P0087 fuel rail pressure low limp under high loads

[DmaxMaverick]

Its not... if you didn't catch on, its a dig at me...

I guess asking how you use a software change to get more volume out of a pump that is already working at is capacity poses a problem.....

I don't think it was a dig at you.

Anyway, I think you are limiting the scope to only what is available within the allowable envelope of the vehicle calibration, and discounting the physical capability of the HP pump. Technically, a true "100%" duty cycle of the pump would likely see it destroyed in a very short period (unless #2 Diesel were infinitely compressible, but it's not, so....). The pump itself is "dumb", only varying its output according to the flow control, which is controlled by PCM commands, according to sensory data input and programmed demands. The operating envelope of the pump is determined by the calibration parameters, not the physical capability of the pump. Demanding a 100% duty cycle of the pump is only commanding the full duty cycle allowed by the calibration, and not, necessarily, the full capability of the pump (otherwise, the upper threshold of the pump's performance would have to be identical from pump to pump, vehicle to vehicle, under every conceivable condition). It's comprehensive, according to dozens of channels of sensory data. The PCM doesn't know, and doesn't care, what the physical limitation of the pump is (unless it's incapable of answering mechanical demands, not according to calibration parameter demands). The FPR/FRPR is limited only by the vapor, AKA: the PCM, via the vehicle calibration, sensory data, emission system control, and powertrain performance demands. Moving the operating envelope (range) of the pump performance sensory data, such as John is suggesting, is nothing more than that. Simple, and perhaps a band-aid fix, but it works often enough to make it a viable solution, if only temporary. The alternative is to pony up a few grand for a repair that may not be necessary for years to come. If it doesn't work, the only loss is a little time.

[dougmac]

Generally the high pressure pump does not produce its full volume because it is regulated by a pulse width modulated solenoid. It will increase and decrease volume as the demand changes. The only time you would see it at full volume is when it has fallen below the commanded pressure.

If it cannot maintain the requested pressure the system will log a code and derate the engine.

[DmaxMaverick]

Generally the high pressure pump does not produce its full volume because it is regulated by a pulse width modulated solenoid. It will increase and decrease volume as the demand changes. The only time you would see it at full volume is when it has fallen below the commanded pressure.

If it cannot maintain the requested pressure the system will log a code and derate the engine.

If that's the case, then why is it 9 generations of Duramax calibrations commanding 95% duty cycle all produce very different pressure and volume parameters? If you are correct, then all of them at "maximum duty" would all produce the exact same pressure. As you suggest, it's the PWM that limits the pump output, not its absolute physical capability. The problem isn't the pump, but the other end of the fuel rail. The root cause of this discussion is the sensory data failing to report acceptable fuel usage accountability, for whatever reason. Addressing a functioning pump is talking to the wrong end of the horse. This was never a pump problem. Although the problem is almost always the injectors, it was never as prevalent until the calibration parameters were changed. Same pump, same injector performance, same fuel pressure and volume regulation means. So, why wouldn't it be reasonable that a PCM calibration adjustment just might correct the condition in many cases?

The injectors in question are suffering the same exact failures as previous and later series. The component interoperability hasn't changed. The only difference is when the PCM perceives them to have failed, and will demand correction (SES lamp, limp mode, etc.). The pump isn't failing to perform just because the PCM says it is, and neither is the remaining fuel system components. No more than they have with any other series.

[Kennedy]

Ok... I concede ... I am dumber than you..

Now explain in simple terms that a dumb guy can understand. How you use a software change to get more volume out of a pump that is already working at is capacity?

I did not say that you are dumb. What I am pointing out is that you have made 2 factually incorrect statements and likely a third

1) There is no FICM

2) The pump flow at 100% duty cycle is theoretically 0

3) So how do you know the pump command is really giving all it can when the DTC is set?


The way I see it for those who face this condition there are 6 options:

1) Replace the injectors
2) ECM programing
3) Ignore the problem and reset the code on the fly as MRE did for quite some time
4) Spend hundreds if not thousands in diagnostics and parts changing everything short of the injectors because they cost most.
5)Sell or trade the truck
6) Step into in Mr Peabody's WABAC machine and go back to the day the truck was delivered. Add a lift pump, secondary filtration, and quality additive to every ounce of fuel that you burn.



