1988 Ranger 2.9L 5spdMitsubishi, 4x4, Manual Tcase and hubs, ext cab, at least 175K miles, owned about 6 months.
Last week I cut off the stupid 1foot long cherry bomb and replaced with an oem style muffler to quiet it down, and new air filter. I pulled the left front spark plug and it looked great so I put it back in without replacing any of them.
Fuel filter is only a few months old.
Around town it runs great. no complaints at all.
Until this week it would run great anywhere, any speed.
Last spring the previous owner went from Colorado to Branson Missouri and back with no issues.
The Problem that started this week is maintaining 75mph on the hiway using only part throttle it will sometimes feel like it is stumbling.
I can get on the hiway and run 5 or 6 miles at 65 with no issues in either 4th or 5th and it runs great. When I get out of town and the speed limit goes up to 75 I can easily accelerate to 75 but when I back off the throttle to maintain 75 is when it sometimes will feel like it is stumbling.
This stumble occurs in either 4th or 5th gear.
Another odd symptom is sometimes when I go down the hiway and it starts stumbling I exit to simply turn around and the return trip at 75 may or may not stumble. Turning around like this I do not stop the truck or turn it off or anything, I simply exit the hiway then get back on again, sometimes it runs great and sometimes it stumbles.
I have ran Gumout injector cleaner through 2 tanks but it does not seem to change the symptom.
Replacing the Throttle Position Sensor was suggested but that did not change the symptom.
Very inconsistent, been wrenching for many years and this is a new issue for me.
I was thinking of replacing the fuel filter again just to see.
I did look through the Chiltons troubleshooting sections but this is not covered anywhere.
Anyone have any thoughts or advice on this?
Thanks in advance.