Need a little help

[babywag]

I am NO fitech expert!

Pumps create fuel flow NOT pressure. PWM drops voltage to reduce the load and HEAT on a fuel pump. It should NOT drastically alter pressure.

The regulator sets the pressure and is referenced via manifold vacuum.
Normal EFI systems maintain a set pressure via the regulator.
Under load and heavy accel the pressure should rise and be rock steady.
They do this for several reasons but mainly for consistent fuel delivery.
An injector is rated to flow "x" amount of fuel @ this pressure.
When pressure drops, the expected amount of fuel the engine receives is no longer accurate.
The pcm is then operating in unknown territory and the programming is not able to compensate because that constant is not accurate.

It seems to me you have a fuel delivery issue. Something is no longer functioning correctly. Be it the circuit, the pump, the regulator, etc.
Is this a fitech fuel pump?

As an experiment maybe temporarily disable PWM or set it to 100?
See if it behaves better.
Also check to see what disconnecting the vacuum line @ regulator does to fuel pressure...it should increase.

[rang-a-stang]

Yes!! (What tony said)
Also, make sure you take good notes on what you have done. You do not want to make any changes, then forget about them, and have to troubleshoot them when you figure out your fuel delivery issues. I would put all settings back to where they were when it ran well and focus on your fuel pressure.

If you make a change and that does not fix the problem, put that setting back to where it was.

[DarkMonohue]

Alright, I know nothing about FiTech or about this particular system, so I'm doing a little reading here:

https://fitechefi.com/product/39001-go-efi-2-barrel-400hp-system/

Evidently there is a regulator built into the system, preset to 43.5 psi. FiTech says it's an "OEM style" regulator. The location of the regulator and its OEM application were not clear, and i didn't find installation instructions for this kit, but it looks like it may be mounted inside the throttle body itself.

If the regulator is set to 43.5 psi, you should have that pressure at zero vacuum (WOT) and less at idle. As Tony said, the regulator's job is to maintain a constant difference between manifold pressure and fuel pressure. Since intake manifold pressure is lower than atmospheric (i.e. in what we call vacuum) at idle and cruise, fuel pressure is lowered by the same amount by the regulator. Fuel pressure should always be 43.5 psi higher than manifold pressure. If fuel pressure is not consistently 43.5 psi above manifold pressure, it's time to figure out why.

PWM settings are beyond my experience. The systems I have worked with all have fixed voltage going to the pump, with pressure controlled solely by the regulator.

It would be interesting to read the installation instructions.

[Crankyolman]

I am NO fitech expert!

Pumps create fuel flow NOT pressure. PWM drops voltage to reduce the load and HEAT on a fuel pump. It should NOT drastically alter pressure.

The regulator sets the pressure and is referenced via manifold vacuum.
Normal EFI systems maintain a set pressure via the regulator.
Under load and heavy accel the pressure should rise and be rock steady.
They do this for several reasons but mainly for consistent fuel delivery.
An injector is rated to flow "x" amount of fuel @ this pressure.
When pressure drops, the expected amount of fuel the engine receives is no longer accurate.
The pcm is then operating in unknown territory and the programming is not able to compensate because that constant is not accurate.

It seems to me you have a fuel delivery issue. Something is no longer functioning correctly. Be it the circuit, the pump, the regulator, etc.
Is this a fitech fuel pump?

As an experiment maybe temporarily disable PWM or set it to 100?
See if it behaves better.
Also check to see what disconnecting the vacuum line @ regulator does to fuel pressure...it should increase.

It does seem like a fuel delivery issue but that is all handled by the fuel injector itself. I have no idea how to change that. Fitech has made a lot of changes to it's website in the past year and it now says the fuel regulator is set to 43.5. Today pre start fuel pressure is around that 43.5. which is weird because it used to be higher but that seems to be where they say it should be. After startup pressure drops to 38psi, then after revving a bit it settles to 34. Maybe running it so low on gas damaged the pump or maybe that is just because of the return line or maybe something else but that is what's happening today.



