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kemperhills
User
Feb 9, 2013, 6:27 PM
Post #1 of 22
(2252 views)
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Hi, I am new here and I have a problem I haven't been able to solve.
I am working on a 1992 Chevy Cheyenne 3500 pick-up. It won't start unless you pour fuel into the throttle body. I know the fuel pump isn't working. The only wiring diagram I can find says that the fuel pump works through through an oil pressure/fuel pump sender. It is mounted at the back of the engine just below the distributor. The orange wire is the 12v that is supposed to feed through the oil pressure/fuel pump sender to a gray wire that goes to the fuel pump relay, then to the fuel pump, according to the diagram I have. The orange wire at the oil pressure/fuel pump sender is dead, no voltage.
The diagram says that the orange wire is to get it 12v's from the ECM B fuse, but the fuse box doesn't have an ECM B fuse, nor an ECM 1 fuse. It only has an ECM Ignition fuse and an injector fuse. 12v's is getting to the injectors. The wire from the injectors to the ECM is good where the ground is applied to make the injectors fire. The ECM powers up when the ignition is turned on. I have checked all the wiring I can without major work.
So here is my question. The diagram says the fuel pump is supplied 12v's from and ECM B fuse that isn't in the fuse box. There is no power box under the hood, so where could this ECM B fuse be.
Again, I am going by the only wiring diagram I have access to and it is from the Auto Zone website and I don't even know if it is correct as the oil pressure/fuel pump sent has three wires and the diagram only shows two wires though it is labeled on the diagram as the oil pressure/fuel pump sender.
Any help would be appreciated.
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Hammer Time
Ultimate Carjunky
/ Moderator
Feb 9, 2013, 6:45 PM
Post #2 of 22
(2221 views)
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That wire is powered by a fusible link attached to the battery junction block in the engine compartment at the firewall. The gray wire going to the fuel pump also has an inline fuse that will be in the engine compartment also, somewhere near the harness.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
(This post was edited by Hammer Time on Feb 9, 2013, 6:46 PM)
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kemperhills
User
Feb 11, 2013, 9:14 AM
Post #3 of 22
(2174 views)
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Thanks Hammer Time, I appreciate the response.
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kemperhills
User
Feb 18, 2013, 2:11 PM
Post #4 of 22
(2100 views)
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Ok, can anyone tell me where I can find a wiring diagram for this truck. I have verified that the fuel pump is working, fuel to injectors. There is 12v to the + wires on the injectors, but the injectors won't fire. I need to know what pins the - wires of the injectors go to on the ECM. The person who owns the truck has replaced the ECM, fuel pump and injectors.
So I need the wiring diagram to follow the - wires from the injectors to the computer. If this is good I can only assume the new computer is bad unless someone can give me another probable cause for the injectors not firing. Again you can pour fuel into the throttle body and the truck runs until the fuel is consumed.
The person that replaced these components isn't a mechanic, he was trying to save money, and could have installed the computer without disconnecting the battery cable. Thanks.
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Hammer Time
Ultimate Carjunky
/ Moderator
Feb 18, 2013, 2:16 PM
Post #5 of 22
(2097 views)
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Does it run if you spray starting fluid into the intake?
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Hammer Time
Ultimate Carjunky
/ Moderator
Feb 18, 2013, 4:23 PM
Post #7 of 22
(2084 views)
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I don't see an engine size anywhere.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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speed
User
Feb 18, 2013, 6:03 PM
Post #9 of 22
(2071 views)
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whats the 8th digit of the vin, thats the engine code.
GM ASEP 26 SCC Milford ASE certified in Brakes and Electrical on Thursday April 5th 2012
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Hammer Time
Ultimate Carjunky
/ Moderator
Feb 18, 2013, 6:04 PM
Post #10 of 22
(2071 views)
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Pretty hard to repair something if you don't even know what engine you're working on.
What is the 8th digit of the VIN#?
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Hammer Time
Ultimate Carjunky
/ Moderator
Feb 27, 2013, 4:15 PM
Post #12 of 22
(2021 views)
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OK, you do have a 5.7 TBI
These older GM diagrams are not the easiest to follow.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Discretesignals
Ultimate Carjunky
/ Moderator
Feb 27, 2013, 6:07 PM
Post #13 of 22
(2018 views)
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I'm prolly wasting my time because most DIY play swaptronics instead of diagnosing problems to the source, but I'll give it a try.
If the ECM is in clear flood mode, it won't fire the injectors. The ECM uses the TPS sensor to determine clear flood mode. Measure the output voltage of the TPS sensor at the signal wire. With the throttle closed the TPS voltage should be somewhere around 1 volt. If the ECM is seeing 4 volts or higher from the TPS, it will disable fuel injection.
If the ECM isn't recieving the distributor reference signal from the ignition control module, it won't fire the injectors. Check for a reference signal to the ECM using a lab scope. I know what your thinking, the ECM must be getting the signal because the coil fires. Well, the coil isn't controlled by the ECM. The ECM only controls ignition advance. Base timing coil firing is done by the ignition control module. Infact, you could unplug the ECM and you would still have spark.
