Hello guys! I have a problem with my fuel pressure and I need some help from you guys to be able to fix the problem.

I've upgraded the fuel lines with SS hoses with 8AN and 6AN for return, Walbro 525 with welded AN fittings on hanger, Fuelab pressure regulator and AEM fuel rail with fuel pressure sensor from Innovate ECF mounted in the fuel rail and logged to ECMLink.

Once I started the fuel pump from ECMLink to set the base fuel pressure to 43psi I could see the pressure fluctuating from 35psi to 45 psi. I could adjust the pressure lower than 43psi so the drilled siphon wasn't a restriction.

Starting the engine and drive the car the fuel pressure is all over the place. I wanted to fix this problem so I removed the fuel pump and test it again for leaks, tested ok all the way to 80psi with no fuel leak. Since I had the pump out I've changed the fuel pump filter and after starting the fuel pump from ECMLink without the engine running the fuel pressure was steady at 43 psi but once I started the engine it started to fluctuate again.

Stopping the engine and test again only with the fuel pump running pressure was still fluctuating. Few days later I tested again only with the pump running and got a steady fuel pressure but once I start the engine it's starting to get jumpy. So my conclusion is that once the system is losing the pressure over few days or by disconnect the lines then at first start of the pump the pressure is steady but once the engine is stated the pressure will fluctuate and will do so until the fuel pressure is dropping again.

I'm thinking it might be the regulator having the orifice to small for the Walbro pump or the 10 micron fuel filter I have installed before the fuel rail. I would like to hear what you guys think it might be the problem.

Thank you!

Sounds like the fuel pressure regulator spring is weak or can't support base pressure, maybe due to increased flow/ volume. Especially when the car is running/alternator on. Or somehow the pressure bleeds off back into the system/gas tank. Also check if the vacuum line on the regulator is full of fuel, maybe the diaphragm inside is torn.
I would also check for loose grounds or put the old pump only and see what the pressure is doing. If pressure is steady and everything works as it should, all the new lines, filter and the regulator is not the problem. That would probably be my first moves.

What fuel pressure regulator are you using? The diaphragm inside them can leak and cause the symptoms you are describing.

Can you try measuring the pressure at the regulator to make sure your not just seeing some sort of local oscillation in the fuel rail that a fuel dampener might fix.

I checked the fuel pressure regulator and the diaphragm it's not damaged.
I'm using a Fuelab 515 series and a Fuelab 818 fuel filter.
I will send an email to Fuelab to get some feedback from them about the spring pressure and the overall situation.

The ground wire for fuel pump is bolted really good and the power cable is connected on the battery.
I was thinking also to change the fuel pump with the old one just to see if something is different.

About pressure oscillating in the fuel rail I can say the analog gauge mounted on the regulator it's also moving although not so much and hard to see but it's not steady for sure. I even changed the fuel sensor with another one and I got the same readings.
I have some logs and I could also see on the Innovate gauge where the fuel pressure goes from 35psi to 45 psi on normal cruise driving.

Personally I would say it's ether the fuel filter being restrictive, the fuel pressure orifice being to small for so much flow.
I'm also thinking to disconnect the return and run it into a bucket. I have the feeling there is to much fuel flowing on the return hose and because of the siphon dumping the fuel on top of the inlet of the fuel pump it can cause a cavitation.

How does the voltage look like while the pressure is fluctuating by running the pump via ECMLink? Did you check for voltage drop at fuel pump and in ECMLink?

DSMPT said:

How does the voltage look like while the pressure is fluctuating by running the pump via ECMLink? Did you check for voltage drop at fuel pump and in ECMLink?

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The voltage is steady at 13.8V. I can post a log later on today so you guys can see the voltage and the fuel pressure.

I just looked at the numbers and it says that car off, 12v the pump produces up to 470 lph, that's about 125gal per hour or 2.08 gallons per minute. With alternator ON 13.5+ v it will flow 525lph. 525 lph is about 140gal per hour. That is about 2.3 gallons per minute.

Then I tried to look up maximum flow through rate on a 515 fuelab and I get mixed info, but generally speaking it's anywhere from 2 to 2.5 gal per minute and that's giving that the regulator is at its best performance and it hasn't fatigued over time. Maybe that's why key ON engine OFF it's still trying to do it's job but give the pump a little more juice and the damn regulator spring is fighting for its life.

