Intermittent engine problem

Hi,

My 71 1600 Superbug has been playing up for some time (about 2 and a half years now) and no mechanic has been able to solve it.

The problem is: while driving along it will feel as if something is grabbing the back of the car and then letting go and grabbing it again (so-on-and-so-on) like suddenly losing power and then it comes back etc - lurches a lot when it happens. This can happen for half a second or up to 3 or 4 seconds. It can happen when accelerating, going uphill, or even when cruising between 80-100 kph (tends to feel more severe and more regular when at high speed and the engine has been going for over half an hour and is warm) though there is no real guarantee when it'll happen. When it does occur the engine sounds like it's knocking about and you can feel it through the whole car.

I've had the carby cleaned (there was dirt and stuff in it, and the jets, which was cleaned out), had it fully serviced, replaced the fuel filter (which had what looked to be fine black dirt in it) and yet it still keeps happening. I also don't believe it's the points as they have been replaced/adjusted each time to no effect.

I'm hoping someone can shed some light on a possible cause as I'm getting close to the point where I just want to put a bullet through it. 😬

Thanks!

Where are You located??

Lee

Could be a worn distributor...

loss of spark ??
Distributor cap has hairline cracks??
wash inside with Petrol..
also check the carbon button in the disributor cap..

and check the rotor too..
VW rotors have a resisitor built into the top of them..

or the electromagnetic fuel cutoff switch is faulty..
easy to fix - unscrew it out of the carby, and
.. cut the pointed end off..

until you get another one... lol

loose electrical connection to the coil
or the electromagnetic cutoff switch on the carburetor..
try another coil...

cheers

Lee

Number 8 - electromagnetic fuel cut off switch
that has been cutoff and disconnected.. Lee

Have you checked your spark plugs to see if they are fouled or not?
Simon

Thanks for the info Lee.

To your first question, I'm located up in Tamworth.

So I'm (more than likely) looking at an electrical problem(?).

Truth be told, the electrics/wiring are all original (ie. in need of replacing/exposed/cracked coating/etc) and it could do with a trip to the auto-electrician.

It annoys me because the amount of money I've spent on it since it started doing this could have easily covered a full electrics overhaul (and a considerable "then some") but it's going to have to wait a while now...

Cheers.

PS. My engine bay looks nowhere near as good as that one. LOL In fact, I'm pretty sure I'm missing bits... :-P

hey Simon, there shouldn't be anything wrong with the sparkplugs as they were replaced when it was serviced. But I'll have a look just to be sure. The mechanic did say he put in "cooler" (??) sparkplugs because Tamworth is a hot town and it'd help it not run as hot (well, that was his reason, anyways...). But, as I said, it's been doing this for 2 and a half years now and it's had replacement plugs put in every second service or so.

The reason for fitting Colder spark plugs is
that VW spark plugs are no longer carried by most autoshops etc..

but a colder version IS available...

B6HS is a cold plug
B5HS is a standard heat plug
BOSCH W5AC is the standard VW plug.. [W175T1 ]

its best to order your parts from a VW shop
like Mick Motors in Brisbane or- Classic VeeDub in Sydney -
as examples..
they have the correct parts at reasonable prices..

Do You ever come down Scone way??

LEE

PS: I don't think plugs would cause the problem you are having...
I believe its most likely electrical.. Lee

Yeah, I visit people in the Hunter Valley from time-to-time so I go through Scone whenever I do.

How long have you had the car??

History of the motor??
Ever had a compression check??
Valves set??

I had a similar problem once - then one day the motor just stayed that way
Pulled it all down and the valve guides were totally shot

are the big wheel nuts tight and are all all fuel filters clean the one in the tank whitch most seem to forget about

i would clean and check the tank and fuel lines before you go too much futher the one in tank as per above

remove the tank and flush it out and poke wire down the fuel line front to back

Hey dude go see Blue at Peel Mechanical, in Bass St.
He does my dyno tunes and grew up racing offroad
VW,s.He will be able to simulate your problem on the dyno then isolate and fix.

Cheers Col

colin wrote:Hey dude go see Blue at Peel Mechanical, in Bass St.
He does my dyno tunes and grew up racing offroad
VW,s.
He will be able to simulate your problem on the dyno then isolate and fix.

Cheers Col

He may not either...

better off with a VW mechanic...

Lee

Thanks for all the help/info guys, it's appreciated. Hopefully I can get to the bottom of the problem.

🙂

Maybe you misread my post 68Auto he grew up racing offroad VW,s !

Cheers Col

One other electrical connection to check is the wire inside your dissy (small braided wire) has a habit of breaking at the end and appears connected when its not. So gently give it a pull to be sure. If it or the coil wires are a little bit loose they will play up at higher rpm or over bumps. Also if your coil electrical wires are cracked they can earth out on your manifolds briefly when vibrating at higher rpm.

One rule I apply that is USUALLY reliable & I can't remember letting me down:

If it misfires regardless of load on the engine, it's a fuel problem

If it misfires or is worse under load, it's electrical, usually High Tension. Seeing yours SEEMS to be under load ie under acceleration & at high speed I'd be looking there

Find a long hill & explore.

Just wondering if it may be a dodgy fuel pump? I ask because it will labour as I slow down and if I have to hit the brakes hard for any reason to come to a quick stop it's prone to stalling. The timeframe (now that I think back on it) does seem to correspond with having to get the fuel pump replaced when the last one went and died.

You didn't mention stalling on hard braking.

That sounds like a vacuum leak.

Does the misfire go away at FULL throttle ie flat to the floor? Is it worse at part throttle? Is the idle OK or rough?

With the engine running, spray some WD40 etc at :

carby throttle spindle bearings
carby mounting flange
rubber boots on manifold
where the manifold attaches to the heads.

Grey/white smoke at exhaust indicates a leak.
Your carby should be a 34PICT-3. They are very sensitive to vacuum leaks, far more than earlier variants.

Fuel pumps are very reliable & when they fail it's usually all or nothing. They only have 3 component:
1. an inlet valve
2. a diaphragm
3. an outlet valve

A quick rough check is to detach the fuel line from the carby & blow back with your mouth. The one way outlet valve mean it should be impossible. Now if u r brave suck. You should get fuel. If you are not as crazy as me, attach a long fuel hose to the pump outlet & hold below the level of the tank. Fuel should flow. ( gravity is a useful diagnostic tool)
A torn diaphragm would mean fuel leaking into your sump. Does the oil level mysteriously go UP with time??
To check the inlet valve you need to detach the fuel line from the tank. Again, check the flow, it should flow freely depending on how full your tank is. Plug the line with a golf tee. Attach a bit of fuel hose to the fuel pump inlet pipe & this time blow (it should let you do it) then suck ( it should NOT let you do that)
Be patient & methodical & you'll get there.
Good Luck!

hey mate im up at uralla so not far
ross freestone is the big vw man in tamworth now that nev's gone !