89 F150 4.9l with broken knock sensor. - Ford Truck Enthusiasts Forums



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89 F150 4.9l with broken knock sensor.

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Old 04-13-2017, 02:25 PM
Robert Reim Robert Reim is offline
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89 F150 4.9l with broken knock sensor.

The whole thing started with it running rough and at idol was surging up and down. Anyway after replacing the pcv, idol control and all plugs, wires along with the throttle control I still had same problem after each one. Drained the tank and new fuel filter also. Was going to see if I could remove the knock sensor next and as I was unplugging it, it just disintegrated. Have checked junk yards (no 89 150's at this time) and all auto parts stores and even Ford (obsolete). Anyone know if it's possible to bypass it? Because it won't start now..
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Old 04-13-2017, 03:21 PM
mark1986F150 mark1986F150 is offline
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Old 04-13-2017, 03:31 PM
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The knock sensor will NOT keep it from starting....
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Old 04-15-2017, 07:54 AM
Robert Reim Robert Reim is offline
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Originally Posted by White 97 xlt View Post
The knock sensor will NOT keep it from starting....
It started five minutes before I removed and broke the knock sensor.
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Old 04-17-2017, 08:56 AM
Robert Reim Robert Reim is offline
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Thanks Mark but mine now will not start without it. It did start just prior to breaking it.
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Old 04-17-2017, 09:20 AM
mark1986F150 mark1986F150 is offline
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Originally Posted by Robert Reim View Post
Thanks Mark but mine now will not start without it. It did start just prior to breaking it.
It's hard to figure out why your truck isn't starting without more details, but the basic rule is air + fuel + spark = start. In your case, one of those is missing. But it is extremely unlikely that the knock sensor is the cause.

Does it crank but not fire? Or does it not crank at all?

Did you possible disconnect something from the distributor / coil / TFI module that are located near the knock sensor?

I'd start by verifying that you have spark since you were doing stuff near the distributor.
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Old 04-21-2017, 07:55 AM
Robert Reim Robert Reim is offline
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I tried repairing the broken knock sensor with no luck. It cranks but won't start with the sensor installed. I checked all distributer connections. I will get back to the basics and check fuel, air, and spark as you mentioned. Spark first. Thanks for your reply Mark.
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Old 04-21-2017, 09:44 AM
Robert Reim Robert Reim is offline
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By chance, does the gas line need to be purged of any air after fuel drain and new filter?
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Old 04-21-2017, 01:08 PM
mark1986F150 mark1986F150 is offline
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Originally Posted by Robert Reim View Post
By chance, does the gas line need to be purged of any air after fuel drain and new filter?
No it doesn't.

Here's a link to some tests you can do to figure out why the truck won't start: Part 1 -How to Troubleshoot a No Start (Ford 4.9L, 5.0L, 5.8L).

Additional tests you can perform to pinpoint issues: Part 1 -Ford 4.9L, 5.0L, 5.8L Index of Articles

Hope this helps
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