Fuel issue

M

Mickey Dale

True Classic
Hello good, good people.

Car has been running great once it gets started (but if the car had been stood for a few days, it always took some cranking to get it started). Last week the car ran better than it had in a while. It was as though I'd found an extra 10 horse power! I took the car home, parked her up and she sat for a week or so. And now, she won't start at all. Then I saw that the inline glass fuel filter fitted to the hose between the tank and the fuel pump was bone dry. I pulled the hose from the pump that goes to the carb. Pump not pulling anything through. I can suck fuel from the tank, so it would appear that there is no blockage there. Perhaps it's just the fuel pump (it's not old, maybe 2 years). I ordered a pump in the UK from Eurosport. They don't sell the actuator rod that operates the pump from the engine block. I bought new hoses too. Pump will arrive tomorrow. I hope there's nothing more serious lurking inside the engine...

I'll know more tomorrow, but I have no garage so it's a case of jacking the car up and getting very dirty on the ground!
 
or take the opportunity to install an electric pump, there's a recent thread on the same (possibly) issue;
https://xwebforums.com/forum/index....after-sitting-for-about-a-week-then-ok.31911/
Most would consider it an upgrade I believe, the electric pump would kick in with key on and cranking meaning it would prime right away, they won't fail very often but they do make an annoying noise and you have to wire it in (which "should" include a safety device, like running the power off the oil pressure circuit or installing an inertia switch, so that in the event of a crash the pump stops because pumping gas onto a crashed engine is a bad thing)
Electric pumps will gloss over the issue of fuel evaporating from the carb over time.
You'd need a blanking plate to cover the spot the old mechanical pump was.
A simple 4 psi (or whatever) pump is pretty cheap. I'd put a filter in front of it too.
 
Hey Mickey. How are you ?

Had this happen to me once. Turned out that the hose between tank and pump had a small crack in it. After sitting - and depending on the position of the hose - the pump would just suck in air through the crack instead of fuel. Kinda like trying to suck Coke through a straw that has a crack in it.

At least something to look for. Good luck. Doug
 
To reiterate Jeffs recommendation if you go for an electric pump, having a safety feature is strongly recommended as dumping fuel when the engine stops running (due to a burst fuel line for example), is not going to make for a good day.

VW uses a nice relay which basically has a timer on it that is set by a wire to the coil, if it doesn't see coil activity then it shuts down the fuel pump.

Other approaches are the inertia switch which can be gotten from the trunk or firewall inside of most modern Ford cars cheaply at a junk yard. They are manually resettable so if a rough road (very rough) were to trip it you can reset it.

The oil pressure type circuit is a fine route as well but a bit fussy to me given the sometimes less than ideal state of idle oil pressure.

So this is my take: I would replace the mechanical pump with another mechanical pump. They are intrinsically reliable and trouble shooting them is not difficult. I have never had one fail in the 40 years I have been driving and that includes my cars which sit for most of their life, I have had two electric pumps fail during the same period.

An electrical pump requires some mods which are easy to do but may add to the problem of diagnosing why my car isn't running be it due to a fault in the new wiring, the pump is broken or is delivering too much pressure for example. Adding more complexity isn't always a good thing.

Your mileage may vary.
 
I have a related question Karl. I have the inertia switch already installed. The coil based relay seems safer, but wouldn't the relay method prohibit the "Feature" of priming the carb prior to cranking? If I am reading the doco from the link correctly, it will only pump when the distributor starts to spin.
 
The VW relay will allow provide power to the pump for two seconds when it is first energized by the key as I recall (which may be faulty). After that it is relying on impulses from the coil activity.

An electric fuel pump can move as much fuel at start as it does at full throttle so even though you don't get the full "prime" feature of turning on the key and letting it run for as long as you want, you should get enough fuel to start in a few turns. Personally I don't mind the engine needing a few turns to get some oil pressure up before the actual start cold.

It's a pretty nice part and is quite reliable. It can be found in 1985 to 1997 VWs of various types. I did have one fail from a cold solder joint intermittently which was a hard one to trace.

I think the later VWs use a different set up, though similar. With a little more research, the newer '409' units are more complex as they have inputs from a few more systems:

Terminal 30 - power from Fuse S163
Terminal 31 - ground
Terminal 85 - to Engine Control Module
Terminal 86 - from ignition switch (D15)
Terminal 87 - to fuel pump circuit - Fuses S228, S232, S234, & S243
Terminal C - from crash signal circuit
Terminal TK - from door contact switch circuit
 
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I tried to buy the push rod that comes out of the block into the mechanical fuel pump but could not locate one in a store, so I'm hoping it's intact when I get the pump off! Incidentally, what drives that rod (that drives the pump)? Maybe I'm just being paranoid!
 
Mickey Dale said:
I tried to buy the push rod that comes out of the block into the mechanical fuel pump but could not locate one in a store, so I'm hoping it's intact when I get the pump off! Incidentally, what drives that rod (that drives the pump)? Maybe I'm just being paranoid!
Click to expand...

The push rod is unlikely to be a problem and shouldn't need to be replaced. It is driven off a cam on the auxiliary shaft that also runs the distributor and oil pump.

Just because you are paranoid doesn't mean people are not watching you... :)
 
I only ask cos my oil pressure gauge was reading low on the day I last drove my car... but I just put it down to a bad connection on the sender (damp weather etc) and also my paranoia that the aux drive is caput! We'll soon find out! I fitted all new fuel hoses today as far as the fuel pump (tank to pump, pump to carb), but the new fuel pump has not arrived yet, so we're probably gonna enjoy the sunshine today and do this job tomorrow.
 
The oil pump is driven off a gear shared with the distributor. The fuel pump is driven off a cam.

There isn't much that can go wrong with the auxiliary shaft on a single cam motor, it all works or it doesn't.
 
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