Misfires, flatspots, stalling and a sudden lack of urgency are all things that can ruin the pleasure of driving an older vehicle. But why put up with a rubbish runner when you can turn detective, find the source of the engine running problems and devise a suitable remedy to get your motor running smoothly again. With that in mind, here’s some useful pointers to help restore your engine’s get up and go again…
Fuel for thought
Two things are needed to make an engine burst into life, fuel and a spark – and an inconsistent supply of either isn’t likely to end well. Debris or fragments of rust in the fuel system isn’t good – a common problem is the Mk1 Golf fuel filler pipes which can cause the fuel system (and injectors on the GTi) to clog. Older cars may also have rust sitting in the bottom of the tank. If fuel is contaminated, you’ll get a misfire so why not install an inline fuel filter. Try to locate it in a cool location to avoid the risk of fire.
We have ignition (or not!)
If you’re not getting a reliable spark from your spark plugs, then you can say goodbye to a smooth running motor. Inspect your ignition system, check points for pitting if fitted, and be prepared to systematically replace parts like the ignition leads and coil packs until you get to the bottom of your rough running headaches. Fitting electronic ignition will help with general reliability, and certainly make general maintenance a lot easier.
A matter of timing
On older cars without an ECU, if your engine’s struggling to run smoothly, it could be that the ignition timing’s out of kilter. A backfire, or running hot will be a clue that it’s not right. On lots of VWs it’s something you can easily do yourself once you’ve consulted the necessary workshop manual. Oh, and on air-cooled cars, valve clearance is critical too – so once the timing’s set, climb underneath with a feeler gauge to check those as correct as well.
Air we go
Often engine running problems are caused by having the wrong mixture of air and fuel. It could be that there’s too much air (so your engine’s running too lean) or there’s air getting in where it’s not supposed to. Adjust your carburettor according to the recommended procedure and inspect any vacuum hoses and inlet manifold gaskets for leaks to improve things. A good tip is to spray WD40 on a suspect gasket to see if the engine speed changes; if it does, there’s a leak somewhere.
While on the subject of air, on water-cooled cars with an ECU, air flow meters can also be the cause flaccid performance, flat spots, excessive smoke and diminished fuel economy. It might not throw up a fault code if it goes wrong, so replace it to see if it makes any difference.
Engine running problems and in particular failure to start or idle smoothly, can sometimes be due to faulty engine sensors, most commonly ones that measure oxygen and temperature. A diagnostics check should help identify the culprit, but if that fails it’s a case of swapping parts out until the problem is cured.
On air-cooled VWs, there’s an electronically controlled fuel cut off valve which prevents the engine running on when the ignition’s turned off. If it becomes faulty, the car can stall or fail to start completely. They’re not expensive to replace.
It might be that your engine’s feeling a bit low. Low on compression, that is, which will account for its general lethargy or inability to idle. Get a compression test done to rule out burnt valves and the like. A workshop manual should say what the compression should be, but if one’s significantly different to the others (in excess of 20% out) it’s likely to be bad news.
Mostly plaguing later diesel-engined VWs, misfires, erratic running and excessive fuel consumption can sometimes be down to problem injectors. It’s tricky determining which injector is to blame, so get a specialist to carry out the necessary investigation. Thankfully, replacement injector’s aren’t expensive.
Oh blow it!
Finally, VW helped pioneer the use of variable vane turbos on their TDi diesel engines which made traditional turbo ‘lag’ a thing of the past. However, with age the vanes which control the amount of boost can clog and stick and this can dog performance. Replacement is the best option, but get a specialist to rule out other possible causes before you splash out on a new blower.
Rest assured, we’re painting a picture of the worst scenario here because generally your german car should prove ruggedly reliable. A few tweaks here and there, however, can make the pleasure of owning and driving one even better…