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1990 jeep: amperage..fuel pump..motor turns..3.5 to 4.2..ECM…

Customer Question
1990 jeep yj....
1990 jeep yj. When we test the amperage on the fuel pump wire,it starts at 1.5 to 2. As the motor turns over it increases to 3.5 to 4.2 . What could be the problem as the ECM diode starts to heat up.
Submitted: 8 years ago.Category: Jeep
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Answered in 19 minutes by:
6/11/2010
Jeep Mechanic: Amedee, Jeep Technician replied 8 years ago
Amedee
Amedee, Jeep Technician
Category: Jeep
Satisfied Customers: 28,310
Experience: ASE certified Technician advanced level specialist. Wisconsin certified emissions state inspector
Verified

Hello there!

 

Does the engine not start up? Are you looking for some diagnostic information?

 

WHy are you checking the fuel pump current?

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Customer reply replied 8 years ago
Did you receive my email with the explanation?
Jeep Mechanic: Amedee, Jeep Technician replied 8 years ago

Yes... I am a little bit confused on what you are asking.

 

Does the engine not start?

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Customer reply replied 8 years ago
The engine will start but if we let it run it will burn out the diode in ECU. Pins 3 and 19. I discussed this problem with another expert and he said it was a bad ground. So we began eliminating sensors and connections one by one. We understand the normal amp draw is about 3 . The fuel pump is reading up to 4 . Why would it be that high, does it involve a bad ground or possibly defective? We have worked on this a long time and would appreciate any help. There should b a history log of our emails underCustomer . Anthony was the other expert and I explained all of our questions were not answered and would need more help, but apparently it was about the money.It has a new motor in it but we are at the breaking point. Regards, Dennis
Jeep Mechanic: Amedee, Jeep Technician replied 8 years ago

Hello!

 

Would you like to continue working with Anthony on this matter?

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Customer reply replied 8 years ago
No, I think we need another point of view or perspective, but I would be ok with it. This is like just starting over. I am open to any suggestions.
Jeep Mechanic: Amedee, Jeep Technician replied 8 years ago

Ok.. I will try my best but the response time might be long on my part because I am at work.

 

How do you know the diode in the PCM is shot? Is the PCM bad? Did you replace it?

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Customer reply replied 8 years ago
In 87to90 , my understanding is an ECM compared to PCM. When we removed it and took the cover off, the diode 140/2 (pins 3and 19) was obviously burnt. We replaced it with anothet ECM from a 1990, ie:same part numbers and it burnt it also . We repaired both with the appropiate diode and then proceeded to find the cause by eliminating one thing at a time. As I mentionned before with cover off we placed a finger on the diode and after a quick start it would immediately begin to heat up to the point shutting it off or burning your finger or the diode was the only alternative. Throttle injector wires and idle actuator advance. Same heating problem (diode) . The power appears to stop somewhere and return directly to the ECM .I appreciate your help and understand your time frame. If we invoved Anthony ,would it be easier? Thanks ,Dennis
Jeep Mechanic: Amedee, Jeep Technician replied 8 years ago
If we involve anthony, I will opt out of this question. It is up to you.
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Customer reply replied 8 years ago
No, As I said, I think another point of view is needed.
Jeep Mechanic: Amedee, Jeep Technician replied 8 years ago

Ok.. lets just keep this computer stuff in mind and start from scratch.

 

Does the engine not even start? Do we have low fuel pressure?

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Customer reply replied 8 years ago
The engine will start. I do not know the pressure .
Jeep Mechanic: Amedee, Jeep Technician replied 8 years ago
So what got all of this started? DOes it run bad? What would I notice if I drive the vehicle?
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Customer reply replied 8 years ago
We purchased the vehicle with no spark,so it would not start. The owner said , it just quit. Because of the expense regarding a new motor,he did not want to put any more money into it. When we got it home ,the red alternator wire was shorting out as it had come out of the clip where the tan and red wire go to the side of the alt. . When we fixed that ,we could smell a burnt odour coming from inside when we started it. It quit running and we found the burnt diode in the ECM.When it runs, it runs bad and heats up th e diode. Obviously we cant drive it.
Jeep Mechanic: Amedee, Jeep Technician replied 8 years ago
But it will start and run? How long will it run for?
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Customer reply replied 8 years ago
About 30 seconds before the diode starts to heatup. Then we shut it off.
Jeep Mechanic: Amedee, Jeep Technician replied 8 years ago
SO the engine will just stall? DO you loose spark or fuel?
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Customer reply replied 8 years ago
Both, sometimes it quits itself or we shut it off before the diode burns up again. No loss of spark ,possibly fuel . It idles real rough, but smooth on other occasions.
Jeep Mechanic: Amedee, Jeep Technician replied 8 years ago
Sorry for the delay!

So will it stay running? Can you keep it running long enough to test whats going on?
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Customer reply replied 8 years ago
If we leave it running the diode will burn out again, it gets so hot you cant keep your finger on it.We are trying to eliminate things one by one by disconnecting which is how we found the amperage on the fuel pump wire seemingly overloading.
Jeep Mechanic: Amedee, Jeep Technician replied 8 years ago
Well I am very good with no starts and performance issues. Stalling and wiring problems. But since I cannot get my hands on wiring diagrams for the inside of your computer, I don't think I would be much help. We would be merely guessing at the problem. I would love to help you out, but I am not sure I have the time to spend with you for 30 or 40 posts trying to guess at this.

I don't think its going to be the fuel pump because it would blow a fuse first. Sometimes the oxygen sensor can do this is if shorts out or if there are nay other wiring problems on the vehicle. If I were you, I would just let it run and see what happens. IF you are confident that it will fry the computer, then I would send the computer in to a rebuild place and they should be able to tell you what circuit to start looking at on the vehicle.
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Customer reply replied 8 years ago

ok, Will get back to you tomorrow.

Jeep Mechanic: Amedee, Jeep Technician replied 8 years ago
Sounds good!

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