Understanding Fprv, and 0087? Please don't b 2 mean

[jnieberlein]

Ok so I have read and read about 0087, and popping the Fprv, shimming and lift pumps, my questions are as follows, I get the 0087 on wot, new fuel filter, so I did some logging, it appears that I consistently pop my Fprv at 24620.20, obviously I am commanding for more than this so I drop to about 10000, and trip the cel. So from all my reading I don't understand how to fix this, this is the part I am requesting mercy for my ignorance, if it pops at 24620, I am guessing a lift pump would not help, or would it? Would shiming it, fix it? I am
assuming the purpose of the shim is to increase the pressure on the spring and thus cause it not to pop until a higher pressure. What pressure should a non shimmed fprv pop at, I understand some are luckier than others but is there a set pressure it should pop at? I also have not bottle tested. This is all new I have not had efi long just starting out and I haven't begun to scratch the surface.

 

[MMLMM]

your prolly not holding rail pressure.. It may not be giving the CEL on a spike but a low condition. How big of a tune is it.

Usually if you are running more fuel, there is a good chance you will need to shim it either way.

Are you saying you see 24k on the rail (ACTUAL) and it starts dropping down to 10k ACTUAL, then it pops the CEL, if so, you are draining your rail. A smaller tune, or lift pump would help. You might as well shim too.

 

[LWATSON]

Do not install a shim kit until you are sure you need it! It sounds like you need a lift pump. I would install one before you do anything else.

 

[jnieberlein]

Yes 24k is actual the desired is somewhere around 25k and change, 10k is also actual, so what I am trying to understand or what I can't wrap my head around is if my Fprv pops at 24620, won't it still pop at the same number even with a lift pump or am I not understanding this correctly? Thanx again for the help

 

[crazycrew]

It will stil pop at that pressure, even w/ a lift pump. All the lift pump does is help keep the rail full under those higher demanding fuel tunes

 

[jnieberlein]

More logging

So I did some more logging, this time I used josh's race tune, there is about 500 psi difference between desired and actual @14k to about 20k then the difference is about 1000psi, desired is about 1000psi higher than actual, until we hit the magical actual 24620, desired is only 24635 , how can I decrease the desired to say 24600? All of this happens at a wooping 25 mph!!!! I am guessing since everything I have tried from a 45hp tow tune to this race tune pops my Fprv I am going to need to shim?

 

[stacks04]

Shim your valve, double it up if you like. That should cure the massive drop in pressure. It probably still wont be able to desired at 24k like you want it on any bigger tune, but you wont or should not fall to 10k, maybe 20-21k. Then a lift pump would help you. A lift pump wont ever supply enough fuel or make the cp3 work better to keep up with a massive dump off that comes from the fprv opening.

 

[jnieberlein]

So shiming it doesn't make it harder to pop just doesn't let it open as far? I guess that makes sence I hadn't looked at it that way, thanx

 

[JoshH]

Shimming does make it harder to pop open as it increases the seat pressure of the valve. I'm a little curious as to why your valve pops open at 24k something PSI. Stock tuning runs 26k on the LBZ. Can you post your log? For the record, if you're talking about my race tune that I posted here, it is way bigger than you should run without a lift pump.

 

[jnieberlein]

This time it was ur race tune, but earlier I ran a supposed 45 hp tow tune, and it popped on that one too. I havent tried but i am thinking i could probably get it to do it on a stock tune maybe i will try that in a lil bit. I can't post a log right now I don't have access to an Internet connection at the moment, been posting from my phone. I can probably post it later tonight or sometime tommorrow, every tune I have tried, all fail at exactly 24620.20, if there is any info I could write from the log that would be helpful let me know and I will absolutely post it up, thanx for the help

 

[JoshH]

So as soon as it gets to 24,620 it immediately drops to 10,000? How many miles are on the truck? Have you tried a stock tune?

 

[jnieberlein]

Just under 86k on the truck, I am going to go try a stock tune right now, yeap everytime it hits 24620.20 it falls to 10

 

[JoshH]

Sounds like it might be the FPRV, but you should do a bottle test just to be sure.

 

[jnieberlein]

Stock tune

Ok first run slightly down hill max desired was 23969, max pressure was 24125.62, second run coming back slight up hill, max desired was 26029 max was 24620.20 fell to 14950 than to 10240, the desired was 24350,24465, 24562,24700,24771,24805, the actual during those was 24620, than at desired 24822 dropped to 14950, etc, this was at 22 mph, I saw a boost of 35 psi during this run not sure when I read the tattle tale on my
Gauge afterwards and a max egt of just shy of 1200*, ?

 

[LWATSON]

Your going to need a lift pump anyway, put one in and that will eliminate that as the problem. Or it may fix your problem?

 

[jnieberlein]

Log of run on stock tune

Log of Stock tune run, fuel pressure drops!!!!!!

 

[Mike_S]

If you are not holding rail pressure with a stock tune, fuel supply is most likely not your problem, and if your relief valve is opening at 24K PSI then you most likely have a weak valve IMO. If it were me i would probably see about getting a new valve, and then possibly shimming the new one.

 

[GeneralTJI]

Yea it sounds like you need to shim the valve. At least that is cheap... then you can go after a lift pump.

 

[LWATSON]

A shim kit may fix your problem. I'm going to say this one more time, do not install a shim kit until you know you need one! My LBZ has 120k miles on it and I've been running a hot EFI tune for a long time. I have had 0087's but tuning changes and a liftpump fixed it. You can damage your fuel rail installing a shim kit. No need to take the risk until you know its the problem. LBZ have a fairly strong FPRV.

 

[jnieberlein]

So a bottle test will confirm if my Fprv is popping, or is the log good enough? Could a bad CP3 cause the drop in pressure as well, i am just trying to cover most of my bases before I start throwing parts at it. I posted a log if anyone cares to give my their thoughts from my log I would appreciate it. Once again I appreciate everyones help and opinions thus far