Hey guys. I am about to go nuts here.
I have a '99 F-150 XL stick shift V6 4.2L with 70K miles on it.
It has always run like a champ (knock on wood) and since I got her at 32K, I have changed the oil every 4K, filters, plugs (stock), plug wires, battery, etc...nothing major - never had a big service or been to a dealership.

Since I have been noticing the problem, I have changed the fuel filter, put a bottle of FI cleaner through her and checked all the spark plug connections.

It idles perfect, drives fine for the most part but when under acceleration or driving a constant speed on the highway (60 or 70) it will sputter every mile or so, as if I am losing spark or something. There is no check engine light and I have taken it to AutoZone twice to try and read a code - but shows up as clear every time.

Is there anything else I can check at home before I take it to the dealership? I am hesitant to do this because it is nothing very serious, but more annoying cuz I know it is not operating 100% perfectly - and I know it is going to cost me an arm and a leg at the dealership.

Any help or advice would be appreciated.
Thanks
ET

 

When is the last time you changed the plugs?

I drive a '97 with the V6 at work, and mine was having some issues similar to that (had trouble starting up sometimes, bogged down on acceleration, etc), and we changed the plugs on it last week. The things were worn down really badly, the gap had to be like 3 times the stock gap. Anyway, after putting new ones in (we used some Autolites, copper, I dont remember the P/N), and it does alot better now.

Just a thought.

 

Try cleaning your throttle body.They usually carbon up pretty good and cause a hesitation upon acceleration.Be sure to use a product just for throttle bodies; no carb. cleaners! Also,do you have an after market air filter? The oil from them can get the MAF sensor dirty.Even if you dont have this type filter,clean the MAF sensor too.

 

I replaced the plugs about 4K miles ago. I believe I have a Purline air filter - nothing like a K&N, just plain o'l air filter with no oil added to it. I am going to sound stupid now, but where is the MAF sensor located?
Thanks
ET

 

Right after the air filter.

 

What type of spark plug wires did you run when you changed out the plugs? I had the same problem when I ran a set of cheapies from Autozone several years back on an old chevy while giving it a major tune up and after a month or two of fustration I found that the wires I installed were faulty. You could actually see the spark jump at night with the engine running....

 

I am not sure what the brand is, but they were about $46.00 for 6 wires.
I will check for a jumping spark tonight.

Also found the MAF and will be cleaning that this week. The TB was very dirty. Cleaned that out with spray. First I thought the problem was gone, but when I hit the highway, the sputter was back.

 

hey there,
still got the same problem.
i purchased a new coil pak today from discount auto parts. took about 5mins to install. SAME PROBLEM....
I am seriously going to go nuts if i do not figure out what the problem is.

do you guys think it could be the Fuel Injectors? i may have to make an appointment to have the FI system flushed because I have had about 10 of theose little diesel smelling cans through my system and it still has teh same problem

to recap - replaced, plugs ($ motocraft ones $), wires, air filter, fuel filter and today the coil.

 

I'm not a pro tech or anything but if you think logically wouldn't it sputter all the time if it was spark plugs/coils/MAF? I'd venture on the fuel delivery since the issue comes up at higher rpm. Since the fuel filter was changed what about fuel pump? Maybe it's time to take it in.

 

Gang, still having the same problem.
Now, it only sputters until I hit aprox. 3000rpm, then it seems to clear up.
ANY IDEAS, PLEASE ?!?!??!?!

 

The IMRC runners in the lower intake remain closed below 3k rpm to improve low end driveability.After 3k rpm they open to increase high-end performance.They are controlled by the IMRC actuator and cable assembly.These could be defective........or.......the runners are very carboned up and are stuck open.

 

thank you but oh boy, you are gonna cost me a a lot of work this weekend!!!
I assume by removing the intake I will have to replace the gaskets. I guess I will be starting this project tomorrow night. through a search i learned that there are two intake manifolds, am i correct to assume that I will have to remove both to get to the IMRC runners and the EGR ports?

Thanks again!

 

Yep!

 

Mine has 180,000 miles on it. I've noticed the same problem for years. No trouble codes ever come up. Tried spark plugs and plug wires. It just seems like a misfire every so often at highway speeds. The little jolt that occurs seems to happen when pulling a slight incline and increasing the gas pedal ever so slightly, so the load on the engine has to be changing just a bit. Some type of a timing advance problem perhaps?

I've had others in the truck with me and they notice the "stumble". Sometimes it feels like you just hit an expansion joint in the highway and the "bump" gets sent thru the truck.

 

That could be something as simple as the A/C compressor cutting in. Otherwise, it's time to look at the coil pack.