Fuel Issues

[David]

While I was replacing the factory OEM fuel filter, I added an additional generic clear filter inline to see if I was pulling in any gunk from the gas tank. (the car had recently died on me, apparently due to a clogged filter)

However I don't see much fuel flowing through the filter. Ive seen a few spurts of fuel come through occasionally , but for the most part Id swear its empty. In the photo below the car is running, but as you can see the filter is empty.

Shouldn't I see a steady stream of fuel coming through ? Ill say the car does run a little rough, but I assumed that was normal for an old carb'd car. Now Im thinking Im not getting enough fuel to the carbs-either because the pump is going bad, or maybe the screen at the tank is clogged.

Thoughts ?

Photo was lost. Sorry.

 

[HB Chris]

Well, then filter is facing the right direction, and in my 2002 I also see very little fuel in the filter but you should see some. Once fuel bowls are full the car will run even if filter looks empty. When I had a similar problem in the 02, it was the fuel pump. If lines are old air can leak in and pump can't draw fuel as well. Pull the hose from the pump and place the end in a cup or jar to see how efficient it is pumping. Hope this helps.

 

[deQuincey]

Well, then filter is facing the right direction, and in my 2002 I also see very little fuel in the filter but you should see some. Once fuel bowls are full the car will run even if filter looks empty. When I had a similar problem in the 02, it was the fuel pump. If lines are old air can leak in and pump can't draw fuel as well. Pull the hose from the pump and place the end in a cup or jar to see how efficient it is pumping. Hope this helps.

+1

when my car is not running i can see half of the clear filter with petrol, but when the car is running you can hardly see any petrol in it

regards

 

[61porsche]

Fuel Filter Wierd Science

What you're seeing is vapor. It's caused by pressure and temperature which is why sometimes it seems visibly there's more fuel and less than other times. Fuel is flowing through the filter. If you see more fuel than usual, the restriction is getting greater. (dirty filter). It happens slightly less if the filter is vertical; but in a E9 fuel route that isn't possible. ( But VW and Porsches; it is.)

Rough running only slightly can be fuel level. You can isolate 1 carb temporarily by disconnecting the fuel, then restart. Yes, it will run on 3 cylinders. And when the factory says the fuel level is sensitive on a Zenith, they meant it. I usually try the different washers until it drips out the venturi and then go one size thicker washer. ( Mercedes sells the whole set still...) Zeniths for other cars actually had a sight plug for fuel level like a Holley.

Pop the top and see what washer is under the float needle. Grey is 2mm, red is 1. I've seen both and shims on the float when all it was was the wrong gasket holding the float from swinging.

Rough running can be all sorts of other things also. Cheap bouncing points and drifting timing, excess wire resistance on one wire, bad gapped plugs.

If you can describe it.... maybe we can help.

Don't worry about the fuel filter.... do make sure the clamps/rubber fuel lines are tight as Chris says. Find a small guage and stick it on the fuel pump- min. 2,1/2 psi.

 

[David]

Thanks guys. Ill figure out a way to measure the flow at the pump and post results.

Anybody know where I can get an inline flow meter ??

 

[Mike Goble]

With the present orientation of your filter you will never have fuel in the upper half of the filter under running conditions, the air is trapped there. That's one of the beauties of the metal filter, it's been mostly full of vapors for 40 years but you couldn't see it. It's like Las Vegas.
If you want a filter full of fuel, elevate the output above the input like the Datsun filters of that era.

If you suspect that the suction side of the pump is leaking air, remove the line from the top of the tank and plug it, then create a vacuum in the line at the filter and see if it leaks.

 

[David]

I added a fuel pressure gauge, but Im still baffled. Not sure it the photo is clear, but its reading 0.

 

[MMercury]

I added a fuel pressure gauge, but Im still baffled. Not sure it the photo is clear, but its reading 0. In this photo the car is on.

http://i627.photobucket.com/albums/tt359/david91107/2011-01-01_22-55-49_788.jpg

Many possible explanations:

I am unable to make out the picture on my tiny screen (which is the primary reason for the bigger type). Is your gauge functioning and is it accurate? Is the gauge in line with the fuel input without any "T" fittings or shut off valves that might impair accurate readings? Is it possible you fitted the gauge to a return line?

