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No Start, Low ICP

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I got an late 04 F-550 with 120,000 miles on it. Had a P2290 stored in it. It's been siting outside for about 24 hours. When I crank it I get between 500 and 600 of ICP pressure and the ipr stays at 85%, but it will not start. It sounds like it's trying to, but won't. If I remove the FICM relay the icp builds normally (I saw up to 2200 psi) and the ipr starts backing down. I put the FICM relay back in and started unplugging injectors 2 at a time. I've been through all 8 injectors and can't get the icp to build enough to let it start. I currently have the back 4 cylinders unplugged and it still won't build icp. Recent history indicates that we replaced injectors 1,4 and 8 back in June of 2015. I'm planning on dragging it inside in the morning and unplugging the 5 old injectors and seeing what happens. I don't suspect a pump because of the fact that it builds pressure like normal with the ficm relay out, plus the icp is steady while it's pumping. All the hpop's that I've replaced where always had really jaged icp on the dataloger.

 

Anyone have any thoughts?

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First thing I think of is a weak hpop, especially since it's an 04.  I have had a handful of the textbook sawtooth ICP no starts but then again I have had a few bad pumps that didn't do that. 

 

The last one I had would start and run at like 3-400 RPM, IPR was maxed out and ICP was just barely enough to stay alive with no load on the engine.  Drop it in gear and it would die.  Checked the IPR, swapped it out with a known good, no change.  Put a pump in it and it was fine.  Also had one the pump body was cracked, it ran fine but wouldn't hold desired ICP under load. 

 

I have not had injectors that would cause low ICP when cold unless it was one with a completely blown out top o-ring.  You could try air checking it with the oil filter cap off, that seems to be a good tell for a bad hpop. 

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I didn't come up with anything 100% conclusive. I dragged it this morning and air tested it through the icp sensor hole. I pulled the oil filter out and left it for about a half hour before I closed the ipr and I didn't find any air coming out of the filter housing. I then put the icp sensor back in and cranked it over with just 1 injector plugged in, then I unplugged that one and switched to one of the new ones and got the same results.

 

We ordered a high pressure pump.

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