4.9 issues while driving
Thread Starter
Junior Member
Joined: Jul 2012
Posts: 8
Likes: 0
From: Lincolnton NC
4.9 issues while driving
Need some help, while driving the engine will drop a few hundred RPM's then catch back up and go, was thinking distributor issue with pick up but wanted to put my theory to the group of experts. I have attached a video of what it is doing while driving. FYI the Break Light is off now, 
Senior Member
Joined: Dec 2017
Posts: 403
Likes: 58
From: Chattanooga, TN
I'm assuming that it is fuel injected, and not a carburetor. The last 4.9 I drove was a long, long time ago and it had a little 1 barrel carb on top.
Anyway, it points to the ignition intermittently shutting down. I'm way too old-school to diagnose this very far for you. Plug wires maybe. Ignition coil. Distributor (does it have one????).
Also maybe bad gas. Did you fill up recently, prior to the problem showing up?
Anyway, it points to the ignition intermittently shutting down. I'm way too old-school to diagnose this very far for you. Plug wires maybe. Ignition coil. Distributor (does it have one????).
Also maybe bad gas. Did you fill up recently, prior to the problem showing up?
Thread Starter
Junior Member
Joined: Jul 2012
Posts: 8
Likes: 0
From: Lincolnton NC
It is fuel injected, Ignition coil has been replaced. Issue was before I filled up, I run it low just so I could remove as much gas as possible then filled it up with high octane and a fuel cleaner for good measure and changed the fuel filter. Still the same issue.
Member
Joined: Jan 2018
Posts: 11,256
Likes: 1,770
From: Memphis, TN, Earth, Milky Way
You need to put ALL the truck's details & history into your signature so we can review it before each reply. Click this & read the caption:
(phone app link)
When (time & miles) and why was EACH part replaced? The 4.9L is a low-compression engine - it won't run right on high-octane fuel (which ISN'T better or worth more). Put the recommended octane (89) in every time. For more detail, read the TSBs in this caption:
(phone app link)
(phone app link)
When (time & miles) and why was EACH part replaced? The 4.9L is a low-compression engine - it won't run right on high-octane fuel (which ISN'T better or worth more). Put the recommended octane (89) in every time. For more detail, read the TSBs in this caption:
(phone app link)
Thread Starter
Junior Member
Joined: Jul 2012
Posts: 8
Likes: 0
From: Lincolnton NC
89 Ford F-150 4x4
Head and head gasket replaced
Transmission replaced with one that had 80000 miles on it
Complete rear break rebuild with new parts
Ignition coil
New water pump
New radiator
New thermostat and gasket
New belt
Heavy duty clutch, pressure plate, throw out bearing, all springs replaced
Hydraulic assembly for the clutch replaced
New harmonic balancer and rubber bushing
New car quest battery
New fuel filter
Timing gears inspected with no issues found,
New Spark Plugs
Wires replaced
New Starter
Head and head gasket replaced
Transmission replaced with one that had 80000 miles on it
Complete rear break rebuild with new parts
Ignition coil
New water pump
New radiator
New thermostat and gasket
New belt
Heavy duty clutch, pressure plate, throw out bearing, all springs replaced
Hydraulic assembly for the clutch replaced
New harmonic balancer and rubber bushing
New car quest battery
New fuel filter
Timing gears inspected with no issues found,
New Spark Plugs
Wires replaced
New Starter
Member
Joined: Jan 2018
Posts: 11,256
Likes: 1,770
From: Memphis, TN, Earth, Milky Way
SIGNATURE - use the link I provided. And you didn't mention when or why each part was replaced, or describe the truck very thoroughly. GIGO - if you don't supply the necessary information, you're not going to get the answers you want.