If you are using a mechanical fuel pump, it is not likely to produce more than 3-5 lb/in2 of pressure. If your gauge is not calibrated to handle low pressures, it may read "0" despite there being pressure. I think the type of gauge you are using is probably better suited for testing fuel injected systems i.e., 30 -45 lb/in2.

Testing low pressure does not require much of a gauge. In the good old days, the trusty and relatively inexpensive vacuum gauge was used for this. If you think this is jest, notice the face of the gauge where it says "fuel pump [p]ressure test[er]."

If your carbs are receiving fuel (floats/needle valves are not blocking incoming fuel) you may only notice minimal pressure. When the carb bowls are full and will not accept additional fuel - is when you would likely read maximum pressure. As noted, your mechanical pump may not be producing much pressure to begin with. If it is marginal, especially if it is feeding two carbs and has a return valve installed - or you have installed a fuel pressure regulator, this might explain the negligible pressure reading. It bears mentioning that pressure is NOT the same thing as volume.

I hate to suggest this, considering obvious safety considerations, but if you are truly concerned about flow (volume/pressure), you really don't need a gauge. First, if you are running the mechanical pump off of the cylinder head, you ought to be able to disconnect the inlet side of the pump and - with a finger blocking the inlet and someone cranking the engine (to operate the pump) - you should readily feel the vacuum on your finger. If you like adventure, you could also run a hose from the fuel pump outlet into a container. Crank engine and watch (measure what happens). You may see a dribble indicating blockage or a weak pump - or you may be surprised by a deluge. Frankly, a simple variation of the later method is used to measure volume discharged from fuel injectors.

Good luck.

 

[HB Chris]

Disconnect the hose to the carbs and put the end in a plastic cup, crank engine, you should get lots of fuel.

 

[David]

Thanks for the replies. I dont think I have this connected wrong, but here is a photo showing more of the orientation. The gauge itself is a 15psi unit, so I should be able to read down to 1 psi. That having been said, its a cheap-o unit from the local parts shop so its anyones guess as it its accuracy. I ordered a VDO from NoHo Speedo which Ill use when it arrives.

The car has crapped out on me twice. I know Im getting fuel, but I guess Im trying to answer two questions:

1.Am I pulling junk into the carbs ? The last incident seems to have been resolved by putting new fuel filters inline, so if the source was junk in the lines I should probably now check the filter in the tank.

2. Am I getting enough fuel to the carbs ? The car runs a little rough, there is marginal fuel evident in the clear fuel filter and now the pressure gauge is not registering any pressure. So, perhaps this means the fuels lines are clear, but Ive either got a leak or the pump needs to be replaced.


Had a photo. but lost it along the way. Sorry.

 

[Stevehose]

Have you checked your in-tank screen to see if it is clogged, or that the short fuel line from the sending unit to the metal fuel pipe ftting in the trunk is clamped well and not allowing air in?

 

[cpeavey]

The photo is pretty dark, but it looks to me like you have the pressure gauge installed on the intake side of the pump. You are not likely to see much pressure there - it would be slightly negative. To measure positive pump pressure you need it on the other side, between pump and carbs.

Charlie

 

[61porsche]

32/36s ( The carbs, each) have a brass cap below the fuel connection that contains a strainer located horizontally. Be sure to check these.

Yes, the guage goes on the other side of the pump. You won't get more pressure than 2,/1/2 or 3 lbs on a factory style pump.

You can disconnect the fuel line near the filter and blow through it with air to back flush it. Don't go through the pump - there's a small check valve there. A mighty vac is good if you have one- it has a guage and you can measure pressure and vacumn ( suction )

Fuel filters don't catch everything in my experience and don't put multiple filters on- it just creates more resistance. ( Once saw a car with 4 filters, three in the trunk!)

On the pump- tighten the nuts up. Not very much is needed. But tight is. If you're pressure is low at the pump; a temp fix would be to sand the insulator block down maybe a 1/16" which gives the pump rod more distance to operate the pump. ( Once saw a carb'd Porsche with 10 psi- the guy really cut the block down- nice job- didn't catch it at first.)

If the pump/ lines/ tank check out- it's likely the float needles gunked up and not opening or enough past idle.

 

[gwittman]

I am having a hard time see exactly where the lines go but it seems to me the fuel pressure gage is on the inlet side of the fuel pump. If that is true, you will not see any positive pressure there. The fuel pressure gage needs to be on the outlet side of the fuel pump. Am I wrong on what I am seeing?

