Miss from idle to 200ish rpm

[slowstang88]

1999 Mountaineer 5.0. So I have a miss (difficult to detect at exhaust) but the engine vibrates until about 2000rpm. Also under load (in gear holding brake) its pretty obvious. Ive replaced the plugs, wires, checked firing order against cylinder numbering, there is a code for IAT, but nothing else. Previous owner changed the fuel pump, filter, all 4 o2 sensors, MAF, a whole bunch of parts trying to fix the problem. I also tested fuel pressure, KOEO- 5psi, priming 3 or 4 times yielded 30psi, KOER- 45psi and after shutting it off bleeds down to 0 in about 45 seconds, so theres one more problem and I just filled the tank... I need this thing running good ASAP for a DD, please help!!!!

 

[slowstang88]

I actually meant 2000ish rpm. I just took the EGR valve out and checked it, the valve is seated and the diaphragm is intact but at idle there is vacuum on the hos going to the EGR valve, is there supposed to be any vac at idle? I also checked the PCV valve and it doesn't seem to be seated very tight in the lower intake, should it be fairly snug? It don't seem have a grommet in the intake manifold.

 

[slowstang88]

I cranked the engine today and heard what sounded like a thin liquid dripping that coincided with the fuel pressure dropping when I shut it off, sounds like it's in the intake.. Would a stuck open injector cause a low rpm miss? I know it would definitely cause rapid loss of fuel pressure when the engine is shut off

 

[Turdle]

In regards to your issue, I would like to see video proof of a v8 return style explorer fuel system holding pressure when the key is switched off. I think the drop is normal. I experienced it when I replaced the whole fuel system on our 98 mounty.
New 42lb injectors, Aeromotive rails and regulator-bbk fuel pump and high pressure lines--all new and I still saw this same bleed down when the engine was shut off.

The fuel pressure is vacuum controlled. I believe when vacuum is lost the regulator lets the return line bleed off.

However, do you see a slight loss of coolant?

Did the problem arise after the new spark plugs? You might remove them again, and place them in order to see if you can tell a difference in color, this might help ---

 

[slowstang88]

In regards to your issue, I would like to see video proof of a v8 return style explorer fuel system holding pressure when the key is switched off. I think the drop is normal. I experienced it when I replaced the whole fuel system on our 98 mounty.
New 42lb injectors, Aeromotive rails and regulator-bbk fuel pump and high pressure lines--all new and I still saw this same bleed down when the engine was shut off.

The fuel pressure is vacuum controlled. I believe when vacuum is lost the regulator lets the return line bleed off.

However, do you see a slight loss of coolant?

Did the problem arise after the new spark plugs? You might remove them again, and place them in order to see if you can tell a difference in color, this might help ---

I was under the impression that they were returnless fuel systems and therefore not vacuum controlled. I did change the plugs and have taken them all out to check them, typical coloring on them but number 3 was a little bit wet and smelled like gas. When I say the pressure bleeds down fast, I mean REALLY FAST after shutdown. After hearing liquid dripping after shutdown, I'm kind of inclined to think number 3 is stuck open, your thoughts?

 

[Turdle]

Ooops, yes you are correct your 99 is returnless.

I wonder if you could check this with air pressure aplied to the fuel rail and the #3 plug removed?If it was stuck open, it should hiss loudly I would think

Be sure to regulate the pressure down to 50 psi or so.

 

[slowstang88]

Ooops, yes you are correct your 99 is returnless.

I wonder if you could check this with air pressure aplied to the fuel rail and the #3 plug removed?If it was stuck open, it should hiss loudly I would think

Be sure to regulate the pressure down to 50 psi or so.

Thats what I'm gonna try, just don't want to remove the upper intake to get to the rail... lol.. I'm sure a lot of people look at them and grumble, the 5.0 is a tight fit in these things... Would a leaky injector cause a miss? I pulled the plug wire off for #3 while it was idling and it didnt really change much, pulled it off at the coil, put it back on, then the plug boot and same thing and its getting fire for sure cause the spark is jumping a 2-3" gap and it bit me bad!