I was thinking the same about that return hose and a bucket idea, to see if it flows like a race horse with kidney stones, but I doubt that with that much pressure and flow, little flactuation would even be possible to recognize. I did not however think about possible fuel aeration. With that much fuel going back to the tank it's possible. Fuel pressures will act up for sure. I once had a bit of a different problem on a different car, where I had my fuel lines extremely close to the exhaust, and after about 15 minutes driving my fuel pressure was all over the place...fuel tank was hot to touch. Maybe you have to find a way to route the return to the bottom of the tank sideways or something, so it creates a vortex or something, but doesn't meet air..... 525 is kinda an overkill of a a pump, I can't even imagine what I would need all those pixies for

CDgr97GSX said:

The voltage is steady at 13.8V. I can post a log later on today so you guys can see the voltage and the fuel pressure.

Click to expand...

What about the voltage on the pump? I meant if you compared the battery voltage and on the fuel pump (supplied voltage) while the pressure is fluctuating.

Vladimir said:

I just looked at the numbers and it says that car off, 12v the pump produces up to 470 lph, that's about 125gal per hour or 2.08 gallons per minute. With alternator ON 13.5+ v it will flow 525lph. 525 lph is about 140gal per hour. That is about 2.3 gallons per minute.

Then I tried to look up maximum flow through rate on a 515 fuelab and I get mixed info, but generally speaking it's anywhere from 2 to 2.5 gal per minute and that's giving that the regulator is at its best performance and it hasn't fatigued over time. Maybe that's why key ON engine OFF it's still trying to do it's job but give the pump a little more juice and the damn regulator spring is fighting for its life.

I was thinking the same about that return hose and a bucket idea, to see if it flows like a race horse with kidney stones, but I doubt that with that much pressure and flow, little flactuation would even be possible to recognize. I did not however think about possible fuel aeration. With that much fuel going back to the tank it's possible. Fuel pressures will act up for sure. I once had a bit of a different problem on a different car, where I had my fuel lines extremely close to the exhaust, and after about 15 minutes driving my fuel pressure was all over the place...fuel tank was hot to touch. Maybe you have to find a way to route the return to the bottom of the tank sideways or something, so it creates a vortex or something, but doesn't meet air..... 525 is kinda an overkill of a a pump, I can't even imagine what I would need all those pixies for

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Thanks for all the specs! On the paper it's seems the fuel regulator it's on the limit.
That was the reason I wanted to get some thoughts about this problem before I'm buying another 300$ fuel regulator.
I will remove the fuel pump hanger and i'll flow test it, I want to see what's happening.
About the return line i don't know if i can re route it or bypass the fuel tank siphon then i'll have another problem with the tank fuel transfer, isn't it?

DSMPT said:

What about the voltage on the pump? I meant if you compared the battery voltage and on the fuel pump (supplied voltage) while the pressure is fluctuating.

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I haven't checked the voltage on the pump but I suppose that's the easiest thing to check. When i have some free time i'll check it. Thanks

CDgr97GSX said:

Thanks for all the specs! On the paper it's seems the fuel regulator it's on the limit.
That was the reason I wanted to get some thoughts about this problem before I'm buying another 300$ fuel regulator.
I will remove the fuel pump hanger and i'll flow test it, I want to see what's happening.
About the return line i don't know if i can re route it or bypass the fuel tank siphon then i'll have another problem with the tank fuel transfer, isn't it?

Click to expand...

You had a good idea about writing or calling fuelab. I would trust their words a lot more. They have all correct specs available. I just did a 10 minute search online and provided general info.

Not sure about the siphon, it is needed for fuel transfer. I would think even drilling it out going from factory 140ph to 500 is a stretch. Plus isnt it's plastic, I don't understand how I didn't fall apart to pieces . I'm not an engineer, best I would do is throw the tank and put a fuel cell. Make all the complex Japanese engineering as easy as possible )))

Vladimir said:

You had a good idea about writing or calling fuelab. I would trust their words a lot more. They have all correct specs available. I just did a 10 minute search online and provided general info.