FWIW the WABAC machine pre-dates me by a significant number of years bet here it is:

[rapidoxidationman]

This is an interesting conversation to me and I've been following it closely. I'm hoping the new guy won't get frustrated and quit visiting this forum cuz it does sound like he knows a bit about the dmax and could be a valuable asset here - if he can take the initiation...

I'm trying to understand just how the HPFP and related system works, given the info that's been presented by both sides of the discussion. Hopefully someone will confirm or deny what is presently my understanding:

The high pressure fuel pump is driven by the engine (cam, chain, gear, it doesn't matter). It is mechanical and directly connected so its ability to pump fuel is directly related to the engine speed.

The fuel pressure regulator does the control side of things, is electronically controlled, and does the bidding of the ECM according to load, RPM's, and requested pressures to make the injectors work properly. It has the ability to be fully closed (delivering 100% of the pressure the pump is able to put out but very low volume) or it can be fully open (essentially dropping the pump output pressure to zero but with high volume in layman's terms) but the normal range of operation is - what - between 5% and 50%?

So when the injectors (or whatever failing component) have too much free flow and the regulator has to go beyond that normal range of operation the computer gets pissed off, sets a code, and goes into limp mode.

Kennedy's solution tweaks the "normal range of operation" to something that is technically out of the engineer's specs, but allows normal operation albeit with higher flows from the regulator to compensate for worn parts.


How'd I do?

[DmaxMaverick]

This is an interesting conversation to me and I've been following it closely. I'm hoping the new guy won't get frustrated and quit visiting this forum cuz it does sound like he knows a bit about the dmax and could be a valuable asset here - if he can take the initiation...

We value the input of anyone willing to engage, with something to offer (or nothing to offer, for that matter). This is especially true of the technicians actually working in the field. We, TDP, need to do the best we can to ensure everyone is on the same page, so to speak, especially when unorthodox methods are being implemented. A $5K repair is not always the immediate solution, such as in this case.

I'm trying to understand just how the HPFP and related system works, given the info that's been presented by both sides of the discussion. Hopefully someone will confirm or deny what is presently my understanding:

The high pressure fuel pump is driven by the engine (cam, chain, gear, it doesn't matter). It is mechanical and directly connected so its ability to pump fuel is directly related to the engine speed.

The fuel pressure regulator does the control side of things, is electronically controlled, and does the bidding of the ECM according to load, RPM's, and requested pressures to make the injectors work properly. It has the ability to be fully closed (delivering 100% of the pressure the pump is able to put out but very low volume) or it can be fully open (essentially dropping the pump output pressure to zero but with high volume in layman's terms) but the normal range of operation is - what - between 5% and 50%?

So when the injectors (or whatever failing component) have too much free flow and the regulator has to go beyond that normal range of operation the computer gets pissed off, sets a code, and goes into limp mode.

Kennedy's solution tweaks the "normal range of operation" to something that is technically out of the engineer's specs, but allows normal operation albeit with higher flows from the regulator to compensate for worn parts.


How'd I do?

Essentially correct. The regulator will compensate for the failed component's (unaccounted) increased flow, causing the PCM to complain when the regulator requirement is greater than what is expected, according to the conditions. The PCM accounts for every drop of fuel through the system, and "knows" where the fuel should be going, as well as what is required of the components to accomplish that.

[dougmac]

The regulator will compensate for the failed component's (unaccounted) increased flow, causing the PCM to complain when the regulator requirement is greater than what is expected , according to the conditions. The PCM accounts for every drop of fuel through the system, and "knows" where the fuel should be going, as well as what is required of the components to accomplish that.

I don't believe this to be true and I don't understand the term "complain" as it relates to the pcm. I see no trouble codes that indicate a fault condition exists when "the regulator requirement is greater than expected" and it is not listed as a condition for setting the P0087 trouble code or even mentioned anywhere in the P0087 trouble shooting chart.

Excessive injector spillback is however mentioned as a cause.

What leads you to this conclusion?

[dougmac]

It is completely flawed logic that the pump does not pump to capacity when it sees a pressure below requested condition.

Equally flawed is the statement that it reduces output as a protection mode for the pump. There is less pressure on the internal parts because the the rail pressure is reduced under these conditions. There is more fuel flow through the pump allowing for better cooling and lubrication. This condition is a less stressful to the pump than operating at full pressure with more limited fuel flow.... I am not sure what they would be trying to protect it against?

