No start cannot read ECU

Tiny
HHIIBEL
  • MEMBER
  • 1997 LINCOLN MARK VIII
  • 4.6L
  • V8
  • 2WD
  • AUTOMATIC
  • 156,000 MILES
I was having to replace ECU relays. Did this about three times. Maybe got about 10 or 12 starts in this manner. Always on startup, cranking but not starting. Now replacing rely doesn't help. Car cranks and builds fuel pressure. ECU doesn't register on reader. But with low voltage, 7.5v, reader does see ecu for a little bit. Then it can't see ECU. I have tested ECU relay by wiring it to a 40amp fan. The low voltage situation is such that the ECU is clicking or something is clicking in glove box area. I went back through the relays I kept and they power the 40 amp fan. So scratching my head about why replace relay did help. Of course, I don't have the very first relay I replaced.
Saturday, July 6th, 2019 AT 4:09 PM

5 Replies

Tiny
MOTOR MASTER
  • MECHANIC
  • 279 POSTS
Hello my name is Dave.

Unfortunately, it sounds like there is a chance your ECU has an issue. my first suggestion would be to check the injectors for power and signal. I have attached a link to our tutorial on testing the injectors. I suspect you will find they are not getting any signal and/or power. If you are getting power to the injectors that would indicate that you have power to the ECU, here is the link to the tutorial:

https://www.2carpros.com/articles/how-to-test-a-fuel-injector

If that checks out to be okay I would move on to testing for fire. I have attached another one of our tutorials on testing the coil for fire.

https://www.2carpros.com/articles/how-to-test-an-ignition-system

If either of these tests fail the most probable cause would be the ECU however there is a chance there is a wiring issue. I have attached the wiring diagrams for your car's ECU. I would test all the power circuits for continuity to ground with a volt ohm meter with the ECU unplugged and if you have any that read less than infinite (no) continuity you would need to repair that circuit, if you find that none have continuity to ground than I would feel confident in replacing the ECU. I have attached a link to our tutorial on testing wiring.

https://www.2carpros.com/articles/how-to-check-wiring

I hope this helps you find your problem and thank you for using 2CarPros. please feel free to ask us anything else you need help with.
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Monday, July 8th, 2019 AT 4:58 AM
Tiny
HHIIBEL
  • MEMBER
  • 3 POSTS
Thanks Dave. Will do test to ground.
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Monday, July 8th, 2019 AT 11:15 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,138 POSTS
MOTOR MASTER is one of our best! Please let us know what you find. We are interested to see what it is.
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Thursday, July 11th, 2019 AT 11:21 AM
Tiny
HHIIBEL
  • MEMBER
  • 3 POSTS
None of the various ECU power's see ground. I may test to see power at them (ign/acc on) or I may just put in a new ECU. And the ECU grounds (various do see ground). I may test to see if they see power (that would be bad). Just trying to find time and some extra hands. I'll update as I progress.
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Friday, July 19th, 2019 AT 9:32 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,138 POSTS
Sounds good looks like we are getting closer.
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Friday, July 19th, 2019 AT 5:16 PM

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