green) with the key on. We started it the other way but it dies after a minute.
GM Mechanic: Dave Nova, GMC Technician replied 7 years ago

The blue and green do not show a ground with the key on. The ECM pulses a ground to the blue and green wires when the engine is cranking and when the engine is running.

This is what we are testing for when connecting the test light across the injector connector and cranking the engine. If the light does not flash, this means the ECM is not sending the ground pulse to the injectors.

The ECM is located behind the dash on the passenger side.

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