I have a 97 F150 4.6 4WD with 130k miles. Recently I have noticed that when going uphills at low-speed, 35-40 mph that the engine will shudder like it is misfiring. If I accelerate it goes away. Having searched for "shudder" and reading 20 pages of old posts, I see that this is a common problem, especially with COP engines (which mine is not). There are no codes being thrown at the moment.

At 100k miles (4 years ago) I had the original plugs/wires replaced with Motorcraft plugs/wires when the CEL came on with a cyl 8 misfire code.

Is this something that a dealer or properly equipped mechanic should be able to diagnose? I guess I could have the plugs/wires replaced again, but would like to avoid randomly throwing money at the problem.

Thanks in advance for any advice/suggestions.

 

Comment first; usually a studder with no code or lamp is a coil with low output 'when' the EGR system is operating.
This could happen in 3rd gear at lower speeds and light throttle or in OD at the higher speeds and light throttle for 45 to about 60 mph road speeds.
Aside from replacing coils, the other way is to use a good scanner to trap the problem when it occurrs, then you would know with some assurance which cylinder/coil is causing the missfire.
The reason you see no missfire code set is the fault is not hard and goes away with added throttle and load, only to return again the next time the driving conditions prevail.
Good luck.

 

I have this problem on my 97 and wife 98 for a while now. sounds like it might get a little pricy for coils. Does anyone know of a sorce for coils at a reasonable price.

 

Get your transmission checked.
It could be the old torque converter shudder.

I had similar symptoms with my 91 F250.

It started occasionally on one steep hill on my way to work. If I stepped on it it would stop.
A few weeks later on a trip to Florida with the camper in tow it came back and got worse.
After a day or two i figured out it was the torque converter clutch.

Try this, next time it's doing the shudder, lightly ride the brakes.
Just enough to get the brake lights to come on, if it stops, it's converter shudder.

The PCM unlocks the torque converter when the brakes are applied.
If you confirm torque converter shudder, you're looking at torque converter replacement at a minimum.
The trans has to be pulled to replace it anyway, so if you have high mileage you might want to consider a tranny rebuild while it's out.

 

Thanks. One question about your comments. Does the "when the EGR system is operating" mean that if there is an issue with the EGR system that your diagnosis would not apply? I have not had issues with the EGR, but with 135k miles, I am sure it only a matter of time. I have never pulled the TB off and cleaned it although that is on my list to when I get a free weekend.

 

i have a 97 f-150 with a 4.6, i have changed the plugs, wires, and a coil pack, and still have a skip have tried everything

 

I have done a test of disbling the EGR system when haveing an issue with a low output coil.
Still had a missfire condition.
I find the engine operating program is designed to run on the lean side so a coil can still be a problem without EGR called in.
But in OD when EGR is operating, the missfire was much worse.
I have been working with this peticular situation just to learn about it as much a practical when the oppertunity presents it'self.
Otherwise I use a scanner to trap the fault and work with it to learn before replacing the coil.
For the last 6 months after flushing out the bad coils, the motor has been running perfect.
Good luck.

 

I have a similar set of circumstances as WMD. 97 4x4 with 4.6 engine, 125000 miles. Plugs and wires changed at about 100k. Vehicle has similar shuddering issues as he describes, but with a couple of other issues. If the truck is parked on level ground or on a hill nose up, the vehicle misfires strongly on startup for about 30 seconds and then smooths out; however if it is parked nose down, it starts and runs smoothly but the shudder is still there as WMD describes. Ideas?