Let's play coil, condenser, or fuel pump!

[nbvolks]

So here's what's happening.

When the car is cold, it starts up bang on no problem. If it's run lightly (around the block or a short distance) everything seems perfect. Idle is great and the car seems very happy.

Trouble seems to arise on longer trips with intermittent higher speeds (higher speeds = 55-65). If I'm doing that for say an hour or more, then when I come to a stop it really doesn't want to run and I'm having to modulate the throttle a little to keep it from conking out. The longer the drive, the worse it gets.

Doing the test on the coil when it's cold, it shows that it's within spec at ~4 ohms on the primary winding.

The condenser seems to be okay paired with the points, and on a dwell meter is solid at ~54 dwell angle at 1k and 2k rpms, which is within the used spec for this setup (58 being the max).

The fuel pump seems to be the culprit, I think. It's the typical Brosol alternator style pump. I've noticed that the area around the base, on the block, appears slightly damp if the car has been sitting. However, I am not getting any fuel smell in the oil, so I don't think it's leaking down into the block. I really wanted to keep the stock appearance with the non-rebuildable fuel pump, but I think for quality and peace of mind, I'm going to just go with the square top from Bill.


So my question is, whether my experience sounds consistent with a failing fuel pump? I know the coil can be an issue as it heats up, so maybe that's also an issue, but given that it's okay when cold, I'm inclined to start with the fuel pump and go from there.

[busdaddy]

I'd be most suspicious of idle mixture settings and float levels, especially if you don't have a thermostat in the cooling system.

When it finally warms up properly (highway drive) it's too rich to idle well.
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[airschooled]

So if the engine won’t idle but it will rev, how could it be the fuel pump? Cars use more fuel at high speeds and revvs. It’s impossible for a mechanical pump to suddenly increase pressure to the point of overwhelming your idle mixture.

This really sounds more like a vacuum leak or bad tune/mix/idle solenoid.

I would start with a test for vacuum leaks. All these spots. With real carb and choke cleaner, not WD40 or other less-combustible sprays.

Robbie

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[nbvolks]

[VW_Jimbo]

[volksworld]

normally a fuel pump thats failing will not produce enough volume...and act like a clogged filter...usually on a full throttle run the car will hit a certain rpm and slow down like its running out of gas...which it is...and if the rpm drops enough it will pick back up and run fine again...too much pressure can be checked with a gauge and float bowl levels will be high and the carb will dump too much fuel...you may just need to richen the mixture up a bit for the decell problem...perfect idle mixtures dont always translate to high speed decell without stalling...especially on a car that doesnt have a throttle positioner

[jinx758]

Check the coil when hot.
Scour YT for video on condenser check, any condenser vid will work. Even for HVAC.

You can bypass the #15 positive terminal by running a wire from battery positive or large post of alternator (if equipped) in engine bay. If it stays running ok then disregard & trace the starter solenoid wire as suggested.
A few good whacks with a 2lb sledge could free the Bendix on starter if needed. Sometimes they hang up. I like to use a drift punch or large piece of rebar but only hit the solenoid, not the main starter body.
Dirty grounds can also cause your symptoms. Current needs a clean path from positive to load & back to ground.

A little maintenance goes a long way ... stay safe

jinx
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[nbvolks]

[TDCTDI]

Are the EVAP hoses in place & not blocked?


Remove the fuel cap the next time you experience this & see if you hear a “whoosh”. If so, you have a venting issue with your tank & as the fuel gets consumed, it creates a vacuum on the tank, this, in turn, will deprive the fuel pump of fuel.
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[nbvolks]

[bsairhead]

Check the electro-mechinical fuel cut of switch for tightness. It gets hot it leaks, it cools of it does not.

[jinx758]

"it's definitely not dirty" ...

Y-A-W-N ... !

At least mine starts, runs, stops, & drives as it should.

jinx
_________________
" It's not valuable unless you learn something from an experience. " Henry Ford

It's not unlike the same difference ...

