Mustang5L5’s progress thread - Rear window fun

Mustang5L5 · Apr 14, 2026

hoopty5.0 said:
Are you sure there arent two issues here? The FP dropping is an issue to be sure, but for the blip, is the accel enrich set up right? That would cause an instant lean and stumble condition.

Yes, possibly two seperate issues. I went down this rabbit hole when i first noticed the problem to try and determine if it was tune related. I'm convinced it's not related to the tune. I threw my base tune back on. I've done extremes one way or the other and the symptoms remain.

Also worth noting that since I haven't been on a drive in some time, that the FP would drop at a sustained WOT pull as well. I had to add a lot of fuel to the VE table to compensate.

I do think this is a real problem.

Kid wita 5oh · Apr 14, 2026

I'm sure you did, and it's probably back in the thread somewhere...but did you check the S hose really well when you swapped the pump the other day?

FastDriver · Apr 14, 2026

Yes he addressed that earlier too.

Kid wita 5oh · Apr 14, 2026

I figured as much just too lazy to go back and find it.

Mustang5L5 · Apr 14, 2026

I did. I peeked in from the fill tube inlet and visually inspected it while the pump ran. Also, it’s a new plastic type hose

Mustang5L5 · Apr 14, 2026

Backed it out today. Wanted to clean out the garage. Let it warm up a bit and it died. Turns out the Deutch Weather pack I installed just isn’t making a solid reliable connection. Apparently the pins only stick out 1mm or so?? Seems very odd but I followed the directions and all the illustrations show this.

See the pins waaaay back there? Ive just lost my trust in this connector now that it failed within 10 feet of backing out the driveway. Looks like I’ll be swapping that out for some sort of other connector type.

Anyway outside in the fresh air. Did not drive it though.

I’m half tempted to pull the intake and pull the fuel rail off, along with the metal lines down the side of the engine with the pressure transducer in it and blow through them/ run a peice of weed whacker string and just verify they are clear. Also going to put the car on jackstands and go over every inch of the fuel line and just verify no pinches anywhere.

AeroCoupe · Apr 14, 2026

Get the basic stuff looked over as it will drive you nuts if you do not. I hate the whole second guessing myself so I just bitch about it and then go do it so I know for a fact its right. I used these connectors and they work great.

Even ordered the correct crimping tool and that made a world of difference.

Kid wita 5oh · Apr 15, 2026

I use Deutch connectors daily at work. Theyre one of the best... There should be about 1 cm of male pin protrusion in the connector body.. something is wrong there

Mustang5L5 · Apr 15, 2026

Kid wita 5oh said:
I use Deutch connectors daily at work. Theyre one of the best... There should be about 1 cm of male pin protrusion in the connector body.. something is wrong there

That’s what I assume it should be. I definitely don’t have that so maybe the male pins aren’t fully engaged into the connector. I’ll check it out shortly.

I think I’m gonna end up pulling the intake off and pulling the fuel rail. I think that’s actually pretty straightforward to check just to rule out no blockages anywhere in those lines.

I’ve got a busy week ahead so this might be delayed.

Prob gonna drive the SN95 a bit and get it out of my system after a long winter, then I’ll jump back into it. Prob no updates here for a little bit

rednotch · Apr 15, 2026

They real dts Connectors or the $10 China clones. I like the the barrel vs open crimp leads, but some of the knock offs are garbage from the ones I've tried..

Kid wita 5oh · Apr 15, 2026

rednotch said:
They real dts Connectors or the $10 China clones. I like the the barrel vs open crimp leads, but some of the knock offs are garbage from the ones I've tried..

THIS

Kid wita 5oh · Apr 15, 2026

If you need some connectors and/or barrel crimp terminals let me know

Kid wita 5oh · Apr 16, 2026

Here what it should look like, not quite 1cm of pin but close

Mustang5L5 · Apr 16, 2026

rednotch said:
They real dts Connectors or the $10 China clones. I like the the barrel vs open crimp leads, but some of the knock offs are garbage from the ones I've tried..

Dammit. This was it!

China clone sold as the real thing!

I'm getting my butt kicked on this project here

nicholase · Apr 17, 2026

We've all been on the receiving end of a beat down. I had a similar but opposite issue as you regarding fuel pressure. However I was getting high fuel pressure and unable to get it down to factory spec. It went away when I replaced all the lines w/-6an. But I believe the issue was a partially clogged return. The lines looked perfect everywhere I could see. But when I pulled the pass inner wheel liner I saw the return line was corroded in one spot. There's a peice of sound deadening insulation that rests on the fuel lines. The return was corroded only where that insulation was touching it. I believe the exterior rust was collapsing the interior of the line. It was clean inside and free of rust, but looked restricted. If you haven't, probably a good spot to look.

