Scotty

At least I think thats what its called. There was a guy stopped on the hwy a few weeks back and I helped him get to a dealer. I just found out it was not his lift pump but as he described it, a return valve in the Common Rail of the truck.
what is the proper name for this?
The dealer said that this can mimic a faulty lift pump showing low fuel pressures, stumbles like a bad injector and/or no start.

Scotty

J BODY

Are you talking about the pressure limiting valve? or the electronic fuel control actuator? The psi limit valve is on the rail and is designed as an emergency "pop off" in case there is excessive rail pressure. It will only allow fuel to pass a few times before it fails as the excessive rail psi will actually cut the seat of the valve allowing it to leak and cause a no start or very poor drivability. The efc actuator is on the high pressure pump and is a solenoid controlled by the ecm to control the amount of fuel that enters the high pressure pumping chambers. I've seen these fail and basically return all the fuel back to the tank.

Scotty

Thats it! The pressure limiting valve.

Dealer said they have had more and more popping up.
their comment was some had fueling boxes but most were stock.

I read somewhere that there was some that were deemed to be defective that got out on some trucks too.

thanks for the correct name.

Scotty

SuperGewl

Sure let DC balme it on the boxes. We all know nothing ever goes wrong with a DC product it has to be somthing we did or added, that's why DC gives us a lifetime warranty on our trucks

silver_goat

Is the efc in the CP3 pump or attached to it? I am also wondering if it is between the pump and the rail?

J BODY

Silvergoat the efc is attached to the CP. It's the black object bolted to the back of the pump with the wiring connector. By unhooking the connector with the truck running you can run your fuel rail psi to the moon and see how long your pressure limiting valve will last (..don't do this!!)

Supergewl, the only efc I've replaced was on a modded truck.....go figure. Alot of the early performance mods admitted raising the rail psi to increase performance. So you have a safety valve on your fuel rail and you add a box that pushes the limit closer to that threshhold.....dancing with the devil wouldn't you say? If you don't like that statistic consider this. We just got a towed in 03 banks equipped truck with a scored #4 cylinder. We've replaced five CTDs in the last seven years and every one of them has been modded. Bombed: 5 Stock: 0 Interesting odds wouldn't you say? I'm not saying stock engines don't fail, but adding "go fast" items can indeed increase your chances of failure. Your owners manual has a fancy way of saying "if you want to play.....expect to play".

big red psd cc

Had mine replaced...

Hounddog

Theres been a number of reported engine failure due to faulty injectors on stock trucks.One post only had 500 miles and had a hole blow torched threw a piston while the TECH and SHOP FOREMAN were on a test drive with owner waiting in the write up lane.eaither on this forum or TDR.One post was with aftermarket injectors and did same thing.

silver_goat

J Body,

Thanks for the detailed info. I plan on taking my truck to the dealer to check an uneven idle that I am having. Is the EFC something they should look at for this. I spoke to the Service Manager and they did seem to know what I was talking about.

CTDHokie

Where is this pop off valve located on the fuel rail? I've looked and I don't see it. I assume it returns its fuel to the fuel tank when it pops?

doug

the pop-off, pressure limiting, or pressure relief valve is a spring loaded plunger device mounted directly onto the rail. It is designed to allow short duration rail pressures equal to its set point. Bosch calls it the pressure limiter valve. My investigations to date are not rigorously established but compelling none the less. My thinking is:

1. there may be considerable variability in spring tolerance. some will pop-off before another will.

2. It takes about 1,000 PSI increase in maximum rail pressure to make a peak rear wheel horsepower gain in the twelve too very very (very) low teens region. At that rate, 100HP requires well over 30,000 PSI from pressure fooling.

3. There was some work at Edge suggesting that the set point is about 28,000 PSI. Hence their 65 RWHP recommendation. [on edit: interestingly enough, my measurements agree precisely with these numbers ]. That means agressive pressure boxes either pop the valve, or else the ECM helps things out a bit by adding duration and timing when presented with a low rail pressure situation. [ on edit: or both].

4. any way you look at it, a pressure box increases the probability of pop-off valve failure. The valve is not designed for continuous use, althought I have heard of guys opening them up and shimming the spring.

5. The device itself is located just to the right of the rail pressure sender. it has a banjo on the top and returns fuel from the rail into the low-pressure side.

6. don't confuse the pressure limiter valve on the rail with what Bosch calls the pressure control valve on the CP3. The latter is pulse-width modulated and is designed for continuous duty use to deliver the pressure requested by the ECM. The former is desiged as a safety device and represents the design limits of the rail.

7. pressure limiter valves are like injectors. increased pressure accelerates failure. DC is only obligated to replace a part under warranty that is subjected to stock level stresses. they are not obligated to replace a part that has been subjected to higher than stock stresses.

8. I don't doubt for a minute that some pressure relief valves (stock) would be shipped with weak springs or faulty ball valves. That just makes the concept of raising rail pressure even more exciting (risky) in terms of approaching the set point of the valve.

9. When the valve pops it bleeds excess fuel from the rail into the low pressure side. that implies that the rail behaves as a constant pressure device after some point, perhaps 28,000 PSI.

10. no body on the planet that I know of has actually measured or verified maximum rail pressures above 26,000 PSI (the sender saturates at that point) or the set point of the pressure releif valve. We don't know if commanded pressures are actually acheived, and we don't know how reliable the on-board sender is above 26,000 PSI.

11. In my opinion, all of the pressure boxes I have studied raise rail pressure well above 26,000 PSI. its just that nobody knows exactly how high they go because nobody can measure pressures above some figure (which on my truck is 26,100 PSI), and no box is capable of telling you what actual pressure is (above 26,100).

12. All of my work is on the 305 HP engine with eight different pressure boxes.

Gypsyman

Doug,

Does this mean that you consider even the mild little VA box unsafe now?

Richard

doug

no, I should have made that clearer. I meant aggressive pressure boxes, which excludes the VA pressure box, the EZ on level 3, and all other boxes on lower power settings. The VA box is only a 40 HP box. At the HP/pressure slope I have generated based on the boxes I studied, this puts the VA at approximately 26,000. This I was able to verify with an actual measurement. So not only does the VA pressure box stay below the pop-off valve set point, it stays within the measurement capability of the on board pressure sender. It is also very strong in the low end, even coming respectably close to the low end HP of some aggressive pressure boxes making much more peak horsepower and peak rail pressure. Somebody at VA knew what they were doing; the design point is just too coincidental with my interpretation of the experimental results.

Also, I want to clarify the "nobody on the planet" comment. I mean nobody in the after market that I'm aware of has developed a way to measure rail pressures in a way that provides accurate knowledge into actual rail behavior for aggressive pressure boxes above 26,100 PSI.

Gypsyman

Thank you for the clarification Doug.

Richard