Possible fuel starvation issues with the GTS

[Brenjacques]

Hi everyone

I thought I'd make a separate thread for this issue after the discussion of the weber. I took the scirocco on holiday with me to the coast last week and it worked fine from Saturday through to Wednesday with no issues until it started to play games.

I was driving from another town back to where we were staying and I could feel that the engine was no longer responsive. We were behind a few other cars, in high gear and not really accelerating but on touching the accelerator there was virtually no response from the engine, it felt like a real flat spot and I knew something was off. I managed to make it the journey back, parked it in the town for 5 minutes before returning back to the lodge and after that it was jerking/kangarooing heavily when accelerating but easing off the accelerator it would roll along quite smooth.

It did get to a point where it nearly died completely and I was rolling along at around 10mph, any press on the accelerator just caused the engine to nearly die but with care I managed to get it back to where we were staying. Luckily another scirocco owner was visiting that day, we replaced the fuel filter and took it for a quick spin and it seemed fine.

Later that day I took it for a longer drive and the same happened again. Thinking it may be caused by the new swirl pot I fitted I tried the weld tip mod as I carried a few spare and initially that seemed to do the trick.

The following day I went to King's Lynn which was around a 40 minute drive, all was fine for the most of it but just as we were on the main road into the centre it started again. I managed to pull it over into an industrial estate to investigate and found that when stationary the engine was struggling to rev over 3krpm. Looking through the new fuel filter it was nearly empty with only a dribble coming through the inlet.

Switched the engine off and I was able to blow down the tube until I was blowing air into the tank and even managed to pressurise the tank enough to send petrol running back up the fuel line and flow out of the end freely. After some time faffing around and checking other things like the fuel pump I carried on to the centre without trouble.

On the return journey back to the lodge I had the idea of keeping the revs over 2k while driving to help the fuel pump get as much fuel through but to use the accelerator only when necessary. This allowed me to get back okay with no problems on the return journey.

With all of the above I'm thinking I've got a blockage in the line or maybe the tank pipe is partially blocked at the end (as another owner suggested). My only concern is that it's strange it would only do it on a longer run and not when the car was first started unless there's a few flakes of rust of dirt that managed to get stuck as the fuel sloshes around the tank on longer drives.

I need to really get it sorted as its my daily and I don't want it giving me grief on the commute so I just thought I'd ask here for any thoughts before I start. I was thinking to check and replace the carb flange as it is a bit wobbly (last changed 2 or 3 years back). The other thing is to remove and check the tank sender unit. I know these are brittle and notorious for breaking but if the fuel pick up pipe is partially blocked at the end then I need to remove it. This will also allow me to look into the tank and see if anything is floating around that shouldn't be in there.

Quite a long post but I wanted to be accurate on the description in case anybody else thinks of other ideas, the weber setup has been fine for 3 or 4 years now and has done a lot of miles completely trouble free so something has changed on the last 100 of so miles to cause this fault.

[WreckTangle]

Apologies, I know no one likes to be told “I told you so”, but read my final comment in post 10 in your thread about excessive fuel pressure and getting your fuel return line working again.

An immediate fix which will probably get you home is to block off the fuel return altogether and run the Weber “deadhead” style. I had to do this once to get me home when I was still wasting time on a Weber and I wish I’d known this trick when I was waiting for the AA in the small hours of the morning the day after I bought my Scirocco. The redneck method I used was to fold the return line over on itself and jam it in something under the bonnet to keep it that way. If you’ve got some tools with you then you can probably do better than that.

Longer term, before messing too much with your carburettor adjustment, get and fit a new carb flange 050 129 761 E. There a plenty of non-OEM ones that are cheap and quite adequate. Unless you are 100% sure yours is newish and has no air leaks this may be enough to fix the problem. I am fairly sure it was the root cause of the problems I was having and forcing more fuel into the Weber only helped to mask the air leaks. The tears in the original can be extremely hard to spot.

Good luck sorting it out.

[Village Idiots]

This sounds a bit like bits of rust, crud, etc. in the tank. These gradually get sucked up round the filter on the end of the pick up after driving for a while, resulting in lack of power/throttle response. Stopping often allows this obstruction to drop back to the bottom of the tank, but to recur when next driving. The cause is corrosion/rust on the inside of the filler pipe and/or the fuel tank. If so the cure is either a new (stainless) filler pipe and/or new tank. This is possibly a bit of a long job for a weekend for a daily driver and needs time to get the necessary new bits, I did it for my Scala (now moved on), but I had another car as, together, these were needed as daily drivers.

[Brenjacques]

Thanks both for the replies.

