For past 6 months I’ve had new plugs, plug wires, Dist. cap& button, fuel filter changed, 2 o2 sensors changed. The truck periodically appears to idle roughly, is hesitant in acceleration when shifting, (5 speed) after 7-10 mins. begins to run smoothly! Could it be a coil, catalytic converter, or fuel pump? How can one know for sure? Absolutely stumped!!
What motor?
~Michael
4.9 liter, inline 6, manual 5 speed
Check and tighten all the fasteners that hold the manifolds to the head. When they work loose, you can get vacuum leaks. Remove and clean the EGR valve and make sure it’s closing all the way and works freely. If it sticks open, it will destroy the idle and acceleration.
Check engine light ever come on?
Throttle position sensors aren’t too good on some Fords. Tighten the intake and exhaust manifold bolts first and see what happens. Change the coil without checking it. Have the codes read. Buying a few parts hasn’t hurt you yet. It COULD be anything you have said. Check the firing order again.
I really agree with this one.
The check engine light hasn’t come on since June . At that time I had the #1 Bank O2 sensor replaced and the egr valve removed and cleaned! The Ford dealership two weeks ago misdiagnosed the condition on two occasions with the problem still remaining! I had them reinstall the two O2 semsors they previously removed, and refund my money. Believe it or not the thought of tightening the manifolds, and or replacing all vacuum lines was suggested by a clerk at an advance auto shop!
In the past two months I’ve removed and cleaned the egr valve, replaced several vacuum lines, tightened both intake and exhaust bolts, and determined that it’s not the catalytic converter or the fuel pump!! I’ve also replaced the coil…still the seemingly roughness in acceleration… When the truck is very cold from sitting a lengthy time I have no problems, but let it run for 20-30 mins. and then start it back 30-45 mins. later and you have what appears to be moisture under the dist. cap!! Also, when the weather warms up it has a roughness in acceleration, or if the truck is under a load from carrying a utility trailer!! I’ve tried everything, new plugs, plug wires, cap, button…you name it I’ve tried it!!! Extremely frustrated!
You say, “…appears to be moisture under the dist. cap!!” Moisture, or oil, under the distributor cap can definitely cause misfiring. Investigate that further. Does the distributor have vacuum advance? If it does, moisture could be coming in from the intake manifold. If no, vacuum advance, there is a seal around the distributor shaft. That could be bad. Examine/replace the distributor seals. For the particulars, you need a repair manual.
Smells like a sticky EGR valve to me, too.
This problem has been on the board for a while. The heat stove for the air intake. If the inlet tube from it to the air cleaner housing is broken or disconnected, you could have stalling or low power. Considering that you are supposed to get at least 50% heated air into the intake, that may be the problem. Then there are mechanical things to consider. Sometimes the cam shaft just wears out. You might need a compression check.
I’d like to hear a bit more about the moisture under the distributor cap.
You’ve removed the cap and verified this problem is really that chronic?
I meant to say that it gives the appearance of moisture under the cap, not that there is a crack, or moisture there, as there is not!! I’m not a mechanic, and not sure if the distributor has vacuum advance!!
I meant to say that it gives the appearance of moisture under the cap, not that there is a crack, or moisture there, as there is not!! I’m not a mechanic, and not sure if the distributor has vacuum advance!! Then there are mechanical things to consider. Sometimes the cam shaft just wears out. You might need a compression check. This truch has only 75,000 miles of use!!!
I had a rare problem like this, but over the years have heard about it from about 6 others on the net. Fooling with the O2 sensors makes me think this might be the same problem. Some fuel pressure regulators have the spring installed slightly off center. This causes the seat to only wear on one side. At times it will slide over ans stick. This usually happens at idle and at high load conditions like climbing hills when vacuum is highest. This can give a lean check engine light, but often only happens for short periods without a light. I found it by monitoring fuel pump current. Current will drop from about 4A to 2A, easy to monitor in cab by running wires from fuel pump fuse. This condition will almost never show up when they do pressure check in the shop. I cut open the old regulator and verified the problem.
The simile (or, analogy) about the distributor cap misled several people. To restate your problem, “When the engine is very cold [cold weather?], there is no problem until a warm restart 30 to 40 minuets later; then, it runs roughly. When the weather is warm, it has a roughness while accelerating, or, when pulling a load (like a utility trailer).” Is this correct? Or, is it it something else? Make corrections in this statement where needed. Please, no more similes, or analogies. They’re too confusing.
Try what Opera House suggested with a fuel pressure gauge installed. You want to check for a constant fuel pressure, at different throttle positions and loads. Watch the fuel pressure gauge while you put the gear shift into drive and press the gas while pressing the brake. If the fuel pressure is inconstant, it could be the fault of the fuel pressure regulator.
Certainly appreciate the advice, will have a professional look into it!!