Yes the fuel pump is a Fitech fuel pump. It is essentially a replacement pump for the fuel command center but mounted in the fuel tank.


I'm considering buying an externally mounted pump and seeing how that works out but my buget is so far in the rear view mirror another $100-150 is a real stretch.



I have been making adjustments. They may just be work arounds but it seems to be running fairly right. No more popping or lean spike on acceleration, but there is a slight spike on deceleration.


I would post a new data log but for some reason the controller is no longer storing data logs. It acts like it is making them but when I plug it into the computer there is no log to be found. I'm waiting to hear from Fitech about that, hopefully it's just a software issue.

[DarkMonohue]

I would avoid making any more changes to the tune. It seems much more likely that you have a physical problem that needs to be corrected.

The regulator seems to be inside the throttle body assembly. Can you remove it to make sure everything is clean? I don't know if you have any means to test it by applying vacuum to see if it responds, but at least you can verify that it doesn't look gummed up and that it is sealing to the TB and getting a good vacuum signal.

[Crankyolman]

Well, it was running good in the driveway so I decided to see what happened when I drove it around the block. About half a mile out it went lean and died. I started it back up and it was fine the rest of the way.


Since I don't have a fuel pressure gauge inside the cab I don't know what the pressure was doing but I'm assuming it dropped causing the lean condition. So I am now assuming the pump is failing and I think I'm going to buy a frame mounted pump and see what that does.

[DarkMonohue]

STOP STOP STOP!

Don't introduce any more variables! Don't spend any more money! DON'T GUESS!

Test, check, diagnose, scratch your head, whatever, but this thing is already two tons of moving parts.
Throwing more parts at it without a plan will only cost you more time and money.

This can and will be figured out.

We don't even know how this fuel system is plumbed yet. Once we determine that, we'll start making some progress.

If you are absolutely determined to try a different pump, I have a spare I can send you to try.

[babywag]

One thing about fuel is it doesn't last long these days.
a near empty tank will also absorb a boatload of water...
Any long term storage the tank should be full and treat gas.

If easy suck tank dry, add some fuel injector cleaner and fill with fresh fuel.
Could easily be some crud/goo in there?

I have seen reports about bad regulators and pumps on fitech stuff, but internet attracts only bad reports so unknown if they do have actual issues?
Lotsa cheapnese junk on market these days and pretty sure fitech uses GM style parts which may or may not be cheapnese manufactured.

Might be worth a call to fitech to inquire about potential faulty regulator/pump?
A quality system shouldn't have bad parts popping up in this short a timeframe imho.

Get a fuel pressure gauge with a longer hose and tape it to windshield so you can watch pressure from inside.

Edit: forgot to mention squeezing return line should also raise fuel pressure.

[Crankyolman]

STOP STOP STOP!

Don't introduce any more variables! Don't spend any more money! DON'T GUESS!

Test, check, diagnose, scratch your head, whatever, but this thing is already two tons of moving parts.
Throwing more parts at it without a plan will only cost you more time and money.

This can and will be figured out.

The fact is we have been doing just that and come to the conclusion that fuel pressure is too low for one reason or another and there are really only 2 possible causes, the fuel pump itself or what controls the fuel pump. I have all original settings recorded so putting everything right back where it was is no problem. I'm going to lose all those settings anyway when I reflash the controller to get it to start data logging again.

We don't even know how this fuel system is plumbed yet. Once we determine that, we'll start making some progress.

It's plumbed like a fuel system, it has a pretty standard high pressure pump ( Fitech 40102) attached to a shortened original style pickup tube with wires run through a bulkhead fitting. The yellow wire from the throttle body is soldered to the hot wire for the pump as Fitech recommends. The ground wire is attached to the frame at the same point as the ground for the fuel sending unit. The fuel goes from the pump to the fuel line, to a 30 micron (not positive but it's the size fitech requires) fuel filter into another line past a fuel pressure gauge into the throttle body. On the opposite side of the throttle body is the outlet for the return which is connected to a line that returns fuel directly to the fuel tank.

