Fuel supply issue (or is this supposed to happen?)

[MoparKidD-4]

After getting dual exhaust cobbled together on my '88 5th Ave it does have more noticeable "punch", or as much as it can anyway with the stock 2.21 gears. Problem now is it seems to run out of fuel if I hold it at WOT for more than 6 seconds or so; doesn't matter if I'm in 1st or 2nd gear if I keep the pedal to the floor long enough it will just "blurrrrr" like it's not getting enough fuel flow into the carb. It still has the stock Holley feedback 2-bbl and "Electronic Fuel Control" quasi-Lean-Burn whatever. At first I thought it might be some dumb built-in fuel cutoff at high RPM but like I said even in 2nd gear if I keep it floored long enough it will 'bog'. I replaced the fuel filter today to no avail, should I look at the fuel pump? Or is this carb just such a weak POS it can't handle the newfound power? lol

 

[AJ/FormS]

Unless the "blurrrr"ing is accompanied with backfiring, afterfiring or rpm high enough to float the valves,I'm guessing your exhaust got choked during the exhaust work.
Pumped up lifters is an easy test. Immediately when the rpm goes flat, release the throttle and slam her into neutral. If the engine returns to idle, your lifters are fine.
A lean MJ is an easy test. As soon as the Rs go flat, ease off the throttle to 75%. If the car surges ahead, the fuel delivery is insufficient.
A restricted intake is an easy test. Flip the air-cleaner lid and try again.
A plugged or restricted exhaust is a harder test.What I do is drill a 3/16" hole in the pipe as close to the engine as is comfortable to drill. Then I take about 2 feet of brake line, cut the end off at about 45* and stick it in there. I bend the brake line so I can clamp it to the pipe with a hose clamp. Then bend the rest of it away from the pipe and run enough vacuum hose to get up into the drivers seat, and install a low-pressure gauge there. An old 10 psi fuel pump pressure tester works well. Then I go for a drive.And then the roadtest. I am looking for 2 psi or less, at full-power. I suspect up to 3psi or perhaps as much as 4psi might be OK, but the less the better.If you get pressure in excess of this, you will have to repeat the test after the next restriction, like the cat, or the muffler, and so on. I would start on the new side. If you don't see anything there, move to the other side. After you find it and fix it, you will want to plug all the little holes you may have drilled.
If the left and right sides are separated with no crossover then there is a preliminary shortcut. You will need a helper, inside the car. You go stand at the back, between the pipes, with gloves on. Cover the pipes as best as you can with your gloved hands, looking for a pressure/volume difference. Have your helper rev it up slowly to about 2500rpm, while you note any difference. At 2500 ask the helper to slam the pedal down hard, until the revs climb to in the area of 3500 to 4000, and release the pedal, while you note the difference. Do this with the transmission in neutral and the brakes firmly applied.Tell the helper to put his right hand into his pocket; safety first!
Any pressure or volume difference is grounds for further testing.

 

[Aspen500]

A free flowing dual exhaust will usually require stepping up jet size. It could be the carb can't supply enough fuel (too small jets) but from what you describe I'd be suspicious of the fuel pump. It sounds like the bowl is running low or dry.

As AJ mentioned, it can also be caused by a restricted exhaust. If it's all new, not likely but worth double checking. It will be loud but if all else fails, and it's possible where you live to "safely" do this,,,,,,,loosen the exhaust at the manifolds and go for a ride and see if the problem still exists. My first thought is the fuel pump however. Of course there's always a chance the filter sock in the tank is partially plugged but that would be uncommon.

 

[MoparKidD-4]

It's definitely not the exhaust, I put it together myself and the problem did occur when I was driving around with just ~18" pipes off the manifolds. It also did seem to be lean at first but being at high altitude it actually ran rich with the stock exhaust (had high CO emissions) so I think the current combination with the free-flowing exhaust is within the "tuneable range" for the factory carb and computer. Just from seat-of-the-pants feel it ran a little better and more responsive each time I drove the car and ran it through a full warm-up cycle after I yanked off the restrictive factory exhaust. @AJ/FormS it's definitely a case where if I let off the throttle for a bit and get back on it it will recover and pull clean again for a few more seconds.

I have an OEM-style replacement fuel pump I pulled off my wrecked 360 I think I will just swap on there; I know for sure that one had no problems delivering fuel at high load/RPM to the 750 Street Demon on top of that engine when it was running.

 

[BudW]

Both of my 318 2-bbl cars have a “running out of gas under WOT (Wide Open Throttle)” conditions.
It happens at high RPM (4k RPM or so).

What happens is the power curve is fine (considering they are stock 318 2-bbl’s) then all of a sudden the engine falls flat on its face. If I wait a moment OR let off of the gas, it power picks right back up like beforehand.

My ’77 wagon (with 40k miles) – I suspect the problem is float level being set too low. That car doesn’t do it often but I can tell (one out of every 30 wide-ranging WOT exercises, or so).

