You problem isn't real clear. Can you restate it? You can't maintain speed going downhill? Is the check engine light on? Does it downshift when in fifth?

 

yes i can not maintain speed going down most hills. alomost feels like my trailer brakes are locked but they arent. my truck has to down shift when i want to speed up so it does like normal and as soon as fifth gear engages i slow back down. i had to do this trip in fourth at 52mph instead of 65.ive never hooked my ppe standard up while towing but like i said i hooked it up last wekend and at wot i saw 9k fuel pressure. not sure if that is normal ive read that some of these guys are hitting 16k fuel pressure.

 

no check engine light. i have had the p1093 code a few times but not while i was towing.

 

If you can, read the codes, both current and historical, and advise us.
What RPM will it run to, 3200 or what?
3200 in fourth is about 80 MPH, no need to fiddle around.. Seriously, we need more info to think about what your problem is.
If you roll slowly into the throttle, and monitor the rail pressure, will it dip and recover? What range versus RPM is your rail pressure? What does the rail pressure do when you come off the throttle and how quickly does it do it? Look for about 5,000 PSI at idle no throttle, to 23,000 at 3200 RPM and light throttle. May dip at WOT and lug down.
Does it pull like a bear to 2000 RPM? Then limp, or govern at that RPM? Then only shift up if you lift your foot off the throttle pedal?
Or is it only using third gear? You would know, it will hardly lift off the line, and run a max of 53 MPH at 3200 RPM. Through all this do you feel it shift?

 

Subscribing... Just curious if you've changed your fuel filter. I had the same problem on my truck, just after 500 miles on the new filter.....It seems I got a batch of bad fuel.....Once I changed the fuel filter again the truck ran fine...

 

just took the truck out and had my buddy read the pressures to me as i drove. i went through all the gears at regular speed first then wot through all the gears. fuel psi never went above 9500 psi. it was pretty consistent between 7500 and 9500 the whole time. could this be why my truck doesnt pull in fifth gear?

 

and yes i have changed the fuel filter recently but this problem has been ongoing for a while so ive actually changed it a few times.

 

the only code i get that i know of is p1093

 

Check all of the rubber lines from the tank to the CP3. Look for any that are soft and/or collapsed. The section near the transmission is known for collapsing under a large fuel demand. There is a section up on the engine too.

 

thanks ill check those right now

 

dont appear to be any fuel lines that have collapsed

 

Did you squeeze them to see if they were soft?

 

Have you bottle tested the FPRV. Mine failed on my '05 LLY C5500 at 41k miles.

 

yes all the lines i could see were squeezed. and no i havent bottel tested it. i imaine the rubber hose connected to the fprv would need to be disconnected and then secured in a bottle? how far should i drive it and what kind of load?

 

Bottle test http://www.kennedydiesel.com/docs/Shim mod Bottle Test etc.htm

 

Bottle test http://www.kennedydiesel.com/docs/Shim mod Bottle Test etc.htm

thanks im going to do this next saturday morning and see if it is leaking. i will let you know

 

if it is leaking what is the best course of action? i have read on here that sometimes a new valve will also leak. should i just do the shims? if so what size washers do i need to buy?

 

Just bottle test it and buy/install an FPRV shim kit for good measure (every vendor on here will carry it).......9k is very low rail pressure for sure.

 

The valve leaks because the seat gets worn. No amount of shims can correct that. Buy a new stock, or modded, FPRV, if it's leaking. Kennedy offers shimmed and stock.

 

The valve leaks because the seat gets worn. No amount of shims can correct that. Buy a new stock, or modded, FPRV if it's leaking. Kennedy offers shimmed and stock.

great advice from everyone. i imagine the seat will be visibly worn if that is whats causing it. other wise will be the spring. i will check with kennedy and see how much the modded one is. if my relief valve isnt the prob then the next step would be tomove on to the pressure regulator i would imagine. thanks again everyone and sorry for the dumb q's.

 

Most of the seats get damaged by people during the shimming process (they ruin the sealing surface on the FPRV when compressing it during reassembly....use a piece of wood to protect the surface and you'll be fine). Occasionally you will have a totally worn out spring or seat damaged from wear but those would be the exception not the rule IMHO.

