Hesitation/Bucking coasting at 35-40 MPH

[fastkurve]

Hi,

I own a 98 Explorer V6 SOHC, auto 4X4. The truck is stock, no mods, same original tires size.

For the last 2 months, the problems is just getting worst. While coasting at 35-40 mph (city driving), you can feel the vehicle hesitating or bucking , similar to a clogged fuel filter (replaced the fuel filter last fall due to same symptosis but under load while towing the boat) & having codes too for misfire. On highway, coasting at 60 mph , noting abnormal. Just this specific sweet spot of 35-40 mph.

This time no code what so ever, idle is poor, stalls sometimes. But accelerate Ok, from idle, mild or from full throotle accel.

I went through many posts here, can't find a similar one with my problem.

I used Autotap diagnostic scanner for the codes, nothing!

Recorded some rides & cannot figure what could be wrong by playing back the recordings.

Help would be greatly appreciated

Thanks

Fastkurve

PS: Just came back from another recording session. Stumble/hesitation is noticed at the described speed above with transmission in 4rth gear. If I downshift in third (by bringing the shifter in position 2 and keep the vehicle in cruise control mode)) the hesitation disappears. As soon as I put in back in drive position, the bucking starts over again.

*************************************************************
March 2nd,


Here's some news:

-Cleaned the MAF with contact cleaner, no luck ! still having the problem (visually the tiny leads looks fine, not damaged or broken)
-had vacuum gauge hooked up and red low values 12"Hg, pulsating by approx - 1" Hg

I did a clip of it that you can look at on youtube: http://www.youtube.com/watch?v=sDxWw8sDhL0

Please, have a look and tell me your impression. From what I red so far, it is relating this low vacuum level to the followings:a lower reading indicates possible incorrect timing, incorrect valve timing or adjustment, incorrect setting of idle mixture, worn piston rings, or leak in intake manifold.


I had the M0012 done about 5 years ago, just did the o-ring job at that time (not the timing chain tensionner).
Could it be the same o-rings needing replacement again? I do not have the cold start idle hunting behavior so far.

Thanks for reading folks

Fastkurve

 

[Josh]

Maybe your MAF is dirty? Try doing a search for MAF cleaning and try that.

 

[fastkurve]

Thanks for the suggestion , I will try that...I red on another thread that we can disconnect the MAF and rerun the vehicle to see if the engine runs more stable, I might try this too.

Fastkurve

 

[puzzell]

check for cracked plugs or arking

 

[fastkurve]

problems caming from plugs should had triggered a code for missfire,no?

Still, thanks for advice.

Fastkurve

 

[abomb4601]

a mis fire due to a cracked boot will not always throw a code. the bucking you are feeling is most likely because of a cracked sparkplug boot. you feel it most in OD because your transmission is locked in at 1:1 and any stutter in the engine is felt in the drivetrain. i racked my brain about this when i first got my mountaineer. i thought i was going to need major transmission work. turned out to just need a tune-up. thats my guess

 

[puzzell]

i had no code eather and i had a cracked spark plug

 

[fastkurve]

Just a bump to advise of the text update done at the beginning of the thread...

Thanks

Fastkurve

 

[Jerzey]

Replace ur plugs and wires, sounds like you have a small misfire. I have the same problem with my truck right now, and the #3 plug is misfiring.
PS~ good luck on the #3 replacement
Jerzey

 

[Vinniety]

I didnt see anyone ask but when was the last time you did a tuneup? Give it a complete tune up and go from there. Trust me a complete tune up will make a big difference the way your truck runs.

 

[Glen4X4]

Does your truck also maybe spit sputter kind of whenever you start it up?

 

[fastkurve]

I didnt see anyone ask but when was the last time you did a tuneup? Give it a complete tune up and go from there. Trust me a complete tune up will make a big difference the way your truck runs.

Did it about 4 years ago which represents approx 60,000 Km (36,000 miles)
I used platinium spark plugs an original equipment as for spark plug leads.

I would thought that it was not so bad....

Fastkurve

 

[fastkurve]

Does your truck also maybe spit sputter kind of whenever you start it up?

No, in fact it starts quite well, idle hunt for 1-2 seconds then stabilize.

I think I gone a try the tune up (spark plugs and leads)....and see what would come out of this.

Fastkurve

 

[fastkurve]

I troubleshootinh my truck (explorer 1998 V6 SOHC) for bad idle
behavior as I already explained at the beginning of thread.

Using the Autotap scanner (PC version) one f the parameter that I am trying to monitor was the IAC duty cycle.
When monitoring/recording, the value stays fixed at 0.4% and I red from
Autotap that it should be cycliing between 20 to 98%.

My question is: Anybody here using autotap who could check on their own vehicle if you can read the IAC duty cycle ?

