studders/bumps when accelerating sometimes

[toy4x4]

Just picked up a 2003 explorer 4.6 4x4. It sometimes studders surges and bumps when accelerating hard or up a hill. Other than that shifts smooth and runs smooth. No service engine lights yet.

What are your thoughts? Random misfire or tranny issue?

When it messes up, it starts off as a surge and then a soft stumble then it goes to a hard bump bump bump until you let off the gas then it may do it again a few more times if you get into the gas too much. By then you are up to 55 60mph it will do it in OD and 4th if at 55+mph if you get into it or hit a long hill. Other times I've tried to make it do it and it is shifts and runs flawless.

 

[Tech By Trade]

Plugs and coils. Looking about 900 bucks to have the shop change them for you.

 

[rrgone]

Try a little test. Disable the 4WD system and drive it for a few days and see if it still bumps and surges under acceleration, especially uphill. If it still does it then time for a tune up as mentioned. If it goes away then time to diagnose the 4WD system.

 

[rwt101]

Should still check for codes!!!
Bob T

 

[Snowcone]

Probably a coil pack.
Just buy a new set of 8 off eBay - heaps cheaper than the stealerships.
Change the plugs while you are at it.
Cost you nothing in labour and take you about an hour to do

 

[toy4x4]

Thanks for the tips guys...
Things really got bad on way home yesterday I could definitely tell it was missing and it set a misfire code on cylinder 8 which is back driver-side I think. I found I have coolant leak from the intake manifold under the thermostat area. Its getting into the plug boots. I found coolant in the front two spark plug holes but didn't have time to check the back 2 last night.

I know the misfire would cause the studder and surging feelings but what really scared me is the harsher bump bump bump I was feeling at 60mph. It felt pretty harsh on the drivetrain to have been a misfire. I guess I will have to wait until I get this intake leak and misfire sorted out before I will know.

 

[toy4x4]

Update:
New intake manifold -Dorman (stock intake was leaking coolant also causing a misfire)
New Coils - MSD
New Plugs -Motorcraft Platinum
Compression test passed. 170psi on lowest cylinder 180psi on highest.
Engine runs and idles smooth no missing and no codes.
$400 later I still have this bump bump bump issue when accelerating.

So now I've been able to play with it while it's not missing, here is what it's doing... If I'm cruising at say 50mph and take my foot off the gas for 2 -3 seconds and then put it back into the gas kinda quick like I get this bump.... (This in itself seems strange to me but harmless) but now if I do this and put my foot into the gas a little harder (but not far enough to force a downshift) I get a harder bump... and then I get after shocks... 2 or 3 more quick bumps after the first one. Now if I do this and try to gain speed or do this on a hill It just keeps bumping and the bumps will get harder until I back off the gas I even feel like a shuddering sometimes between the bumps but the truck will gain speed. It doesn't seem to make a deference how fast I'm going or what gear I'm in I found I can make it do this whenever I take my foot of the gas first then get back into it quick like. It has done it in OD and with OD/OFF and in 3rd and even 2nd gear. Tranny seems to shift fine and run smooth other than this.

Is it normal to feel a bump every time I put my foot back on the gas?
Any Ideas on what this could be? - I'm feeling tranny pains

 

[rrgone]

Is it normal to feel a bump every time I put my foot back on the gas?

Of course not

Any Ideas on what this could be? - I'm feeling tranny pains

Might try my suggestion above.

 

[IPcamper]

You might want to check the drive train U-Joints and the rear differential. A lot of 2003 had differential problems, mine included. I had the rear diff rebuilt at 90,000 due to bad bearings. It would give a mild buck on hitting brakes, and slap the gears on acceleration, and whine like a 747 taking off.

 

[Mustang Guy]

I had a very similar issue with my 2002 XLT that I chased for 6 weeks. It ended up being the DPFE Exhaust Gas Recirculation Feedback Sensor. They cause an engine stumble, hesitation, miss thing when they start to fail but don't throw a code. They are sending bad info to the computer and momentarily dump too much EGR exhaust into the intake causing a very lean condition. It is very easy to install and completely solved my problem. Don't get a parts store brand, stick to Motorcraft only. They are $39.00 on Amazon.