4.9L jumpy timing at idle.
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5th Wheeling
Joined: Jan 2021
Posts: 30
Likes: 1
4.9L jumpy timing at idle.
1995 E250 4.9L auto. 85000 miles. Has a growing rough idle. Intermittent last summer and getting to be pretty constant. Only code was for a brake BOO. Brakes seem fine. I checked the timing and it was advanced but when I tried to dial it in to 10BTD I noticed at 800 rpm it jumps up and down about 8 degrees extra at idle. Stalls at lights sometimes. I have never had a computer controlled ignition so I have never seen a timing mark jump so much at idle. Thinking the distributer wouldn't be advancing at 800 rpm so that wouldn't do it. ICM ? I have a spare new one but I thought I would think it over a bit. first. Seems tun smooth when driving above 1000 rpm or so. I do notice a weird flutter on the right side of the motor. Maybe a vacuum leak??
What would make the advance flutter so much at idle? I'm going to retest the timing in the am when cold to see if it stays more steady.
Thanks for any help.
What would make the advance flutter so much at idle? I'm going to retest the timing in the am when cold to see if it stays more steady.
Thanks for any help.
Hotshot
Joined: Jul 2020
Posts: 10,606
Likes: 2,680
From: Near Salt Lake City
I've never seen one run where the timing was NOT jumping all over the place
Used to see Mustangs and Crown Vics run 15-60 degrees regularly with the spout plug in place
Your truck with the 4.9 will be the same
Agree, disconnect the spout and time it
Then watch the timing move while running with the spout as you rev it up
All should be okay
Used to see Mustangs and Crown Vics run 15-60 degrees regularly with the spout plug in place
Your truck with the 4.9 will be the same
Agree, disconnect the spout and time it
Then watch the timing move while running with the spout as you rev it up
All should be okay
Lead Driver
Joined: May 2004
Posts: 5,052
Likes: 138
From: Maryville
Is the brake booster leaking, that will cause idle issues in gear, timing must be done with the spout disconnected because you fight the computer when the spout is plugged in.
Is your ignition module on the distributor or on a heat sink on the fender?
Is your ignition module on the distributor or on a heat sink on the fender?
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