If you are absolutely determined to try a different pump, I have a spare I can send you to try.

The thing is the only time my truck has ever failed to get me home was caused by that damn in tank pump and the price of the tow was more than the cost of having a second pump as a hot spare. Currently the only way I see to test the circuit vs the pump is to get another pump.

One thing about fuel is it doesn't last long these days.
a near empty tank will also absorb a boatload of water...
Any long term storage the tank should be full and treat gas.

If easy suck tank dry, add some fuel injector cleaner and fill with fresh fuel.
Could easily be some crud/goo in there?

The tank is completely full of brand new gas. taking the truck apart I had pretty much completely run it out of gas then afterwards added 2 fresh gallons to get it to work and the gas station. The tank is a fairly new poly tank and is pretty clean inside. I pulled the fuel filter and it was reasonably clean. Fitech requires something like a 30 micron filter, or something like that, which is what I'm running. I suppose adding some fuel injector cleaner won't hurt.

I have seen reports about bad regulators and pumps on fitech stuff, but internet attracts only bad reports so unknown if they do have actual issues?
Lotsa cheapnese junk on market these days and pretty sure fitech uses GM style parts which may or may not be cheapnese manufactured.

I have seen those issues too, which is one thing I'm wondering about. People don't seem all that unhappy about it they just sort of mention that they had a failure and switched to an external regulator.

Might be worth a call to fitech to inquire about potential faulty regulator/pump?
A quality system shouldn't have bad parts popping up in this short a timeframe imho.

I agree, I reached out to them and got actual answers about my actual system and questions this time. They say to set the PWM to 100 and "the
psi for a 2 bbl 39001 should be around 45-50 psi. as it has 36 lb
injectors and it has a built in fuel pressure regulator that regulates
down to 43 psi." I am definitely not getting that kind of pressure. This afternoon it's starting at 43ish then dropping to 37 while running, on acceleration it jumps momentarily back up to 40 or so then drops back off to 37.

Get a fuel pressure gauge with a longer hose and tape it to windshield so you can watch pressure from inside.

Not sure where I would get long enough hose to do that but I might try. I do have a digital oil gauge that gave questionable readings due to being sensitive to electronic interference but it would probably work for fuel pressure.

[DarkMonohue]

I agree, I reached out to them and got actual answers about my actual system and questions this time. They say to set the PWM to 100 and "the psi for a 2 bbl 39001 should be around 45-50 psi. as it has 36 lb injectors and it has a built in fuel pressure regulator that regulates
down to 43 psi." I am definitely not getting that kind of pressure. This afternoon it's starting at 43ish then dropping to 37 while running, on acceleration it jumps momentarily back up to 40 or so then drops back off to 37.

I'm a little cornfuzzled here. Where are you measuring fuel pressure?

The pump produces whatever gross pressure it makes (or rather, pressure is created because the pump tries to move more fuel than the injectors want to flow), and then the regulator tries to drop that gross pump output pressure down to 43.5 psi above manifold pressure at the injectors by bleeding off excess fuel flow (pressure) and returning it to the tank.

I guess I'm having trouble picturing how you can measure fuel pressure between the regulator and the injectors. Does the throttle body provide a fitting for that? Or am I missing something?

As for pump testing, I was thinking you could monitor voltage at the pump and make sure that it remains where it should be when fuel pressure drops. That way you can make extra sure that the pump is failing and not the power supply to the pump.

One other point: how is the ground for the fuel pump? EDIT - nevermind. I overlooked where you mentioned that it was grounded to the frame. Still, may be worth double-checking that it's solid.

[DarkMonohue]

Forgive me for working in circles, but I'm now in front of a real computer screen and trying to read a little more carefully.

After doing some reading, it seems like you're far from the only one with fuel pressure problems after running for a while. So there may be some examples to follow.