Not sure about the siphon, it is needed for fuel transfer. I would think even drilling it out going from factory 140ph to 500 is a stretch. Plus isnt it's plastic, I don't understand how I didn't fall apart to pieces . I'm not an engineer, best I would do is throw the tank and put a fuel cell. Make all the complex Japanese engineering as easy as possible )))

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I will get it fixed somehow. I wouldn't go for a fuel cell, I have to keep the car as street legal as possible.

With the engine not running how well does the fuel pressure track changes in manifold pressures?
Use a charger to make the system voltage closer to running voltage.

Yeah the Fuelab spec drawing, have to look at it for a while to figure out how to read the flow rating.
You have to know or figure out which 515 sub-model you have.
I looked to see what model STM sells, and they sell the 51501 and 51502, so those are probably the most common ones.

According to the drawing, the 51502 is "E" pressure range, "Standard" seat, and has two -6AN inlet ports.
The 51501 is also "E" pressure range, "Standard" seat, and has two -10AN inlet ports.
So either way you find the line on the chart that has "E" and "Standard". (chart in lower left corner of the drawing)
And that line has a rated flow capacity of 2.5 GPM (568 LPH)
Seems like it should be enough for the F90000285 Hellcat pump.
But not a lot of extra headroom there.

BTW this same chart is where you find out what the Regulation Slope is for your regulator. Which is something nobody ever talks about. I think some of the other manufacturers don't even talk about it. But just because they don't want to talk about it doesn't mean they don't have it.
Well it's probably not important to know it. If it exists, it just becomes part of your tune and you don't even realize it.

That siphon thing with the 2g, wish I knew more about it. All I know is that 2g guys usually wind up drilling it, I think it's with 1/8" drill. I'm glad I don't have one. I see this with Evos too.

I

steve said:

With the engine not running how well does the fuel pressure track changes in manifold pressures?
Use a charger to make the system voltage closer to running voltage.

Click to expand...

I would say it's the same. I even bought a AGM battery to test, changed full before install it. If the car stays in the garage for few days on first start of the pump from EcmLink the pressure it's OK. I can start and stop the pump, pressure it's still 43 psi and steady at around 43 psi. Once I start the engine everything then it's fluctuating, stopping the engine and run only the pump it's still fluctuating.

CDgr97GSX said:

I would say it's the same. I even bought a AGM battery to test, changed full before install it. If the car stays in the garage for few days on first start of the pump from EcmLink the pressure it's OK. I can start and stop the pump, pressure it's still 43 psi and steady at around 43 psi. Once I start the engine everything then it's fluctuating, stopping the engine and run only the pump it's still fluctuating.

Click to expand...

Sorry, I wasn't clear what I was asking.
How well does the fuel pressure track changes in the manifold pressure presented to the port on the FPR?

Because I'm trying to eliminate variables having the engine not running will erase the question of injector pulsing and also test worst case flow through the FPR return since the engine won't be consuming any fuel.

Even fully charged a good battery isn't going to provide more than 12.6V where the electrical system with the alternator running would be between 13.something and 14.4v. The fuel pump is going to output more at the higher voltage than just off battery. Again looking at worst case to see what's going on.

As I'm sure you know, the fuel pressure needs to track the manifold pressure 1:1 so at idle when you have vacuum in the manifold the fuel pressure you measure roughly will be Base - (1/2 Vacuum) because the conversion from inhg to psi is about half, and under boost Base + Boost.

Sorry to be pedantic but if you covered this already I missed it and I don't want to assume answers to unasked questions.

We're on Boost said:

Yeah the Fuelab spec drawing, have to look at it for a while to figure out how to read the flow rating.
You have to know or figure out which 515 sub-model you have.
I looked to see what model STM sells, and they sell the 51501 and 51502, so those are probably the most common ones.

According to the drawing, the 51502 is "E" pressure range, "Standard" seat, and has two -6AN inlet ports.
The 51501 is also "E" pressure range, "Standard" seat, and has two -10AN inlet ports.
So either way you find the line on the chart that has "E" and "Standard". (chart in lower left corner of the drawing)
And that line has a rated flow capacity of 2.5 GPM (568 LPH)
Seems like it should be enough for the F90000285 Hellcat pump.
But not a lot of extra headroom there.

BTW this same chart is where you find out what the Regulation Slope is for your regulator. Which is something nobody ever talks about. I think some of the other manufacturers don't even talk about it. But just because they don't want to talk about it doesn't mean they don't have it.
Well it's probably not important to know it. If it exists, it just becomes part of your tune and you don't even realize it.

