compression fittings and fuel starvation

[eljefino]

Is this a thing?

I patched a couple feet of fuel line on my 02 corolla. It uses 5/16 line and I think it's returnless, not that it matters. Anyhow I hacksawed the old stuff out and put a couple feet of new metal in. There's a vinyl quick release coming from the tank and since its o-rings were leaking and I couldn'd find a splice-in part, I lopped it off and used a proper vinyl-steel fitting there, too.

If you look at these fittings closely there's an "internal tunnel" projecting into the line, presumably to brace everything against the compression the ferrule enforces. This seems like it uses a considerable amount of cross area.

I "gunned it" and seemed to fall flat at 2/3 throttle and 4500 RPM. I don't want to burn any valves from running lean. I'm not familiar with the car, just picked it up, so IDK if it always ran like that or not.

-- Does anyone else think 5/16" is barely sufficient to power a 130ish HP car to begin with?

-- Any studies out there on these stupid fittings?

-- Any replacements or other techniques that would work? I could use a few inches of SAE 30R9 injection hose and clamps for the all-steel junction, for example, but not the vinyl-to-steel part. The female quick releases available to me have 3/8" vinyl and 5/16" connectors "or vice versa" but no straight 5/16.

I have a 5/16 barb that I tried (and failed) stuffing onto the cut vinyl line. Its ID may be slightly better than the compression fittings, though it's still a reduction.

 

[jaj]

I don't know what the problem is, but I did a few calculations based on the engine size and some fairly standard numbers.

At your engine's torque peak, 4000 RPM, it produces 125 ft-lbs of torque. That's 95HP.

For many engines, producing 95HP takes about 6 pounds per minute of airflow and at an AFR of 12 (rich) that's about 1/2 pound of fuel per minute. That's 10 fluid ounces.

So, the other way to frame your question is "can I get 10 ounces of fuel per minute through the fittings I have". Actually, to wind it up to the full power of 125hp at 5800 rpm, you need more like 13 ounces per minute.

So, take some hose, a funnel and a fitting and see how much water goes through. If you get two cups of water through in a minute, then the problem is somewhere else.

 

[Kira]

This will not answer your question.

The inlet and outlet diameters of my fuel filter (2.435cc, 5 cyl., 167hp Volvo engine) are about 1/4" as I recall and my car doesn't starve for fuel.

Would a fuel pressure-at-the-rail test (fuel pump test) tell you anything?
Is your filter old or new?
Also, how fast were you going at 2/3 throttle and 4500rpm? Kira

 

[HerrStig]

The ECU controls the fuel pump speed in 95 and later Toyota OBDII systems. It's one line, not shunt regulated. The pump could be going or the fuel filter might be clogged although that doesn't happen very often these days.. I've got 330K on the OEM filter on a Camry, and the pump is OEM. If things get too far out of whack I think you'd get a mixture CEL.

 

[eljefino]

Originally Posted By: jaj
I don't know what the problem is, but I did a few calculations based on the engine size and some fairly standard numbers.

At your engine's torque peak, 4000 RPM, it produces 125 ft-lbs of torque. That's 95HP.

For many engines, producing 95HP takes about 6 pounds per minute of airflow and at an AFR of 12 (rich) that's about 1/2 pound of fuel per minute. That's 10 fluid ounces.

So, the other way to frame your question is "can I get 10 ounces of fuel per minute through the fittings I have". Actually, to wind it up to the full power of 125hp at 5800 rpm, you need more like 13 ounces per minute.

So, take some hose, a funnel and a fitting and see how much water goes through. If you get two cups of water through in a minute, then the problem is somewhere else.


I like the way you think. For example old carb'd cars had 5/16 or 3/8 line and the pump pushed/ pulled 6 psi or so.

It could be the pathetic auto trans sucks all the life out of the car.

I was going about 40-50 in probably 2nd gear.