[rapidoxidationman]

I don't believe this to be true and I don't understand the term "complain" as it relates to the pcm. I see no trouble codes that indicate a fault condition exists when "the regulator requirement is greater than expected" and it is not listed as a condition for setting the P0087 trouble code or even mentioned anywhere in the P0087 trouble shooting chart.

Excessive injector spillback is however mentioned as a cause.

What leads you to this conclusion?

I'm going to preface this by saying two things:
1) I have nowhere near the knowledge base that other members here have, possibly including you.
B) When I need to I'm pretty good at sussing things out.

BUT:
Wouldn't "excessive injector spillback" cause the regulator requirement to be greater than expected?
and
As far as the term "complain" goes, is the lodging of a trouble code not a complaint as a result of the PCM seeing something out of spec?

I'm not trying to start an internet pissing match, but there's a great deal of real world experience on this board that may not be found in a tech manual or a P0087 troubleshooting chart...

'scuse me while I go pop another batch, this time with butter...

[dougmac]

I'm going to preface this by saying two things:
1) I have nowhere near the knowledge base that other members here have, possibly including you.
B) When I need to I'm pretty good at sussing things out.

BUT:
Wouldn't "excessive injector spillback" cause the regulator requirement to be greater than expected?
and
As far as the term "complain" goes, is the lodging of a trouble code not a complaint as a result of the PCM seeing something out of spec?

Yes, I would consider a code a complaint... there is no trouble code for "the regulator requirement is greater than expected"...

I'm not trying to start an internet pissing match, but there's a great deal of real world experience on this board that may not be found in a tech manual or a P0087 troubleshooting chart...

'scuse me while I go pop another batch, this time with butter...

I am supposed to rely the "real world experiance" with their calims that make no sense at all over the GM technical documents? I'll stick with the GM information. I have been in this business long enough to tell the BS from the truth, thank you....

[Kennedy]

I don't believe this to be true and I don't understand the term "complain" as it relates to the pcm. I see no trouble codes that indicate a fault condition exists when "the regulator requirement is greater than expected" and it is not listed as a condition for setting the P0087 trouble code or even mentioned anywhere in the P0087 trouble shooting chart.

Excessive injector spillback is however mentioned as a cause.

What leads you to this conclusion?

There is a LOT of diagnostics going on behind the scenes and it is my belief that most of this is only provided on a need to know basis.

It is completely flawed logic that the pump does not pump to capacity when it sees a pressure below requested condition.

Equally flawed is the statement that it reduces output as a protection mode for the pump. There is less pressure on the internal parts because the the rail pressure is reduced under these conditions. There is more fuel flow through the pump allowing for better cooling and lubrication. This condition is a less stressful to the pump than operating at full pressure with more limited fuel flow.... I am not sure what they would be trying to protect it against?

The pump can move to near capacity, but not full capacity. Additionally, it is controlled by a complicated set of PIDs, expected flow rates, flow limits, etc. These are based on small errors and large errors both positive and negative. These are likely there to provide a smoothing effect to prevent the pressures from spiking and sagging. I will not claim that I can even begin to understand the entire interworkings of these tables, but wheat I will say is that I have had solid success in tuning to help the pump stay on target.

I am supposed to rely the "real world experiance" with their calims that make no sense at all over the GM technical documents? I'll stick with the GM information. I have been in this business long enough to tell the BS from the truth, thank you....

So basically you joined the forum to call BS on me...

[More Power]

I have been in this business long enough to tell the BS from the truth, thank you....

I/we appreciate your input. Please don't let a simple disagreement dissuade you from helping others here. Your input is valuable.

One thing to keep in mind is that, from an owner/enthusiast position, we may view problems and resolutions a little differently than a GM tech or even GM might. For GM, they are concerned about emissions regulations and adhering to documented service procedures. For a GM tech, I imagine that what the GM service schools taught was considered the best way forward to solve problems. Sometimes it is, sometimes it isn't, depending on a point of view and who's money is on the line.

For most owners and enthuiasts, saving money, improving performance or reducing downtime are more important.

A Duramax injector changout is so very expensive. I don't think GM or the dealerships fully appreciate that. If there's a potential in some idea, program modification or product that will reduce the cost of ownership, we'll discuss it, analyze it and recommend it if it helps solve problems. None of us here like snake oil. Those products or procedures that fit into that category don't last long around here.

