I have a 1990 isuzunpr 4bd1t diesel.Truck won't stay running.It is a fuel issue.Drained water seperator,changed fuel filter,cleaned inline screen before the primer pump.Had primer pump rebuilt.Replaced fuel lines.After some of these items were done truck would start idle for 15-20 min seem good,then try to drive would run normal for 5 to 10 min.then start loosing power as if running out of fuel.HELP HELP ?Got me confused

if it aint broke don't fix it

Unscrew the filter canister and check for debris. If you haven't changed the fuel filter in a while it would be a good idea to do that as well.

should be a primer on fuel filtere

simple,you are getting water into the fuel tank,few possibles 1st the seal has gone on the fuel filler cap,2nd the fuel filler neck pipe is corroded. replace these parts,get the fuel tank drained clean out all the muck,blow the fuel lines with air,fit new filters clean carb ,id advise also bypassing fuel vapour seperator and fit a new fuel pump and whilst your there change the carp flange gasket....this will sort everything.

JUST DRAIN OUT GASOLINE IN FUEL TANK.CHANGE FUEL FILTER AND.FILL UP TANK WITH DIESEL FUEL. ENGINE WILL RUN ROUGH UNTIL ALL GASOLINE LEAVES THE FUEL LINES.

These trucks are very prone to fuel blockages and leaks. I have an 84 w/6.9L, check the water seperator.......it is located toward the back of the drivers fender near the firewall. Look everywhere for any wet spots, and also be sure to change the fuel filter. When you have the filter changed, and you have triple checked the water seperator, you will notice a valve on the side of the housing for the fuel filter. You can take a small screwdriver and depress this valve (looks like tire valve) and see if it spits fuel.....also if and when you get it running run about 2 or 3 quarts of Automatic trans fluid through with your diesel, works wonders. I usually run a quart with every fill up......the additives and cleaners in the trans fluid clean your injector pump out and release any debris. Also trans fluid is burnable just like diesel...........let me know if you need anything else. I had a few other issues with my truck as well.........AJ

fuel filter or water seperature?

yes, on engine.base part #9155, Item #40, big round thing in picture

SECTION 303-04C: Fuel Charging and Controls — 7.3L Diesel 2000 F-Super Duty/Excursion/Motorhome Chassis Workshop Manual
DESCRIPTION AND OPERATION Fuel Charging And Controls Fuel System
The fuel system used on the 7.3L direct injection (DI) turbo diesel engine is controlled by the powertrain control module (PCM) (12A650).
The fuel system components consist of:

• electric inline fuel pump (9350).
• high-pressure oil pump.
• fuel filter (9155).
• oil pressure regulator.
• oil pressure sensor.
• fuel pressure regulator (9C968).
• high-pressure oil pump reservoir.
• water in fuel switch/fuel heater thermostat.

Fuel System Components

CHANGING THE FILTER ON FOUR DIESEL WILL only HELP IT-- SOUNDS AS IF YOU HAVE A FUEL SUPPLY OR CONTAMINATION PROBLEM both go through the FILTER so When Changing Filter Try to keep as Full As Possible and Pour into a GLASS Jar let it sit for 10-20 mins. Then you can see the Water (IF ANY) on TOP of the fuel, if you Find Water and Your tank is Low Top Off with DIESEL FUEL this Should Solve your Problem Fuel Filter Must Be REPLACED as Contamints can stow away in it, Bio is Good Both Ecologicly and >>CLEAN will Burn Well > FLUSHING with CLEAN DIESEL FUEL is a good Idea., A VALVE ADJUSTMENT if not performed in a long time or many miles, This can Do Wonders for Your Diesel I hope this helps you with your T L C Have a Good Day and if im Worthy RATE me Accordingly. Thank You, RejakWilson

It was as simple as changing the fuel filters. I change them regularly but never experienced a symtom like this, must have gotten a few bad loads of fuel. I used a clean clear 2 gallon container and drained the water seporator first (located in the chassis rail under the driver floor, (7mm. allen key) about 2 quarts came out slowly because I did not remove the plug completly until it was empty,(10 minutes on level ground) then removed the water seporator filter, pain in the *** with 4 whheel drive.
Removed old filter and used a whole can of brake parts cleaner in allen key hole as well as filter orfice, lots of rust, debri, and muck. That was not enough I whiped out filter housing (messey) and put a small magnet into the water drain several times until clear.Reinstalled new filter and water drain plug. Turned ignition to on position and listen to fuel pump prime up until it stopped,(about a minute or two) started the engine
and let run for one minute, shut down and changed the filter under the hood. It's important to do it that way because after cleaning all the gunk out of the water seperator filter the left residue will collect into the fuel injection filter. Results were awsome. Like a new truck. Never expected it to be a filter problem because I service it regular.P.S. the clear container contained no water, but rust, dirt, and alot of algie.