i have a 2000 F150, 4.2l v6, 5 spd man tran, 100,000+ miles in excellent condition (all highway miles), maintained beyond required maint sched. i use super gas only. my problem is, recently it started to stutter when i accelerate. if i accelerate slowly it is okay, however if i try to accelerate aggressively it starts to stutter. No cel, new fuel filter, new air filter, complete tune up 2000 miles ago. so whats up with it?

 

Probably a low-grade misfire. Normally caused by plugs, wires, coils, or base engine mechanical concerns, in that order.

Use your scan tool and look at the Mode 6 data for the misfire counts. You'll likely find one or more cylinder counts elevated. If no scan tool is available, identify the driving condition under which the misfires occur, then really concentrate on forcing the misfire until the CEL does come on or flashes, then have your codes read to see what your on-board computer has identified.

You say you had a "tuneup". What plugs were used? Were the wires also replaced and what brand?

Running "super" is a waste of 20 cents per gallon. Unless you're running a custom tune, your engine can't take any advantage of the extra octane rating. Your engine was designed to run on 87 just fine.

Steve

 

im curious, not being a mechanic, why wires or plugs? would the stutter be there at low acceleration as well as agressive acceleration if it were the plugs or wires? i have been told it was an O2 sensor that is causing my stutter. plugs and wires checked out ok

 

The greatest load on the secondary ignition system occurs when the engine is accelerating briskly with the greatest load occurring under agressive acceleration. That's why marginal components fail more frequently under that particular condition.

It is extremely unlikely that an O2 sensor could cause this. I've never seen or heard of such an O2 failure causeing this symptom.

"plugs and wires checked out ok" doesn't quite cut it. If these components weren't replaced with the correct items, you have no idea as to what their actual condition is.

Steve

 

can you explain why there would be no problems for the last 2000 miles if it were the wrong plugs or wires to begin with ? I am just trying to understand, please bear with me. 2000 miles seems like a considerable amount of miles if they were the wrong products to begin with. plugs and wires are FORD replacement parts by the way.

 

gebopper , Steve knows what he's talking about - just keep that in mind.

People run into problems all the time with bad parts, you take that risk when you go with other third party venders that will sell anothers parts for season tickets - you just never know.. Have you ever heard of knockoff's? Well, there out there..

Replace your wires/plugs with "Motorcraft" brand. That's OEM spec parts - It's what the manufacturer uses, you can't go wrong that way.

There's numerous problems that cause a product to go bad.

These motors are picky, especially the ignition system.

 

i do not doubt he knows what he is talking about ( the reason why i said bear with me, and why I am trying to understand). the parts i used are motorcraft spec parts. the only reason why i question plugs or wires is because i have a guy who has been a ford mechanic for over twenty years telling me the O2 sensor could be bad and that he has seen this many times. I just dont want to change parts and waste money, that is why i am trying to understand after 2000 miles of use, how it could be the wrong parts. I do appreciate all he is trying to do for me, please dont mis-interpet my questions. I am an engineer not a mechanic and any help i get is appreciated

 

I'm an engineer as well - not a mechanic , just a hobby . There is a V6 section you might try posting in as well .

If you have new wire's it would have helped if you said so - I'm guessing that you do . A tune up doesn't necessarily mean you have new wires. Confirm if that's the case.

State all parts that have been replaced - State the manufacture name of the part used to replaced.

 

all the parts i use are MOTORCRAFT simply because i want to ensure proper product spec. i too have had bad experience with after market products in the past. i currently have new plugs, wires, fuel filter and air filter within the last 2500 miles.

 

To change the plugs you have to remove the plug wires. If they were not properly removed they could have been damaged. Pulling on the wire instead of the boot can break the wire and not show it. Reinstalling the damaged wire may have pushed the ends back together till vibration, 2000 miles worth, again separates them. They may have been rerouted and are now rubbing on something that is causing them to arc. Some Bosch plugs are known to cause a miss. Did you scan for codes or pending codes.

JMC

 

i am not sure why you would tell me that i have to remove the wires to get the plugs out, and why you are talking about using the old wires when i have all new plugs and wires. it seems to me i would know how to get the plugs out if i have installed new ones. ???????

 

I know you said that you used all Motorcraft parts . A little unconvinced with your postings . You used Motorcraft plugs correct ? They say Motorcraft on them correct ?

When you drive your vehicle normally and @ about 45mph when it shifts into overdrive , does it misfire right away ?

 

it is apparent that i am trying to fix my truck, so why would i lie about the products i am using??? it is a man 5 spd trans.

 

I was just trying to explain the follies of not replacing plug wires. It still stands that if the wires were replaced with sub standard ones they will fail. I would test the plug wires to see if they are up to spec. They should have no more than 7000 ohms of resistance per foot. I would wiggle the wire while testing it. Did you gap the plugs? (.052-.056 in)

JMC

 

i will check the resistance on the wires here in a minute. i did gap them per spec. @ .054 (a happy median)