Jon Schwenke
Registered User
Hey guys, I'm in the final stages ( I hope) of diagnosing some issues I've been having, and need some input from the more experienced. 1992 f250 7.3 idi NA. I have a loping rough idle, worse when at operating temp feels like air intrusion, but I'm pretty certain it's not. After high idle disengages the RPMs are 700 ish. The RPM gauge bounces ever so slightly in time with the surges. In addition, sometimes when at operating temp my transmission will freak out, throw a code (vss related) and then continue to waffle between which gear it wants to be in with the occasional position of none. I'm not sure the issues are related, but I'm laying it all out there. The engine starts well cold and hot (better hot). No visible fuel leaks, no visible air in lines as I plumbed in clear tubing after lift pump, after filter housing, at tank return line, and top of IP at overflow. Minimal smoke at startup, no bubbles in coolant reservoir, doesn't lose coolant.
It could be IP failing as its maybe 150k mi+, but it starts well and doesn't seem to lose power when driving. I'm leaning towards pump timing (if it's IP related) or possibly a bad torque converter. Maybe exhaust leaks? Would that cause rough idle? Please help!!! After reading all of this tell me what you think and where you think my efforts are best focused, and/or if there is anything else I should check / test.
List of mods, repairs, tests (not all were done to chase this problem)
New reman injectors (pop tested within acceptable specs 110 - 125 bar)
new return lines (includes o-rings and caps)
new fuel filter
new air filter
clear fuel lines to check for air bubbles ( no bubbles)
new and properly adjusted neutral safety switch
tested cam shaft sensor
tested vss in diff
20331 Dura-Lift electronic fuel pump
cracked each injector line while running (all get fuel, all change idle condition)
Adjusted TPS to be within spec
changed trans fluid / filter, filled with Napa dex/merc
New throttle cable
New water pump
It could be IP failing as its maybe 150k mi+, but it starts well and doesn't seem to lose power when driving. I'm leaning towards pump timing (if it's IP related) or possibly a bad torque converter. Maybe exhaust leaks? Would that cause rough idle? Please help!!! After reading all of this tell me what you think and where you think my efforts are best focused, and/or if there is anything else I should check / test.
List of mods, repairs, tests (not all were done to chase this problem)
New reman injectors (pop tested within acceptable specs 110 - 125 bar)
new return lines (includes o-rings and caps)
new fuel filter
new air filter
clear fuel lines to check for air bubbles ( no bubbles)
new and properly adjusted neutral safety switch
tested cam shaft sensor
tested vss in diff
20331 Dura-Lift electronic fuel pump
cracked each injector line while running (all get fuel, all change idle condition)
Adjusted TPS to be within spec
changed trans fluid / filter, filled with Napa dex/merc
New throttle cable
New water pump
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