Author Topic: Overfuelling  (Read 676 times)

Offline Herpies

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« on: August 16, 2017, 09:28:33 pm »
Hey guys,

I know you all are so helpful from previous calls of aid so thought I'd post again before getting someone to look at it and scratch their head for a while trying to work everything out.

Basically my g40 has been sat a while and upon digging it out to give it some well deserved love, it is super over fueling. Probably some sort of karma for leaving it in a bush in my garden.

I drained all old fuel, put fresh in to find it lumpy, smokey, sometimes idles, everything you don't want. The plugs were carbon fouled so I cleaned them and then were instantly fouled again after about 5 seconds of being ran.

I thought it may have settled after it had warmed up and let the oil pressure dropped but no such luck.

Its very smokey and a mechanic friend who was doing electrics on my beetle said it definitely smelt like overfuelling smoke.

One reason I can think of is that it had a few parts pinched from the engine and the boost pipe (inc CO2 pot) was one of them. The other part nicked was air filter. I sourced replacements which had obviously a different CO2 pot. Does this different CO2 pot need to be mapped or something to the ECU? It just strange because I've had it running since then and it was absolutely normal, it just seems to have developed over the last few months.

Could it be just the idle valve needing a clean?

Its had a noisey tappet since the dawn of time. Could it be that completely stuck in a position now letting too much mixture in? But surely that would mean a valve is now screwed from it being ran with piston hitting it and the fouling is over all cylinders.

I'm going to get a new dizzy and rotor arm (previous owner said that helped him once when running rough)
Maybe pull rocker cover and check valve to cam lobe clearance/valve springing action, to see of any sticking etc.
And clean the idle valve, before taking it somewhere to have a professionals diagnostic.

Just thought I'd post on here as someone may be a massive help and know exactly whats up!

Thanks in advance!


Offline ereeiz

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Re: Overfuelling
« Reply #1 on: August 18, 2017, 10:45:09 am »
Does it clear up if you leave it running for ten mins? When you first start it will dump fuel in for the "cold start" cycle and ignore signals from the lambda sensor (o2 sensor) in the exhaust so it will smell of fuel, but once up to temp it should read the temperature from the blue temperature sender and the oxygen level from the o2 sensor, adjusting the amount of fuel being injected, alongside the boost sensor and WOT switch signals.

I've had annoying issues like this before, my current GT for example gobbles fuel (240 miles to 45 litres) and misfires 3 times on a warm restart, then it's fine. Probably the o2 sensor but I've never bothered looking into it, just lived with it. If your car has sat for a while I'd say check things like your earths are clean and flexible, not crusty and hard/ corroded. Possibly water has got into the ECU and causing odd running? Have you got another G40 ecu you could plug in and try?

Also check the usual things, blue temperature sender (next to the black one on the front of the engine next to the distributor, as you look at it.

I doubt it's the valve, the spring would keep it closed, the tappet (technically it's called a "hydraulic lifter" in this specific case) is what sits between the cam lobe and the top of the valve, so if it's not filling with oil, it won't be filling the gap between the valve and the cam lobe properly, causing it to open less than required...... thinking about it now I've written it, maybe it is the tappet? Whip it off and have a look. Last time I replaced them they were about £8 each from a parts store, that was 10 years ago though.... Pretty sure they're the same on all model polo though so should be easy enough to replace.

Offline randombadger69

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Re: Overfuelling
« Reply #2 on: August 27, 2017, 07:59:37 am »
First thing to check is the alternator output. Make sure the battery voltage isn't dropping below 13.2V

Check the restistance between pins 1 and 3 on your replacement CO pot, should be something like 550 ohms.

If you work through the diagnostics guide you should be able to sus the issue.,214.0.html