Mustang5L5’s progress thread - fuel pressure shennanigans

[Mustang5L5]

Tossed a tune in.

Certainly starts up and runs better. Probably the best it's idled in a long time. Definitely helped with some of the wild AFR swings

However the fueling issue still exists. I still drop 6-7psi of pressure on a small rev. No change there. I see this on my mechanical gauge as well.


Now my mind is wondering if it's a relationship with the fuel sock/baffle causing some sort of fuel starvation when load increases? I might have to drop the tank and see if i can put the fuel pump hanger assembly in a bucket without the sock and see if that changes anythung

 

[nickyb]

Full circle, back to dropping the tank? I can't take it much longer you gotta get this fixed please.

 

[Mustang5L5]

Full circle, back to dropping the tank? I can't take it much longer you gotta get this fixed please.

Yup. Going to be my next step. I'm thinking it might be how the pump is sitting. During every single test i've done, the pump was fully installed with a sock.

I might pull the pump and just stick it in a bucket of gas with the sock removed.

 

[gkomo]

Maybe the sock is bent over on itself and like doubling up on the filtration media. Seems weird though that two pumps something like that would happen.

 

[All Stock93]

Go drop the tank right now.The suspense is killing me lol

 

[Mustang5L5]

Go drop the tank right now.The suspense is killing me lol

It’s an awesome night out weatherwise. I went for a ride in the convertible. I needed a break.

 

[FastDriver]

Ran into a guy from Boston at the hotel bar tonight. Loudest guy in the place, very spirited, and somehow still obviously a good dude. Is this just standard Boston behavior?

 

[FastDriver]

"and during the blip it drops to 11.8 and then instant 19.0. (I think this is actually a excessive rich condition)"

Not likely. This is ovethinking. A lot goes on when you blip the throttle:
1. tip-in/accelerator pump fueling
2. every cell in your Load/VE table that you travel through.
3. dMap enrichment on acceleration
4. dMap leaning on deceleration (probably causing the spike)
5. Compensation for voltage regulation (injector data)

And whatever else that's not top of mind. What makes your claim unlikely is that I've never seen an AFR gauge that was unable to drop below 11.8:1. You'd get into the 9s, probably, before having spark issues. So, it's more likely that your dMap is commanding a pull back in fuel that's too severe. That said, you cannot hurt the engine on decel like that. There's just not enough fuel to result in detonation that can hurt anything.

 

[General karthief]

It’s an awesome night out weatherwise. I went for a ride in the convertible. I needed a break.

Yeah, I feel ya on the drop top drive.
Seems I remember being able to do that once upon a time, long ago.
What kind of hat do you wear while you wave at the common people along the road? Conspicuous? Pretentious? Yeah I think that's the one...

 

[Mustang5L5]

Ran into a guy from Boston at the hotel bar tonight. Loudest guy in the place, very spirited, and somehow still obviously a good dude. Is this just standard Boston behavior?

Eh, that is the Boston stereotype for a reason. There are a lot of folks here like that, but then there are a ton of normal folks as well. I'm prob more the latter and keep to myself mostly.

 

[Mustang5L5]

Maybe the sock is bent over on itself and like doubling up on the filtration media. Seems weird though that two pumps something like that would happen.

I had to search back in my posts and found this pic.

Pump does sit tight to that baffle, and the sock in the corner is bent up slightly.

Why i didn't think much of it was because at the time (2017) i had a mech fuel pressure gauge on my cowl and was chasing a hesitation issue. It ended up being the accel coil, but i have some posts where I state it holds 39psi at wot fine.

Obviously now I need ot go back and check this.

EDIT: also, i did have 3/4 of a tank in the car when this all started. I remember grumbling about having to siphon that all, so I don't think it's fully a baffle issue.


I wonder if my comment from 2017 is accurate. Wouldn't it be something...

 

[Mustang5L5]

Dropped tank. Took off fuel sock. Hung it free back in the tank into the fuel.

Zero difference. I stuck both a mechanical gauge and the transducer up on the FRP and both register a drop. Even a slow rise in RPM's registered a drop of 1-2 psi. A blip drops 6-7psi. I see it on both the mechanical and transducer. I see it on the stock location with another gauge as well.

So i'm at a loss.

There must be something that has remained constant through all my testing that I'm just not seeing.


I did another flow test at the tank by removing the return to the pump and putting it into a 1 gallon bucket. Took about 60 seconds to fill. Same as before. That;s about 200 liters per hour.

 

[nicholase]

Did you check the fuel line behind the pass fender inner fender? They can corrode there. I would think a restriction in the pressure line could cause low pressure issue after it. To prove that theory out...

" T" in your mechanical guage between the pump outlet and fuel pressure line by the tank. Is the guage behavior the same there or different?

I'd start right at the pump outlet and move the gauge up to every connection you have a way to connect it to. Your local parts store should have a mechanics guage to rent. They are usually free, just a deposit until you bring it back. They come with various fittings which might prove helpful.

Just a theory to check....

 

[Mustang5L5]

Did you check the fuel line behind the pass fender inner fender? They can corrode there. I would think a restriction in the pressure line could cause low pressure issue after it. To prove that theory out...

I checked. Nice and shiny and new looking. These are new lines I installed about 10 years ago. They still look brand new

" T" in your mechanical guage between the pump outlet and fuel pressure line by the tank. Is the guage behavior the same there or different?

That was my next step. Was going to get a gauge in at the pump and see what it does there.

I'd start right at the pump outlet and move the gauge up to every connection you have a way to connect it to.

That's a fine idea. Going to work through that next.