My ’86 5th Ave – There are one of three possibility’s with it. Float level, in-tank sock – or what I most suspect most is the fuel hoses are cracked and sucking air (the hose between fuel tank and main line (rear of car) and/or the hidden fuel hose just behind the R/F tire). This car does it once every three WOT exercises, or so.

This car has sat in the sun most of its life and other rubber hoses were cracked significantly. Sometimes parking at an angle, it takes forever to get engine started (well, OK, it starts, runs for a moment then dies – then takes forever to restart).

FMJ cars (I don’t know if J’s have the hidden fuel hose, or not) has rubber hoses in 4 locations/areas.
- The fuel filter (3 short sections of hose, which generally come with filter – always change hoses with a filter change).
- Between frame rail and fuel pump
- The hidden hose behind R/F tire
- By fuel tank.

The hidden hose is talked more on thread 318 down
Post # 31

I would recommend a fuel volume test before going through the effort of changing out a fuel pump.
Watch for air pockets when performing the test (if possible).

Note: a cracked and leaking fuel hose is not good for fuel mileage. If it can leak air, then it can also leak fuel. A safety hazard, as well.

I doubt I have a problem with fuel sock or hoses on my wagon because of (low) mileage and fact car has been kept in a garage most of its life. most hoses on it are great for being 40 years old. I could be wrong, though.
BudW

 

[AJ/FormS]

@AJ/FormS it's definitely a case where if I let off the throttle for a bit and get back on it it will recover and pull clean again for a few more seconds.

You misread my post.
"A lean MJ is an easy test. As soon as the Rs go flat, ease off the throttle to 75%. If the car surges ahead, the fuel delivery is insufficient."
This is with the throttle backed off, to anything near to 75 %, but specifically held at that opening. The car surges ahead cuz it's making more power at that reduced throttle opening.

If you are still running the 2bbl,the factory single exhaust was not that restrictive. (unless the cat or muffler was restricted). This means the twinning is not that big an improvement. The factory cam is pittiful, and the valve spring pressure may just barely keep the valve train together at 4000, nevermind 5000.
But I heard what you said, about mashing it and getting through it.This indicates that the pump is ok, and that the valves are not floating.And probably that the exhaust is Ok.
What surprises me is that you never mention backfires, afterfires or hiccups, all of which should accompany as lean a condition as you describe.
So it also may indicate that the bowl is just too slow to fill.
So I agree with Bud as to a volume test, but I would take it a step further; I would test the volume coming out thru the floatvalve. There may be debris caught in it, or the hole may be just too small.
But I must reiterate, I am confused that there are not more symptoms accompanying the lean running.
I think I would back off the timing 4 degrees before I would go any further, and retest.Just to make sure it is not an ignition problem.And I would close up the plug gaps to .030, to make it easier on the coil. Like I said the lack of other more obvious lean-running symptoms has me off in another direction.

 

[kkritsilas]

The "hidden fuel line" behind the RF wheel is there on a J body (on my 1981 Mirada CMX, at least). I just had mine rust out, so I had to go find it, and I did..

 

[rcmaniac791]

Another way to see if the fuel pump diaphragm is leaking is to remove the pump, cover the suction port (a finger usually works) and manually move the pump arm. This should create a vacuum in the pump and the arm should not move back. If there is air getting in with the suction port blocked, that may tell you the pump is bad. If there are pinholes in the pump diaphragm, the pump may still work fine at idle/low rpm, but with the high engine speed, the pump can't keep up with the fuel requirement.

Little tests like this can prevent you from spending money on parts you don't need!

 

[AJ/FormS]

That's what the vacuum test was invented for, that all but a few have forgotten about.
Another thing to think about is the return spring on the arm. When it dies, the pumping stops, even tho the pump is otherwise 100% OK. Of course the volume test will be pitiful,as will be the vacuum test. And so you go and order a new one. And at swap time,there you are holding a perfectly good pump with a floppy arm. Hmmmmmmm, what to do?
Well you don't know it's perfectly good. You see the floppy arm and condemn it.Thankfully this is a rare occurrence.
When I pull a pump off, I always bench test it before tossing it. In 1999 I had accumulated about 8 or 10 SBM pumps over about 25 years or more. At the bench test, choosing a pump for my new engine,every one of them still pumped. Some went back to the sixties.Most made about 4 or 5 psi, but a couple made over 7. I could feel the difference in the return springs.I bolted on one of those bad-boys.

 

[MoparKidD-4]

Well I went ahead and replaced the fuel pump, only marginally more difficult than on my A-body due to those tight inner fenders and the replacement pump had the fittings pointed in different directions than the original. I'm pretty confident that fixed the problem, it now pulls cleanly to where I can feel the power "naturally" drop off due to the engine running out of airflow vs. running the bowl in carb dry and leaning out; I don't have a tach hooked up yet but judging by the sound and speedo I doubt it was getting much over 3000-3500 RPM before running out of gas. Before it was fixed I kept feeling like it ought to pull harder in the higher revs than it was, well now it does lol. Haven't tested the old pump but judging by the level of grime on it I wouldn't be surprised if it was more than 10 years old.