My Craigslist rescued 100 footer :
1971 Standard Bug
1776cc dual port
034 distributor
38mm EGAS Carburetor

[scrivyscriv]

John at aircooled.net has stated before that a lot of people blame the carburetor for poor running when the real issues are ignition based. I have personally, anecdotally, experienced that to be true. I've seen person after person putting a new fuel pump on "just because" they want to throw a part at it.

Check your fuel pump volume and PSI. If they are in spec, then cross the fuel pump off your list and don't go back to it until you've eliminated everything else.
Replace your condenser. Don't just check it, replace it. They are cheap and their quality, used AND new, varies a lot; I recommend keeping used spares on hand to swap in for troubleshooting.
Make sure your points rubbing block is intact and has sufficient grease.
Blow the fuel lines/fuel hoses out and make sure they're not obstructed.

But before really any of that, I'd say take the top off the carburetor. Inspect the bowl for FOD. Drain it, spray the bowl and jets and accessible passages out with carb cleaner, and blow dry with shop air.

It may well be a vacuum leak too. The manifold boots are a known leak point, and less common and harder to find are leaks at the end casting/head seals.
Lastly, I have heard of people with FOD in the fuel tank that floats up to and obstructs the tank sock screen. Visually inspect the screen and inside of the tank
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[ashman40]

Problems after running at high rpms or at constant speed for long distances... my first though is fuel filter clogged. When was the last time you replaced the fuel filter?
A common problem is having a see thru fuel filter and looking at it to determine if it needs to be replaced, or not. Most fuel filters are metal canisters and you cannot see the insides. You replace them after a number of miles or an amount of time (1yr). They are cheap and should be replaced at least every 2yrs, regardless of how many miles you have put on the car.

Also, as scrivyscriv pointed out above... check if you have a clogged screen at the outlet of the fuel tank.


If you can reproduce the problem, pull over to the side of the road and remove the top of your carb. Measure the level of the fuel in the carb bowl. The float/inlet valve and fuel pump should maintain the level at 3/4" from the top of the bowl. If you remove the top of the carb when it is running bad and find the fuel bowl is empty, you know you have a fuel delivery problem. But if the fuel bowl is full it is not the fuel pump. The engine runs off the fuel in the fuel bowl. The fuel pump maintains the fuel level in the bowl. If the fuel bowl level is correct but the engine is not running right it is not the fuel pump.
If the fuel level is too high... this could be from too much fuel pressure or from a faulty inlet valve/float. Too much fuel in your fuel bowl could cause the problem you describe. Another reason to check the fuel level next time it starts to run badly.
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[nbvolks]

[airschooled]

After you've checked for vacuum leaks with spray cleaner, check for a leaky air filter vacuum system by pulling the red hose off the manifold and either:
- sucking hard on it, and plugging with your tongue. No vacuum should leak out. Or…
- Testing it with a handheld vacuum pump. By the time I type out how to do this, you'd be done with the mouth test.

Robbie
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One-on-one tech help for your vintage Volkswagen:
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[nbvolks]

[airschooled]

Smoke machine is preferred.

A good thermostat valve can still allow a bad flap valve to stall the engine under the right conditions. Testing is free and instant.
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One-on-one tech help for your vintage Volkswagen:
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Road trip reports and tech blog:
https://www.patreon.com/airschooled

[doug bugg]

Bad place for a fuel filter...

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[nbvolks]

Smoke test immediately identified the culprit. It's the California-spec, dual chamber EGR. I had tested that with a simple vacuum gauge and it held pressure. So I don't know if it's something to do with it being dual chamber that allows for it to hold a vacuum when demanded, but allowed for smoke to pass in a non-vacuum state. One chamber working and one failed, or something like that.

I have another unit I just tested and it seems to work.

And yes, I know I could block it off, but I'm shooting for original appearance. So, what I may eventually do is just put a solid thin piece of aluminum as the gasket between it and the manifold, and then plug the inside of the short vacuum hose. That way it looks original, but seals off the EGR from functioning...or leaking.