Stock 1978 FI Super beetle

[Marcas]

http://postimage.org/image/9yt1v6w9p/

I live in Ireland but have owned a US convertible for the last 20 years. I rebuilt the engine about 10 years (65000 miles) ago and replaced most of the FI parts except for the "brain." The car has run well for most of the period achieving 27 us mpg+ on a long run with just an occasional vacuum leak to worry about.

Recently I had trouble with a fast idle which with some help on another forum I traced to the deceleration valve which I adjusted with help from a post that I found by Ray Greenwood (thanks if you read this Ray).

In the last few weeks I have had trouble with the engine cutting out. It had become a little hard to start when cold and I have replaced the coil, plug leads and spark plugs and also tried a different distributor. It is now easier to start but still suffers from what feels like a missfire. It will sit stationary ticking over at normal revs but when driven the engine sometimes cuts out, normally when I am coming to a stop with the clutch pressed in at traffic lights. Sometimes the revs seem a little higher than normal when I come to a stop but then settle after about 10 seconds.

I have tried checking for leaks and replaced a lot of hoses. I have also checked the pump and pressure regulator as per the Bentley manual and replaced the temperature sensor. The engine is stock except that it has a federal rather than California exhaust, it has an aircooled.net svda distributor with pertronix points replacement and the egr valve has been removed and the holes blocked off.

Any suggestions would be greatly appreciated.

[Marc]

How old's the double relay? Could be that its contacts have developed some resistance, or the control winding's going bad. Either could cause power to the pump to drop out occasionally. When you decel the flap in the airflowmeter can shut momentarily; if when it opens back up to a normal idle position the relay doesn't restore power to the pump as it should the engine might stall. That'd be consistent with occasional difficulty to start, too.
You could rig a temporary source of power to the pump, if the symptoms clear up the double relay would be the prime suspect.

[Marcas]

Marc, Thanks for the suggestion. A new relay on this side of the atlantic costs almost $200 so I might try rigging up a power supply to the pump. Is there anything i should know about doing this. My electrical knowledge is poor.
I bought the relay that is in the car second hand about a year ago as my back window had leaked and destroyed it. The one I bought was in a plastic rather than a metal case but I don't know the age of it.
If I have to get a new double relay can anyone help me with the correct part number. The one I am using and the one it replaced and had used for many years without a problem had the vw number 071 906 059 which doesn't appear to be for California cars which mine was originally. I think it should have been 071906 059A. Does anyone know the difference. The other odd thing is that the Bosch part numbers on the two I have had were 0 332 514 129. Should I have been looking for one that has the number except for a zero at the end? I have found these available for just over $100 but listed for German Opel cars not Beetles.

[Marc]

I'd imagine that there are several different Bosch part numbers for the relay, but if the pinout's the same any of them should work. I wouldn't rush to purchase a new one just yet, i only brought it up as a possibility that you might not have considered.
One way that you could "rig" power to the pump would be to disconnect the factory lead and furnish your own wire. A source of power that switches off with the ignition should be chosen - fuse #11 (horn/brakelight) or #12 (t'signals/dash) should be able to handle the additional load. Not an optimal arrangement for long-term, the ignition switch wasn't intended for this, but it should be OK for long enough to see if it makes a difference.
If it'd be more within your comfort zone, you could instead "back-probe" the connector for the relay - jam wires into the supply and output wires' openings in the plug, and route them to a place you can reach from the driver's seat to touch them together (adding a switch would be slightly less crude). Wired like that, the pump won't shut off automatically with the ignition so you'll be responsible for it.

The stock system is designed to assure that the pump will shut off if the engine stalls, to prevent filling the engine with fuel if an injector is leaking AND to keep from spewing fuel in the event of an accident severe enough to open up the fuel lines. An alternate arrangement like either of the ones described above defeats the safety feature so should only be used for troubleshooting purposes - at your own risk.

[Marcas]

Thanks Marc. I have been looking out for another second hand relay to keep as a spare. I think I might buy one in case I mess anything up trying to by-pass it. At the very worst I will have the spare I wanted anyway.
I'm still happy to look at other possibilities if anyone has another suggestion

[Marcas]

I got a new relay today. Since then I have driven for 20 miles without any problems. It is too early to tell for certain but it looks like Marc's suggestion was right - many thanks.
The only other thing I replaced at the same time was the coil as I realised I had one of the suspect "Blue coils." However, as I had run this for a few years without problems, I don't think it would have made any difference (I had compared the spark against an old coil and it was much whiter/brighter).

[Piledriver]

It may be a good idea to pop open the old relay and buff up the contacts, and save that for a spare.

Often the only thing wrong is oxidation from age.

[Marcas]

Thanks for the suggestion. I will give that a try. Forgive my ignorance, but would it be ok to put a bit of oil on it afterwards to keep it in good condition?

[Piledriver]

Thanks for the suggestion. I will give that a try. Forgive my ignorance, but would it be ok to put a bit of oil on it afterwards to keep it in good condition?

No, proper contact cleaner/lubricant is OK.
(contains just a touch of silicone diaelectric grease)

[Marcas]

Thanks for the advice. I'm still quite surprised that changing the relay appears to have solved the problem. I had expected it to work or not work rather than work most of the time.

[SportyBug]

Thanks for the advice. I'm still quite surprised that changing the relay appears to have solved the problem. I had expected it to work or not work rather than work most of the time.

Glad to hear you got the problem fixed.

Just to share, if you ever have the fuel pump dropping off again there is a spade connector in the mess of wires just above the fuse box. If you put power to it directly it will power the pump. I have had to do this before when my double relay quit