 

[David]

I finally received the VDO pressure gauge and hooked it up, correctly this time. I feel like such an idiot. Not sure if you can tell from the photo, but it reads a measly 1 psi. Does anyone know if this is correct ? Id like to avoid another breakdown and replace the fuel pump now if it looks suspicious. On that note, has anyone replaced a mechanical pump with an electrical unit??



Had photos, but lost them along the way.

 

[61porsche]

Should read about 2, 1/2 lb.

Try pinching each carb hose in turn to see if the guage goes up. ( Carb float needle leaking) Or you can pull the carb hose and plug them, then start for a minute. You should have enough fuel in the carbs to run for a short while.

If you decide to put in an electric pump, my suggestion is near the tank.

Snazzy filter mount there!

P.S. Only run one filter.

 

[JohnHein]

My coupe had a retrofit electric pump mounted pretty much where your second, larger, filter is located. You might be able to mount there also and pull power from the fuse box. However, I had problems with fuel flow also (as Jerry "Porsche61" can attest) and moved the pump to the back near the tank outside the car. That cut down some of the pump noise that I had with mount on the firewall. My results have been better. Get a high quality pump.

Good luck

 

[decoupe]

Fuel Pump

David:

If the gauge is only showing 1psi from the outlet of the mechanical pump why not replace the pump rather than going to an electric? Did you test the pump for flow as MMercury suggested? If you can still use them, mechanical pumps are silent and the electric sound like a flock of steroid-ally charge mosquito's. Costs $120 - 140 for OEM Pieberg.

I had a Carter Rotary pump in the trunk when still using weber 38's and did all manor of things to reduce the sound and nothing really had an appreciable effect. No choice as the mechanical pump interfered with the throttle linkage but yours looks like there are no issues (zenith's?).

Good luck.

 

[David]

I thought an electric would be more reliable, and putting it in the trunk would let me reduce some of the eye-clutter in the engine bay. But it sounds as though the electrics are loud, so Ill stick with mechanical.

I need to run the test several folks have posted to figure out what's wrong. Thanks to everyone for their help.

-David

David:

If the gauge is only showing 1psi from the outlet of the mechanical pump why not replace the pump rather than going to an electric? Did you test the pump for flow as MMercury suggested? If you can still use them, mechanical pumps are silent and the electric sound like a flock of steroid-ally charge mosquito's. Costs $120 - 140 for OEM Pieberg.

I had a Carter Rotary pump in the trunk when still using weber 38's and did all manor of things to reduce the sound and nothing really had an appreciable effect. No choice as the mechanical pump interfered with the throttle linkage but yours looks like there are no issues (zenith's?).

Good luck.

 

[Honolulu]

ahah! (maybe) rambling...

Like another poster, I too thought at first the gage was on the suction side of the pump, but no. A fancier gage will only cost more, and I doubt it will provide further information.

I question whether you have a fuel supply issue at all. If fuel starvation is the actual problem, you could have a good idle or low speed operation, only to buck and stutter at larger throttle openings. You only say that the car has stalled, without much description... so I question whether this is really a fuel issue.

My '58 VW used to sputter to a stop once a week because the pivot pin kept walking out one side of the pump housing. I got pretty good at taking the pump off and pushing the rod back into the housing, in the dark, rain, while the chick waited, etc. But one time it was different. I took the pump apart to find a pinhead-sized grain of crap stuck in the reed valve, so there was no one-way action on the pump. If you disconnect the pump hoses, you should not be able to blow through the pump in the reverse direction of normal fuel flow.

I mention this because supposedly you've had stalls caused by crap in tank plugging the filter. Something may have gotten past the filter (don't ask me how, I dunno) and though the pump is trying, there's no one-way action. Unfortunately, the pumps are nowadays sealed and though I guess you could try shooting air through it while you work the actuator rod, clearing the pump may not be possible.

Recent experience with the clear filter on a friend's 2002 shows that you won't see much fuel through the clear filter, but it's flowing. They can be tough to bleed all the air from, but you don't have to.

Some electric pumps make a heckuva racket and you have to hang them on the hoses above the half shafts, or better mount it with resilient bushings like the AFM mounts from later injected cars. Some (more expensive) pumps are quiet(er). I think the noisy one is about $40.