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Intermitent no start

Tiny
BOZOBOATS
  • MEMBER
  • 1994 FORD BRONCO
  • 5.8L
  • V8
  • 4WD
  • AUTOMATIC
  • 175,000 MILES
Vehicle has good spark at spark plugs, fuel pressure at 32psi. I have tried a known good computer, a known good efi module. When it will not start, I can spray some carb cleaner in a vacuum port and it starts. When it runs it runs ok. I had a vacuum leak at the intake plenum gasket and replaced it. I tested all injectors, they make a good click, ohms reading for all is 12.5 to 13 ohms.
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Saturday, February 20th, 2016 AT 1:09 PM

9 Replies

Tiny
WRENCHTECH
  • MECHANIC
  • 20,757 POSTS
You need to test for injector pulse using a noid light, That fuel pressure is a bit too low. The spec is 35 to 45 PSI when the engine isn't running
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Saturday, February 20th, 2016 AT 3:38 PM
Tiny
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  • 6 POSTS
The 5 injectors, that can be accessed without removing the intake plenum, all react correctly when a noid light is used, each flashes during cranking when in the no start condition. Also the more I crank the engine the higher the fuel pressure rises to approx. 38psi
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Saturday, February 20th, 2016 AT 4:27 PM
Tiny
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Thank you for your response.
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Saturday, February 20th, 2016 AT 4:28 PM
Tiny
WRENCHTECH
  • MECHANIC
  • 20,757 POSTS
OK, unless there is a very low compression problem, there has to be something wrong with your testing. If the engine has good spark, injector pulse, fuel pressure and compression, the engine will run so you'd better start over with your testing.
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Saturday, February 20th, 2016 AT 4:41 PM
Tiny
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I agree, when I checked compression, all cylinders were at 150psi to 165psi, with the throttle plate open. I checked again for spark with a test light that plugs onto the spark plug and the other end plug into the wire, I have a weak yellow spark now.
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Saturday, February 20th, 2016 AT 4:57 PM
Tiny
WRENCHTECH
  • MECHANIC
  • 20,757 POSTS
The best way to test spark is with and adjustable spark tester. You should be able to jump at least 1/2 inch.

https://www.2carpros.com/images/external/ignition_spark_tester.jpg
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Saturday, February 20th, 2016 AT 5:00 PM
Tiny
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  • 6 POSTS
Thanks, that is the other portion of the tool I am using, except I do not have it with me. I will get it and let you now what I find. Thanks again for your help.
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Saturday, February 20th, 2016 AT 5:05 PM
Tiny
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  • MEMBER
  • 6 POSTS
Success, after starting all over with the diag, using the suggested tool found spark would only jump approx. 1/8 inch. Tried known good coil and vehicle starts right up and runs good. Sometimes too much diag give me a brain fart. Thanks again for your help with this intermittent problem. I learned something today!
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Sunday, February 21st, 2016 AT 9:42 AM
Tiny
WRENCHTECH
  • MECHANIC
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Glad to hear you found it. Testing is always a better method than swaptronics.
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Sunday, February 21st, 2016 AT 9:45 AM

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