DerrenZ

Can someone evaluate what I have done and tell me where I have gone wrong?

I put an LS1 into my 1986 IROC as described here:

https://www.thirdgen.org/forums/ltx-...to-carbed.html

The car was originally a carbureted 305 LG4. It had a fuel line running from the tank to the engine compartment and it looked like one slightly smaller line running back from the engine compartment to the tank. And I think there was one line from the tank to the charcoal canister up front.

I tapped into the larger line and hooked in a Trick Flow fuel pump: http://www.summitracing.com/parts/TFS-25004P
It’s located as low as I could get and bolted under the car below the back seat.



It’s powered by a 12v IGN hot, so I guess it’s always running at maximum?

The fuel is pumped to a corvette style LS1 filter/regulator at the engine compartment. Then the supply side feeds the fuel rail and the smaller return outlet ties into the smaller fuel line running back to the gas tank.



Before I describe my problems, is there anything inherently wrong with this setup?

Comments, suggestions, criticisms welcome.

LilSki

iTrader: (1)

Other than the regulator difference that is how my current fuel system is on my TPI conversion. But I did mount my pump up against the back seat closer to the tank. I doubt you location makes that much difference.

I'm going to soon install an in tank pump as my pump is way to loud and annoying inside the car.

Lonnie P

Pump should be closer to tank & should have a larger feed line... looks like 5/16" in the picture. Any restriction here can cause pump cavitation. Also fuel sock in the tank should be checked, possibly replaced with something of minimum restiction.

Also I hope you are not planning to put a rubber hose between the pump & supply line.
58psi & hose clamped rubber line can be dangerous.

LilSki

iTrader: (1)

They make EFI rubber hose and EFI Hose clamps that work fine.

DerrenZ

Can you explain cavitation to me? Is it different than vapor lock?

And yes I used EFI rubber hose and clamps. And yes I plan to replace with steel line because the location is vulnerable to road hazards so I'm not comfortable with rubber there.

LilSki

iTrader: (1)

Mine does it once and while. The pump won't be steady when you turn the key on. It will cavitate for a second or two and then pull prime and the pitch of the whine it makes lowers. It is hard to explain but it sounds like the pump is free wheeling and has a higher pitched whine. When it picks up prime the pitch lowers and becomes steady.

EDIT: I realized I had a video I made of my car years ago when I did the first EFI conversion to TBI. Right when I turn the key on turn your speakers up and you can hear the fuel pump kick on. It cavitates for a second and then picks up prime.

http://www.youtube.com/watch?v=iTY8w...I41r1pnq38NcY=

QwkTrip

iTrader: (22)

Cavitation is the collapse of a void or bubble in fluids and it causes a shock wave that wears parts prematurely. It can happen in the fuel pump if the pump design isn't optimized or air is introduced to the fuel.

Instead of playing 20 questions, how about you just tell us what is happening so you can actually get some help?

DerrenZ

Thanks for the vid link LilSki. Mine also sounds like that when I start it. And it's also very loud where it's located.

Thanks for your tips Lonnie, and yes, I believe it is 5/16.

I have been concerned that I maybe mis-wired or mis-plumbed the system, and probably omitted some necessary component that regulates everything.

1. So it's ok for my 85psi, 43gph pump to run full tilt all the time? (I know the 'vette filter keeps it about 58psi to the rail.)
2. Is the layout I described basically sound (except for the improvements Lonnie mentioned)? I didn't leave anything out?
3. Sometimes there is pressure in my fuel tank when the cap is removed. What causes this? Isn't the tank vented to avoid this?

LilSki

iTrader: (1)

Fuel pumps are just on or off that is it.

Lonnie P

You should be fine with the rest of your system. The pressure you experience is typically the pressurization due to the fuel being heated (expansion in the tank), generated by both the under car heat & the heat put in the fuel by the pump.

Late model tanks are typically vented to allow air to enter, but not escape. Some have a safety valve that will vent if pressure is excessive, but the evap system usually vents this into the engine.
Sounds like you may have used this vent line for your return line.

