Anyone have any ideas on this problem? FINALLY SOLVED

[Leigh_bullitt]

Yes I’ll try that a little later
Many thanks for the advice

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[Leigh_bullitt]

Is this normal?.
Went for a drive and the car was acting up again felt a bit rough and a little underpowered.
I was watching the fuel pump duty cycle and it was firmly pegged at 40% but it didn’t change to any of my driving conditions like going WOT it just stayed at 40% all the time.

also fuel pump was logged as constantly on and the relay didn’t switch between on or off either ?.

could it be a faulty / Failing pump ?.

 

[Leigh_bullitt]

Sorry fuel pump duty cycle was constantly at 22%.

fuel pump monitor always at 40%

 

[sk47]

also fuel pump was logged as constantly on and the relay didn’t switch between on or off either ?.

Hello; My hands on experience with electric fuel pumps is some limited. I have not worked on direct injection engines so may miss a beat or two. The systems I do know about use the fuel pump to pressurize the fuel rail to somewhere around 60 psi. The fuel pumps can & do have capacity to maintain higher psi. I am not exactly sure just how high but will use a made-up number of 100 psi.

On fuel rail systems I know there is a pressure relief valve built in which functions to bleed off excess pressure and send some fuel back to the gas tank. The idea seems to be that the injectors can & do work fine with 60 psi of pressure. The fuel pump + pressure relief valve only has to maintain a steady 60 psi. I think the pump runs all the time???

Here is where I may show some ignorance. I do not know if the fuel pump changes output at all during normal operation. The pump may simply run at some predetermined set rate known to be able to maintain a 60 psi through all expected engine power outputs. Someone correct this if it is wrong. I have watched videos (roadkill) where the fuel pump needed to be upgraded because bigger demand injectors were installed.

A seat of the pants system to gauge a fuel pump based on your posts is the fuel pump keeps up with demand when you run the engine hard.

I asked earlier for you to check the fuel rail pressure an hour after the engine and key are turned off. I have a mechanical pressure gauge to do this check with. If the fuel rail has the proper fitting, I can attach the pressure gauge and get a direct reading. The idea is to see if your fuel rail is sound and holding pressure or if it is leaking somewhere. If the system holds 60 psi after an hour or few it is sound. If the pressure drops off there is a leak or even leaks.
The fuel pressure can leak off thru the pressure relief valve sending fuel back into the gas tank. A sign of this can be a slow to start when cold condition.
The other common leaks are the injectors themselves. The tiny pentile of an injector is opened when an electromagnet inside the injector gets an electric impulse. With the key off the pentile is supposed to close and hold the fuel pressure. Junk in the fuel might clog up this but the injectors do have screens. Probably more likely is a buildup of gums, old fuel varnish and perhaps even carbon deposits. Anyway, leaky injectors have been among my wild guesses for your occasional rough running as I have described earlier.

Old story time- A friend had the bad habit of parking his 1972 Porsche 911 for months, even years, at a time. He would drive it for a while, weeks or months, and then just park it with no preparation for a long nap. Just shut it off like he planned to drive it the next day. So, no surprise when I get a call that the car will not start. I go and get it running. On one of these occasions i determined the low-pressure electric fuel pump was bad. He orders a new one at some expense and drives the car for a few weeks-months, then parks it again for maybe a year or few.
I get the call and start checking. The recently replaced electric fuel pump was not working. (note -this is an external sort of pump, not buried in the fuel tank) He is upset that the expensive pump with so few miles was not working. I take the pump apart (it was not meant to be taken apart by the way) by prying up some metal tabs. The guts of the pump were clogged up with old jelled fuel deposits. The parts were ok. So, i clean it up and put it back together. Had to play with the position of the cap to get it running, but run it did. I showed it to him on my bench with the intention to drive home the idea he should not park it for months or years.
He insisted that we use that pump as he did not want to pay for another. I objected arguing I could not be sure to get it sealed properly. But it turned out I did seal it just fine, and it ran for many more years. He did, of course, park it for a long time a few more times. Eventually beyond my ability to get it running. I suspect the mechanical fuel injection was gooped up. I did not have the skills nor tools to open that up.