Back before the arrival of the Duramax, and even sometime after, the standard GM recommended repair for a 6.5L diesel "stalling" problem was to install a new electronic fuel injection pump. Millions upon millions of hard-earned dollars were paid/wasted by 6.5 owners for a new pump when all they really needed was a new electronic driver module that would have cost just a fraction of what a pump change did. Once we understood the problem and how to inexpensively repair it, we documented the resolution. Both GM and Stanadyne (pump manufacturer) eventually came to (were dragged kicking and screaming to) the same conclusion, but it took years. That's just one example of how we (vehicle owners and enthusiasts) helped to solve a problem.

Welcome to the board. Information is our biggest asset. Please continue to contribute. Jim

[Wingeezer]

Hi Folks,

New to the group and joined to see what I could learn about P0087 !!

I will say immediately that my diesel experience is virtually nil, so I am afraid I am much more here to learn than anything else!

We have a 2006 GMC 2500HD Duramax bought new to tow our 31 ft Airstream travel trailer (about 8000 lbs loaded).

The truck has been great until earlier this month when returning from Cape May NJ to our home near Toronto.

Just after crossing from Pa. to NY, our truck suddenly went into (what I have now learned to call!) limp mode.

I got a "reduced engine power" message followed by a "service fuel filter message." All a bit scary when towing in the fast lane on the interstate!

Of course I knew nothing of the common P0087 problem but have read a lot since!

I had checked our fuel filter status earlier in the day and it showed 53%, now it showed zero.

I got over to the shoulder and tried shutting the engine down and re-starting but no change. We still could only maintain about 20mph max. (Now I think that with what I have learned, that maybe I should have waited 20 minutes or so and we might have gotten out of limp mode - but for how long?)

We limped for 5 miles to a Chev dealer at Dansville NY. We had fuelled up at a pretty seedy service station earlier in the day and I was sure our problem must be bad fuel with the apparent rapid demise of the fuel filter.

I explained what had happened and left the truck with teh Chev dealer, asking if they could check it out, change the filter that was apparently needed, and dump the remaining 1/4 tank of fuel if they deemed it wise and could do so.

When we returned, they had changed the filter, the engine light was off and the truck was back to normal, but they said that they felt the fuel was ok and they did not dump it.

I was told there were no codes, and they felt we would be ok to continue our trip home. They had no explanation as to what had happened.

At the time, I new absolutely nothing about OBD2, but now I am wondering how the engine light could be on with no codes present ? Maybe that is possible?

We did get home without further problem, but I am now concerned about recurrence. We normally head to Arizona in winter and hope to do so next Feb.

I certainly lack the insight most of you guys have, and so far, all I have done is to buy a spare Delco fuel filter that I will carry, learned how to change it on the road if I have to, and also bought an ET-80 code reader to at least be able to erase future codes and hopefully carry on, if only to a GM dealer!

Before we head south in Feb. I plan to explain what happened to our local GMC dealer and ask if there is anything further they can check out for us - I sure don't like having to worry about this sort of thing when towing on the interstates!

This morning, I tried out the code reader for the first time. Lo & behold, there was a P0087 code logged - but all indications are that the truck has been running fine since we left the GM dealer in NY. The fuel filter life is showing showing 98%.

I am at a loss as to why the code is there.

Did the dealer lie to me about checking for codes? Could he have turned off the dash engine trouble light without checking for codes and deleting them?

Maybe the code has been logged since being at the dealer - but if so, would we not also have have gotten the engine light back on again and maybe also gone into limp mode? Confusing!

After copying out all the freeze frame data, I erased the code and will see if it comes back - though it may not since we won't be towing the trailer again until Feb. It may be we need the heavier towing operation to cause a repeat

One way or another I still plan to see what our local GMC dealer might be able to do to hep us.

I still have extended warrantee on the truck until Nov 2014. I sure wish the problem was just a load of bad fuel, and maybe it was, but the dealer in NY didn't seem to think so, and after reading the thread on this forum, I now realize there could be a lot of other issues besides bad fuel.

The fact that the fuel filter life dropped from 53% to 0% in one morning makes me still suspicious about bad fuel, but i don't know how this monitor actually works.

I would have thought it monitors pressure drop, but I have read that it may just be mileage based. But if that is so, how could it drop from half life to zero in a couple of hours driving?