As for powering the pump, you should try to run it off a safety circuit so it does not run with the key. In an accident, the car can stall & the pump can empty the contents of the tank from a broken line... nothing like feeding a fire with fuel.
Try to hook the pump to a relay powered by the LS1 ECM for safety.

DerrenZ

Thank you both for the clarifications.

My pump may be run from the ECM, I'm just not sure. But I sent that question to my harness builder. He's pretty awesome so if it ought to be run off the ECM, it probably is. (And yes you all know him.)

I actually had a separate line for return and another for venting to the charcoal canister. Is it normal for a carbureted LG4 motor to have a fuel return line? Hope that's what it was for...

Plus, I just checked under the hood. The line that used to go to charcoal, now just goes nowhere, sitting open. Hope it's not allowing dirt into the tank. Seems that an open line to the tank would prevent pressure or vacuum from building inside the tank, but I think I've had each at one time or another.

Brando5641

iTrader: (-1)

They dont work that fine. Rubber efi hose about costed me my car. Don't cheap out on the fuel system. I whent on the cheap on mine the first time and i had 2 rubber efi hoses with efi clamps blow off, one of those was on a dorman gm quick connect fitting on the fuel rail, the hose blew off the end of the dorman fitting and soaked the hot engine. I dont know how my car didnt burn to the ground but I ended up going SS braided line and AN fittings.

I know there are people running it right now that are going to say I didn't install it right or somthin but its not worth the risk to me.

LilSki

iTrader: (1)

I didn't use any rubber hose other than the factory lines up in the engine bay. I only used EFI hose and clamps back my the pump far away from engine heat. I have 10k miles on my setup thus far and I inspect everything during the oil change and everything looks and works fine. Just that the pump is too damn loud and is getting replaced with an in tank setup soon.

DerrenZ

The other day, after a few miles of hard driving on a hot day, the fuel pump started running faster than normal and squealing, then the car lost power and stalled. Seemed like maybe vapor lock, but might have been the cavitation you mentioned. It cooled and then drove.

Thought maybe the pump was toast, then decided it was about time to evaluate the whole design.

I think one of these days I will need to drop the tank and check that "fuel sock."

LilSki

iTrader: (1)

My pump gets very loud as well after long drives. I have never had it stall but I have heard the pump start to cavitate. This is the primary reason bought an EFI sending unit and am going to install the in tank pump.

I think some of the reason is the EFI return line goes to the bottom of the tank and the carb version just returns at the top of the tank. I think this causes an excessive amount of fuel vapor causing the pump to loose pressure but it it is just a theory. I thought it also might be the pump is overheating but where I put it I cannot reach it to feel it.

Flip 2

iTrader: (1)

The return is in there for the cars with fuel injection. Guess it was cheaper for GM to buy one part, even if some cars had an extra line.
I think mounting the pump against the back of the back seat is a good idea. There the feed line from the tank is quite short, and the location is low. I have had a pump there for years. It was the recommended location from Accel when I went from Qudrajet to EFI. If you put it there, you could move your filter/ regulator to where the pump is now and have a shorter return. Bene side effect would be to get the deal out of the engine bay.
IF you use any braided stainless line, make sure you use one with Teflon lining. The others will allow the gasoline to sweat through, and your garage will always stink of gas. The wife, if you are so equipped, will complain constantly- with good reason.
The original line to the carbon canister is too long and narrow to vent the fuel tank pressure. At least, it never did for mine.
The fuel pump wants to run free. It should not have to pump against pressure; that will ruin it. The filter should be between the pump and the injectors. The tank sock acts as a screen to keep large junk out of your pump. Another approach to that can be to put a screen type filter between the tank and the pump. Not enough room for that with the pump on the back seat.
Good luck.

LilSki

iTrader: (1)

The carbed cars had the return line coming out of the mechanical pump. But im sure very little fuel actually returns to the tank.

Flip 2

iTrader: (1)

On that return, I just used the part back by the tank, that goes into the tank. That part of the system works fine. I can't speak for the hard line that runs front to back.

DerrenZ

Thanks for the extra info Flip.

