Possible "stump the chump" Ford Explorer bump?

Posted about this last December - issue getting more frequent.
I have a very well maintained 1998 Ford Explorer 4.0 SOHC 4X4 with only 67,000 miles. Sometimes at highway speeds ( 65MPH ) there is a fairly pronounced bump / jerk. I will also happen occasionally when accelerating from a stop. IMHO, it’s not a slip. Fluid has been flushed and is bright red. The best I can tell the RPMs are not jumping when this happens. I’ve all but counted out an engine misfire. There are no engine or OD light on.
Can someone tell me where I should begin troubleshooting? I don’t want to spend tons of money trying to isolate the issue but this Explorer is in exceptional condition so I want to have it fixed. Thanks so much.

When you say bump/jerk do you mean basically the engine is “hiccuping” or is it a physical, tire/suspension related bump/jerk?

If its engine related Id start with a tune up. You could have some old fouled up spark plugs. You could have old, failing spark plug wires or coils. It might be a clogged up fuel injector (although I doubt it).

Thanks Fender … the best I can tell the problem is not fuel sending / engine related. The fuel system has recently been cleaned at the dealer ( problem was there before the cleaning ). Plugs are wires appear fine. Checked at night time and no signs of external sparking from the wires.

Tough to say. If a plug, wire, or coil was going bad I dont know that itd be visible to the naked eye. However, if one of those was bad youd likely have the problem more than just at one speed. How is the start up and idle? Really, your electrical and fuel systems need to be fully gone through and properly tested to elimnate each possible thing. With that low of miles and good maintenace, I doubt a transmission problem. Really what youve got against you here is age. Has this been happening for a while or just kind of recently? Could be some bad gas. You said a problem was there before the cleaning of the fuel system? Maybe they didnt clean it well enough. With that low mileage and old year, this car has sat around a lot. I bet your problem is still fuel related, and if not that then your electrical system. Lets see what others say when they chime in.

When I think about it, take off from a stop, and going down the highway are both conditions where you require more fuel. Fuel pump, fuel filter, pressure regulator, injectors are all at question in my mind. Did this car sit for an extended period of time?

Check the bolts on the driveshaft at the rear axle. These came loose on a friend’s Explorer and caused a weird bump.

Fender - I have owed the Explorer about 10 months and been happening a while. The original owner indicated the car had sat for extended periods and would only take in a road trip once a year. The problem was apparent even before the system was cleaned. Maybe I can have someone check the fuel pressure? If it is fuel related would the RPMS drop? I have not noticed the RPMs drop, but it happens so suddenly and short lived I may not be looking at the guage at the right moment. Thanks for the replies!

Even if its fuel related, it sounds like the engine is stuttering, it would be too quick for the RPMs to have a chance to visibly drop.

I agree to also check the driveshaft for loose bolts or play. Although my guess would be that you’d have an audible clunk on take off or a consistent shutter if that were the case. Did the previous owner tow with it? That could lead to possible wear in the drive line, but right now, with the fact that it was used very little, my moneys on a fuel system related issue.

Honestly, unless you’re mechanically inclined yourself, Id take it to a good local shop, describe the issue and have them test out the fuel system, checking for pressure and any clogs, etc. Or, because you paid the dealer to clean the system already, I might take it back and ask the pressure to be tested. Your fuel tank should have been dropped and emptied and cleaned. There is a sock-like filter in the outlet likely and that can get clogged as well. Your fuel filter should be replaced. Your fuel pump and pressure should be checked. Your injectors should be checked. It could be a little piece of dirt or something gummed up thats causing this intermittent stutter. Really, that all should have been gone through and done if you paid the dealer to clean the whole system. What they likely may have done is just run a concentrated fuel system cleaner through, but not taken anything apart and actually cleaned it. Which is not good enough for a car thats sat around for extended periods of time. That tank really should be removed and cleaned out in my opinion. Until each thing in the system has been cleaned and checked out you cant rule it out.

Nice comprehensive suggestions – thank you very much - I will have fuel related issues checked before the drivetrain.