Differences I see though with our situation compared to what I have read that other folks have experienced with this problem include:

- temperatures were not high, maybe 70-75F

- we were not towing on a steep grade when this happened, although we had been in hilly country an hour or so earlier

- our truck only has about 62,000 km (38,750 miles)


Not sure what else I can do at this point. I have read about the kinked fuel line possibility and will discuss with our dealer. I have read about lift pumps, but I imagine GM does not support such a modification and it may well void my warrantee were I to get one installed so I would be reluctant.

Presume that with my code reader I can at least erase the code at the side of the road (believe engine must be stopped to erase) and that would at least temporarily remove the limp restriction.

I will also take a look at the fuel cooler and pressure wash it, although in our case, I doubt this would be an issue, the truck stays pretty clean!

I can also try to ensure we always refuel at half tank.

Not sure there is much else I can do, but any advice appreciated! I sure would like to regain confidence that this won't be a recurring issue in future! Up to now I have been very happy with the truck!

Apologies for the lengthy post !


Regards ........ Brian M.

[IGO1320]

I was getting the dreaded P0087 towing in the heat up steady/steep inclines. I first tried changing the fuel filter, then installed a Kennedy lift pump, both had no effect. Used a tech2 and commanded the injection pump full fuel pressure which it did and held. I talked to a Fuel injection shop and they told me I would need to replace my injector pump and "maybe" the injectors, they could not get to me for three weeks. I read another thread on another site and John Kennedy told someone with similar symptoms to mine that the problem was the injectors and that he could possibly tune around it. I called John and we discussed my problem he told me there was an 80% chance that he could write a tow tune that would make as much power and not set the dreaded P0087 thereby extending the life of my injectors (John says the injectors wear and start bypassing diesel) so I bit the bullet and ordered one of his tunes. I could not be more impressed, I have now made two trips to Hershey Pa., one to Billings Montana, Mesa Az., then Ohio to Florida by way of Kentucky and Tennessee where I have towed 8K-12.5K Fifth wheel TOY haulers/campers with no codes. John wrote the tune for my truck and had it out in an afternoon. I also stopped by to meet him at his shop, he made a couple minor changes to my tune no charge and took the time to answer a laundry list of questions, very impressive individual. I don't want anyone to think I am bad mouthing my old "box" tuner the Hypertech did serve me well for only $300 and without a way to clear the codes I would have really been in a pickle. I am using the Hypertech to clear codes if needed again.
As a side note with the old tune my EGT's had to be watched with a heavy load as up a steep incline in the heat they would go over 1400 forcing me to slow and downshift with this Kennedy tune the EGT's have not gone over 1320, I can just leave the cruise on and let her climb. I think the mileage is .3-.5 a gallon better but these trips I ran 65 instead (testing to see if I could "force the code") of my normal 61-62 so I will have to average that for a few more trips. The only downside is subjective and that is the truck "seems" to be slightly louder at idle, my wife commented on it without my input so that may be true, but that makes no difference to me the tune is as billed and appears to have extended my injector life without a loss of power and possibly an increase in mileage. I would highly recommend John if you are interested in extending the injector life by holding the dreaded P0087 at bay.
I have 287,000 on my truck now, I had 260'ish when the problem started and I "drove around it" for 10K miles, so I now have roughly 17,000 on the tune.

[AHGSP]

Like Brian, "Wingeezer", I experienced a similar and rather disconcerting situation last eve; while hauling a 12k# horse trailer up a steep grade in Western MD, going Westbound up the Eastern Continental Divide on I68.
This was particularly disconcerting in, if I break down with horses and dogs on the side of the interstate, this could become quite problematic in getting the horses and dogs I have onboard safely back home, or somewhere safe.

Background info:
I had filled up prior to my trip and had checked the fuel filter life on the DIC and it was showing at around 28% life left. With a planned training trip(I Professionally Train and Field Trial Bird Dogs) to SD next Friday, I figured I would change it out next week prior to my trip anyway. Temperature was not particularly high, 70* + or - and when the code set and truck went into limp, I had approx. 24-28 gallons of fuel in the tank, engine temp. had climbed to around 210-220 and tranny temp was running right around 200-210. Right before it went into limp and set the code P0087, the "Change Fuel Filter" came up on the DIC and sure enough, it now showed 0% life left, same as Brian. The truck is a '08 3500 DRW Crew w/ flatbed, has just shy 112k miles on it and has been religiously maintained, with approx. 20-30k of those miles towing this rig. In addition, the truck is entirely stock beyond the flatbed.