My logic for placing the regulator up front was to keep heavy fuel flow through those supply and return lines while idling on a hot day, instead of the branch off the regulator (to the fuel rail) which has minimal flow at idle (and would slowly move fuel past the tranny, exhaust, and motor). Prolly makes no difference, but that was the theory.

Thanks for the tip about teflon lining, not sure if I had heard that one before.

Not sure what's up with that canister line. It may be narrow, but pressure is pressure and it seems even an 1/8th inch open tube of any length would be adequate to vent it. Maybe they clog with junk after, oh, 25 years?

Is mine plumbed correctly to allow the pump to "run free?"

Thanks again guys.

Flip 2

iTrader: (1)

Derren-
Like the fuel flow theory.
Love to see a shorter run from tank to pump, but that's a hunch, not a certainty.
Worried about the pump making strange noises, something's up. Is the fuel line collapsing? Is the sock in the tank clogged? (maybe try compressed air backwards from the pump?- gently at first?).
That Teflon deal is real- 1st hand knowledge ;-(

Brando5641

iTrader: (-1)

Why arn't you running an in tank pump?


*TYPO*

DerrenZ

Do you mean an "in tank" pump? I'd like to, but this seemed to be the simpler, cheaper, and not altogether bad, alternative.

But ultimately, someday, I'd prefer to switch to a 4th gen tank and pump.

Flip 2

iTrader: (1)

I think he is referring to a pump that feeds your fuel pump, to keep it from sucking air. Common hot rodder practice.
Here's a (not very good) pic of my fuel pump mounting. It is below the tank, and there is all of 5 inches of hose, total, between the tanks outlet and the pump.

Brando5641

iTrader: (-1)

No I meant the main pump. I have a walbro 255 in my tank and its quiet. I did the trap door mod and I can change a pump in 30 min. External pumps are usually loud, but they are ez to get too but a good quality external high pressure FP was the same price if not more than a walbro.

Im not trying to say that what you did is all wrong it should work fine and be safe as long as you use the correct fittings and hose.

NOTE TO EVERYONE you should always keep a fire extinguisher in your car at all times. When I had that rubber efi hose blow I would have had nothing to fight the fire with if it had caught on fire. It would have been horrible to have to watch my car burn to the ground. You can buy one at Wal-Mart for like $20

Brando5641

iTrader: (-1)

I have seen this done a few times but to me it defeats the purpose of the external pump if you have to have an internal "booster" pump.

Also does this 86 still have the factory pump in the tank?

Flip 2

iTrader: (1)

LG4s had Quadrajets and mechanical fuel pumps- on the engine- quaint, huh?

DerrenZ

So I could add the 255 to my 3rd gen tank, right?

And we're on the same page about the fire extinguisher. Especially since I wasn't 100% sure about the design, no way I'd leave home without it.

Yeah Flip, that's exactly what I had - mech pump on the engine with a return line.

LilSki

iTrader: (1)

All you need is an EFI sending unit and put it right in your current tank. Once you have the sending unit you can put any pump you want on there. I just got mine for about $120.

Lonnie P

Anytime you can run an intank pump I suggest you do it.
They are so much quieter & they eliminate a lot the of potential cavitation/heat issues.

An intank paired with an inline is not a good way to do things. Just more unnecessary complexity. A good 255lph intank pump will support 550rwhp, so it is a pretty capable pump.

As for using the Vette regulator/filter, they work rather well.
You can rear mount this (as done on the Vette) for a less complex line system, but be aware that any restriction/pressure drop from the filter forward cannot be compensated for. I typically find a 3/8" or -6 line with the rear mount regulator is good to just under 700hp. Beyond this, you should have an engine compartment mounted regulator for best pressure control at the engine.

Hope this helps.

88 350 tpi formula

iTrader: (9)

Im not sure I understand what you had setup and how snug the dorman ends fit the hose but efi clamps and proper ends are fine. if it's not subaru has alot of explaining to do

in all seriousness Ive seen prebuilt and cut to length braided lines fail and spray fuel all over. nothing is perfect! maybe we should agree that using properly rated items for its application with a close eye to detail and fit is whats best.