Wrecktangle, I'm hoping this isn't a effect of changing the swirl pot and restoring the return line to a better working condition. With that said the car was absolutely fine for the journey there which took around 2.5 hours and also the first few days I was there. It did experience some speedy winding roads when the fault developed which does lead me to err towards Village Idiots suggestion. I know there is crud in the tank because the same had happened before though one time it cured itself and the second time I had access to a compressor and blew a strong air line down it, it's not a common occurance though. This time I'll have to carefully remove the fuel pick up and see what's going on in the tank as it could be likely more has deposited itself on the bottom.

I suppose I can let it off though, it's given me years of trouble free dailying so I guess it's allowed to play up at some point, I just rather it was not while I was on holiday! The car is back home now anyway, I got it recovered so I didn't have to take it down the A47 with the chance of it conking out.

I know tank removal isn't the easiest thing so I may just buy a new tank (if they're available) and a pick up from Tom at Dreadnought when he's got some back in stock then either tackle it myself or take it to a garage, that way I don't have to faff around too much cleaning the tank etc. If the tank fitted isn't too bad then it can hang around as a spare.

I'll begin as soon as possible and update the thread with my findings.

[WreckTangle]

In the course of getting my GT2 to run reliably I had the tank cleaned out and a new filler neck installed. I subsequently had the fuel sender out myself (hence the photo I added to your other thread) and confirmed that the tank was spotless inside. However, I still occasionally got the effects you describe.

I fitted my new carb flange in conjunction with fitting a refurbished Pierburg carburettor so I cannot categorically say that the Weber was to blame, especially as I subsequently spotted a hidden tear in the old flange.

You can get an idea of whether there are air leaks in your carb flange by wiggling the carburettor while the car is idling. If this causes any change in idle, swap the flange for a new one.

[Brenjacques]

Thanks for the advice. I did check the flange a few weeks back and the carb was a bit wobbly on it, I know most often advise that if the carb is a bit loose then change the flange, I already have one on order so it'll arrive shortly. Also, there were cracks in the rubber around the bolts mounting it to the manifold so I know it's probably due a change. This is the first port of call anyway as I'll be taking the carb off to clean too. From there I'll give it a test and see how it goes, if it still gives me trouble then I'll have to remove the pick up and look what's going on in the tank.

I know carb flanges can be finicky either causing problems non stop or only after the engine bay gets warm. Also has to be noted that it was cool and rainy on the two hour trip there and the ambiemt temp in the engine bay may have been cooler than the hot days when it began to give trouble.

[Brenjacques]

Well I started work on it yesterday evening, took the carb off and checked/cleaned the 4 emulsion tubes and jets that are removable from the top but all were very clean. Noticed a slight deposit of carbon on one of the jets and on the bottom of the carb but that's probably normal considering it only does short trips normally. I'm not very much inclined to strip the carb down at the risk of introducing more problems unless all else has been explored.

I checked the current flange, it hasn't split through yet but it is splitting so it will be replaced. Stupidly I ordered the wrong flange so I've now got the correct one on the way.

So far I'm still suspecting a blockage/dirt in the tank so I'll check that whilst I wait for a replacement flange.

One other thing is that I removed the little pierburg button heater from the carb body a few weeks ago as the wire is in poor condition and I need to heatshrink it so it doesn't short. Are these webers prone to icing if they don't have the heater on? I presume not as surely they'd come with a heater themselves if they were problematic? Just a thought

[Brenjacques]

Further update: I managed to get the fuel pick up out quite easily this evening to check out, fortunately (or unfortunately) all seems good in this area. Only one of the 16 small holes in the pick up tube was actually blocked but others did feel as though they'd kind of shrunk and furred up so a quick poke with a pin and a good clean had them all sorted. At least I won't have to be removing the tank by the looks of things.

The tank is actually in excellent condition inside but obviously I could only see so much through the pick up hole. No signs of debris or rust floating around at all so I don't think I have filler neck problems. One thing I will do is blow some air down the fuel line before re-connecting to the tank just in case something is stuck in it. Can anybody advise on what the hard fuel lines were made from originally? Mine has copper lines fitted and I'm just wondering if they've been replaced in the past.

One thing I can note when it was playing up is that there looked to be a definite lack of flow at the fuel filter when revving the engine. I do wonder if the fuel pump could be showing it's age though I'd expect a mechanical pump to either be just good or bad as by design an intermittent fault would be slim.

[Village Idiots]

Beware of the effects of ethanol on fuel lines! and carb/injection parts. E10 is obviously twice as bad as E5.
I have been wondering whether or when any problems would surface. Obviously the more the car is used the sooner any likely problems would arise, as a daily driver you are more likely to come across any inherent problems if indeed there are any.

