Fuel Bad regulator diaphragm?

JD1964 · May 20, 2025

I have a Kirban adjustable regulator and I think the diaphragm is bad. Help me confirm. Idling at 19 in vacuum with the vacuum line disconnected I get 40psi fuel pressure. Re-connect the vacuum line and the pressure only drops 2 psi down to 38psi.

Can you confirm this is the regulator not working properly?

I think I damaged it by connecting my FMU lines up backwards.

nickyb · May 20, 2025

Sounds like you blew the diaphragm .

Noobz347 · May 20, 2025

You're likely pregnant.

JD1964 · May 21, 2025

On further thought, if the diaphragm was blown, wouldn’t it be crazy rich at idle? Also, it would probably have gas in the vacuum line. The line is dry and the idle and cruise AFR is mid 14’s.

Another post I dug up indicated that a restriction in the return line would cause the symptom I’m having. Maybe the FMU is having an interaction with the regulator or something.

I’ll tinker some more and post back

JD1964 · May 21, 2025

I played with the Kirban regulator adjustment. It responds to adjustments. Interesting thing is if I crank it up to 50psi and reconnect the vacuum line, it drops 6psi. If I set it at 40psi and reconnect the vacuum line, it only drops 2psi. The ECM will adapt to either setting and maintain idle AFR at mid 14’s.

I’m gonna stop worrying about the Kirban regulator for now and focus on my AFR while under boost which is what my initial is task anyway.

Background: Walbro in tank 255 pump. 42lb injectors with Pro M calibrated MAF. FMU currently has 4:1 disc. Boost begins to come in around 3k rpm. AFR only drops to about 14 flat. I really want it at least into the high 12’s.

I suppose even though I’m running the 4:1 disc intended for 42lb injectors, there’s something about my overall setup that needs a different FMU calibration. I think I might order the kit from Vortech that has the various discs and experiment with them.

Do any of you have any Vortech discs that you’re not using and would be willing to sell me?

Anyone have any other helpful thoughts on this matter.

Thanks, John

Noobz347 · May 21, 2025

Make sure that you have no pinches or restrictions in your return line, going all the way back to the fuel tank.

We had one of those in another thread here, not too long ago. I'll leave it here to see if any of it applies to your situation:

A

Resolved Thread 'Fuel pressure high at 52 new FPR same thing'

Dec 28, 2024

Ok on to the next problem. Plugs fouling looking like soot around the edges. Decided to start at checking fuel pressure.

Fuel pressure check showed it at 50psi. Looked like the original FPR so I replaced it with one of those adjustable units from LMR. This one reads 52psi and I’m not able to get any adjustment out of it. Can’t lower it at all. I replaced the fuel filter with a K&N unit about a month ago when I replaced the fuel pump. It has a walbro 255lb fuel pump and 24lb injectors.

Not sure where to go next? Bad injectors? Could the bigger fuel pump cause this?

UPDATE:

So I...

JD1964 · May 21, 2025

I’ll check the return lines for kinks.

This FMU came with the V3 kit as an entry level kit for stock 19lb injectors. Since it’s lean with the 4:1 disc meant for 42lb injectors, I’m gonna do an experiment by putting the 12:1 disc back in. If the FMU is working right I expect it to be way too rich. With that information I’ll conclude it as just a matter of picking a figuring out disc somewhere between 4:1 and 12:1 works best for my specific application. I wish I would have bought the complete disc kit initially instead of just the 4:1.

JD1964 · May 23, 2025

Well, the 12:1 disc sure delivered the fuel. My problem all along is still with me though. It’s just not holding at the head gaskets. Boost is pushing cylinder pressure into the water jacket. NA it’s no problem. I’ve been through multiple head gasket swaps including the fel pro and cometic. I think these cast iron gt40 heads maybe got milled enough to weaken the deck and they just don’t hold long term.

So , you think a nice pair of aluminum heads would do the trick? I already have the ARP heads stud kit in the engine now so I don’t need to get those.

Noobz347 · May 23, 2025

Question First:

If you pull it all apart, how likely do you think it will be that you will be able to tell which side of the gasket is leaking (head side or block side)?

JD1964 · May 23, 2025

I think I know what you’re getting at. Block deck right? It was shaved .003 to perfect when this last set of Cometics were put on along with the ARP stud kit. The stock block was fully rebuilt including fully balanced. It didn’t really need all that but since I wanted the block shaved, the other stuff was just done along the way.

