Fuel pumps and LT1 dry kit question (Injuneer?)

[MN6WS6]

I have the NOS 5176 kit on my 96 Formula. It came with the extra fuel pump, which I have installed. I've had the kit on it for about a year and a half, but just put a pressure gauge on it because I'm having a hard start problem. My question is, does the extra fuel pump increase pressure in the line, or is it just there to maintain the ~40 PSI that the factory pump puts out itself? If it is supposed to increase the pressure in the line, how high is it supposed to go? If I switch to an in-tank 255 LPH pump, do I still have to run the external pump?

While we are talking about fuel pumps, here's my hard start problem. When the car has been sitting for a while, it takes like 7 to 10 seconds to crank. All the fuses are fine, and you can hear the pump come on when you turn the key. I put the gauge on it today, and when you turn the key on, it reads 0. It doesn't start reading pressure until you actually start turning the motor over, and then it takes it the ~10 seconds or so to actually get enough pressure in the line to crank the car. Once it's running, it's fine, it maintains 40 PSI. But once you turn the car off, it bleeds down to 0 within 5-10 seconds. Could I have a bad fuel pump that is bleeding the pressure back into the tank? Is there a fuel return line on my car, and if so, could it be causing the lack of fuel pressure? There are no leaks in the line and I don't smell any gas.

[KnightFire]

Something else to consider about your fuel psi problem...is that your injectors are leaking down or have worn out O-Rings.

Have you replaced your fuel filter lately?





KnightFire

[MN6WS6]

Somebody already suggested leaky fuel injectors, but they only have maybe 10-15k on them, and besides for them to leak 40 psi of pressure in less than 10 seconds would be one heck of a leak. Not to mention, the car does not produce black smoke or have any problems while you are driving, and a bad injector would have some kind of telltale sign like that.

I considered the fuel filter, but once again that does not explain why the fuel pressure drops so fast. It also only has about 10-15k on it, but the issue is the almost instantaneous pressure drop, not lack of pressure. Once the car is running it maintains pressure regardless of throttle position, which suggests that once the fuel is flowing it's ok, it's getting it to build the pressure up and maintain the pressure once the car is shut off that's the problem. When I put on the FPSS for the nitrous, the car had sat for 3 hours and still had an incredible amount of pressure on the line. Now, by the time you cut the ignition off and walk up to look under the hood at the gauge, the pressure is gone.

[Brady_96Z]

Inline pump

Jeff, I forgot about your inline pump. (It's there to boost fuel pressure on the injectors when you spray.) I'm really thinking the regulator is your problem now.

FWIW, my Weldon pump doesn't have an internal check valve, when I shut the car off the fuel pressure immediately goes to 0. If the car is hot it boils the fuel out of the rails and makes it kind of hard to start - kind of like the problem your'e having.

In your situation though, with 2 fuel pumps, I think it's highly improbable that it's a fuel pump issue. I think the regulator has a leak and let's your fuel pressure drop to zero. Then it takes awhile for the pump(s) to pressure the system up again.

Do you notice any difference in starting it if you start it cold, then shut it off before it warms up, and restart it? (Wondering about the fuel boiling in the rails thing)

let me know if I can help

[Brady_96Z]

That's queer, I know that wasn't my first post here?

[Injuneer]

Brady the Newbie..... Brady the Newbie.....

Adding the inline booster pump will not raise the fuel pressure all by itself. The fuel pressure regulator (FPR) will simply open further and allow more fuel to bypass back to the tank. You will not see any difference in fuel pressure, unless you are spraying the nitrous.

With the 5176 kit, when you open the nitrous solenoid, a small slipstream of nitrous passes through the blue pressure regulator and applies a pressure to the vacuum connection on the FPR, and boosts the fuel pressure to 85-90psi. That is the only time you should see a serious change in pressure.

The pump should start instantaneously when you turn the key to "on" but don't start the engine. It should run about 2 seconds, then shut off. By that time it should have raised the fuel pressure to 43psi. The pump shuts off because the engine is not running. How long the system holds pressure depends on the design of the system. As Brady points out, not all pumps include a check valve. And some aftermarket AFPR's (not the typical stock style replacements) release the pressure on shutdown, in order to take the pressure off the injectors.

I would make sure the inline pump is still working properly. You should hear that pump coming on at the same time as the intank pump. With the Walbro, whether it can supply enough fuel at the high pressure required by the 5176 kit needs to be checked. The 255LPH rating is measured at a particular pressure (pump makers seldom bother to tell you what that it), and as pressure increases, the flow capacity of the pump drops. If capacity drops too fast, you aren't going to have enough flow for the nitrous system. You need to check the flow rate of the Walbro at 90psi to see if it is enough. Assume you want a flow capacity of at least 0.60#/HR/HP. We can convert that to LPH or GPH if you need that.

If you are saying the fuel pressure never rises, even when you spray, either the nitrous system is hooked up wrong, or the FPR is faulty. A faulty FPR would explain the excessive time required to build pressure. Have you ever pulled the vacuum line off the FPR and checked for liquid fuel or excessive smell of raw fuel?

When I first bought my 5176 kit in early 1995, NOS told me it was OK to use and adjustable FPR, as long as I set it at factory pressure. But the AFPR I was using would not respond correctly to the pressure from the nitrous line, and I didn't get the pressure increase I needed. Had to replace it with the stock FPR.

[MN6WS6]

Let me clear a few things up. Should make life a lot easier for everybody. The car is completely stock, sans a K&N, underdrive pulley, MSD ignition box, Ford 24# injectors, and the nitrous system. Stock fuel pump, stock fuel line, stock fuel pressure regulator. The extra fuel pump only comes on when I arm the system, which is usually way before I even consider spraying the car, to give it ample time to do whatever it needs to do.

