Rail pressure readings, what do you think? FCA problem?
 

Finally got my quad rail pressure gauge installed. Idle is around 4500 - 5000 psi. Cruising at 60 or so was about 8500... Max I saw while getting on the throttle was about 14500. (Smarty is set on #8, stock supplied software not a beta file).

Here's the weird part, sometimes if I was cruising along and it read 8500 psi, when I let off the throttle, it would then climb to 14500 or 15000 and stay there until I got on the throttle again. (then would drop down very low (maybe down to 1000 psi) and then back up to normal).

This would kind of explain why everytime I get back into the throttle there is a dead spot or about a 1/2 to 1 second delay before the throttle would do anything.

Why is this happening? FCA sticking or drifting open when I let off the throttle?

FYI, GDP kit is supplying the injection pump with between 22 and 25 psi of fuel.

I always felt that I did the diy cp3 that I didnt do it right(even though I explicitly followed the directions) and everytime I had trouble I would think that might be somethin I did to the FCA.

I replaced the fca with a new part after the truck was giving me troubles and I even turned the prv into a rail cap just to eliminate problems.

After all that I sent my pump to John to have it done right.

On a side note. My TST rp always fluctuated like crazy. Thats why I ended up getting the commander.

Are you getting the trouble code 0251 with your low readings? I am, and I think my rail press is lower than it used to be, but not as low as you are seeing. Maybe 15-20k.

Try increasing you GDP pressure. I'm running mine at about 32psi. It might not solve your problem, but it's a pretty inexpensive try.

The CP3 wants no more than 15psi at the inlet - greater than that and the body seals go - pull the hot boxes off and try the engine on the Bosch tune - when rail pressure is too low\too hi for throttle input\rpm\ECT\IAT you should get a rail pressure DTC.

~4500 is good for idle, 12.5-18k is good for cruise, depending on rpm\mph\weight of truck - what's odd is you're not getting any DTC for out-of-spec rail pressure - maybe the Rail Pressure Sensor is erratic, but still should get the DTC's

This is not true.

John

rail pressure
 

At wot you should be between 21.5 and 23.5 stock. You have problems.

[QUOTE=Floor It;1950602]So what did u scoot the bed pan aside and unkink the catheter just so you could get on the forums? Geez John take a break already. I was just about to try to talk this guy into sendin you his cp3. All you need right now is some good relaxing time rebuilding cp3's from your private room in the ER. You'll be recovered in no time.

So my max pressures are low... This kind of explains why in stock form (no smarty I thought it was a dog), with the smarty on 8 it is acceptable (little better than stock).

Until last night I didn't have a vehicle speed signal fed into the engine ECM, which I read somewhere may cause the engine to defuel. Scott at Destroked said I could use either the tranny sensor or the Ford rear end sensor to fix this. The ford wiring was easier to get to so I spliced it in last night along with the rail pressure gauge install. However, it still drives the same and the rail pressure readings sort of prove that it is defueling. I guess I'll have to try the dodge speed signal next and see if it changes any.

I'll check for codes again, but previously I never had a low rail pressure DTC.

How low of a pressure do you guys see with automatics (with a rail gauge obviously) when you slow to a stop. Does it never drop below 4000?

Just on my way home from church this morning with the family, it dropped to around 1000 as we pulled into the driveway...

Hello,

FYI, My idle rp is right around 700 psi. Has never been in the thousands at idle. Running down the highway 14,000 to 18,000 is normal unloaded. Up hills it gets into the 22,000 psi. Pressure rises and falls with pedal and load. Never has raised or remained constant when off the pedal.

Damon

Glad to here that you are ok John. We (I speak for thousands) were all concerned about you. Glad that your ok. Take care and rest up. Hope to see ya in a little while.

Mine never drops below 4000 psi. it is usually 4800-5200 at idle. It definitely should not be 700!

exactly what I was going to say.

you truck is not running with 700 psi of rail pressure maybe 7000 at idle but not 700

Hello,

You are correct. Brain fart. When I first installed the gauge I was misreading it by not multiplying times 10. That info I guess stuck in my head initially. Sorry you are all right. It is 7000 psi. Oops.

Damon