[Brenjacques]

Yeah I've been keeping this in mind and I only ever use E5 from Shell just because it's the closest station to me. I don't think the pick up holes were furred enough to cause a real fuel supply issue but it's something that would have worsened with time so at least it's sorted. Still doesn't exactly give me an answer as to why I was getting the fuelling issue.

I do have a bit of suspicion towards the new swirl pot I fitted a few weeks prior which looks nearly identical to the original but is a new Topran type. When I replaced I had to fill it with fuel myself otherwise the car wouldn't start. Someone else also stated that they had trouble with their replacement and I wonder if it can cause an air/vapour lock in the new swirl pot or the line up to the carb and due to the back pressure it's causing the pump to stop pulling fuel up from the line.

[WreckTangle]

I still think your problems are likely to be due to an inlet manifold vacuum leak. If your carb flange is leaking, bearing in mind the actual holes can be very hard to spot, then it will be leaning out the mixture which will itself cause running problems and also cause the engine to run hot thus exacerbating vapour-lock type issues. Once your fuel/air mixture is so lean the engine becomes sluggish and starts missing then it won't be driving the mechanical fuel pump effectively which will further exacerbate fuelling problems. There also may be insufficient vacuum to be pulling fuel through the carb, again escalating the problem.

All I can say is that having had almost identical intermittent symptoms to yourself, what finally resolved mine for good was fitting a refurbished Pierburg on a new flange. Like you, I thought my flange was OK but on much closer examination off the car I found a long, thin air gap in it which you could only see by holding it up to the light and pulling on it.

[Brenjacques]

I should have the new flange on today so I'll give the current one a really close inspection once I've got it off and in my hands. I plan to blow an air line down the fuel hose just to be sure no further crud is in it and then I'll have to run the car and see if I can replicate the fault.

If I can get it to act up again then I can see exactly how little or much fuel is making it's way up through the filter and spark some new ideas from there. I've also got a fuel pressure gauge on the way to check what pressure I have at the carb. I hope a new flange will sort it but I'll have to keep my wits that the fault will return.

Also, not wanting to go too far down this rabbit hole I ought to keep my thoughts open about the possibility of an ignition fault too, maybe the coil becoming faulty as it gets hot (had it before on other cars) or the Ignition Module which is as ancient as the car. I'll move onto this once I know that the fuel system is all working okay.

[wakar123]

any update as i have the same issues too, im going to do the same trouble shooting as you and today i will clean the fuel lines.

[Brenjacques]

No real update as of yet, carefully check the flange as I found mine was seated oddly at the back and really was just a poor design so could have caused a possible air leak. Hopefully this weekend should bring some progress as I've been waiting for a few more parts.

Also double check your ignition system, make sure the coil and TCI module are okay. My coil is about 3 years old and a Bosch type but the module is the original from 1985 so if I have no improvement I'll be suspecting one of those, especially as it happens after a period of time. As wrecktangle said above a spluttery engine could give the look fuel starvation as the pump is mechanical. I know the lines are clear on mine now so there's only so much it can be fuel wise before I have to look at the ignition system.

[Brenjacques]

Right, hopefully the last update with this fault. Been a bit of a pain as whilst the carb was off I decided to do the cam cover gasket, that lead me down a whole other rabbit hole with seized nuts, missing studs etc.

The car is now all back together. When I removed the old flange I could definitely see no through splits but what I did notice is that the pattern complied poorly with the intake on the manifold meaning that it could have been possible for some air to slip past the seal especially with metal expansion when warm. Do I think that was the cause? Not really in my opinion but definitely something I noticed.

Secondly I spent some time cleaning and refitting the original swirl pot after another owner stated similar problems when replacing theirs with a new part. That all went well and it's back on the car. I also removed the weld tip as previously this hasn't been required. I do somewhat think this could have been the cause, maybe creating a vapour/air lock and not really doing it's job properly.

I then replaced both the rotor arm and dizzy cap, both were looking pretty cooked, the rotor arm especially so with the filled epoxy part on the top surface all bubbled up and crispy towards the contact end.

I took it for a 40 minute drive with varying speeds and all seems fine at the moment, no problems at all so I hope it now stays that way.

Just one thing I did note regarding the horn - when I drove it during this problem the plug for the carb heater rested on the manifold, melted and shorted out blowing the fuse for that and the horn which I presume is on the same circuit. I replaced the fuse, everything is fine but does the horn only work once the ignition is turned? I could have sworn it used to work regardless of key in/ignition on etc but perhaps I'm just remembering wrong. Just want to make sure I haven't burned out an earth when the short occured.