If you need a new one, then get a brand new one for an LBZ which is set at higher pressure stock:
http://www.hdiesel.com/P/LCommonRailHighPressureReliefValve/517

 

Every other question you have can wait UNTIL you see the results of the bottle test.

 

did bottle test and no fuel in the bottle. there was a bit of fuel in the hose when i first disconnected it though. the desired pressure is 9000 though and that seems to be what it is hitting but at wot shouldnt it be higher?

 

On mine, cold idle FP is around 6000 PSI, warmed up is around 4500 PSI and just about any blip of the throttle takes it to 15-16kPSI. When driving, just about any significant throttle change will take it to 23k (max). It seems the PCM is programmed to ramp up the pressure fast with any indication you want more power. It's very pressure happy.

I would think you should see well over 9000 PSI doing anything other than idling or very lite cruise. But what you need to know is what the PCM is commanding. That requires a scanner than can both read desired and actual fuel pressure. If you can read the actually, then what is it demanding?

If the actual isn't within 400 PSI of demand (at a steady throttle) then the regulator is the likely culprit.

 

not sure how accurate it is but im using the ppe standard tuner to see what my commanded and actual pressures are. commanded never goes above 9k psi and usually the actual is very close to the commanded value.

 

It will be accurate enough for diagnosis. So it's not even trying. Hmmm. In reading the P1093 error, if the difference between commanded and actual is too great, the PCM will stop trying to get the higher pressures and reduce the power. It looks like it's done by limiting the fuel pressure ... so, that P1093 could be why you are limited to 9000 PSI. But why are you getting the delta. Is it not tracking at higher pressures but ok at lower pressures? I don't know.

Conditions for Setting the DTC

The difference between the commanded fuel pressure and the actual fuel pressure is more than 20 MPa.
OR
The FRP regulator fuel flow is more than 19 200 mm³ at 800 RPM, or more than 44 400 mm³ at 2,000 RPM.
The engine will be in reduced power mode to replace using no more than 2,000 RPM.



Diagnostic Aids

• This DTC does not set for an idle condition.
• The following are some conditions that may cause DTC P0087 and DTC P1093 to set:
  • Excessive fuel return to the tank
  • A fuel injection pump failure
  • A fuel pressure regulator (RPCV) failure
• If you have to prime the fuel system, inspect for the following conditions:
  • A restricted fuel supply line
  • A fuel supply line air leak--Refer to Fuel System Diagnosis .
• A sticking fuel pressure regulator may set this DTC. Refer to Fuel System Diagnosis - High Pressure Side . Perform this test under the conditions for which the DTC set.
• If power enhancing devices have been attached to the fuel rail pressure sensor circuits, this DTC may set and adversely effect the fuel system components. Refer to Fuel System Diagnosis - High Pressure Side .
• If the condition is still intermittent, refer to Intermittent Conditions .

Also, high fuel temps can set a P1093 but the manual says it will also throw a P0168 (which doesn't mean the fuel temps are actually high but the sensor is dorked up telling the PCM the fuel temps are at or above 252F. More of an indication the sensor is messed up.)

If you send me an email, I will send the P1093 troubleshooting tree.

 

I removed my ppe from the truck last night. When I went for the test ride my pressure maintained 7kpsi. So a 2k drop. I will try to get the sensors tested tonight. Terryk, my email is doodlebug091979@hotmail.com. Thanks for the help everybody.

 

I removed my ppe from the truck last night. When I went for the test ride my pressure maintained 7kpsi. So a 2k drop. I will try to get the sensors tested tonight. Terryk, my email is doodlebug091979@hotmail.com. Thanks for the help everybody.

Did the commanded pressure drop too?

Too bad you don't have EFI so we could see a log of what's going on.

 

ok i went for a long ride today and noticed that on the freeway at 70mph my pressure drops and stay around 4kpsi.if i try to accelerate then it drops around 500 and stays there until i no longer want to accelerate. also while at idle 4 (2,6,7,8)of my injector balance rates are 8 or more while the others are around 6.5 to 7. i also took the fitch off might cut it up and see whats inside.

 

yes i have cleared it a few times actually. i think twice over the last couple months but the truck never drives any better. i just recently learned about the fuel pressure on these trucks and got curious. ive had thi truck for 6 years and never really noticed a big change in performance until i bought that rv. but anyway i would like to post the video if someone would enlighten me as tothe process.never tried it before so i dont know where to start.

 

Here it is.