That siphon thing with the 2g, wish I knew more about it. All I know is that 2g guys usually wind up drilling it, I think it's with 1/8" drill. I'm glad I don't have one. I see this with Evos too.

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I just checked my email and the fuel pressure regulator is Fuelab 51502 model.
Until I'm sure the problem it's the regulator I'm not gonna order a new one but I would i probably go for AEM with large seat.
I forgot to mention i have a fuelflex sensor mounted on the return hose after the regulator. Also I have the siphon drilled so with all that I didn't have a problem to set the fuel pressure at 43psi I could even go lower.
I have to do some tests but unfortunately i'll be away for 2 weeks, after I'm coming back home I'll start working on finding the problem.

steve said:

Sorry, I wasn't clear what I was asking.
How well does the fuel pressure track changes in the manifold pressure presented to the port on the FPR?

Because I'm trying to eliminate variables having the engine not running will erase the question of injector pulsing and also test worst case flow through the FPR return since the engine won't be consuming any fuel.

Even fully charged a good battery isn't going to provide more than 12.6V where the electrical system with the alternator running would be between 13.something and 14.4v. The fuel pump is going to output more at the higher voltage than just off battery. Again looking at worst case to see what's going on.

As I'm sure you know, the fuel pressure needs to track the manifold pressure 1:1 so at idle when you have vacuum in the manifold the fuel pressure you measure roughly will be Base - (1/2 Vacuum) because the conversion from inhg to psi is about half, and under boost Base + Boost.

Sorry to be pedantic but if you covered this already I missed it and I don't want to assume answers to unasked questions.

Click to expand...

Now I understand your idea and you are right. The battery measured before installing it was 12.9V and with engine running voltage it's 13.9V. I'm using a Noco genius 5 and I'll check what's the voltage output and if I can get 13.8 while charging the I can have a test under the same voltage as the car is running.
Under boost it's even more strange because the pressure is going from 35 psi to 55psi.
I'll post a log when i'll get to my computer.

CDgr97GSX said:

Under boost it's even more strange because the pressure is going from 35 psi to 55psi.

Click to expand...

If you base fuel pressure is 43.5 and your vacuum at idle is about 17inhg and your boost pressure at the time was 12.5 psi that would be right on.

Here are some logs guys.

Some interesting behavior in the first few seconds of that first log. I wonder how well calibrated the various pressure sensors are.
I'll look at more when I get back from PT.

CDgr97GSX said:

Here are some logs guys.

Click to expand...

Wow, I thought you were talking about a slow fluctuation. But this isn't slow at all.
In both logs, your Fuel Pressure is jumping up and down about 5 times per second, all the time, whether you are on the throttle or not. It's jumping by usually about 6 psi.
This sure looks like bubbles going into the fuel pump. Air bubbles or fuel vapor bubbles.

Except that like you said, it is not jumping like this before you crank to start. Then it is only moving up and down by a small amount that might be the minimum voltage difference that our ECUs can resolve. The Wideband is doing that too in the before-crank region. But not the Omni 4 bar.

steve said:

Some interesting behavior in the first few seconds of that first log. I wonder how well calibrated the various pressure sensors are.
I'll look at more when I get back from PT.

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I dont think the sensor it's the problem. I already checked two of them. It's a sensor from Innovate.

We're on Boost said:

Wow, I thought you were talking about a slow fluctuation. But this isn't slow at all.
In both logs, your Fuel Pressure is jumping up and down about 5 times per second, all the time, whether you are on the throttle or not. It's jumping by usually about 6 psi.
This sure looks like bubbles going into the fuel pump. Air bubbles or fuel vapor bubbles.

Click to expand...

Air bubbles from where? I can't think about anything. The only thing I can think about it it's the return flow right on top of the fuel pump filter.

CDgr97GSX said:

Air bubbles from where? I can't think about anything. The only thing I can think about it it's the return flow right on top of the fuel pump filter.

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Yes, return flow or siphon flow is all I can think of if it's air bubbles.
Maybe there is something weird going on in the tank over on the other side of the saddle, or the hose that brings the fuel over from there.

If it's fuel vapor, that would be I guess from something like a restricted filter sock at the bottom of the pump, and I don't know how that would happen, but maybe the sock is right down against the bottom of the tank or something. Don't even know if that would do it. But anyway, something that causes enough restriction on the pump inlet to cause it to cavitate.

