Acceleration Hiccups/Shutters On HWY During 4th Gear Acceleration, above 45 mph.
I own a 1992 Jeep Cherokee Laredo, 2WD with the 4L engine and have been utterly astounded at how reliable and amazing this car has been over the years. I bought it used from original owners and will drive it to the ground before I consider anything else.
At just over 205,000 miles I've only had to keep up with general maintenance and a few minor fixes here and there, most notably I had some recurring overheating / antifreeze leak issues in the past but for a little over a year now have been successfully fixed, Replaced, thermostat, hoses, water pump, radiator, etc (ended up having a cracked thermostat housing and once I replaced that there has been no issues).
That has been the only major mechanical issue I can recall. Aside from when my neighbor backed her car out of her driveway and into my drivers side door, nothing has been seriously wrong, and tune-ups and oil / fluid changes have been the norm. Since getting rammed into by the soccer mom, the Jeep has had little electrical quirks, but nothing serious and almost everything seemed to work itself out eventually and the only electrical items not working now are the rear wipers, cruise control unit and the overhead compass/temp gauge (none of this could really be linked to the side swipe incident but worth noting).
So within the past two or three months, I've noticed that upon acceleration on the highway (above 45 mph) the jeep hiccups or lurches or shutters (insert layman's descriptor for what feels like a sudden lack of acceleration) about 2, 5 , 8 and maybe sometimes even 10 times in a row. Like a thump thump vrooo thumppp vroommm. They are short and bursty and only happen if I'm slightly accelerating within the high gear (have only noticed it in 4th gear, automatic trans). If I mash the pedal, the transmission will down shift and it all goes away (or feels that way). The hiccups never happen when I coast, and if it's happening, when I let off the gas pedal, it coasts and the hiccups stop. Once I reach a cruise speed, the hiccups go away, and sometime I try and see if I can keep them going, but they do eventually disappear, I think that's because I eventually have to stop accelerating. There are no noticeable rpm fluctuations when it hiccups. It's more noticeable when pointed uphill but I guess that's because gravity is working against my acceleration, seeing that it'll sometimes hiccup when I'm pointed down hill too. Also worth mentioning is that when driving around town (non hwy, using mostly gears 1-3 I assume, 30 mph tops) it never happens or is at least unnoticeable.
At first I thought it was water in gas becasue I drove around for a few hours in the rain with cap off and gas door open (yeah, not very proud of that one...) but I've added plenty of additive, gas cleaner, and filled up many a time since then (over 3 month ago), not to mention I've narrowed down the driving conditions enough to know what to do to create a hiccup now.
I replaced the fuel filter, (initial assumption after water in tank idea)
I had a mechanic test the fuel line pressure and fuel pump
-all good or at least appears to be fine, however has always made an annoying whining noise.
I changed the tps after researching on the web and seeing how that could be realted
I did notice that after driving today to diagnose whether or not the new tps made a difference, the temp gauge on the dash said I was idling a little hotter than normal (just about a 1/4 past the midline, mind you it was a warm day, it was rush hour, but also idled hot when I parked at home).
Other Ideas after more internet research and talking with friends, but have yet to try...
-a tuneup (I drove from California to Georgia since my last one and will pop the hood and ***** the condition of the plugs, etc this weekend?
-some vacuum line issue somewhere???
-grounding / electrical issue???
As a side note, today I did look at the o2 sensor. I remember that I replaced it some time ago, could have been more than 50,000 miles, but also likely it was less than that, Maybe the overheating issue last year killed it early? Just as a test today, I unplugged it (the o2 sensor) from the harness and was surprised to see that no check engine or maintenance light switched on when I started up the car and idled for few minutes (o2 sensor unplugged!), the dash light never turned on? However, the smell of exhaust was very pronounced for such a short time. Makes me wonder if it's throwing codes and trying to trigger the corresponding dash light but something (bulb maybe) is out. When I turn the key halfway, the lights on the dash that I see are "brake" and "check engine," nothing else on that far left panel shows up for that second after turning the key halfway, and if i remember correctly there is suppose to be a "maintenance required" light too??
I've read through many forums to try and self diagnose my problem and tried a number of suggestions without any luck yet. I'm hoping I have a few extra descriptions that might help widdle down potential culprits. There seems to be a plethora of Jeep experts on this forum. Any help would be greatly appreciated. I'l be updating my progress and posting any fix I come across. I'm aiming for the +350,000 mile mark with this one. Crossing my fingers.
Thanks in advance!