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Bronco ii dying at start-up intermentanly


xracer18

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I have an 86 bronco ii. This truck usual runs awesome. But lately it's been doing some funky things. I've noticed that if I go start it and let it run for a while and get it warm. Or drive for a while. Once I turn it off again and try to start it being warm. It starts and then hovers at 500 rpms and then dies. Then it won't run again tll I wait for a while. Then it will fire up and run great the next day. Most of the time it starts and runs good, Really odd. any thoughts?
 


RonD

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xracer18

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Classic TFI spark system issue.

When they are warmed up they intermittently start and stop sparking

Good read here on that: http://www.therangerstation.com/tech_library/TFI_Diagnostic.shtml

Also clean the IAC(idle air control) valve, they usually need it but most likely not your problem.
How-to here: http://www.explorerforum.com/forums/index.php?threads/how-to-iac-valve-cleaning-thread-w-pics.84220/
Thank you, seems like this is a very accurate thing to my issue. But alot of this is a little over my head. Wiring and such is not one of my strengths. From what I gathered the ignition control module could be bad?
 

RonD

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Yes, over time the TFI module can become heat sensitive.

Coils can as well, become heat sensitive, although that is less likely.

You can, of course, just change the module and see if that solves the problem, if it doesn't then you will have to start testing wires, they are 30 years old so can become brittle and crack.
 

xracer18

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Great, thanks so much
 

xracer18

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Yes, over time the TFI module can become heat sensitive.

Coils can as well, become heat sensitive, although that is less likely.

You can, of course, just change the module and see if that solves the problem, if it doesn't then you will have to start testing wires, they are 30 years old so can become brittle and crack.
the problem kept getting worse, but it wasn't just when it was hot. It happened just randomly. Even when cold. And now it won't start at all. I was told by a mechanic that with the random,. Intermentanly symptoms can be caused by the ignition pick-up AKA crankshaft sensor inside of the distributor. For just for kicks I decided to test spark by spraying start fluid in the intake. Well it started for a minute before it ran out of fluid to run off of. So now I'm lost. But if I understand this correctly. The pickup sensor. If bad won't send a signal to the injectors to stay running. I can hear the fuel pump turn on fine. Anyone else heard of this? I'm going to change the whole new distributor and pickup . I work at O'Reillys so I get it cheap. Hopefully this is my issue.
 

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TFI module gets timing signal from Hall Effect sensor in the distributor.
It uses that to time the spark
TFI module also passes on that timing signal to the Computer so it can time the fuel injectors, called the PIP signal.

So yes the hall effect sensor does control spark and fuel injector timing
But since spark is working the sensor is working

Older wiring from TFI module to the computer would be my first stop
The wiring to check is in that link previously posted

Here is EEC(computer) wiring: http://www.auto-diagnostics.info/ford_eec_iv

Pin 56, PIP, is the timing signal from TFI module
Pin 36, SPOUT, is the signal computer sends back to the TFI module to advance and retard running engine spark timing
 

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