It's plumbed like a fuel system, it has a pretty standard high pressure pump ( Fitech 40102) attached to a shortened original style pickup tube with wires run through a bulkhead fitting. The yellow wire from the throttle body is soldered to the hot wire for the pump as Fitech recommends. The ground wire is attached to the frame at the same point as the ground for the fuel sending unit.

So the ECU, which lives within the TB assembly, is providing power directly to the fuel pump. Is that correct?

Fuel pumps can draw a heck of a lot of current. It is possible that the ECU is incapable of consistently powering the fuel pump due to either poor design or heat-related failure. That is one reason I suggested trying to replicate the problem while monitoring voltage directly at the fuel pump with an external voltmeter.

If we didn't have the PWM goofiness going on, I'd suggest just powering the fuel pump through a standard Bosch-style relay. That way the relay could carry the current directly from the battery or alternator to the pump, and the ECU wouldn't have to handle all that current. Not sure that it would fix the problem, or even that it's a viable approach, but it's an idea.

The fuel goes from the pump to the fuel line, to a 30 micron (not positive but it's the size fitech requires) fuel filter into another line past a fuel pressure gauge into the throttle body. On the opposite side of the throttle body is the outlet for the return which is connected to a line that returns fuel directly to the fuel tank.

Aha! You are measuring fuel pressure with a standalone gauge BEFORE the regulator. This is a really important point!

We know that the FiTech regulator is set to 43.5 psi. That means that 43.5 psi above manifold absolute pressure (MAP) is what the inlet side of the injectors are supposed to see after the regulator does its job of reducing pressure from whatever the pump puts out to the desired value at the injectors.

What that means is that, for the regulator to pass 43.5 psi of pressure to the injectors, the pump must always provide adequate flow at pressures in excess of 43.5 psi. If your pump is working correctly, you will see significantly more than 43.5 psi at a gauge between pump and throttle body assembly. If this does not happen, fuel pressure on the injector side will be below the 43.5 psi (above MAP) value that the ECU expects, and you'll probable see a lean condition.

From what I've been able to read, pressure between the pump and the regulator - which is where your gauge is - should be 58 psi. And I believe you should see something close to 58 psi between pump and regulator all the time, under all running conditions. It is possible that the pressure you see at that gauge will dip when you open the throttle; because fuel fuel through the regulator increases, pressure upstream of the regulator decreases. But that sort of suggests that the pump is incapable of providing 58 psi to the regulator under all flow conditions.

Finally, you did say that you see 58 psi with the key on but then it drops when you start the engine. Is that figure what you're seeing on the external fuel pressure gauge or is it what FiTech is reporting from its internal pressure sensor? If the latter, is that sensor reading pressure post-regulator?

[babywag]

If it has a 43.5psi regulator I would not be concerned with 37psi @idle.
My caprice behaves the same way and according to manual that is normal spec for idle.
It should increase with throttle or when vacuum line is removed.
Vacuum will decrease psi some and is normal operating procedure.

What should happen is pressure should rise and stay consistent with throttle/load.
pull the vacuum line on regulator note pressure, rev it and see if it holds steady.
if it does not your pump is likely the cause.
OR possibly the ecm driver circuit for pump like you mentioned earlier?

Before replacing the pump I would verify the regulator like above and temporarily wire up the pump eliminating the ecm/pwm to ensure that isn't the problem.

[Crankyolman]

Forgive me for working in circles, but I'm now in front of a real computer screen and trying to read a little more carefully.

After doing some reading, it seems like you're far from the only one with fuel pressure problems after running for a while. So there may be some examples to follow.

Yes I knew about that, it seems it was a fairly common issue and the solution was to run the pump off a relay with a fuel pressure regulator.

So the ECU, which lives within the TB assembly, is providing power directly to the fuel pump. Is that correct?

Yes that is how they set it up.

Fuel pumps can draw a heck of a lot of current. It is possible that the ECU is incapable of consistently powering the fuel pump due to either poor design or heat-related failure. That is one reason I suggested trying to replicate the problem while monitoring voltage directly at the fuel pump with an external voltmeter.

