cason234
Registered User
Hi folks, not sure how best to describe this, but here goes: I've got an old 7.3 IDI NA with ZF5 and 4.10 gears (4x4). Don't know how many miles, but I pretty sure it's more than 200,000.
It starts instantly, uses no oil between changes, and runs great. If you shift it below 1800 RPM, it is like a spectacular old tractor. However, if you rev it much higher than that (let's say around 2200 RPM), which you must do if you wish to go 70MPH in 5th gear, it loses its dignity, and starts to sound kind of "thrashy", for lack of a better word. Not a knock, but it just sounds unhappy. I've slipped it into neutral at 70MPH to see if it might be the transmission or transfer case, but the sound goes away as the RPM's drop below 2000. It has done this for the 18 months I've owned it, and it hasn't changed. I've driven it for hours at 70MPH, and it doesn't change.
If this was your truck, where would you start looking? Lifters? Injectors? Injection Pump? (also, how can I be sure this isn't gear rollover from the ZF5?) Or, is this just the nature of a 7.3 IDI? I love the truck, but I'd like to 'smooth things out' if I'm revving it at highway speeds.
If anyone has experienced something similar and found a resolution, please share!
Thank you
It starts instantly, uses no oil between changes, and runs great. If you shift it below 1800 RPM, it is like a spectacular old tractor. However, if you rev it much higher than that (let's say around 2200 RPM), which you must do if you wish to go 70MPH in 5th gear, it loses its dignity, and starts to sound kind of "thrashy", for lack of a better word. Not a knock, but it just sounds unhappy. I've slipped it into neutral at 70MPH to see if it might be the transmission or transfer case, but the sound goes away as the RPM's drop below 2000. It has done this for the 18 months I've owned it, and it hasn't changed. I've driven it for hours at 70MPH, and it doesn't change.
If this was your truck, where would you start looking? Lifters? Injectors? Injection Pump? (also, how can I be sure this isn't gear rollover from the ZF5?) Or, is this just the nature of a 7.3 IDI? I love the truck, but I'd like to 'smooth things out' if I'm revving it at highway speeds.
If anyone has experienced something similar and found a resolution, please share!
Thank you