1993 Ford F-150 Hard Start

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DAVEHUSBAND
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  • 2 POSTS
truck wont start unless you put a couple of drops of gas down the throttle body. Will run fine all day after that but when you turn it off again it wont start unless you repeat the process. got spark and good fuel pressure kinda stumped ask mechanics around here but no luck.
Jan 5, 2007 at 2:49 PM
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CARUNDELL
  • ✓Experienced Mechanic
  • 602 POSTS
[quote:c046e9cfee="davehusband"]truck wont start unless you put a couple of drops of gas down the throttle body. Will run fine all day after that but when you turn it off again it wont start unless you repeat the process. got spark and good fuel pressure kinda stumped ask mechanics around here but no luck.[/quote:c046e9cfee]

Hey dave,
Interesting issue! Is the check engine light on? does it tend to "smell funny" out the tail pipe? Let us know!

Chris
Jan 5, 2007 at 8:20 PM
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DAVEHUSBAND
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hey well its not my truck my brother in laws he said hes check engine light is on but because he had to unplug his thermostat sensor cause it was idleing high. We went and asked all the mechanics at the ford dealerships and they didnt even know.
Jan 6, 2007 at 8:20 AM
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TAURUSWHEEL
  • ✓Experienced Mechanic
  • 718 POSTS
You need to find out what codes are there, post them here, possibly someone on here will have some ideas..
Jan 6, 2007 at 9:09 AM
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CARUNDELL
  • ✓Experienced Mechanic
  • 602 POSTS
[quote:2cbf4fcb5d="davehusband"]hey well its not my truck my brother in laws he said hes check engine light is on but because he had to unplug his thermostat sensor cause it was idleing high. We went and asked all the mechanics at the ford dealerships and they didnt even know.[/quote:2cbf4fcb5d]

Bingo!........ i think this issue is solved ....here's why

1. A disconnected coolant temp sensor will cause the ecm to "see" a default temp of something like 230 F

2. A " cold" engine needs a TON of fuel before it can warm up and go into closed loop. In fact this engine never goes into closed loop because of the disconned
coolant temp sensor. If the ecm is "seeing" a high temp then it will lean out the fuel sent to the injectors, causing a hard start when cold.

3. Though high idle may be caused by a bad coolant sensor, there may be another cause of this.

4. I recommend a new coolant temp sensor and if the high idle persists, then further diagnosis.

Let us know!

Chris
Jan 6, 2007 at 1:37 PM

Suggested Repair

Replace the disconnected coolant temperature sensor so the ECM can read actual engine temperature and supply enough fuel for a cold start. If the high idle continues after the new sensor is installed, diagnose the idle problem further.

Conversation Summary

A 1993 Ford F-150 5.0L will not start unless a small amount of fuel is added at the throttle body, then runs normally until it is shut off. Spark and fuel pressure are reported as good, and the check engine light is on because the coolant temperature sensor was unplugged to stop a high idle. An expert explained that the disconnected sensor makes the ECM assume a very high temperature and lean the fuel mixture, preventing a proper cold start and closed-loop operation. The recommended repair is a new coolant temperature sensor, followed by further diagnosis if the high idle remains.

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