Braggs

The diesel pickup pictured below is a 1985 F-350 with the 6.9L IDI. I have owned it for nearly 1 year. In the last year, I've replaced all the injectors, the rubber fuel lines, and changed the oil, oil filter, fuel filter, and air filter. I also repaired the rear brakes (driver's side was missing anchor pin and all the springs were disconnected).

The question I have is related to performance. This diesel pickup is a dog. It starts fine, runs fine, and is great for nice slow trips. The gearing seems fine too (2 mph idling in 1st, max 55mph in 3rd, and 4th tops out at 85 on level ground). The problem is it can barely hold highway speeds (65-70) going up slight hills and, when I had a 20 ft camper attached, would barely go above 55. There's a little bit of black soot (unburned diesel) in the exhaust when I have it floored, but no color under normal power. It seems to do better if I don't stick my toe into the gas pedal but rather trust the raw torque to maintain speed. If I do stick my toe into it for longer periods of time (like pulling a trailer) it just bogs, slows down, and the temperature climbs to 3/4 of the gauge. Once the temperature rises to this much, it bogs even more and goes even slower.

When the fuel tank is nearly empty, the engine seems to surge with more power which makes me think that it's running too rich normally.

Are the performance issues I am seeing normal for this vehicle? I've never owned a diesel before but they're supposed to be great for towing.

Is it running rich (drowning the engine)? How can I tell if it's running rich/lean?

Johnboy429bbf

Have you checked the fuel pressure after the mechanical pump?

MarionCohrs

check the fuel pressure first.

Braggs

What should the fuel pressures be at before and after the fuel injector pump?