1.8 8v EX rough start

[Brenjacques]

Hi all,

I started covering this topic in another thread quite some time ago but I'm still having problems so thought I'd make a new one.

Basically the starting idle on my scirocco is quite rough, seems as though its misfiring for the first few seconds, runs a bit lumpy but with revving smooths out and is fine afterwards. It's been like it for a while but I've racked up a lot of mileage on it so I think it's to do with the ignition system rather than engine itself. Timing is all good and spot on and really doesn't make a difference if adjusted slightly either direction. Carb is a replacement weber, had the problem before this was fitted too but again this has been set up correctly and performs just as it should.

The engine holds fluids fine, doesn't use/lose anything nor is it burning anything off either, spark plugs are in good condition. Over the last couple of years it's had a new coil, HT leads, dizzy cap, rotor, plugs. Tried another ignition module but had no effect.

Beginning to question the Hall sensor/distributor as I have some oil ingress there. Second is the carb flange as it was replaced about 2 years ago and read stories of the new ones splitting easily - although I'd expect running issues to be continuous if this was the case.


Does anyone have any other ideas/input? I have some time off next week and hope that I can get it cured.

[RussGLAuto]

Hi Bren,

Feel your pain. Check the fuel system for rust, it will manifest itself as tiny black particles visible in the engine bay fuel filter. Can be from the fuel filler neck, tank and hard fuel lines routed under the chassis.

And no, the filter won't keep them all from your carb inlet and playing merry hell with the running.

Speaking from experience.

Russ

[Brenjacques]

Hi Russ,

Good point, I'll definitely give it a check. I looked at the filter some months back and it was okay then, but you never know what can happen in a short space of time.

It's an annoying fault, the car otherwise performs fine which makes it hard to diagnose, after 10-15 seconds it's gone.

[mark1gls]

How do you start the car?

It could be your technique starting the car which could be the problem as you have replaced most things and it’s no different.
An old car running a carb with a manual chock where you have to adjust the right mixture of fuel and air for it to start first time from cold is tricky.
I do find my Mk1 Scirocco GLS with a Webber carb needs to idle for a few seconds for it to smooth out while the Mk1 Golf GTi when running right will fire up straight away and idle smoothly at 1000 rpm.

Carb cars you are meant to use the accelerator pedal to help starting, try pressing the pedal to the floor once and 1/2 choke before starting then just a little press on the pedal when turning the engine over...
Try different ways to start the car and see if that makes any difference, it’s not going to cost anything so worth a try....

[GT_II]

It certainly sounds more like a fuel issue than ignition, if it performs well after 15 seconds - mixture too rich or too lean on start up.

Carb cars you are meant to use the accelerator pedal to help starting

... except when the carb is equipped with a throttle position actuator (aka 3-point unit) as on the Pierburg 2E2, unless the engine is hot in which case extra throttle is required...

[Eagle1]

Has the fuel separator been changed and or the fuel pump. If you have the weber fitted you should be able to use the taller Mk2 Golf version. I also routed my fuel pipe from the tank round behind the offside headlight to the fuel pump with a clear barbed fuel filter. It takes it away from the engine heat. You may need to secure the pipe so it doesn't catch the alternator fan pulley. Is it only lumpy at idle or are there more problems at speed or acceleration.

[Brenjacques]

Hi all

I don't think it's really to do with the way the car is started. For about the first year of ownership it was fine, first turn of the key and it shot straight into life, this had a peirburg on it at the time it developed the fault and the fault remained after I switched over to a weber. I normally give it a couple of presses of the accelerator and gradually press down on the pedal as I'm turning over but no matter how you try it will run lumpy for 10-15 seconds. You get the occasional time it will lstart fine but it's not often.

I was thinking about the fuel pump and seperator this morning, they're both original as far as I can tell so they've been on the car since 1985. I have considered changing the fuel pump for this reason but if it was at fault I'd surely have more problems than just starting.

The car is otherwise fine, I drive it daily and once running I have no problems at all, it's just starting that seems to be a problem.

[Eagle1]

I have a Mk1 Golf with a Weber that had similar problems. Changing the separator and fuel pump have made a difference.

[Brenjacques]

I going to replace the pump and see if it makes any difference. Really relying on a 36 year old pump on a daily is asking for trouble anyhow and it'll be interesting to see what improvement (if any) it makes.

As a side thought what about vapour lock in the fuel tank? I don't know how well these tanks breathe but I had another car a few years back that would pull fuel back when switching off due to it creating a vacuum whilst driving. Presumably the vent in the fuel cap had blocked - could a similar thing happen to these tanks or are they vented on the tank itself.

[GT_II]

The original fuel cap has a one-way valve - allowing air in to the tank to replace fuel pumped out, but preventing fumes escaping from the cap as the fuel warms up which pressurises the tank.

[Brenjacques]

I think the tank should be okay then, the cap is in good condition with no corrosion so its probably working fine. I have all of the parts now so I'm going to make a start tomorrow. I'll start with the seperator and fuel pump initially and see if they make any difference. Will be intersting to see if the originals are full of dirt dragged up from the lines.

[Brenjacques]

Just to update the thread, I replaced the fuel pump a couple of days ago. I haven't done the seperator yet as the hose from pump to seperator isn't in great condition and I don't want to disturb it too much, I have some new hose ordered and I'll get the seperator done when that arrives.

Upon removing the old pump and operating it with my hands it was very squeaky and noisy and so far after fitting the new pump I've had no issues *touch wood* with rough starting. Fingers crossed this has cured it and the problem was a weak pump.

As a side note the brake pads have also been changed, been sick of them clacking for the last year or so. Funnily enough all anti rattle shims were there but not really doing their job.

[Brenjacques]

Well the smooth starts didn't last long! The rough starting has returned but its given me some clues now. I think it cleared up due to the really warm, dry weather we've been having. As soon as it turned humid and rainy it came back so I'm thinking this may still be an electrical issue somewhere. The only problem is that the ignition leads etc have all been replaced. The only electrical wire in the engine bay that is looking a bit worse for wear is the alternator cable, but I would presume if this was the cause I'd also be experiencing a sluggish starter motor etc.

Back to the drawing board but I'm going to continue to find the cause!

[Brenjacques]

Hi all,

I've been filling the fuel tank a bit more than normal and I've noticed that often when I switch off there is a lot of sloshing/gurgling from the tank. I'm sure the breather or valve is blocked causing a vacuum in the tank which is pulling fuel back down the lines. It would make sense as the in line fuel filter is always empty of petrol when the car has been stood and would explain the rough starting. Is it worth trying to free the valve in the cap if that's the problem or would it be easier just buying a new cap

[GT_II]

I hear a lot of sloshing in my tank when it is nearly full - but not when the car is stationary.

Is your cap the original one, vaguely like this (don't know if this suits UK non-cat cars, but best picture I could find): https://www.werk34.de/en/fuel-filter-ca ... 551-e.html?

The valve in the cap is one-way - allowing air in but not allowing air out - to stop fuel vapour getting out as the fuel warms up. I think I tested mine by blowing into the hole on the base (which should not be possible) and then sucking (not pleasant, but once didn't kill me!)