For sometime now I have had a engine miss under 1400 rpm that has steadily gotten worse. When it first started I had injectors cleaned and pop pressure adjusted and replaced delivery valve washers at the same time. Engine ran smooth for about 500 mile then it started missing again. Fuel pressure is 25 at idle and 35 at high idle. Have tried cracking injection lines to find bad cylinder best I could tell it was #5. Pulled #5 and #4 injector and pop tested they had great spray pattern and pop pressure. Reinstalled the injectors but swapped location still had a miss at what sounded like #5. Have been told that a leaky delivery valve could cause this but I have replaced washers twice and hooked injector tested to delivery valve holder and put 3000psi on it and it didn't leak off at all. Also I have ran the fuel system from a jug of fuel hooked directly to pump inlet still same problem.

 

What year/hp rating is the pump? the 160 pumps have been know to miss in the lower rpm range. my original 160 pump missed and stuttered at 12 to 13 hundred rpm.

 

The truck is a 1994 175 hp, the only modifications are 100 plate and 3k springs. It hasn't always done this it started not long after I bought it 3 yrs ago.

 

Anybody else with the same injection pump had this problem and found the cure?

 

Many times after hp modifications are done the timing will slip since the IP is having to work harder.
Might be wise to have the timing checked.
15-16 is a good number to shoot for.

 

I have a timing kit and have checked it twice since I advanced it to 17. It hasn't moved in 30,000mi.