I wrote to Autotap for support and I got this answer which I do not feel confident in:

This is the response I got from the Engineer.
Steve,

I looked back through the AutoTap database and compared it to the Ford
database. IAC should read correctly for his vehicle so if he is seeing
a constant value there is probably something wrong with the IAC system.

Fastkurve

 

[Glen4X4]

I'd just try new plugs and wires to start, and make sure your MAF and maybe IAC is clean. And reset the computer.

 

[fastkurve]

Well, after replacing the spark plugs ang leads, not better than before.
Idle is erratic and vacuum still at 12-14 Hg"

By reading numerous threads about bad idliing, I red in one of them to verify
the intake bolts, if still torqued.

I did just that this morning and it seemed Ok to me but I found something else... To do the lower intake bolts, I removed the upper intake & I found the oring between the two intake sections oily,even the seperation surface between the intake runner were oily. There something similar to carbon deposit in the intake runners and oil mist is present.
Could it be a defective EGR valve?

Now, I would tends to believe that the vacuum leak was probable coming from the oring not sealing propelry. I will re-installed new ones.

Now, what is explaining the presence of the oil in the runner?

Anyone has an idea about this?

Here's a link of two pictures showing the condition of the runners and the presence oil:

http://s296.photobucket.com/albums/mm174/Fastkurve/?action=view&current=OilyUpperintakeexplorer.jpg

and

http://s296.photobucket.com/albums/mm174/Fastkurve/?action=view&current=Oillowerintakeexplorer.jpg

Thanks

Fastkurve

 

[chedder12]

99 X-ploder Hesitates / Bucks at 25-40 MPH

I am having a simular issue. Looking at youe pics, I think you have a SOHC?
I have the 4.0 OHV.
My enigine seems to heistate and buck at higher speeds and I was sure the transmission was slipping, but after watching videos for it I realized it was the engine. (Also the CYL 4 Misfire error came up repeatedly; the error can be cleared and will stay away for a day or two. If I run seafoarn through the vacuum system it runs smooth for a few days, no hesitation or bucking. This convinced me the injector was clogged/ bad.
My upper intake is apart at the moment and I am waiting for the injectors to arrive in the mail. I cleaned the old ones, they had almost no build up and all shot 4 clean streams when I tested/cleaned them with a 9volt battery.

Should I swap out the injectors with new ($250) or put the ones I cleaned back in? I dont have confidence it will clear the error.

I did pull the spark plug for #4 and the gap was a wide .058 instead of .054

What is the IAC? I have cleaned the MAF and replaced the plugs and cables in the last couple months. I DID NOT PUT THE DIELECTRIC GREASE on the cables.

 

[jojobull]

I am having similar problems on my wife's 2001 XLT. I get the RPM surge and slight bucking around 25-30 MPH. I will try new plugs and wires as recommended above.

 

[NWTPilot]

I'm having very similar issues.

To Date;

-Cleaned IAC, replaced IAC( donor part )
- Cleaned MAF, replaced MAF( donor part )
-Cleaned throttle Body
-checked all the vacuum lines
-sprayed down intake area with starter fluid,looking for idle change
-removed coil pack, cleaned, tested with mulitmeter, all within spec

I used to get a rough idle, no stall, when hot, but I think that might have been a seperate issue and unrelated as it "seems" to have gone away after replacing the IAC. I've only test-drove it twice since swapping out the IAC, so might be too early to call yet on that front.

I resurrected the Ex from the weeds a year and half ago,where it had sat for over four years. At the time, I replaced Fuel Filter and checked rail pressure. Also replaced plugs & wires. Did a bunch of other stuff too, but nothing I can think of that might relate to this issue.

I'm kind of stumped, so next stop might be a diagnostic session at a shop.

I'm leaning towards a leaky intake manifold or one of my plugs/wires has crapped the bed already.

It only "bucks" on me in 4th, under load at around 1900-2200 RPM. If I click off the OD, dropping down into 3rd, it runs at high RPM smooth as can be. Only when I'm in a " lugging" scenario does it buck. I know its not really lugging, but its on the bottom end of the RPM/Gear/Speed curve.

Let me know if you make any headway on your end and I'll do the same.

Oh, 2000 Ex, 4.0 SOHC

Cheers

 

[NWTPilot]

Just a follow up, as I found my problem and it was an easy fix.

abomb4601 and a couple others called it, was a bad plug connection.

I had replaced all the plugs and wires less than a year prior to the issue, so I kind of discounted that, when all signs did indeed point to a bad spark.

Was mucking around the other day and decided to pull all the wires and plugs, check their condition and put the meter on the wires, just to see. All the wires checked out and the plugs all looked fine. Put it back together with some fresh dielectric in the boots and presto, problem was gone.

To recap the symptoms in case someone is searching for similar;

- Rough idle when hot, no stall
- Missing / bucking under load, particularly uphill or " lugging "
- No code
- Shade tree mechanic/owner with the blinders on.