98 4.6/auto ex-cab 120,000 miles. Great shape, never had any problems, it is fully serviced every 6,000 miles, but recently it's developed 2 quirks:

1. When engine is hot, it will act like it wants to stall when I come to a stop. It will idle down, barely shake, and idle up before smoothing out. Only does that maybe 1 in 5 stops.

2. When Im completely stopped and the light turns green, I let off the brake and hit the gas. Immediately, I hear and feel a very slight 'thud,' almost like the back brakes are grabbing or the rear end is clunking.

On #1, Im thinking its time for plugs, fuel filter, and the oh-so-fun throttle body cleaning and IAC sensor cleaning.

On #2, I'm thinking brakes are grabbing or possibly a U-joint.

Any thoughts??

 

1. IAC
2. Drive and Output shaft union. Clean spline/shaft (w/brake cleaner). Apply thin coat of Teflon Grease to spline (OS). Reassemble.

 

From Service~

CLUNK OR BUMP WHEN STARTING FROM A STOP

FORD:
1997-2005 E-Series, F-150, F-Super Duty

ISSUE:
Some 1997-2005 E-Series/F-150/F-Super Duty 4x2 vehicles may exhibit a driveline clunk or bump that occurs as the vehicle starts to move forward, following a stop. This condition may be caused by the slip yoke not sliding smoothly on the output shaft splines.

ACTION:
Lubricate the slip yoke with Motorcraft PTFE Lubricant. Refer to the following Service Procedure.

SERVICE PROCEDURE:
1. Verify the condition.

2. Remove the driveshaft per Workshop Manual Section 205-01. Be sure to index-mark the driveshaft during removal to maintain alignment during reinstallation.

3. Lubricate the slip yoke with 7-13 grams (0.25-0.46 oz.) of Motorcraft PTFE Lubricant.

4. Re-index and reinstall the driveshaft per Workshop Manual.

5. Verify the repair.

 

For problem #1 also check the EGR too.

 

I am with jbrew on this one. Clean IAC and grease the slip yoke.

.

 

Thanks a lot guys, I'll try and see if I can get it done this weekend.

Also, for the slip yoke, does it have to be Ford lubricant, or will something off the shelf at NAPA work?

 

I agree with all the above but will add one more possible "clunk" cause. I have a 97 that has had the clunk for years. I performed the teflon grease "fix" many times and the clunk would stop for a while (300 miles or so) then return. After reading about the clunk in relation to axle wrap on these trucks I changed the rear shocks over 6000 miles ago and have not had one instance of clunk since. May want to keep this in mind if your shocks are aging and the grease job didn't fix the problem. Take care.

 

A bad trans mount can cause similar issues. I can't say it will cause the clunk, but it can cause stress back there.. My clutch pack would hang on right turns, it would slip or do something goofy, - I can't recall exactly, but it would happen during right turns only. This was corrected after changing the mount and realigning from flywheel back to rear gear. There was nothing left of the mount, - In-fact, I've done this twice already. Mount was fried both times. The last time it split my exhaust damper plate. I've got pictures of that somewhere.. I welded it up/Installed new Mount.

Damn, - I'm glad I replaced the shocks already, - I didn't think that would cause problems, but I can see where it could, now that you mention it.

 

I had an instresting episode yesterday that may clear things up more.

I was on a 2 lane highway, several stop lights and I maintained a speed of 40-50mph. I heard and felt a different clunk this time...it was engine related, not suspension. Each time it happened, I would slowly accellerate to about 37-40 mph, it would drop into overdrive, and I would slowly mash the gas and accellerate without downshifting. It made between 1 and 3 very quick slight pauses or 'chugs' before pulling again. Almost like a 1/10 of a second pause in all power. Once the motor RPM's were up, and I was running 55-60, it would not happen. It never misses a beat when its under accelleration, slight or heavy. But right around 40mph, when it drops into overdrive and the RPM's drop, it would 'chug' a time or two.
Also, it doesnt feel like the tranny slipping bc you can hear the motor stumble slightly and I hear no slipping or grinding.

Im thinking fuel filter. It's running smooth and its getting plenty of air. It's got to be a sensor thats fouling up or its starving for fuel at low RPM's. Also, no check engine light.

Right??

 

Low grade misfire. Plugs, wires, coil packs.

 

I've got the Windsor motor...only 2 coils. Same thing as coil packs?

I bought a fuel filter and its going on tomorrow morning. Hopefully that fixes it.

Edit:
Had a buddy ride with me at lunch. He swears its the tranny but I just dont think so. My trucks got 120,000 easy miles and 4 complete flushes and services. I certainly hope he's wrong!

 

Still on the original plugs and wires?

 

Had the plugs changed once ... 60,000 miles ago

It's running smooth, no sign of misfire or running rough. Has had a little bit of stumbling when ideling.

 

I'm with glc on this in regards to a low grade misfire. A bad fuel filter should also affect the drivability at the higher RPM's of 55-60 as well but we'll see if it helps after you change it. Take care.

 

Are they Motorcraft plugs?