Your "pressure shenanigans" remind me of an LMR video I saw a while back. He dropped the tank several times chasing a low pressure issue. He ended up finding a butt connector stuck in the pump inlet. He assumes it came from a replacement "S" hose kit that ships with the butt connectors in the same package. Likely one was stuck in the hose unseen and worked its way into to the pump inlet. Not saying this is your problem, just saying sometimes some stupid little thing causes a huge headache.

Video starts at 22:20 when he discovers the butt connector.

Mustang5L5 · Apr 17, 2026

Ha. Thats funny. If I do find something in the lines, i'm gonna frame it and hang it on the garage wall.

Needless to say will need to wait a little bit longer. I'm booked through the end of next week with school vacation activities so stay tuned.

Mustang5L5 · May 26, 2026

Welp, I am no closer to solving this.

Did some more testing and verifying. Everything checks out. Nothing changed. I still have a problem. For those just tuning in, if i set my static FP to 39PSI, and then do a WOT pull in 2nd or 3rd gear, my fuel pressure drops to 29psi. This is all datalogged in my MS3 setup

So here's what I've done.

2 190LPH fuel pumps
Replaced S-hose, new filter sock
new lines from tank to hard line
new fuel filter
2 different fuel pressure regulators including rebuilding my original Kirban
new 47# injectors
Physically removed the fuel rail and verified no blockage
removed fuel feed line at engine and timed how much fuel came out to calculate pump volume - confirmed ~200 lph
verify my fuel pressure reading with 3 different transducers and one mechanical gauge
remove and block vac line. verify FP set to 39psi and confirmed even without vac it drops under load
Rewired fuel pump circuit with 10G wire from battery direct to pump. Voltage drop checks show little to no drop

No matter what i've done...zero changes.

Not sure what else i can try here. I popped the feed line off and measured out 1 gallon of gas in 60 seconds at 12V. Doing math comes out to just above 200lph. I think what i can try next it to pop the return line off at the engine, and flow that into a 1 gallon bucket and see how much volume I get. When i took my fuel rail off, i was easily able to blow through it so I do not believe there is any blockage.

I'm scratching my head here. I do have a problem. I clearly get a stumble and lean spike thar correspond with the FP drop if i give the engine a healthy rev. I also went back through old vids and found I also had this issue when i had the A9L. I also found some way older vids of my mechanical cowl-mounted gauge and some revving and can clearly see 2 things. #1 is the engine free revs and instantly jumps to 39psi. And on key prime, the FP builds to 39psi pretty fast just on the prime. When i key prime now, the most I'm able to prime to is.....29psi.

So i'm stuck for now. That last thing is making me scratch my head. Why can't i prime past 29psi? Even if i run the pump constant via Tuner studio override, it just sits at 29psi. When i start the engine it will go to 39psi with vac off. So why engine off i can only get to 29 with the same setting. 12V vs 14V? Keep in mind, i've tried two different pumps and they do the exact same thing.

I gotta be missing something

gkomo · May 26, 2026

I'm just throwing darts here but is there a way to check voltage at the pump when its running? Do you think it could be a wiring issue where the pump just isn't getting the power it needs to work correctly?

Since i've been doing some research of my own on the FP wiring upgrade thats just where my heads going. Sounds like you've replaced every physical component of the fuel system so i'm just wondering if its electrical now?

mattcrp1 · May 26, 2026

Have you voltage dropped the line under load?

Mustang5L5 · May 26, 2026

Knew i forgot to list something.

I did voltage drop checks on the original pump wiring and saw some voltage drop. I rewired the fuel pump circuit with new 10G wired direct off the battery to the pump itself through the hanger. Reverified voltage drop and it's very little to none now.

Made zero difference.

I'm hung up on the key prime now. I can do 2-3 key cycles and it will not prime past 29psi. This is tested with 2 different 190lph pumps. I have old video showing i was able to spike to 39psi on a key prime years ago. Why?

Also to add, i don't think it's the injectors leaking. I had this same issue with my old 19# injectors on as well, before i swapped to the 47's.

Mustang5L5’s progress thread - Rear window fun

That is…until I whipped out my Bissell

I'm definitely not in the original hole

I was uncomfortably high & wearing a helmet

I'm definitely not in the original hole

That is…until I whipped out my Bissell

That is…until I whipped out my Bissell

lube between the nut and the face. I know my lubes

I'm definitely not in the original hole

That is…until I whipped out my Bissell

I'd like to remain having one chocolate starfish

I'm definitely not in the original hole

I'm definitely not in the original hole

I'm definitely not in the original hole

That is…until I whipped out my Bissell

I lubed and pushed, until it was all the way in

That is…until I whipped out my Bissell

That is…until I whipped out my Bissell

now i can hopefully expect to receive the shaft

Active Member

That is…until I whipped out my Bissell

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