300 EFI Missing After Running A While

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Nov 28, 2024 | 06:40 AM

Jeffalex2

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4th Gear

Joined: Nov 2024

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300 EFI Missing After Running A While

I have a recently acquired 89 F150, 5 speed, 4.9 (300) EFI. Love the truck! I usually just drive it around town but recently took about a 1 hour trip and noticed that after a while, she is missing on at least one cylinder. It's totally fine on cold start and 15-20 minute drives. But after a while, there's a miss.
Work I've done on it: removed EGR and CAT, new 02 sensor, new temp sensors, new fuel press reg, new distributor (old coil? maybe problem?)
I'm going to get a fuel pressure gauge and check that out.

Anyone have any other thoughts? Thanks!!

Nov 28, 2024 | 08:27 AM

jas88

Lead Driver

Joined: Feb 2002

Posts: 7,957

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From: Greater Austin, Texas

Once it is warmed up and missing, pull your plug wires one by one and see if you can isolate it to one cylinder.

Nov 28, 2024 | 10:12 PM

Prototypemech

Logistics Pro

Joined: Nov 2013

Posts: 3,922

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From: Mojave, Ca

Remove your ICM from your distributer, clean the mating surfaces to remove any old grease. Slather the back of the ICM with real heat sink compound (not dielectric grease), and reinstall. You can get heat sink compound from Amazon for CPUs. The fancy stuff has nano diamonds.