1998 F-350 start and running problems

patrick122

Hi i have a 1988 ford f350 dually 7.5L 460 xlt Lariat 2wd. When i start the engine the Motor speed is jumping from 600 RPM to 900 RPM up and down after a few seconds the engine goes out. When i hold the gas pedal by over 800, 900 RPM the engine is running but when its comes under 800 RPM goes out. I drive in the city and must brake on the traffic light is red than it comes nearly the 800 RPM the truck Pushes and rock and then its out. The truck has not a catalyst.

I have replaced spark plugs and electric spark wires, change all oil fluids, Ignition distributors, fuel pump, air filter ago one year the fuel filter has changed ago 1,5 years and ago 5 weeks I have changed the Idle valve, O2 sensor, and the fuel Pressure regulator.

anybody now´s what is wrong with the truck what can it be?

thecardoc3

Not without testing and proving what is going on. Your 1988 truck has computer controls on it that while primitive by today's standards still offered onboard diagnostics and fuel control. Diagnostics would start by pulling codes (you must use a scan tool) and then use the scan tool to run the KOEO (key on engine off) and KOER (key on engine running) tests and see what on demand codes are generated. From there all of the testing is done totally by hand. This system would generate some scan data and an appropriate scan tool will display it.

It does not have a misfire counter system so you have to identify which cylinders are misfiring yourself.

FWIW, you could have a vacuum leak. Restricted or leaking injectors. An engine mechanical issue or dozens of other possible issues and combinations. You need to be able to test and narrow the focus.