Your logged item "Fuel Pressure" is coming from a sensor mounted into the fuel rail? Which end of the fuel rail?
What about your logged item "Base Fuel Press"? Where is that coming from?

I know that the 2g fuel hanger is really too short to fit the large-body Walbros in cleanly, so people do some pretty questionable things sometimes to fit them in there. I think it's something like they leave out the rubber part that would normally be at the bottom of the pump, because there isn't room for it. So then the bottom end of the pump (and the sock) is actually lower than it should be in the tank. Does that sound right? And maybe they cut off part of the plastic outlet pipe on the top of the pump so they can fit some rubber in at the bottom, which would bring the pump up a little bit. What did you do?
Do you have any pics of how yours looked when you had the pump and filter sock all assembled with the hanger just before putting it in the tank?
What size drill did you use when you drilled the siphon?

We're on Boost said:

Yes, return flow or siphon flow is all I can think of if it's air bubbles.
Maybe there is something weird going on in the tank over on the other side of the saddle, or the hose that brings the fuel over from there.

If it's fuel vapor, that would be I guess from something like a restricted filter sock at the bottom of the pump, and I don't know how that would happen, but maybe the sock is right down against the bottom of the tank or something. Don't even know if that would do it. But anyway, something that causes enough restriction on the pump inlet to cause it to cavitate.

Your logged item "Fuel Pressure" is coming from a sensor mounted into the fuel rail? Which end of the fuel rail?
What about your logged item "Base Fuel Press"? Where is that coming from?

I know that the 2g fuel hanger is really too short to fit the large-body Walbros in cleanly, so people do some pretty questionable things sometimes to fit them in there. I think it's something like they leave out the rubber part that would normally be at the bottom of the pump, because there isn't room for it. So then the bottom end of the pump (and the sock) is actually lower than it should be in the tank. Does that sound right? And maybe they cut off part of the plastic outlet pipe on the top of the pump so they can fit some rubber in at the bottom, which would bring the pump up a little bit. What did you do?
Do you have any pics of how yours looked when you had the pump and filter sock all assembled with the hanger just before putting it in the tank?
What size drill did you use when you drilled the siphon?

Click to expand...

I'll remove the pump and test it, just to see what going on with the pump and with the return flow. The hose connecting from the other side of the tank, as you mentioned, can be also the problem.
As for the pump, it is indeed a tight fit, I had to cut the outlet tip few mm to be able to have the overall length needed. I used a Toyota o-ring instead of a hose or a normal o-ring to connect the pump and on top of the hanger i got welded AN fittings.

When I had the pump in place I could see it was almost touching two screws from the plastic that goes around the pump. I had the screws replaced with new round head screws to clear a little bit the distance. I didn't like the way the original pump filter was laying so I replaced with another model which is going more in front of the pump and not under like the original one.
With all that I can't say for sure the pump gets no restriction from being to close to the bottom of the tank. Also the siphon was drilled as everyone form this forum recommends it.

Regarding the logged sensor "Fuel Pressure" it's mounted in the fuel rail close to the end. Base pressure I really don't know why I have it displayed and what's exactly showing. Now that you asked I had a look at it and I can see it's almost the same pattern as "fuel pressure". I have to check!



There is another problem, this time with ECMLink I think. I haven't mentioned because I wanted to fix the fuel pressure first and then get some help with this one but now I'm thinking maybe they are related and one problem causing the other one.

I started the car to take it out from my garage to drive it to the workshop where I can do some work on the car and right after I start driving I noticed the engine wasn't running as before. I stopped, checked the ECMLink, did few changes in the SD table and start driving again. It was better but the AFR was to rich so I went back to the old settings. Start driving again and suddently the engine stopped while driving. I thought i did something wrong in ECMLink so I loaded some old settings from an old log which I knew the car was running good. I got back home but the car was running bad and I never had this problem before.

From what I can tell, looking at the logs, the problem seems to be when car goes in open loop the injectors are shutting off. The car haven't been started for a long time and the only thing I did before starting it was to connect the battery ground wire and check all the settings in ECMLink without doing any changes.

Here are some logs, maybe someone with more knowledge then me can tell me what's going on. Thank you!