With the nitrous system off (no extra fuel pump), you turn on the key, hear the pump come on and off after about 2 seconds (like you said), but no pressure is read at the gauge. Turn over motor, still no pressure. Turn motor over a few times and it starts showing pressure, but doesn't get to 40 PSI until maybe 5 seconds of turning the motor over.

With the nitrous system on, you get the same results, the system will not pressurize until you are turning the motor over.

Could this be some sort of vaccuum problem? I understand it could still be the fuel pressure regulator, but could the diaphram in it be bad, or should I be looking at the vaccuum lines going to the 5176 regulator as well? If that got cut or a hole in it, would it cause the regulator to only allow pressure while the car is turning over (and pulling vaccuum to pull in the diaphram? Then again, could the diaphram be bad, collapsing when I shut the car off which dumps all the fuel pressure back in the tank, then has to close back up when I start turning the car back over again allowing the system to re-pressurize?

Brady, if you have that factory FPR I'd like to get it from you. Anything has got to be easier than dropping the tank

[Injuneer]

I think you are making a mistake if you only run the inline pump when you arm the nitrous system. That pump is intended to run all the time. In effect, you are forcing your stock pump to work harder to force fuel through the inline pump. Then the inline pump is suffering because it is turning, but not turned on. Might explain some of the problem. Like I said, I bought my kit in 1995. The inline pump that came with it at that time was a Bosch 205LPH pump, and it was out of a Porsche Turbo. (I think they dropped to a cheaper pump in later kits). I ran mine full time, never turned it off, up until the stroker buildup in 2000. Then I reused the Bosch pump as an outboard "parallel" pump (as opposed to "inline") pulling off a sump at the back of the stock tank. That pump only gets turned on when the nitrous system is armed, but that pump is not "inline" and is not blocking the stock intank pump. Point is, you can run a good pump contniuously, and it doesn't hurt it. Mine is now 8 years old and still going strong.

I think you may be contributing to the problem by not running the inline pump. But if you get slow pressure buildup when you turn the key on, even if you turn on the inline pump, either 1) the stock fuel pump has been killed by the inline obstructing it, 2) there is a crimp in one of the lines, 3) the fuel pressure regulator is bad (yes, the diaphragm might be broken - that's why you "sniff" the vacuum line for fule), or 4) the fuel filter is plugged up. Another possibility would be the "sock" on the intank pumpt being gummed up. But the clogged filter, crimped line and dirty sock would also show up as running low on fuel at WOT.

Since you have a pressure gauge.... when the engine is running (inline pump off), what is the pressure with the vacuum line disconnected? What does the pressure drop to when you connect the vacuum line to the FPR? Turn on the inline pump and repeat... pressure with the vacuum line off, and with it reconnected. That will tell you if the FPR is responding correctly to vacuum.

[FRMLAV8]

This sounds very similiar to what happened to me.

I just finished dropping in a 383, worked out all the bugs everything was great, then all the sudden I started getting hard starts.

We checked spark plugs, wires, opti codes, coil, then on to fuel.
The pressure was fine while the car was running, but when you stopped the car and restarted it the pressure would drop, and it would take a long time to start.

It ended up being the diaphragm in the AFPR. It had ruptured and allowed gas to flood into the intake when you turn the car off- thereby making it hard to start. According to Aeromotive - when they reformulated the gas a while back it started killing the FPR diaphragms, and injectors, so they had to redesign their parts and upgrade the internals.

Yours might not have anything to do with the gas formula, but it sure sounds like an FPR problem.

[KnightFire]

Figures...NOW I read Aeromotive has problems with their AFPRs...I just put a NEW Aeromotive AFPR in my 355!
I have pretty much the same problem, but not the hard start situation...the fuel psi drops to 0, but its always done that with the 28lb/hr OEM LS1 injectors I had. So I just ordered some 44lb/hr flow matched Accel injectors, hopefully that will cure my problem and help the DFI in tuning the beast.

Hopefully the AFPR I have has been updated and the issues have been addressed...if not, I guess I'll know what my next purchase will be.



KnightFire

[Brady_96Z]

Jeff, you make it hard to troubleshoot when you keep adding/changing the conditions

As usual, Fred covered everything. I just wanted to add that I'm holding my extra FPR in my grubby little hand. You're welcome to it. It worked fine on my car a couple years ago, I don't suppose it would go bad in our 110% humidity?? I took it off when I bought an AFPR from Fred

call me today or tomorrow 232-4927

Brady "the newbie"

[FRMLAV8]

Hey Knightfire,

Is it the annodized red one. It is shaped like a cylinder, I think the part # is 13106 or 13107. If so those are the old ones.

I just sent mine back to Aeromotive for a new one, I'll let you know how it turns out!

[MN6WS6]

I'm not changing the conditions, I'm just clarifying.

By the way, my inline pump has a bypass line going around it with a fuel filter in it as well, so even if I turn the pump off, the factory fuel pump should still pressurize the line just fine. There is no obstruction.

Thanks for all the input, looks like I'll start with an FPR and go from there.

[KnightFire]

Originally posted by FRMLAV8
Hey Knightfire,

Is it the annodized red one. It is shaped like a cylinder, I think the part # is 13106 or 13107. If so those are the old ones.

I just sent mine back to Aeromotive for a new one, I'll let you know how it turns out!

PLEASE do!!! That is the EXACT unit I purchased. This problem is common and known to them? Do you simply send them the "old" unit and they update it for you with a "new" one?

If you have any contact info, I would greatly appreciate it if you could email/post it.

Tks!!!

Sorry for hijacking your thread broh...but hopefully it is your AFPR thats giving you your problems. Wouldn't that be an easy fix?



KnightFire