Noobz347 · May 23, 2025

Yeah... There are no pours in an aluminum head so your solution is a good one so long as you're confident the block deck is [not] the issue.

I was looking at the rest of your combo in your sig too. A set of heads would probably do [wonders] so, WIN WIN!

Noobz347 · May 23, 2025

Oh, and I would do the Cometic gaskets again. That what I run too. Kenne Bell... Boost comes on fast.

JD1964 · May 23, 2025

10-4 on the Cometics. I have everything I need to tune with Moates. All the hardware and full software license. I got the full tuning guide too. I just need to teach myself. The only reason I was messing with the FMU this time was to see how the engine held with the new 42lb injectors. I got my answer now. The blower is coming back off until figure the game plan.

Blown88GT · May 24, 2025

JD1964 said:
I have a Kirban adjustable regulator and I think the diaphragm is bad. Help me confirm. Idling at 19 in vacuum with the vacuum line disconnected I get 40psi fuel pressure. Re-connect the vacuum line and the pressure only drops 2 psi down to 38psi.

Can you confirm this is the regulator not working properly?

I think I damaged it by connecting my FMU lines up backwards.

I have the Kirban & a Walbro in tank 255 pump & 47lb injectors.
That is normal functioning for the Kirban. The return port on the Kirban is not very large & can only compensate for a certain about of flow as can the return line on the car. I drilled mine out slightly & maybe dropped to 37 instead of 38 psi.
FMU's were needed before aftermarket ECU's arrived. They were designed to only work at WOT. They can be troublesome & I got rid of mine.

Noobz347 · May 24, 2025

Yeah, I ditched all my FMU stuff too (I think it's still laying in a box someplace) when I went to Bosch 42s.

A9L and SCT chip / OEM Rails / 255L HP / Boost-A-Pump / 480 Peak WHP on my smallest pulley - Turned out a little too gnarly for my tires and suspension but the fuel system held in there despite my thinking it would not.

Don't know if any of that helps.

Noobz347 · May 24, 2025

One other note: I removed the boost sensing switch for the Boost-A-Pump

I found the entire thing a [lot] more consistent when I just [set and forget] the fuel pump voltage at a rate that everything is happy.

JD1964 · May 24, 2025

I’ve been contemplating my next move. I think I’ll train myself in tuning with the Quarterhorse while configured in NA on my current setup. NA, the GT40 iron heads hold fine. Since my goal is DIY tuning, I’ll get familiar it before I start spending another few K on AFR’s and supporting goodies. Hopefully my investment funds will get fatter meanwhile and I’ll feel less pain from the pending expense.

Noobz347 · May 24, 2025

You've likely already seen this but I'll leave the link here anyway: https://stangnet.com/mustang-forums/resources/fuel-flow-forensics.55/

Hit the download button toward the upper-right hand side.

JD1964 · May 24, 2025

When I had my PRO M MAF recalibrated for 42lb, I paid extra for the data sheet that lists all the voltage values across the RPM range. They told me that will help me with turning since I can just plug all those numbers into the binary editor instead of having figure them out on my own.

Noobz347 · May 24, 2025

JD1964 said:
When I had my PRO M MAF recalibrated for 42lb, I paid extra for the data sheet that lists all the voltage values across the RPM range. They told me that will help me with turning since I can just plug all those numbers into the binary editor instead of having figure them out on my own.

You're referring to the "transfer function" of the MAF itself.

Yeah... That will help.

Fuel Bad regulator diaphragm?

there is enough sticking out to grab on to

I gotta say i never painted my nuts, Never Ever

Stangnet Facilities Maint Tech... Er... Janitor

there is enough sticking out to grab on to

there is enough sticking out to grab on to

Stangnet Facilities Maint Tech... Er... Janitor

Resolved Thread 'Fuel pressure high at 52 new FPR same thing'

there is enough sticking out to grab on to

there is enough sticking out to grab on to

Stangnet Facilities Maint Tech... Er... Janitor

there is enough sticking out to grab on to

Stangnet Facilities Maint Tech... Er... Janitor

Stangnet Facilities Maint Tech... Er... Janitor

there is enough sticking out to grab on to

Stangnet Facilities Maint Tech... Er... Janitor

Stangnet Facilities Maint Tech... Er... Janitor

there is enough sticking out to grab on to

Stangnet Facilities Maint Tech... Er... Janitor

there is enough sticking out to grab on to

Stangnet Facilities Maint Tech... Er... Janitor

Similar threads

Privacy & Transparency

Privacy & Transparency