----------------------------


I messed around a bit more with it tonight and found that the pressure drop is proportional to the rate of RPM increase. So if i whack the throttle hard, it's a hard 6-9psi drop. If i roll into the rev slowly, it's a gradual drop. 1-2 psi or so and maybe creeps up a bit as i get past 3K rpm.

Makes me wonder if there is a slight restriction up to the engine bay somewhere. If I can get a gauge at various points, i might be able to pinpoint where it is.

 

[Mustang5L5]

Ok. Another mystery.

I wanted to triple check my guages. Borrowed a test guage from work and setup this little rig to verify. I ran it from 50psi down to 20psi taking a video and then comparing pressures. Bottom liquid gauge was off, so that got retired but top one was spot on.

So take itto the car and add the transducer. I'm using pressurized air at this point but do the same thing. Fill to 60psi and bleed it down to 20psi.

39psi on my nice gauge was 39psi on the mech and 38.2 psi on the transducer

51psi on my good gauge was around 50psi on the mech and 49.8psi on the transducer.

SO lets call it 1psi low on the transducer. Knowing that, i figure i can set the pressure to 40psi and that's good enough.


So i set up the gauges on a tee at the regulator. You can clearly see them in the pic. I fire up the engine

Mechanical gauge is reading 37psi and the transducer is reading 45psi! WTF? Remember, i ran them both up to around 50psi and down and they were within 1psi of each other.

Maybe it's 12V vs 14V, so i go to measure the 5V reference. SPot on at 5.0 volts at both 12 and 14 volts. Specs on that gauge state it can be mounted at any angle

I'm confused.

Regardless, we can work on this later.

 

[FastDriver]

Ok. Another mystery.

I wanted to triple check my guages. Borrowed a test guage from work and setup this little rig to verify. I ran it from 50psi down to 20psi taking a video and then comparing pressures. Bottom liquid gauge was off, so that got retired but top one was spot on.

So take itto the car and add the transducer. I'm using pressurized air at this point but do the same thing. Fill to 60psi and bleed it down to 20psi.

39psi on my nice gauge was 39psi on the mech and 38.2 psi on the transducer

51psi on my good gauge was around 50psi on the mech and 49.8psi on the transducer.

SO lets call it 1psi low on the transducer. Knowing that, i figure i can set the pressure to 40psi and that's good enough.


So i set up the gauges on a tee at the regulator. You can clearly see them in the pic. I fire up the engine

Mechanical gauge is reading 37psi and the transducer is reading 45psi! WTF? Remember, i ran them both up to around 50psi and down and they were within 1psi of each other.

Maybe it's 12V vs 14V, so i go to measure the 5V reference. SPot on at 5.0 volts at both 12 and 14 volts. Specs on that gauge state it can be mounted at any angle

I'm confused.

Regardless, we can work on this later.

Put a multimeter directly on the transducer signal wire while the engine is running and compare voltage to what MS reports.

 

[Mustang5L5]

And the data log.

Pressure sitting at 45psi. Quick rev and it drops to 36psi. AFR goes lean and duty cycle goes from 1.8ms to 18ms trying to add fuel.

 

[WhiteCobra95]

I think this confirms that the MS software is using MAP as a FP reference and giving you the dP across the injector. From what I can see in your picture, the mechanical gauge is reading 37 psi (confirmed in your text) and the ECU is reading MAP at -7.9 psi. If the transducer's raw voltage reading (please check the raw voltage and do the slope offset by hand to confirm) is correct for the gauge pressure, then the math is: transducer pressure (37 psi) - MAP (-7.9 psi) = 44.9 psi delta pressure. This is roughly the 45 psi shown on the MS software screen for fuel pressure.

It seems like there are multiple issues. There must be a flow restriction somewhere, which is the only way to explain the pressure drop @ flow. But at the same time, the MS software is treating ANY fuel pressure input as gauge and providing dP instead of fuel line gauge pressure. If MS will allow you to read the transducer's raw voltage during the blip, you can confirm that the reading on the screen has more math behind it than a straight conversion. If it's calculating dP and seeing a larger value than your reference pressure value, then it could be correcting your injector slope dynmaically by the square root of the measured dp over the ref pressure, which will result in an even larger injector flow rate / lower ti for the ECU's ti calculation.

As a second step, can you bring in the FP transducer as just a raw transducer input and NOT map it to fuel pressure? If the voltage or calculated pressure looks correct in MS as a generic element, not linked to any exact sensor feature, this would confirm that the MS software has more math behind the fuel pressure calculation.

Regarding the restriction, have you considered running an external line from the tank to the rail? This would be very dangerous if not done correctly and carefully, but might answer some questions. If you already have a bucket setup, you could also run the pump hat from a bucket with short lines to the rail and see what happens.

 

[WhiteCobra95]

One other thought to confirm, and this could be wild - with the engine off and ignition on, put a mighty vac on your MAP sensor and pull it down to 40 kPa absolute. See what the MS fuel pressure reading does and confirm that the MS MAP value is going down with the vacuum applied.

 

[Mustang5L5]

Put a multimeter directly on the transducer signal wire while the engine is running and compare voltage to what MS reports.

Took me a min to figure out how to get what MS is reading from that sensor which is Analog in1 that i have it set up as. I can set it to display volts, but not at the same time as pressure or i get conflicts. Requires a key cycle. SO next time i run the engine i'll see what MS is reporting for volts and manually convert that.

But, 12V engine off. I cycle the pump. 37psi on the transducer, MS is reporting 2V and i see 37psi on my mech gauge. SO far so good.

Too late to start engine now so i'll fire it up tomorrow and see what happens. Maybe i'll swap the transducer and guage and see if any difference.