I changed the fuel filter along the roadside and while the check engine light did not clear, I experienced no further limp and was able to turn around and safely return home with the horses and dogs. Should the light have cleared?

My questions are:
Was the fuel filter condition/poor fuel the most likely culprit in this case, combined with the steep grade and temps?
What scan tool is recommended so that at the very least, I may be able to clear the code/limp and continue on safely, should I be a thousand miles from home when this happens, IF it should happen again? I could care less about myself, I'm a big boy, but these horses and dogs depend on me to take care of them and assure their safety.

I plan to follow through with some of the many suggestions here, on this MOST HELPFUL thread and clean the cooler, check fuel lines, most likely add the dual lift pumps as soon as I can afford the extra expense of the mod. I have also read Kennedy's Tech Tips for other idea's and suggestions; but what else might you folks suggest?

Thanx Kindly in Advance for any and all suggestions, as well as this extremely helpful resource!
Bruce Shaffer

[IGO1320]

I would follow John Kennedy's recommendations. I bought a pressure/vacuum gauge from him, if the code occurs again you can plug it in and see what the vacuum is then you know if the filter is plugged. Off course you need to know what normal for your truck is first, there is some variance. You can buy any cheap scanner to read and clear the ECM codes, to read the other cpu's (ABCM, SRS,TCM, ect.) you will need something much more expensive.

[More Power]

Glad to see some new faces here in the board! More info is better.

Used a tech2 and commanded the injection pump full fuel pressure which it did and held.

Perhaps the best time to test for commanded/actual pressures is when you're having a problem. Once the truck has cooled and the fuel has cooled, pressures could be normal.

Wingeezer: Differences I see though with our situation compared to what I have read that other folks have experienced with this problem include:

- temperatures were not high, maybe 70-75F

- we were not towing on a steep grade when this happened, although we had been in hilly country an hour or so earlier

- our truck only has about 62,000 km (38,750 miles)

There will always be an exception to the rule, an example that doesn't fit the norm for a P0087. In your case, I'm surprised you don't see this P0087 problem become much-much worse when it's hot outside and you're working the truck harder - assuming that a fuel filter service didn't solve it.

Thanks for posting. Jim

[Kennedy]

winegeezer,

My guess is that the dealer did not bother to hook up and check for codes. The fuel filter life dropped due to the P0087. We see this quite frequently where filter life gets zero'd out due to pressure maintenance issues.

You've made great strides in equipping yourself as I have been recommending for years.

You should always have a minimum of one fuel filter as well as the tools required to change it. I've also been working on a mini compressor and tire plug kit for my vehicles as well.

To save you getting dirty next time the P0087 code comes up and potentially prevent replacing a fuel filter unnecessarily, I also recommend the kit shown below. This way you know instantly whether the filter is truly restricted, or not.

[Jeff Paxton]

Update: We completed the trip from eastern CO to New Jersey about a week ago. The temps were mild, less than 75 degrees. The truck performed very strong through the mountains of PA which is where the problem erupted last spring, but at higher temps, 90-93. It shifted into 4th far fewer times than previously, and when it did, the climbs at 65mph were comparatively effortless. In the spring, each time it shifted into 4th, there was not much throw left on the throttle, and within a few seconds, limp mode and power loss. There was plenty left this trip. It seems the replacement fprv is doing what I need. I will not be 100% confident until it is tested in high temps next spring, but I am pleased at this point.
I believe the old fprv weakened quickly with each limp, and had reached the point where it was never "closing" all the way. I think it explains everything, especially since the balance rates on the injectors checked out fine each time observed by "trusted" sources. High temps will be the last test.

[Kennedy]

I believe the old fprv weakened quickly with each limp, and had reached the point where it was never "closing" all the way. I think it explains everything, especially since the balance rates on the injectors checked out fine each time observed by "trusted" sources. High temps will be the last test.

I did not see if a "bottle test" was performed to verify the leakage?

IF the relief valve was bad it definitely weakened each time it was activated. The valve gets extremely hot when activated and this weakens the spring. We typically get away with shimming the spring and all is well again. The thing is, it typically does not activate unless there is severe pressure cycling. This pressure cycling is caused by supply side restriction ie: plugged fuel filter, or excess air in the system. My recommendation has always been that these trucks need a lift pump to ensure proper filling of the OE fuel filter and to prevent outgassing of the fuel creating large amounts of "air" in the fuel filter housing.