Before you condemn the ECM check powers and ground at the ECM connector. Check your 5 volt reference voltages to your sensors. Easiest one to check for 5 volts it probably the ECT sensor. If you don't have reference voltage to your sensors because there is short to ground in the reference supply, the ECM won't do anything because its 5 volt power supply is pulled low. You'll need a connector pinout to do this and a volt meter to check voltage drops.
Also check all your outputs amperage such as solenoids, coils, injectors, etc . You'll have to manually activate those outputs and use an amp probe to determine if a component is drawing too much current. If an injector pulls too many amps, the ECM will shut down that particular quad driver. It usually sets a code when there is a quad driver issue.
Don't replace an ECM until you know the ECM is getting what it needs. If you don't do this and you have a shorted output, you can fry your new ECM. If you have a pulled low 5 volt reference or poor powers and grounds to the ECM itself, your just wasting your time putting another ECM in.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Feb 27, 2013, 6:35 PM)
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kemperhills
User
Feb 28, 2013, 9:29 AM
Post #14 of 22
(1986 views)
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I'm prolly wasting my time because most DIY play swaptronics instead of diagnosing problems to the source, but I'll give it a try.
If the ECM is in clear flood mode, it won't fire the injectors. The ECM uses the TPS sensor to determine clear flood mode. Measure the output voltage of the TPS sensor at the signal wire. With the throttle closed the TPS voltage should be somewhere around 1 volt. If the ECM is seeing 4 volts or higher from the TPS, it will disable fuel injection.
If the ECM isn't recieving the distributor reference signal from the ignition control module, it won't fire the injectors. Check for a reference signal to the ECM using a lab scope. I know what your thinking, the ECM must be getting the signal because the coil fires. Well, the coil isn't controlled by the ECM. The ECM only controls ignition advance. Base timing coil firing is done by the ignition control module. Infact, you could unplug the ECM and you would still have spark.
Before you condemn the ECM check powers and ground at the ECM connector. Check your 5 volt reference voltages to your sensors. Easiest one to check for 5 volts it probably the ECT sensor. If you don't have reference voltage to your sensors because there is short to ground in the reference supply, the ECM won't do anything because its 5 volt power supply is pulled low. You'll need a connector pinout to do this and a volt meter to check voltage drops.
Also check all your outputs amperage such as solenoids, coils, injectors, etc . You'll have to manually activate those outputs and use an amp probe to determine if a component is drawing too much current. If an injector pulls too many amps, the ECM will shut down that particular quad driver. It usually sets a code when there is a quad driver issue.
Don't replace an ECM until you know the ECM is getting what it needs. If you don't do this and you have a shorted output, you can fry your new ECM. If you have a pulled low 5 volt reference or poor powers and grounds to the ECM itself, your just wasting your time putting another ECM in. Thanks for the reply, I appreciate your help. But as a 45 year mechanics I don't pratices swaptronics, that is the reason I asked if anyone could tell me where to find a wireing diagram. Your diagnosis may be correct and I will check it. But the fuel pump doesn't run either. I worked on autos for 28 years and, at 62 years old went back to small engines ten years ago because arthritis has made it hard to do the auto work. Now I don't have access to the information I did when working as an auto mechanic. Thanks again for the respones.
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kemperhills
User
Feb 28, 2013, 9:44 AM
Post #15 of 22
(1985 views)
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Hammer Time, thanks for the diagram. I appreciate you help.
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kemperhills
User
Feb 28, 2013, 10:16 AM
Post #17 of 22
(1973 views)
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I have verified that the fuel pump is working, fuel to injectors. Your diagnosis may be correct and I will check it. But the fuel pump doesn't run either. Slight contradiction???
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kemperhills
User
Feb 28, 2013, 11:11 AM
Post #19 of 22
(1954 views)
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The ECM powers up when the ignition is turned on You stated you have no power at the orange wire. Do you have power at the orange wire for the fuel pump relay? The orange wire has a fusible link up at the battery junction connector in the picture HT provided. The orange wire is also the ignition feed for the ECM, so don't know how the ECM checks out if it doesn't have any power. |
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kemperhills
User
Apr 2, 2013, 10:36 PM
Post #20 of 22
(1837 views)
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Ok guys, I do thank you for your help, but I can't find the problem. The wiring diagram Hammer Time supplied helped some but didn't have all the wiring info I needed.
So my friend will have to take it to a mechanic that has the info needed to trouble shoot this problem.
Thanks again for you help.
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kemperhills
User
Apr 3, 2013, 3:12 PM
Post #22 of 22
(1820 views)
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I don't know if the ECM is working correctly because I didn't have a diagram to tell me what pin on the ECM did what. But you do have the ECM pin numbers. I guess you just don't know how to read them.
I guess not. Thanks for you help, I appreciate it.
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