I looked at that hidden fuel line as well, all looks fine especially considering this car has ZERO rust as it spent all its life in Nevada and Colorado (dry climate).

 

[BudW]

I looked at that hidden fuel line as well

Actually the hidden rubber fuel hose.

I thought about dragging out a fuel line assembly I had removed from an ’84 Gran Fury - to take pictures to show where the hidden hose is at, but forgot to do so, last night.
BudW

 

[MoparKidD-4]

Actually the hidden rubber fuel hose.

I thought about dragging out a fuel line assembly I had removed from an ’84 Gran Fury - to take pictures to show where the hidden hose is at, but forgot to do so, last night.
BudW

Even though I seem to have fixed the problem, that would be useful for future reference...

 

[kkritsilas]

The fuel line that goes between the tank and the fuel pump on my 1981 Mirada is metal. It has rusted out.This is the line that runs behind the passenger side front wheel, and it enters the engine compartment thought a hole in the fender well.

I wll probably be changing over the entire line to rubber, as the rust is pretty extensive through the length of that line.

 

[BudW]

These pictures of the 3 fuel lines off of a ’84 Gran Fury (police).
5/16” main fuel line
¼” return fuel line
(Not sure – 3/8” maybe) fuel vapor line – going to charcoal canister.

The "hidden" fuel hoses.

(Note: we got 2½" rain last night and was still sprinkling while I was taking pictures).

These lines are somewhat rusted (but intact). I saved them so I could make a set of stainless ones for my big block (at 3/8" - maybe).

Note: I highly do not recommend running all rubber hose from front to rear. Metal is cheaper and a whole lot safer.
It is easier to prevent a car from catching fire, than to clean up the mess after it burnt down - after a fuel line fire.

BudW

Note: I did not measure the line but there is a lot of length there. It looks a lot shorter in the picture than it actually is.
The longer piece of plywood is 4 foot wide.

 

[jasperjacko]

agree about the rubbe hose, plus more likely to collapse and restrict.

 

[kkritsilas]

The intent is to use fuel injection hose, not just regular low pressure fuel hose. I don't really see a mechanical fuel pump collapsing a hose rated at 300 PSI. I also need it in case I end up having to use ethanol, which fuel injection hose can handle easily, and regular fuel hose is iffy (some do, some don't). I am willing to be corrected if any of this is not right.

 

[BudW]

Kinks in rubber hose is a big issue - which is troublesome to diagnosis, but not what I’m referring to.

Fire hazard is my concern.
Steel can take a lot of damage before rupturing – rubber can’t. Rubber sags over distance – steel won’t. A lot smaller package with steel than with rubber. Steel costs less than rubber.

Steel line could survive a grass fire without issue (no comment about rest of car, though). Rubber cannot/will not hold up to a grass fire – and may make things much worse.

Most sanctioned bodies will not allow more than 12 inch stretch of rubber fuel line and no more than 10 connections from fuel tank to final source (carburetor or FI). Rules vary by location. Also will not allow rubber fuel hose (any rubber) a certain distance from any heat source (exhaust) of 4 inches (I think – this item is going by memory).

What if comes down to is, this is your car, not mine. Rubber hose from front to rear is not a good idea – but can work in temporary situations (like to get home).

I don't want to read about your car in my newspaper or on national news due to a preventable fire ball.
BudW

 

[kkritsilas]

Bud:

Valid concerns, mostly. But I will point out that all aftermarket fuel injection systems use rubber fuel injection hose from the tank to the engine compartment. Not only do they not supply hard line, they specifically recommend AGAINST using hard line, even if it were replaced. The F.A.S.T EZ-EFI 1.0 manual specifically warns against using anything other than Fuel Injection hose. It seemed to indicate that the Fuel Injection hose helps reduce the pressure pulses coming from the electric pump near the tank. The return line is also fuel injection rubber hose. I think that they are also concerned with the hard lines picking up heat in the hotter areas of the continent, where as the rubber hoses would act as an insulator against the heat.

While I see your point regarding the grass fire, I think the fuel line is not the major concern in that case, as the tank will be in the same fire, and if the hose burns though, or even if the hard line in intact, the major concern will be the entire fuel tank overheating, and exploding (what is called a BLEVE (Boiling Liquid Explosive Vapor Event).

My main concern with steel lines is two fold: a) I don't know how to flare or bend metal tubing properly, and I don't have the tools to do it: and b) the reason the fuel line/lines rusted in the first place is the water/mud/snow/etc. thown up into the rear underside by the rear wheels. Until such time as I can figure out how to get rear inner fender liners, the rusting out will happen again at some point. I either need to find a way to get inner rear fender liners (preferably of some sort of plastic or fiberglass) or I need to use non corroding fuel lines.