Help: Cant keep rail pressure!

[CBJ61NASH]

Guys I need some help with a problem I am having. Let me start by saying I am new to this site but so far I love it. Alright here is the problem. I cant hold rail pressure with the McRat 500hp tune. Logging has shown that I can only hold 18000psi when it demands 25000psi, a little problem? The truck has a race valve, modified cp3 from industrial injection, Airdog 150 lift pump and new fuel filters. I have also replaced the bleeder screw and the majority of the fuel lines. With all that I have done to the fuel system one would think it would be able to hold at least 23000psi. There are no noticable fuel leaks and no fuel in the oil. There is also very little smoke coming from the stacks, just a little puff at the start and thats it! Any help would be appreciated greatly as I am out of things to try. The only other odd thing that happens is every so often it throws a code p0089 fuel pressure regulator 1 performance. Could this be an issue? Thanks alot, Josh

 

[LBZrcks]

How long have you had the issue? before/after the modded cp3?

 

[RENODMAX]

Maybe need a new FPRV? If you do get one I know the LBZ regulators do the best. Im sure others will chime in. Hope this helps.

Jordan

 

[CBJ61NASH]

I had the problem prior to the new cp3, I hoped that the new modded cp3 would help. I thought maybe the old cp3 was worn out since it had 55k on it. I did gain a good bit of psi through half throttle but after close to 3/4 throttle it starts really dropping off and will top out at 18000psi. I am going to replace the pressure regulator and see if that helps. Thanks, Josh

 

[bullfrogjohnson]

Does this only happen with Pats tune? I notice you have 40 over injectors, there will have to be some tuning changes made for those injectors

 

[mytmousemalibu]

I'm still way new to EFI but my old Bully Dog PMT displayed fuel pressure and im running 50% injectors and if i remember correctly 18,000 was about all i got at WOT. I also have a modded CP3 (did it myself-not II) and a Dual feed line but no lift pump. Think the big injectors are the drain on rail psi IMO.

 

[malibu795]

Does this only happen with Pats tune? I notice you have 40 over injectors, there will have to be some tuning changes made for those injectors

I'm still way new to EFI but my old Bully Dog PMT displayed fuel pressure and im running 50% injectors and if i remember correctly 18,000 was about all i got at WOT. I also have a modded CP3 (did it myself-not II) and a Dual feed line but no lift pump. Think the big injectors are the drain on rail psi IMO.

IMO bingo found the culprit..

pull some ~300uS out of the tune on the top end.. shoudl bring your rail back up above 20K

since you got the 40% inj you can run LESS uS and get more power then compared to a stock inj. untill you get dual fuelers 2800uS and up is alsmot useless... cp3 can keep up with the flow deman

 

[CBJ61NASH]

Alright guys, I pulled out the 40% injectors went back to the stock ones to see what rail pressure I can hold. It peaks at 26000 for a very brief second then falls fast to 20500. It holds 20500 through wot till I let off, then spikes back up momentarily to 24000 or so. I still get very little smoke with the stock injectors, just a little bit more than with the bigger ones. There has to be somrthing else wrong i would believe, I am going to change the fpr and see if that helps. Thanks, Josh

 

[dmaxtruck]

IMO bingo found the culprit..

Bingo.

I'm runnin the big ats sticks, FASS 150, and fuel rail shims on a single unmodded cp3 and using the same tune I was about the exact same rail pressure.

I've been working with Mike to get my tuning right and the max pulse width I'm running on this version is 2100.

I think the FPRV could be causing some of the issues, but I'd bet you dollars to doughnuts the big sticks are the main cause.

You may want to up the commanded/desired rail pressure a tad in conjunction with lowering the pulse width. That sure has helped me a lot.

 

[GMC_2002_Dmax]

Big Sticks do not respond to the same tuning as stock sticks do.

MDE, aka Volkker explained this to me last year at Danville when I tuned Nasty Girl the first time, I have since tuned a few other big stick trucks and without injector flow data you are guessing at what is optimal.

Rail pressure is a gauge, but not every CP3 is the same and not all injector return rates are the same, so if the return rates are higher than they need to be you will never get the rail psi to sustain with a single CP3.

 

[RENODMAX]

Alright guys, I pulled out the 40% injectors went back to the stock ones to see what rail pressure I can hold. It peaks at 26000 for a very brief second then falls fast to 20500. It holds 20500 through wot till I let off, then spikes back up momentarily to 24000 or so. I still get very little smoke with the stock injectors, just a little bit more than with the bigger ones. There has to be somrthing else wrong i would believe, I am going to change the fpr and see if that helps. Thanks, Josh

Like I said Id do the fprv and see what happens. seems like that would be the only place to go and they are known to go bad on occasion. i know pat was also selling some high flow ported jobs for like $270 if you want to check one of those out. Let us know what fixes her!

 

[CBJ61NASH]

Ordered new fuel pressure regulator today, will see if that makes a difference. Also Larry Jewell is working on my modding the tune to hold some more pressure. So far he has got a few thousand more psi out of it. If the fpr helps any I should be getting close to 22000psi. I can now sustain 21000 but hoping for a little more with some work. I'll keep you posted if I can find anything else that works. Josh

 

[bullfrogjohnson]

I am only able to sustain 21,000 and thats with a modded regualtor