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  #21  
Old 07-28-2020, 09:54 AM
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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.
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  #22  
Old 07-28-2020, 10:00 AM
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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.
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  #23  
Old 07-28-2020, 10:16 AM
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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.
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Last edited by babywag : 07-28-2020 at 04:08 PM.
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  #24  
Old 07-28-2020, 09:15 PM
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Quote:
Originally Posted by 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.
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.


Quote:
Originally Posted by DarkMonohue
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.


Quote:
Originally Posted by DarkMonohue
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.





Quote:
Originally Posted by 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?


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.


Quote:
Originally Posted by babywag
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.


Quote:
Originally Posted by babywag
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.


Quote:
Originally Posted by babywag
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.
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  #25  
Old 07-28-2020, 09:35 PM
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Quote:
Originally Posted by Crankyolman
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.
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Last edited by DarkMonohue : 07-28-2020 at 10:16 PM.
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  #26  
Old 07-28-2020, 11:30 PM
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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.


Quote:
Originally Posted by Crankyolman
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.


Quote:
Originally Posted by Crankyolman
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?
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  #27  
Old 07-29-2020, 09:10 AM
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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.
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  #28  
Old 07-29-2020, 11:53 AM
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Quote:
Originally Posted by 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.


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.



Quote:
Originally Posted by DarkMonohue
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.


Quote:
Originally Posted by DarkMonohue
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.


Quote:
Originally Posted by DarkMonohue
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.

Quote:
Originally Posted by DarkMonohue
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


Quote:
Originally Posted by DarkMonohue
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.



Quote:
Originally Posted by 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.




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.
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  #29  
Old 07-29-2020, 12:02 PM
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Quote:
Originally Posted by Crankyolman
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.
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Last edited by DarkMonohue : 07-29-2020 at 07:31 PM.
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  #30  
Old 07-29-2020, 12:41 PM
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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.
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Old 07-29-2020, 02:15 PM
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Disregard. Mistakes were made.
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  #32  
Old 07-29-2020, 02:17 PM
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Hold on, I'm confusing myself here. I have a lot on my mind and am trying rather unsuccessfully to multitask. Feel free to disregard anything I have said. Same as usual, really.
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  #33  
Old 07-29-2020, 07:27 PM
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Alright. I messed up. Not sure what I have been smoking. The regulator is downstream from the injectors. Whatever pressure you see on the external gauge is the pressure at the injectors.

We can still block off the return hose as a test to see whether the low pressure is the result of a faulty regulator sticking open or a result of the pump not moving enough fuel.

Sorry, guys. I don't know how I got so wrong, but definitely made things worse here. I guess I have a lot on my mind lately.
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  #34  
Old 07-30-2020, 01:48 PM
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I don't think you made anything worse Darkmoon. I basically knew that the system will show whatever pressure it is at no matter where you place the gauge upstream of the regulator.



My current thoughts are

1) Get an AN6 cap to block off the return line and see what happens. The system is capable of running as a returnless system but I understand this is bad for the pump but it's a way to determine what the output pressure of the pump is.


2) run pump directly off the battery and see what happens.


3) place my little spy cam under the hood and record what the fuel pressure is doing while driving and see what's happening.
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  #35  
Old 07-30-2020, 01:57 PM
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These are all excellent ideas.

I wonder whether you could wire the pump through a switch so that you can select between powering it through the ECU to powering it directly off the battery. That would allow you to switch to battery power when it starts to run poorly and see if it returns to normal running behavior.

And I still have my doubts about the ability of the ECU to provide adequate current under load. Reading voltage at the pump would be nice as well.

You're getting close. This will get fixed one way or another!
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