All of a sudden.... I need your ideas, please.

[Klaus Schlueter]

Good afternoon all,
yesterday my wife and I made a 80 km trip south of Munich. Perfect Stag weather, perfect Stag, beautiful country roads. But all of a sudden the engine lost its smoothness and started to run on less than 8 cylinders, rough with a steady tendency to stall when the throttle was on idle.
We had still 23 kms to go home passing some round abouts, traffic lights and driving in the beginning rush hour. I had a terrible time to get us back home with 20 to 30 times engine starving when I had to stop the car. Each time the engine restarted without a problem however after the restart I had to support the engine's running with a little bit of choke. Helpful was to increase the revs by changing to a lower gear on the ZF autobox. So we limped home and then a miracle happened: 800 metres from home suddenly all was well again. Smooth engine and relieved faces.

My idea for starting the investigation is to open the carbs' float chambers, check for dirt and clean the float valves. What do you think? Any other idea where to start?
And what do the electric experts think? Could it be an electric problem as well?

The plugs are new and the fuel filter is approx. three years old.

Looking forward to get some input from you
Klaus

And I forgot to mention: 3 weeks ago I experienced this running effect on a Munich motorway but just for appr. 2 km. After that everything was fine again.

[staggering]

Hi Klaus,
Just a very quick checklist from me:
1. Maybe dirt / water in fuel that keeps getting up past the filter intermittently - have you got a fuel filter between the tank and fuel pump
2. Poss faulty fuel pump connections and / or start of pump failing
3. Unlikely but coil may be starting to breakdown
4. Possible start of safety inertia switch on bulkhead starting to get sticky / faulty
5. Some electronic ignition systems have connector blocks that need reseating
6. is central sprung connector on inside top of distributor held firmly and moving up and down freely
7. poss start of breakdown of main coil to distributor lead / other plug leads

I am sure others will come up with other ideas soon - good luck in sorting

Cheers
Ian

[Phil S]

could also be something blocking the fuel pickup in the tank if the others draw a blank

[JeffW]

Hi Klaus

I had a similar thing last year. For mine it was plug leads breaking down with high resistance. I think I had two that were bad and the misfiring / not running on 8 cylinders like you had would only appear when the engine bay started to get warm.

Hope this helps and you get it sorted soon!

Jeff

[Klaus Schlueter]

Many thanks for your ideas Ian and Phil. Thats an interesting list to start with.

Your #1: I just checked-there is no fuel filter between tank and pump. But a good idea and simlel to install.
Your #5: 20 years ago the 3 pin connector of the Lumenition had started to corrode and caused a running problem (very common fault). I will check-easy to fix

Klaus.

[Klaus Schlueter]

Thank you Jeff. My set of BERU plug leads are from 2001 and have reliably worked for appr. 110' km. So it can well be that there is a hidden problem. Electrics is not my domain: is there a way for me to check the set or have it checked by a BOSCH service?
Klaus

[dasadrew]

If it helps Klaus, I can bring spare leads, distributor cap, rotor arm, coil to try out when I'm next in FFB.

Personally, I'd check the float chambers. Do you need spare gaskets?

Drew

[wilf]

DO you still have the cold start "hot air" system connected?

[Klaus Schlueter]

That's very generous Drew.
I can start earliest on Saturday with the work and yes I'll check the float chambers and valves first. If I find nothing there I'll let you know.
When do you intend to go to FFB?

Klaus

[JeffW]

Thank you Jeff. My set of BERU plug leads are from 2001 and have reliably worked for appr. 110' km. So it can well be that there is a hidden problem. Electrics is not my domain: is there a way for me to check the set or have it checked by a BOSCH service?
Klaus

Hi Klaus

Easy to eliminate - test the resistance of each one with a multimeter set to Ohms resistance and see if any are really high - the longer ones will naturally be higher than the shorter ones, but if you find any that are really high, try replacing those and see if it happens again.

I think I have seen Mike Lingen post numerous times 'if it seems like a fuel problem it is usually electrics and if it seems like an electrics problem it's usually fuel.'

Good luck!

Jeff

[dasadrew]

That's very generous Drew.
I can start earliest on Saturday with the work and yes I'll check the float chambers and valves first. If I find nothing there I'll let you know.
When do you intend to go to FFB?

Klaus

I'll be there at the weekend

[Klaus Schlueter]

No Wilf, that's not working since many years-for peace of mind I leave it as it is.

[SteveD]

I had a similar problem and it was the SU mechanical fuel pump since changed to electronic.

Steve.

[Guest]

Hi Klaus
I had similar problems as well a couple of years ago and spent a lot of money on buying 2 fuel pumps, distributor, refurbished the tank, new rotor and cap, plus plus until somebody took the carbs apart for me and found what I belive were parts of a disintegrating fuel filter maybe due to use of E95 and E10 fuel.
Regards Hans

[Klaus Schlueter]

Jeff, that sounds easy to check-even with my knowledge. Many thanks.

Steve, I have installed a German electronic,fuel pump from HARDI, Berlin. Of course I will check the electric connections as proposed by Ian.

Hans, I'll try to avoid spending all the money for new parts. So if the carburettor disassembling doesn't show any result I will definitely come back to Drew's offer of trying different parts.
The phenomenon I experienced is exactly the on we all hate. If there is a broken part we know what to do. But in this case.....It will be difficult to win the confidence back.

Klaus