Fuel pressure causing misfire? Help!

[Shahek]

Guys, just installed a walbro 525 and deleted the suction jet system as I should. I have IE rails and 1000cc injectors. I’m using my stock fpr (which I swapped with a known good working one too).

I have an inline fuel pressure gauge and it’s showing 75psi and not dropping. No restrictions in lines and I’ve made sure none of my injector seals are leaking.

At idle im getting multiple misfires on all cylinders, under load 0 misfires, only when I come to a stop. I’ve done a boost leak teast too and nothing. I’m thinking the high fuel pressure is causing the misfire but don’t know what else to look for.

Any help is appreciated, the b5 life is starting to get to me. Thanks


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[MetalMan]

Your stock FPR is definitely being overrun, which is known to happen on lower-flowing fuel pumps than yours (i.e. Walbro 450). You have 3 options: 1) get re-tuned so that the extra fuel pressure can be accommodated; 2) get a FPR with larger orifice which will be able to bypass more fuel to drop fuel pressure; 3) ideally, both 1) and 2).

[Shahek]

Your stock FPR is definitely being overrun, which is known to happen on lower-flowing fuel pumps than yours (i.e. Walbro 450). You have 3 options: 1) get re-tuned so that the extra fuel pressure can be accommodated; 2) get a FPR with larger orifice which will be able to bypass more fuel to drop fuel pressure; 3) ideally, both 1) and 2).

Thanks for the fast reply, I just started tuning so we're still trying to monitor fuel trims. Would you recommend going to a 3 bar?

[S4James]

GFB sells a dandy one that supposedly fixes this issue.

[Shahek]

GFB sells a dandy one that supposedly fixes this issue.

Can I run the GFB with my IE rails?


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[MetalMan]

Can I run the GFB with my IE rails?

It will fit where the stock FPR fits, I believe. There are a couple threads on here from the past year that will have more information.
https://gfb.com.au/products/fuel-man...ulator-detail/

[S4James]

If you are using IE rails, with the stock FPR, then in theory the GFB unit will work assuming its in a position that clears everything... That said, does IE not have an upgraded FPR available for its rail kit? The GFB is expensive and might take awhile to get.

[Shahek]

I will look into both options today and report back


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[Shahek]

ok guys...IE does not have an upgraded fpr to go with their kit. Other than the GFB I found the ECS adjustable fpr but it's back ordered until March. So GFB may be the only option but don't know how long it will take

[S4James]

I find it hard to believe they have no advice for you.. Check some of the threads there, i know there was discussion on one of the variants of the 4bar FPR that was known to have a slightly large orifice, that helped with the backpressure issues.

Another possible solution might be to undervolt the pump using a controller that picks up off the MAP signal to drive the voltage up and down.


Side question, you running that pump on stock wiring or a relay kit? That something blake provided? Might be switching to that pump myself and tuning for e85

It will be good to get your experience on this.

[Shahek]

I find it hard to believe they have no advice for you.. Check some of the threads there, i know there was discussion on one of the variants of the 4bar FPR that was known to have a slightly large orifice, that helped with the backpressure issues.

Another possible solution might be to undervolt the pump using a controller that picks up off the MAP signal to drive the voltage up and down.


Side question, you running that pump on stock wiring or a relay kit? That something blake provided? Might be switching to that pump myself and tuning for e85

It will be good to get your experience on this.

Thanks for the advice will look into it...yes I bought the pump from Blake but the relay kit was from summit racing they have a couple different kits. Hopefully I can get this all figured and can give you some more tips. But PM me when your installing the pump because there is a delete that needs to be done and I have a pic that can help you (although I think someone posted it in my previous thread)

[JustManson]

Check eBay for the GFB FPR - that’s where I got mine, there are a few resellers there.


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[JustManson]

Also it works great!

I have the Walbro 450 with jegs wiring kit. Set it and forget it :)


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[JustManson]

https://www.ebay.com/itm/GFB-FX-S-Bo....m46890.l49292


Looks like it’s in stock.


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[S4James]

Thanks for the advice will look into it...yes I bought the pump from Blake but the relay kit was from summit racing they have a couple different kits. Hopefully I can get this all figured and can give you some more tips. But PM me when your installing the pump because there is a delete that needs to be done and I have a pic that can help you (although I think someone posted it in my previous thread)

lol yeah that was me telling you... :)

[Shahek]

lol yeah that was me telling you... :)

hahahahahaha sorry brother I was in so pissed that day because of this junk car I didn't even pay attention.

[Shahek]

https://www.ebay.com/itm/GFB-FX-S-Bo....m46890.l49292


Looks like it’s in stock.


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Just ordered thanks man! Hopefully it will solve my problems


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[Shahek]

ok guys got the GFB fpr (showed up super fast shout out to JustManson for the ebay idea) and it is beautiful. Adjusting is super easy and so far no misfire at idle got it to 62psi @ idle. It does not fit the stock rail without some "customization" lol. The fpr is a bigger than stock so the driver valve cover does not let it sit. I'll post a pic of what I did to my stock rails. But I do have a set of IE rails and it definitely fits no hassle in case anyone was wondering.

Thank you S4James and Metalman for the help. Blake wants me to do some logs tomorrow so will let you guys know how it does with the hellcat fuel pump.

[S4James]

lovely glad it worked out. Nice to a thread like this as it will help future users.

[s4andtls]

Just FYI I also have the hellcat fuel pump and added the summit relay so it’s got good voltage. Have IE rails stock fpr also , was tuned by Brad, no issues supports 800 hp


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[Shahek]

Just FYI I also have the hellcat fuel pump and added the summit relay so it’s got good voltage. Have IE rails stock fpr also , was tuned by Brad, no issues supports 800 hp


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Nice! Could be just me luck, regardless the GFB is freakn nice


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[S4James]

Ive lost track of it, but there was some discussion showing that certain part numbers for the 4bar fpr had larger or smaller orifice sizes that could have impacted this. Unfortunatly i cant find the original source so I cant say one way or another if that was indeed true. There was also some talk about drilling out the stock FPR to fix the flow issue.

[armageddon-]

Ive lost track of it, but there was some discussion showing that certain part numbers for the 4bar fpr had larger or smaller orifice sizes that could have impacted this. Unfortunatly i cant find the original source so I cant say one way or another if that was indeed true. There was also some talk about drilling out the stock FPR to fix the flow issue.

Think you are talking about "like stock" adjustable fuel pressure regulator that 034 sell and as others, they have larger orifice but remember some say that wasn't enough

Edit: https://store.034motorsport.com/fuel...k-fitment.html

[Shahek]

Ive lost track of it, but there was some discussion showing that certain part numbers for the 4bar fpr had larger or smaller orifice sizes that could have impacted this. Unfortunatly i cant find the original source so I cant say one way or another if that was indeed true. There was also some talk about drilling out the stock FPR to fix the flow issue.

This is actually how I confirmed my issue. I drilled out my stock fpr as much as I could and my in line gauge dropped about 10 psi.


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