See, I don't know what voltage it should be getting but it could be some more info for the fitech guy.

If we didn't have the PWM goofiness going on, I'd suggest just powering the fuel pump through a standard Bosch-style relay. That way the relay could carry the current directly from the battery or alternator to the pump, and the ECU wouldn't have to handle all that current. Not sure that it would fix the problem, or even that it's a viable approach, but it's an idea.

My understanding is the fuel pump is capable of up to 80psi but needs to be regulated down to 58 but the new Fitech guy says it should be 45-50. Prior to this issue fuel pressure before starting was always 58 then might have dropped slightly but not much and was always over 50.

Aha! You are measuring fuel pressure with a standalone gauge BEFORE the regulator. This is a really important point!

Yes I am measuring fuel pressure just before it goes into the throttle body


This is a pretty bad picture but you can see the gauge here





and if you look close you can see it here under the snorkel where the oil vapor hose connects to breather

We know that the FiTech regulator is set to 43.5 psi. That means that 43.5 psi above manifold absolute pressure (MAP) is what the inlet side of the injectors are supposed to see after the regulator does its job of reducing pressure from whatever the pump puts out to the desired value at the injectors.

What that means is that, for the regulator to pass 43.5 psi of pressure to the injectors, the pump must always provide adequate flow at pressures in excess of 43.5 psi. If your pump is working correctly, you will see significantly more than 43.5 psi at a gauge between pump and throttle body assembly. If this does not happen, fuel pressure on the injector side will be below the 43.5 psi (above MAP) value that the ECU expects, and you'll probable see a lean condition.

From what I've been able to read, pressure between the pump and the regulator - which is where your gauge is - should be 58 psi. And I believe you should see something close to 58 psi between pump and regulator all the time, under all running conditions. It is possible that the pressure you see at that gauge will dip when you open the throttle; because fuel fuel through the regulator increases, pressure upstream of the regulator decreases. But that sort of suggests that the pump is incapable of providing 58 psi to the regulator under all flow conditions.

Finally, you did say that you see 58 psi with the key on but then it drops when you start the engine. Is that figure what you're seeing on the external fuel pressure gauge or is it what FiTech is reporting from its internal pressure sensor? If the latter, is that sensor reading pressure post-regulator?

Currently the starting pressure is around 43psi and dropping to 37 and as low as 35 at that gauge. The fuel number on the hand held controller are something like Liters per hour or a percentage or something that doesn't really give me much info about actual fuel pressure.

If it has a 43.5psi regulator I would not be concerned with 37psi @idle.
My caprice behaves the same way and according to manual that is normal spec for idle.
It should increase with throttle or when vacuum line is removed.
Vacuum will decrease psi some and is normal operating procedure.

What should happen is pressure should rise and stay consistent with throttle/load.
pull the vacuum line on regulator note pressure, rev it and see if it holds steady.
if it does not your pump is likely the cause.
OR possibly the ecm driver circuit for pump like you mentioned earlier?

Before replacing the pump I would verify the regulator like above and temporarily wire up the pump eliminating the ecm/pwm to ensure that isn't the problem.

Thank you both for the info.



My world is about to get crazy busy and I don't know how much time I will have to work on it over the next week but I will try to find the time to try a few things and see what happens.

[DarkMonohue]

Yes I am measuring fuel pressure just before it goes into the throttle body.

<snip>

Currently the starting pressure is around 43psi and dropping to 37 and as low as 35 at that gauge.

OK, great! That really clears things up.

It seems unlikely that the ECU will ever be able to fuel the engine correctly if the fuel pump isn't providing the pressure and volume it expects.

EDIT: I misspoke. We want to see 43.5 psi on your gauge with key on, engine off. When the engine starts, pressure should drop to something less than that. About 35 psi at idle if my math is correct. And it should rise again to around 43.5 psi under WOT, under load.

[babywag]

pumps don't create pressure...the regulator does.
pressure shouldn't be any higher off pump in a standard return style system.
if you block return then yeah pressure will max out or if the regulator malfunctions.