 

[Leigh_bullitt]

Hi Guys
I think I’m getting really close to figuring out this problem and just need some of your genius brains to help me track it down.

so I’ve managed to do a couple of runs and managed to catch it when it’s running really good and a little rough.

nothing has stood out as being a problem. However the fuel rail pressures seem to be different between runs.

on both runs they both peak the same and following the specified numbers, however when I pull over and let the car idle, when it’s running Rough the fuel pressure almost doubles what the specified is asking for and keeps rising.

when running good the fuel remains firm the same as specified. This may be why the car shakes a little at idle there is more engine noise?.

what would be causing this ?.

have a look at the two tables. Sorry I logged fuel pressure in Kpa.

 

[Leigh_bullitt]

Also fuel pump is running higher cycle when it’s running good too. Only by a little though.

 

[sk47]

on both runs they both peak the same and following the specified numbers, however when I pull over and let the car idle, when it’s running Rough the fuel pressure almost doubles what the specified is asking for and keeps rising.

Hello; Again, keep in mind I am not hands-on experienced with the direct injection engine. That said my initial take is the pressure relief valve may not be bleeding off excess pressure as it is intended to do. This is backward from the sorts of issues usually know for these valves. If such is the case it does sort of fit your symptoms.
The injectors work by spraying fuel into the combustion chamber. The amount of fuel sprayed is determined by the length of time the pentile valve is held open and the pressure in the fuel rail. The length of time is controlled by the ECM (computer). The pressure, my guess anyway, is expected to be constant. If the fuel rail pressure is too high, then too much fuel is being sprayed (rich).
Might account for the hot cats reported.
Last fuel pressure regulator I replaced was many years ago on a F-150. Not a bad job on that truck. Did not cost a lot back then. Unfortunately, did not fix the issue so I put the stock regulator back on and kept throwing parts at it. still have that pressure regulator in a box. As can be expected from life after lots of work and several hundred dollars of parts I got the truck fixed just before it was totaled.

 

[engineermike]

What’s the gdi blend % at the time wien the pressure creeps up?

 

[Leigh_bullitt]

I read somewhere that the increase in fuel pressure could be adaptation of the injectors.
but it’s weird every time it’s rough it idles with such high pressure

 

[engineermike]

It’s not likely the issue.

 

[sk47]

read somewhere that the increase in fuel pressure could be adaptation of the injectors.

Hello; I do not understand what this means. Would beof interest to learn how injectors can alter fuel pressure.

weird every time it’s rough it idles with such high pressure

Already made a best guess based on my limited understanding. No doubt there could be important unknowns on my part.

The amount of fuel sprayed is determined by the length of time the pentile valve is held open and the pressure in the fuel rail. The length of time is controlled by the ECM (computer). The pressure, my guess anyway, is expected to be constant. If the fuel rail pressure is too high, then too much fuel is being sprayed (rich).

Let me ask you this. I follow you have pulled some readings from the tuner used on the car. I recall you have looked at the plugs. Not clear what other steps you have taken towards addressing the problems. Trying to gain some insight so as to narrow down the parts to throw at the problem makes sense as parts can be expensive. What have you replaced? What sensors have you tested in some way?

 

[engineermike]

The gen3 measures fuel pressure and compensates by altering injector pulsewidth. The gen3 will run perfectly fine in a very large range of fuel pressures.

 

[compprep]

My 2019 has a fuel pump used mostly/only at low RPM and was bad. Replacing it cured the problem. Sorry can't be more specific as this was an issue my indy discovered. Not sure what is called.

 

[Leigh_bullitt]

What symptoms did you encounter ?.
Mine seems to hesitate or surge at lower rpm’s and basically it feels a bit rough. Almost like the first cold drive in the morning where it feels off slightly.

it feels better higher Rpms but still feels slightly underpowered as to when it runs great.

also cruising at say 60mph if I remove my foot off the gas and slowly apply again I get this sudden hesitation but that goes as well running great.

 

[compprep]

What symptoms did you encounter ?.

I never saw them. This was during my add a Procharger, blow engine, new engine then the issue. He diagnosed it on the dyno. This was 1-1/2 yrs ago.

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